-
Notifications
You must be signed in to change notification settings - Fork 0
Expand file tree
/
Copy pathindex.html
More file actions
2187 lines (1153 loc) · 133 KB
/
index.html
File metadata and controls
2187 lines (1153 loc) · 133 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
<!doctype html>
<html class="theme-next muse use-motion">
<head>
<meta charset="UTF-8"/>
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1" />
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1"/>
<meta http-equiv="Cache-Control" content="no-transform" />
<meta http-equiv="Cache-Control" content="no-siteapp" />
<meta name="google-site-verification" content="iozdnVVzYBR7rSeAQJFiH0gM-BqS17gSIihpKyu8IHs" />
<meta name="baidu-site-verification" content="6QWE4cUSE6" />
<link href="//cdn.bootcss.com/fancybox/2.1.5/jquery.fancybox.min.css" rel="stylesheet" type="text/css" />
<link href="//fonts.googleapis.com/css?family=Lato:300,300italic,400,400italic,700,700italic&subset=latin,latin-ext" rel="stylesheet" type="text/css">
<link href="//cdn.bootcss.com/font-awesome/4.6.2/css/font-awesome.min.css" rel="stylesheet" type="text/css" />
<link href="/css/main.css?v=5.0.2" rel="stylesheet" type="text/css" />
<meta name="keywords" content="java,架构师,spring,js,javascript,jdk,j2ee,源码" />
<link rel="alternate" href="/atom.xml" title="我在这里" type="application/atom+xml" />
<link rel="shortcut icon" type="image/x-icon" href="/favicon.ico?v=5.0.2" />
<meta name="description" content="java | 架构 |">
<meta property="og:type" content="website">
<meta property="og:title" content="我在这里">
<meta property="og:url" content="http://www.zhishuo.info/index.html">
<meta property="og:site_name" content="我在这里">
<meta property="og:description" content="java | 架构 |">
<meta name="twitter:card" content="summary">
<meta name="twitter:title" content="我在这里">
<meta name="twitter:description" content="java | 架构 |">
<script type="text/javascript" id="hexo.configuration">
var NexT = window.NexT || {};
var CONFIG = {
scheme: 'Muse',
sidebar: {"position":"left","display":"post"},
fancybox: true,
motion: true,
duoshuo: {
userId: '0',
author: '博主'
}
};
</script>
<link rel="canonical" href="http://www.zhishuo.info/"/>
<title> 我在这里 </title>
</head>
<body itemscope itemtype="//schema.org/WebPage" lang="zh-Hans">
<script>
(function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
(i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
})(window,document,'script','//www.google-analytics.com/analytics.js','ga');
ga('create', '52139183-1', 'auto');
ga('send', 'pageview');
</script>
<script type="text/javascript">
var _hmt = _hmt || [];
(function() {
var hm = document.createElement("script");
hm.src = "//hm.baidu.com/hm.js?d3d666579a0130a85850d5665d083280";
var s = document.getElementsByTagName("script")[0];
s.parentNode.insertBefore(hm, s);
})();
</script>
<div class="container one-collumn sidebar-position-left
page-home
">
<div class="headband"></div>
<header id="header" class="header" itemscope itemtype="//schema.org/WPHeader">
<div class="header-inner"><div class="site-meta ">
<div class="custom-logo-site-title">
<a href="/" class="brand" rel="start">
<span class="logo-line-before"><i></i></span>
<span class="site-title">我在这里</span>
<span class="logo-line-after"><i></i></span>
</a>
</div>
<p class="site-subtitle">传说中的软件工程师</p>
</div>
<div class="site-nav-toggle">
<button>
<span class="btn-bar"></span>
<span class="btn-bar"></span>
<span class="btn-bar"></span>
</button>
</div>
<nav class="site-nav">
<ul id="menu" class="menu">
<li class="menu-item menu-item-home">
<a href="/" rel="section">
<i class="menu-item-icon fa fa-fw fa-home"></i> <br />
首页
</a>
</li>
<li class="menu-item menu-item-categories">
<a href="/categories" rel="section">
<i class="menu-item-icon fa fa-fw fa-th"></i> <br />
分类
</a>
</li>
<li class="menu-item menu-item-about">
<a href="/about" rel="section">
<i class="menu-item-icon fa fa-fw fa-user"></i> <br />
关于
</a>
</li>
<li class="menu-item menu-item-archives">
<a href="/archives" rel="section">
<i class="menu-item-icon fa fa-fw fa-archive"></i> <br />
归档
</a>
</li>
<li class="menu-item menu-item-tags">
<a href="/tags" rel="section">
<i class="menu-item-icon fa fa-fw fa-tags"></i> <br />
标签
</a>
</li>
<li class="menu-item menu-item-search">
<a href="javascript:;" class="popup-trigger">
<i class="menu-item-icon fa fa-search fa-fw"></i> <br />
搜索
</a>
</li>
</ul>
<div class="site-search">
<div class="popup">
<span class="search-icon fa fa-search"></span>
<input type="text" id="local-search-input">
<div id="local-search-result"></div>
<span class="popup-btn-close">close</span>
</div>
</div>
</nav>
</div>
</header>
<main id="main" class="main">
<div class="main-inner">
<div class="content-wrap">
<div id="content" class="content">
<section id="posts" class="posts-expand">
<article class="post post-type-normal " itemscope itemtype="//schema.org/Article">
<header class="post-header">
<h1 class="post-title" itemprop="name headline">
<a class="post-title-link" href="/posts/java/JDK1.8源码之ConcurrentHashMap.html" itemprop="url">
JDK1.8源码之ConcurrentHashMap
</a>
</h1>
<div class="post-meta">
<span class="post-time">
<span class="post-meta-item-icon">
<i class="fa fa-calendar-o"></i>
</span>
<span class="post-meta-item-text">发表于</span>
<time itemprop="dateCreated" datetime="2016-12-09T16:16:30+08:00" content="2016-12-09">
2016-12-09
</time>
</span>
<span class="post-category" >
|
<span class="post-meta-item-icon">
<i class="fa fa-folder-o"></i>
</span>
<span class="post-meta-item-text">分类于</span>
<span itemprop="about" itemscope itemtype="https://schema.org/Thing">
<a href="/categories/java/" itemprop="url" rel="index">
<span itemprop="name">java</span>
</a>
</span>
</span>
<span class="post-comments-count">
|
<a href="/posts/java/JDK1.8源码之ConcurrentHashMap.html#comments" itemprop="discussionUrl">
<span class="post-comments-count ds-thread-count" data-thread-key="posts/java/JDK1.8源码之ConcurrentHashMap.html" itemprop="commentsCount"></span>
</a>
</span>
<span id="/posts/java/JDK1.8源码之ConcurrentHashMap.html" class="leancloud_visitors" data-flag-title="JDK1.8源码之ConcurrentHashMap">
|
<span class="post-meta-item-icon">
<i class="fa fa-eye"></i>
</span>
<span class="post-meta-item-text">阅读次数 </span>
<span class="leancloud-visitors-count"></span>
</span>
</div>
</header>
<div class="post-body" itemprop="articleBody">
<h3 id="什么是ConcurrentHashMap"><a href="#什么是ConcurrentHashMap" class="headerlink" title="什么是ConcurrentHashMap"></a>什么是ConcurrentHashMap</h3><p>以下观点都是建立在JDK1.8之上。</p>
<p>我们知道HashMap是非线程安全的，所以JDK给我们提供了几种线程安全的Map，<code>HashTable</code>，<code>Collections.SynchronizedMap</code>，<code>ConcurrentHashMap</code>几种线程安全的Map来使用。<br><code>HashTable</code>是每个方法都是synchronized修饰的。<br><code>Collections.SynchroinzedMap</code>则是用一个Object来当锁，每个方法里都使用<code>synchronized(obj)</code>来锁定。</p>
<p>这里没有理解以上的2种方法有什么区别，<code>HashTable</code>是作用在方法上的，所以锁的是this对象，后者是锁的Object，有什么区别吗？</p>
<p>最后一种<code>ConcurrentHashMap</code>则是使用了最新的锁技术来实现的。</p>
<h3 id="实现原理"><a href="#实现原理" class="headerlink" title="实现原理"></a>实现原理</h3><h3 id="源码实现"><a href="#源码实现" class="headerlink" title="源码实现"></a>源码实现</h3><h4 id="变量"><a href="#变量" class="headerlink" title="变量"></a>变量</h4><figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div><div class="line">31</div><div class="line">32</div><div class="line">33</div><div class="line">34</div><div class="line">35</div><div class="line">36</div><div class="line">37</div><div class="line">38</div><div class="line">39</div><div class="line">40</div><div class="line">41</div><div class="line">42</div><div class="line">43</div><div class="line">44</div><div class="line">45</div><div class="line">46</div><div class="line">47</div><div class="line">48</div><div class="line">49</div><div class="line">50</div><div class="line">51</div><div class="line">52</div><div class="line">53</div><div class="line">54</div><div class="line">55</div><div class="line">56</div><div class="line">57</div><div class="line">58</div><div class="line">59</div><div class="line">60</div><div class="line">61</div><div class="line">62</div><div class="line">63</div><div class="line">64</div><div class="line">65</div><div class="line">66</div><div class="line">67</div><div class="line">68</div><div class="line">69</div><div class="line">70</div><div class="line">71</div><div class="line">72</div><div class="line">73</div><div class="line">74</div><div class="line">75</div><div class="line">76</div><div class="line">77</div><div class="line">78</div><div class="line">79</div><div class="line">80</div><div class="line">81</div><div class="line">82</div><div class="line">83</div><div class="line">84</div><div class="line">85</div><div class="line">86</div><div class="line">87</div><div class="line">88</div><div class="line">89</div><div class="line">90</div><div class="line">91</div><div class="line">92</div><div class="line">93</div><div class="line">94</div><div class="line">95</div><div class="line">96</div><div class="line">97</div><div class="line">98</div><div class="line">99</div><div class="line">100</div><div class="line">101</div></pre></td><td class="code"><pre><div class="line"><span class="comment">// 最大的阀值</span></div><div class="line"> <span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">int</span> MAXIMUM_CAPACITY = <span class="number">1</span> << <span class="number">30</span>;</div><div class="line"></div><div class="line"> <span class="comment">// 如果不指定长度，默认的长度</span></div><div class="line"> <span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">int</span> DEFAULT_CAPACITY = <span class="number">16</span>;</div><div class="line"></div><div class="line"> <span class="comment">// 数组最大长度</span></div><div class="line"> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">int</span> MAX_ARRAY_SIZE = Integer.MAX_VALUE - <span class="number">8</span>;</div><div class="line"></div><div class="line"> <span class="comment">//</span></div><div class="line"> <span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">int</span> DEFAULT_CONCURRENCY_LEVEL = <span class="number">16</span>;</div><div class="line"></div><div class="line"> <span class="comment">//与HashMap一样，负载因子也是0.75 当数组中有75%都有数据时就进行数组扩容</span></div><div class="line"> <span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">float</span> LOAD_FACTOR = <span class="number">0.75f</span>;</div><div class="line"></div><div class="line"> <span class="comment">// 当数组单个位置链表长度超过此值之后，会修改为树结构</span></div><div class="line"> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">int</span> TREEIFY_THRESHOLD = <span class="number">8</span>;</div><div class="line"></div><div class="line"> <span class="comment">//当树结构节点小于6时，会修改为链表结构</span></div><div class="line"> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">int</span> UNTREEIFY_THRESHOLD = <span class="number">6</span>;</div><div class="line"></div><div class="line"> <span class="comment">/**</span></div><div class="line"> * The smallest table capacity for which bins may be treeified.</div><div class="line"> * (Otherwise the table is resized if too many nodes in a bin.)</div><div class="line"> * The value should be at least 4 * TREEIFY_THRESHOLD to avoid</div><div class="line"> * conflicts between resizing and treeification thresholds.</div><div class="line"> */</div><div class="line"> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">int</span> MIN_TREEIFY_CAPACITY = <span class="number">64</span>;</div><div class="line"></div><div class="line"> <span class="comment">/**</span></div><div class="line"> * Minimum number of rebinnings per transfer step. Ranges are</div><div class="line"> * subdivided to allow multiple resizer threads. This value</div><div class="line"> * serves as a lower bound to avoid resizers encountering</div><div class="line"> * excessive memory contention. The value should be at least</div><div class="line"> * DEFAULT_CAPACITY.</div><div class="line"> */</div><div class="line"> <span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">int</span> MIN_TRANSFER_STRIDE = <span class="number">16</span>;</div><div class="line"></div><div class="line"> <span class="comment">/**</span></div><div class="line"> * The number of bits used for generation stamp in sizeCtl.</div><div class="line"> * Must be at least 6 for 32bit arrays.</div><div class="line"> */</div><div class="line"> <span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">int</span> RESIZE_STAMP_BITS = <span class="number">16</span>;</div><div class="line"></div><div class="line"> <span class="comment">/**</span></div><div class="line"> * The maximum number of threads that can help resize.</div><div class="line"> * Must fit in 32 - RESIZE_STAMP_BITS bits.</div><div class="line"> */</div><div class="line"> <span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">int</span> MAX_RESIZERS = (<span class="number">1</span> << (<span class="number">32</span> - RESIZE_STAMP_BITS)) - <span class="number">1</span>;</div><div class="line"></div><div class="line"> <span class="comment">/**</span></div><div class="line"> * The bit shift for recording size stamp in sizeCtl.</div><div class="line"> */</div><div class="line"> <span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">int</span> RESIZE_STAMP_SHIFT = <span class="number">32</span> - RESIZE_STAMP_BITS;</div><div class="line"></div><div class="line"> <span class="comment">/*</span></div><div class="line"> * Encodings for Node hash fields. See above for explanation.</div><div class="line"> */</div><div class="line"> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">int</span> MOVED = -<span class="number">1</span>; <span class="comment">// hash for forwarding nodes</span></div><div class="line"> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">int</span> TREEBIN = -<span class="number">2</span>; <span class="comment">// hash for roots of trees</span></div><div class="line"> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">int</span> RESERVED = -<span class="number">3</span>; <span class="comment">// hash for transient reservations</span></div><div class="line"> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">int</span> HASH_BITS = <span class="number">0x7fffffff</span>; <span class="comment">// usable bits of normal node hash</span></div><div class="line"> </div><div class="line"> <span class="comment">// cpu数量</span></div><div class="line"> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">int</span> NCPU = Runtime.getRuntime().availableProcessors();</div><div class="line"> </div><div class="line"> <span class="comment">/**</span></div><div class="line"> * The array of bins. Lazily initialized upon first insertion.</div><div class="line"> * Size is always a power of two. Accessed directly by iterators.</div><div class="line"> */</div><div class="line"> <span class="keyword">transient</span> <span class="keyword">volatile</span> Node<K,V>[] table;</div><div class="line"></div><div class="line"> <span class="comment">/**</span></div><div class="line"> * The next table to use; non-null only while resizing.</div><div class="line"> */</div><div class="line"> <span class="keyword">private</span> <span class="keyword">transient</span> <span class="keyword">volatile</span> Node<K,V>[] nextTable;</div><div class="line"></div><div class="line"> <span class="comment">/**</span></div><div class="line"> * Base counter value, used mainly when there is no contention,</div><div class="line"> * but also as a fallback during table initialization</div><div class="line"> * races. Updated via CAS.</div><div class="line"> */</div><div class="line"> <span class="keyword">private</span> <span class="keyword">transient</span> <span class="keyword">volatile</span> <span class="keyword">long</span> baseCount;</div><div class="line"></div><div class="line"> <span class="comment">// 阀值用来控制数组是否要扩容,-1时表示正在初始化，-(1+n表示有几个线程在操作)</span></div><div class="line"> <span class="keyword">private</span> <span class="keyword">transient</span> <span class="keyword">volatile</span> <span class="keyword">int</span> sizeCtl;</div><div class="line"></div><div class="line"> <span class="comment">/**</span></div><div class="line"> * The next table index (plus one) to split while resizing.</div><div class="line"> */</div><div class="line"> <span class="keyword">private</span> <span class="keyword">transient</span> <span class="keyword">volatile</span> <span class="keyword">int</span> transferIndex;</div><div class="line"></div><div class="line"> <span class="comment">/**</span></div><div class="line"> * Spinlock (locked via CAS) used when resizing and/or creating CounterCells.</div><div class="line"> */</div><div class="line"> <span class="keyword">private</span> <span class="keyword">transient</span> <span class="keyword">volatile</span> <span class="keyword">int</span> cellsBusy;</div><div class="line"></div><div class="line"> <span class="comment">/**</span></div><div class="line"> * Table of counter cells. When non-null, size is a power of 2.</div><div class="line"> */</div><div class="line"> <span class="keyword">private</span> <span class="keyword">transient</span> <span class="keyword">volatile</span> CounterCell[] counterCells;</div></pre></td></tr></table></figure>
<h4 id="UnSafe相关"><a href="#UnSafe相关" class="headerlink" title="UnSafe相关"></a>UnSafe相关</h4><figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div><div class="line">31</div><div class="line">32</div><div class="line">33</div><div class="line">34</div><div class="line">35</div><div class="line">36</div></pre></td><td class="code"><pre><div class="line"></div><div class="line"><span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> sun.misc.Unsafe U;</div><div class="line"><span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">long</span> SIZECTL;</div><div class="line"><span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">long</span> TRANSFERINDEX;</div><div class="line"><span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">long</span> BASECOUNT;</div><div class="line"><span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">long</span> CELLSBUSY;</div><div class="line"><span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">long</span> CELLVALUE;</div><div class="line"><span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">long</span> ABASE;</div><div class="line"><span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">int</span> ASHIFT;</div><div class="line"></div><div class="line"><span class="keyword">static</span> {</div><div class="line"> <span class="keyword">try</span> {</div><div class="line"> U = sun.misc.Unsafe.getUnsafe();</div><div class="line"> Class<?> k = ConcurrentHashMap.class;</div><div class="line"> <span class="comment">//获取sizeCtl变量在内存中的偏移量</span></div><div class="line"> SIZECTL = U.objectFieldOffset</div><div class="line"> (k.getDeclaredField(<span class="string">"sizeCtl"</span>));</div><div class="line"> TRANSFERINDEX = U.objectFieldOffset</div><div class="line"> (k.getDeclaredField(<span class="string">"transferIndex"</span>));</div><div class="line"> BASECOUNT = U.objectFieldOffset</div><div class="line"> (k.getDeclaredField(<span class="string">"baseCount"</span>));</div><div class="line"> CELLSBUSY = U.objectFieldOffset</div><div class="line"> (k.getDeclaredField(<span class="string">"cellsBusy"</span>));</div><div class="line"> Class<?> ck = CounterCell.class;</div><div class="line"> CELLVALUE = U.objectFieldOffset</div><div class="line"> (ck.getDeclaredField(<span class="string">"value"</span>));</div><div class="line"> Class<?> ak = Node[].class;</div><div class="line"> ABASE = U.arrayBaseOffset(ak);</div><div class="line"> <span class="keyword">int</span> scale = U.arrayIndexScale(ak);</div><div class="line"> <span class="keyword">if</span> ((scale & (scale - <span class="number">1</span>)) != <span class="number">0</span>)</div><div class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> Error(<span class="string">"data type scale not a power of two"</span>);</div><div class="line"> ASHIFT = <span class="number">31</span> - Integer.numberOfLeadingZeros(scale);</div><div class="line"> } <span class="keyword">catch</span> (Exception e) {</div><div class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> Error(e);</div><div class="line"> }</div><div class="line">}</div></pre></td></tr></table></figure>
<h4 id="构造方法"><a href="#构造方法" class="headerlink" title="构造方法"></a>构造方法</h4><figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div></pre></td><td class="code"><pre><div class="line"><span class="function"><span class="keyword">public</span> <span class="title">ConcurrentHashMap</span><span class="params">(<span class="keyword">int</span> initialCapacity)</span> </span>{</div><div class="line"> <span class="keyword">if</span> (initialCapacity < <span class="number">0</span>)</div><div class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> IllegalArgumentException();</div><div class="line"> <span class="comment">/** 这里直接判断了如果指定的值大于了最大长度的1/2，就直接等于最大值了</span></div><div class="line"> * 这里的 MAXIMUM_CAPACITY >>> 1 等于 MAXIMUM_CAPACITY / 2</div><div class="line"> * initialCapacity + (initialCapacity >>> 1) + 1</div><div class="line"> * 这里我没明白为什么要做这些操作，可能是为了求出在做散列时</div><div class="line"> * 更合适的值</div><div class="line"> */ </div><div class="line"> <span class="keyword">int</span> cap = ((initialCapacity >= (MAXIMUM_CAPACITY >>> <span class="number">1</span>)) ?</div><div class="line"> MAXIMUM_CAPACITY :</div><div class="line"> tableSizeFor(initialCapacity + (initialCapacity >>> <span class="number">1</span>) + <span class="number">1</span>));</div><div class="line"> <span class="keyword">this</span>.sizeCtl = cap;</div><div class="line">}</div></pre></td></tr></table></figure>
<p>构造方法都很类似，这里我只举例一个。</p>
<h4 id="put方法"><a href="#put方法" class="headerlink" title="put方法"></a>put方法</h4><figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div><div class="line">31</div><div class="line">32</div><div class="line">33</div><div class="line">34</div><div class="line">35</div><div class="line">36</div><div class="line">37</div><div class="line">38</div><div class="line">39</div><div class="line">40</div><div class="line">41</div><div class="line">42</div><div class="line">43</div><div class="line">44</div><div class="line">45</div><div class="line">46</div><div class="line">47</div><div class="line">48</div><div class="line">49</div><div class="line">50</div><div class="line">51</div><div class="line">52</div><div class="line">53</div><div class="line">54</div><div class="line">55</div><div class="line">56</div><div class="line">57</div><div class="line">58</div><div class="line">59</div><div class="line">60</div><div class="line">61</div><div class="line">62</div><div class="line">63</div><div class="line">64</div><div class="line">65</div><div class="line">66</div><div class="line">67</div><div class="line">68</div><div class="line">69</div><div class="line">70</div><div class="line">71</div><div class="line">72</div><div class="line">73</div><div class="line">74</div><div class="line">75</div><div class="line">76</div><div class="line">77</div><div class="line">78</div><div class="line">79</div><div class="line">80</div><div class="line">81</div><div class="line">82</div><div class="line">83</div><div class="line">84</div><div class="line">85</div><div class="line">86</div><div class="line">87</div><div class="line">88</div><div class="line">89</div><div class="line">90</div><div class="line">91</div><div class="line">92</div><div class="line">93</div></pre></td><td class="code"><pre><div class="line"><span class="function"><span class="keyword">final</span> V <span class="title">putVal</span><span class="params">(K key, V value, <span class="keyword">boolean</span> onlyIfAbsent)</span> </span>{</div><div class="line"> <span class="keyword">if</span> (key == <span class="keyword">null</span> || value == <span class="keyword">null</span>) <span class="keyword">throw</span> <span class="keyword">new</span> NullPointerException();</div><div class="line"> <span class="comment">//根据key的hashcode再次求hash</span></div><div class="line"> <span class="keyword">int</span> hash = spread(key.hashCode());</div><div class="line"> <span class="keyword">int</span> binCount = <span class="number">0</span>;</div><div class="line"> <span class="comment">//开始操作数组 这里是个死循环 会在插入数据成功后break掉</span></div><div class="line"> <span class="keyword">for</span> (Node<K,V>[] tab = table;;) {</div><div class="line"> Node<K,V> f; <span class="keyword">int</span> n, i, fh;</div><div class="line"> <span class="comment">//数组并没有在构造方法里初始化，所以在第一次put的时候，会初始化数组</span></div><div class="line"> <span class="keyword">if</span> (tab == <span class="keyword">null</span> || (n = tab.length) == <span class="number">0</span>)</div><div class="line"> <span class="comment">//这里我理解的是这样的，因为外层是个死循环，所以第一次执行到这的时候会进行初始化</span></div><div class="line"> <span class="comment">//然后就进入了下一次循环，因为已经初始化完毕了，所以就会进入别的分支判断</span></div><div class="line"> tab = initTable();</div><div class="line"> <span class="keyword">else</span> <span class="keyword">if</span> ((f = tabAt(tab, i = (n - <span class="number">1</span>) & hash)) == <span class="keyword">null</span>) {</div><div class="line"> <span class="comment">/** 进入这个判断的条件是在数组下标位置上没有节点，就证明是个新节点可以直接插入</span></div><div class="line"> * 所以就进入了这层，在这层插入的时候，因为只用了一个if判断是用的cas操作</div><div class="line"> * 所以有可能会失败，当失败时，还是因为外层是个死循环，所以会一直执行这个插入</div><div class="line"> * 直到插入成功，break掉</div><div class="line"> * 并且f 和i 也顺便在这里进行了赋值 i等于数组长度-1 与上 hash </div><div class="line"> * f 等于 数组 i 位置上的元素 </div><div class="line"> * </div><div class="line"> * /</div><div class="line"> if (casTabAt(tab, i, null,</div><div class="line"> new Node<K,V>(hash, key, value, null)))</div><div class="line"> break; // no lock when adding to empty bin</div><div class="line"> }</div><div class="line"> else if ((fh = f.hash) == MOVED)</div><div class="line"> tab = helpTransfer(tab, f);</div><div class="line"> else {</div><div class="line"> /**</div><div class="line"> * 到这个判断，就证明数组下标位置现在是有节点的，所以会有2种操作，链表和树的操作</div><div class="line"> * 首先在这里锁住了首节点</div><div class="line"> */</div><div class="line"> V oldVal = <span class="keyword">null</span>;</div><div class="line"> <span class="keyword">synchronized</span> (f) {</div><div class="line"> <span class="comment">//由与上面f 和 i 已经赋值过了，所以这里再次进行了确认是否是同一个对象</span></div><div class="line"> <span class="keyword">if</span> (tabAt(tab, i) == f) {</div><div class="line"> <span class="keyword">if</span> (fh >= <span class="number">0</span>) {</div><div class="line"> binCount = <span class="number">1</span>;</div><div class="line"> <span class="comment">// 以下这个循环是对链表进行循环</span></div><div class="line"> <span class="keyword">for</span> (Node<K,V> e = f;; ++binCount) {</div><div class="line"> K ek;</div><div class="line"> <span class="comment">// 如果hash值 和key 完全相等，就证明是同一个对象</span></div><div class="line"> <span class="comment">// 如果没有设置替换新值到这里就结束了</span></div><div class="line"> <span class="comment">// 如果设置了就替换新值，并且结束</span></div><div class="line"> <span class="keyword">if</span> (e.hash == hash &&</div><div class="line"> ((ek = e.key) == key ||</div><div class="line"> (ek != <span class="keyword">null</span> && key.equals(ek)))) {</div><div class="line"> oldVal = e.val;</div><div class="line"> <span class="keyword">if</span> (!onlyIfAbsent)</div><div class="line"> e.val = value;</div><div class="line"> <span class="keyword">break</span>;</div><div class="line"> }</div><div class="line"> <span class="comment">//这里是循环完整个链表都没有发现有相等的key</span></div><div class="line"> <span class="comment">//直接在链表最后插入新的节点，并且结束</span></div><div class="line"> Node<K,V> pred = e;</div><div class="line"> <span class="keyword">if</span> ((e = e.next) == <span class="keyword">null</span>) {</div><div class="line"> pred.next = <span class="keyword">new</span> Node<K,V>(hash, key,</div><div class="line"> value, <span class="keyword">null</span>);</div><div class="line"> <span class="keyword">break</span>;</div><div class="line"> }</div><div class="line"> }</div><div class="line"> }</div><div class="line"> <span class="keyword">else</span> <span class="keyword">if</span> (f <span class="keyword">instanceof</span> TreeBin) {</div><div class="line"> Node<K,V> p;</div><div class="line"> binCount = <span class="number">2</span>;</div><div class="line"> <span class="comment">//这里判断，如果节点是树类型的，则把节点放入到树结构中</span></div><div class="line"> <span class="comment">//同链表一样，如果设置了需要覆盖新值，更新一下</span></div><div class="line"> <span class="keyword">if</span> ((p = ((TreeBin<K,V>)f).putTreeVal(hash, key,</div><div class="line"> value)) != <span class="keyword">null</span>) {</div><div class="line"> oldVal = p.val;</div><div class="line"> <span class="keyword">if</span> (!onlyIfAbsent)</div><div class="line"> p.val = value;</div><div class="line"> }</div><div class="line"> }</div><div class="line"> }</div><div class="line"> }</div><div class="line"> <span class="comment">//binCount 在树中是写死的2 在链表中会随着操作的增加而增加</span></div><div class="line"> <span class="keyword">if</span> (binCount != <span class="number">0</span>) {</div><div class="line"> <span class="comment">//如果超过了设置的值，就需要把链表转换成树结构</span></div><div class="line"> <span class="keyword">if</span> (binCount >= TREEIFY_THRESHOLD)</div><div class="line"> <span class="comment">//转树操作，但里面还会有扩容</span></div><div class="line"> treeifyBin(tab, i);</div><div class="line"> <span class="comment">// 因为上边的操作存储了oldVal，如果不为空直接返回此值，结束</span></div><div class="line"> <span class="keyword">if</span> (oldVal != <span class="keyword">null</span>)</div><div class="line"> <span class="keyword">return</span> oldVal;</div><div class="line"> <span class="keyword">break</span>;</div><div class="line"> }</div><div class="line"> }</div><div class="line"> }</div><div class="line"> addCount(<span class="number">1L</span>, binCount);</div><div class="line"> <span class="keyword">return</span> <span class="keyword">null</span>;</div><div class="line"> }</div></pre></td></tr></table></figure>
<p>put方法总结：</p>
<blockquote>
<p>存放对象的时候，第一次操作，会先初始化底层的数组对象，然后再进行后续的操作<br>在存放元素的时候有这么几种情况：<br>1.如果计算出的hash值与上数组长度得出的下标位置为null，则可以直接插入<br>2.如果当前元素的hash值为MOVED，就证明有线程在进行扩容，就帮助一起扩容<br>3.都没有的情况下，证明当前下标存在其他元素，则进入元素追加，如果是链表就进行链表的操作，如果是树，就进行树的操作，最后添加元素完成。<br>4.添加完元素，如果需要进行树的转换，进行转换。<br>5.增加计数器，完成所有操作。 </p>
</blockquote>
<p>treeifyBin方法</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div></pre></td><td class="code"><pre><div class="line"><span class="function"><span class="keyword">private</span> <span class="keyword">final</span> <span class="keyword">void</span> <span class="title">treeifyBin</span><span class="params">(Node<K,V>[] tab, <span class="keyword">int</span> index)</span> </span>{</div><div class="line"> Node<K,V> b; <span class="keyword">int</span> n, sc;</div><div class="line"> <span class="keyword">if</span> (tab != <span class="keyword">null</span>) {</div><div class="line"> <span class="comment">//如果当前数组长度小于64，会直接扩容2倍，而不把当前节点轩换为树。</span></div><div class="line"> <span class="keyword">if</span> ((n = tab.length) < MIN_TREEIFY_CAPACITY)</div><div class="line"> tryPresize(n << <span class="number">1</span>);</div><div class="line"> <span class="comment">//获取index位置的节点，并且判断hash值为正常的节点，因为有可能存在-1等情况</span></div><div class="line"> <span class="keyword">else</span> <span class="keyword">if</span> ((b = tabAt(tab, index)) != <span class="keyword">null</span> && b.hash >= <span class="number">0</span>) {</div><div class="line"> <span class="comment">//锁住首节点</span></div><div class="line"> <span class="keyword">synchronized</span> (b) {</div><div class="line"> <span class="keyword">if</span> (tabAt(tab, index) == b) {</div><div class="line"> TreeNode<K,V> hd = <span class="keyword">null</span>, tl = <span class="keyword">null</span>;</div><div class="line"> <span class="comment">//遍历所有节点，转换为树节点</span></div><div class="line"> <span class="keyword">for</span> (Node<K,V> e = b; e != <span class="keyword">null</span>; e = e.next) {</div><div class="line"> TreeNode<K,V> p =</div><div class="line"> <span class="keyword">new</span> TreeNode<K,V>(e.hash, e.key, e.val,</div><div class="line"> <span class="keyword">null</span>, <span class="keyword">null</span>);</div><div class="line"> <span class="keyword">if</span> ((p.prev = tl) == <span class="keyword">null</span>)</div><div class="line"> hd = p;</div><div class="line"> <span class="keyword">else</span></div><div class="line"> tl.next = p;</div><div class="line"> tl = p;</div><div class="line"> }</div><div class="line"> <span class="comment">//然后把TreeNode包装成TreeBin做为数组下标的对象</span></div><div class="line"> setTabAt(tab, index, <span class="keyword">new</span> TreeBin<K,V>(hd));</div><div class="line"> }</div><div class="line"> }</div><div class="line"> }</div><div class="line"> }</div><div class="line"> }</div></pre></td></tr></table></figure>
<p>treeifyBin方法总结：</p>
<blockquote>
<p>如果当前数组长度小于64，则不进行树元素的转换，直接扩容成2倍，如果不是的话，那就对节点进行转换，从链表节点，转换为树节点。</p>
</blockquote>
<p>tryPresize方法</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div><div class="line">31</div><div class="line">32</div><div class="line">33</div><div class="line">34</div><div class="line">35</div><div class="line">36</div><div class="line">37</div><div class="line">38</div><div class="line">39</div><div class="line">40</div><div class="line">41</div><div class="line">42</div><div class="line">43</div><div class="line">44</div><div class="line">45</div><div class="line">46</div><div class="line">47</div><div class="line">48</div><div class="line">49</div><div class="line">50</div><div class="line">51</div><div class="line">52</div><div class="line">53</div></pre></td><td class="code"><pre><div class="line"><span class="function"><span class="keyword">private</span> <span class="keyword">final</span> <span class="keyword">void</span> <span class="title">tryPresize</span><span class="params">(<span class="keyword">int</span> size)</span> </span>{</div><div class="line"><span class="comment">//根据给出的长度，计算出实际的长度</span></div><div class="line"> <span class="keyword">int</span> c = (size >= (MAXIMUM_CAPACITY >>> <span class="number">1</span>)) ? MAXIMUM_CAPACITY :</div><div class="line"> tableSizeFor(size + (size >>> <span class="number">1</span>) + <span class="number">1</span>);</div><div class="line"> <span class="keyword">int</span> sc;</div><div class="line"> <span class="comment">//sc>=0的条件下才会进入SizeCtl的具体值见定义</span></div><div class="line"> <span class="keyword">while</span> ((sc = sizeCtl) >= <span class="number">0</span>) {</div><div class="line"> Node<K,V>[] tab = table; <span class="keyword">int</span> n;</div><div class="line"> <span class="comment">//数组没有初始化的情况，也就是一次都没有初始化，我个人感觉不会执行到这呢？</span></div><div class="line"> <span class="keyword">if</span> (tab == <span class="keyword">null</span> || (n = tab.length) == <span class="number">0</span>) {</div><div class="line"> n = (sc > c) ? sc : c;</div><div class="line"> <span class="comment">//把sizeCtl值修改为-1，为正在处理中</span></div><div class="line"> <span class="keyword">if</span> (U.compareAndSwapInt(<span class="keyword">this</span>, SIZECTL, sc, -<span class="number">1</span>)) {</div><div class="line"> <span class="keyword">try</span> {</div><div class="line"> <span class="comment">//这里再次判断了2个对象是否是一个对象，估计是为了防止其他对象操作？</span></div><div class="line"> <span class="keyword">if</span> (table == tab) {</div><div class="line"> <span class="comment">//初始化数组</span></div><div class="line"> <span class="meta">@SuppressWarnings</span>(<span class="string">"unchecked"</span>)</div><div class="line"> Node<K,V>[] nt = (Node<K,V>[])<span class="keyword">new</span> Node<?,?>[n];</div><div class="line"> table = nt;</div><div class="line"> sc = n - (n >>> <span class="number">2</span>);</div><div class="line"> }</div><div class="line"> } <span class="keyword">finally</span> {</div><div class="line"> <span class="comment">//最后修改sizeCtl的值，这里为什么没有用CAS操作，我理解是因为前边的if里已经修改为了-1，其他的线程不能操作，所以这里只用了普通的赋值</span></div><div class="line"> sizeCtl = sc;</div><div class="line"> }</div><div class="line"> }</div><div class="line"> }</div><div class="line"> <span class="comment">//如果没到0.75数，或者已经大于最大值，停止此方法</span></div><div class="line"> <span class="keyword">else</span> <span class="keyword">if</span> (c <= sc || n >= MAXIMUM_CAPACITY)</div><div class="line"> <span class="keyword">break</span>;</div><div class="line"> <span class="comment">//到这里就证明数组是已经初始化过了的，并且需要扩容</span></div><div class="line"> <span class="keyword">else</span> <span class="keyword">if</span> (tab == table) {</div><div class="line"> <span class="keyword">int</span> rs = resizeStamp(n);</div><div class="line"> <span class="comment">//这里是判断sc的值小于0证明在处理</span></div><div class="line"> <span class="keyword">if</span> (sc < <span class="number">0</span>) {</div><div class="line"> Node<K,V>[] nt;</div><div class="line"> <span class="comment">//没看懂什么意思</span></div><div class="line"> <span class="keyword">if</span> ((sc >>> RESIZE_STAMP_SHIFT) != rs || sc == rs + <span class="number">1</span> ||</div><div class="line"> sc == rs + MAX_RESIZERS || (nt = nextTable) == <span class="keyword">null</span> ||</div><div class="line"> transferIndex <= <span class="number">0</span>)</div><div class="line"> <span class="keyword">break</span>;</div><div class="line"> <span class="comment">//把sizeCtl值+1并且进行扩容</span></div><div class="line"> <span class="keyword">if</span> (U.compareAndSwapInt(<span class="keyword">this</span>, SIZECTL, sc, sc + <span class="number">1</span>))</div><div class="line"> transfer(tab, nt);</div><div class="line"> }</div><div class="line"> <span class="comment">//(rs << RESIZE_STAMP_SHIFT) + 2)没看懂求出来的这个值是什么，sc的值替换成这个之后，也进行扩容</span></div><div class="line"> <span class="keyword">else</span> <span class="keyword">if</span> (U.compareAndSwapInt(<span class="keyword">this</span>, SIZECTL, sc,</div><div class="line"> (rs << RESIZE_STAMP_SHIFT) + <span class="number">2</span>))</div><div class="line"> transfer(tab, <span class="keyword">null</span>);</div><div class="line"> }</div><div class="line"> }</div><div class="line"> }</div></pre></td></tr></table></figure>
<p>tryPresize方法总结：</p>
<blockquote>
<p>这里就是对数组的一些异常情况做了兼容处理，最终保证扩容完成。</p>
</blockquote>
<p>transfer方法</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div><div class="line">31</div><div class="line">32</div><div class="line">33</div><div class="line">34</div><div class="line">35</div><div class="line">36</div><div class="line">37</div><div class="line">38</div><div class="line">39</div><div class="line">40</div><div class="line">41</div><div class="line">42</div><div class="line">43</div><div class="line">44</div><div class="line">45</div><div class="line">46</div><div class="line">47</div><div class="line">48</div><div class="line">49</div><div class="line">50</div><div class="line">51</div><div class="line">52</div><div class="line">53</div><div class="line">54</div><div class="line">55</div><div class="line">56</div><div class="line">57</div><div class="line">58</div><div class="line">59</div><div class="line">60</div><div class="line">61</div><div class="line">62</div><div class="line">63</div><div class="line">64</div><div class="line">65</div><div class="line">66</div><div class="line">67</div><div class="line">68</div><div class="line">69</div><div class="line">70</div><div class="line">71</div><div class="line">72</div><div class="line">73</div><div class="line">74</div><div class="line">75</div><div class="line">76</div><div class="line">77</div><div class="line">78</div><div class="line">79</div><div class="line">80</div><div class="line">81</div><div class="line">82</div><div class="line">83</div><div class="line">84</div><div class="line">85</div><div class="line">86</div><div class="line">87</div><div class="line">88</div><div class="line">89</div><div class="line">90</div><div class="line">91</div><div class="line">92</div><div class="line">93</div><div class="line">94</div><div class="line">95</div><div class="line">96</div><div class="line">97</div><div class="line">98</div><div class="line">99</div><div class="line">100</div><div class="line">101</div><div class="line">102</div><div class="line">103</div><div class="line">104</div><div class="line">105</div><div class="line">106</div><div class="line">107</div><div class="line">108</div><div class="line">109</div><div class="line">110</div><div class="line">111</div><div class="line">112</div><div class="line">113</div><div class="line">114</div><div class="line">115</div><div class="line">116</div><div class="line">117</div><div class="line">118</div><div class="line">119</div><div class="line">120</div><div class="line">121</div><div class="line">122</div><div class="line">123</div><div class="line">124</div><div class="line">125</div><div class="line">126</div><div class="line">127</div><div class="line">128</div><div class="line">129</div><div class="line">130</div><div class="line">131</div><div class="line">132</div><div class="line">133</div><div class="line">134</div><div class="line">135</div><div class="line">136</div><div class="line">137</div><div class="line">138</div><div class="line">139</div><div class="line">140</div><div class="line">141</div><div class="line">142</div></pre></td><td class="code"><pre><div class="line"><span class="function"><span class="keyword">private</span> <span class="keyword">final</span> <span class="keyword">void</span> <span class="title">transfer</span><span class="params">(Node<K,V>[] tab, Node<K,V>[] nextTab)</span> </span>{</div><div class="line"> <span class="keyword">int</span> n = tab.length, stride;</div><div class="line"> <span class="comment">//求出处理数组的线程数，最大是16个线程</span></div><div class="line"> <span class="keyword">if</span> ((stride = (NCPU > <span class="number">1</span>) ? (n >>> <span class="number">3</span>) / NCPU : n) < MIN_TRANSFER_STRIDE)</div><div class="line"> stride = MIN_TRANSFER_STRIDE; <span class="comment">// subdivide range</span></div><div class="line"> <span class="keyword">if</span> (nextTab == <span class="keyword">null</span>) { <span class="comment">// initiating</span></div><div class="line"> <span class="comment">//构造nextTab，长度为原来的2倍</span></div><div class="line"> <span class="keyword">try</span> {</div><div class="line"> <span class="meta">@SuppressWarnings</span>(<span class="string">"unchecked"</span>)</div><div class="line"> Node<K,V>[] nt = (Node<K,V>[])<span class="keyword">new</span> Node<?,?>[n << <span class="number">1</span>];</div><div class="line"> nextTab = nt;</div><div class="line"> } <span class="keyword">catch</span> (Throwable ex) { <span class="comment">// try to cope with OOME</span></div><div class="line"> <span class="comment">//如果失败，则设置sc的最大值为int的最大值</span></div><div class="line"> sizeCtl = Integer.MAX_VALUE;</div><div class="line"> <span class="keyword">return</span>;</div><div class="line"> }</div><div class="line"> nextTable = nextTab;</div><div class="line"> <span class="comment">//这里我理解的就是，因为是原来的2倍，所以转换的下标是n</span></div><div class="line"> transferIndex = n;</div><div class="line"> }</div><div class="line"> <span class="keyword">int</span> nextn = nextTab.length;</div><div class="line"> <span class="comment">//构造节点元素，用来标明此节点是正在处理的节点，此节点的hash值为-1</span></div><div class="line"> ForwardingNode<K,V> fwd = <span class="keyword">new</span> ForwardingNode<K,V>(nextTab);</div><div class="line"> <span class="keyword">boolean</span> advance = <span class="keyword">true</span>;</div><div class="line"> <span class="keyword">boolean</span> finishing = <span class="keyword">false</span>; <span class="comment">// to ensure sweep before committing nextTab</span></div><div class="line"> <span class="keyword">for</span> (<span class="keyword">int</span> i = <span class="number">0</span>, bound = <span class="number">0</span>;;) {</div><div class="line"> Node<K,V> f; <span class="keyword">int</span> fh;</div><div class="line"> <span class="keyword">while</span> (advance) {</div><div class="line"> <span class="keyword">int</span> nextIndex, nextBound;</div><div class="line"> <span class="keyword">if</span> (--i >= bound || finishing)</div><div class="line"> advance = <span class="keyword">false</span>;</div><div class="line"> <span class="keyword">else</span> <span class="keyword">if</span> ((nextIndex = transferIndex) <= <span class="number">0</span>) {</div><div class="line"> i = -<span class="number">1</span>;</div><div class="line"> advance = <span class="keyword">false</span>;</div><div class="line"> }</div><div class="line"> <span class="keyword">else</span> <span class="keyword">if</span> (U.compareAndSwapInt</div><div class="line"> (<span class="keyword">this</span>, TRANSFERINDEX, nextIndex,</div><div class="line"> nextBound = (nextIndex > stride ?</div><div class="line"> nextIndex - stride : <span class="number">0</span>))) {</div><div class="line"> bound = nextBound;</div><div class="line"> i = nextIndex - <span class="number">1</span>;</div><div class="line"> advance = <span class="keyword">false</span>;</div><div class="line"> }</div><div class="line"> }</div><div class="line"> <span class="keyword">if</span> (i < <span class="number">0</span> || i >= n || i + n >= nextn) {</div><div class="line"> <span class="keyword">int</span> sc;</div><div class="line"> <span class="keyword">if</span> (finishing) {</div><div class="line"> nextTable = <span class="keyword">null</span>;</div><div class="line"> table = nextTab;</div><div class="line"> sizeCtl = (n << <span class="number">1</span>) - (n >>> <span class="number">1</span>);</div><div class="line"> <span class="keyword">return</span>;</div><div class="line"> }</div><div class="line"> <span class="keyword">if</span> (U.compareAndSwapInt(<span class="keyword">this</span>, SIZECTL, sc = sizeCtl, sc - <span class="number">1</span>)) {</div><div class="line"> <span class="keyword">if</span> ((sc - <span class="number">2</span>) != resizeStamp(n) << RESIZE_STAMP_SHIFT)</div><div class="line"> <span class="keyword">return</span>;</div><div class="line"> finishing = advance = <span class="keyword">true</span>;</div><div class="line"> i = n; <span class="comment">// recheck before commit</span></div><div class="line"> }</div><div class="line"> }</div><div class="line"> <span class="keyword">else</span> <span class="keyword">if</span> ((f = tabAt(tab, i)) == <span class="keyword">null</span>)</div><div class="line"> advance = casTabAt(tab, i, <span class="keyword">null</span>, fwd);</div><div class="line"> <span class="keyword">else</span> <span class="keyword">if</span> ((fh = f.hash) == MOVED)</div><div class="line"> advance = <span class="keyword">true</span>; <span class="comment">// already processed</span></div><div class="line"> <span class="keyword">else</span> {</div><div class="line"> <span class="comment">//锁住当前元素节点</span></div><div class="line"> <span class="keyword">synchronized</span> (f) {</div><div class="line"> <span class="comment">//再次确认节点是否相等，防止其他线程修改此节点</span></div><div class="line"> <span class="keyword">if</span> (tabAt(tab, i) == f) {</div><div class="line"> Node<K,V> ln, hn;</div><div class="line"> <span class="comment">//链表</span></div><div class="line"> <span class="keyword">if</span> (fh >= <span class="number">0</span>) {</div><div class="line"> <span class="comment">//这里我不太理解为什么是&n，因为在普通put值的时候是&(n-1)，这里求出的其实也是个下标位置</span></div><div class="line"> <span class="keyword">int</span> runBit = fh & n;</div><div class="line"> Node<K,V> lastRun = f;</div><div class="line"> <span class="keyword">for</span> (Node<K,V> p = f.next; p != <span class="keyword">null</span>; p = p.next) {</div><div class="line"> <span class="comment">//这里对链表后面的元素也都进行了求值，但我个人理解这里的b应该绝对等于runBit才对啊，因为他们在put的时候被放入了同一个桶，就应该是hash值相同才对的</span></div><div class="line"> <span class="keyword">int</span> b = p.hash & n;</div><div class="line"> <span class="keyword">if</span> (b != runBit) {</div><div class="line"> runBit = b;</div><div class="line"> lastRun = p;</div><div class="line"> }</div><div class="line"> }</div><div class="line"> <span class="keyword">if</span> (runBit == <span class="number">0</span>) {</div><div class="line"> ln = lastRun;</div><div class="line"> hn = <span class="keyword">null</span>;</div><div class="line"> }</div><div class="line"> <span class="keyword">else</span> {</div><div class="line"> hn = lastRun;</div><div class="line"> ln = <span class="keyword">null</span>;</div><div class="line"> }</div><div class="line"> <span class="keyword">for</span> (Node<K,V> p = f; p != lastRun; p = p.next) {</div><div class="line"> <span class="keyword">int</span> ph = p.hash; K pk = p.key; V pv = p.val;</div><div class="line"> <span class="keyword">if</span> ((ph & n) == <span class="number">0</span>)</div><div class="line"> ln = <span class="keyword">new</span> Node<K,V>(ph, pk, pv, ln);</div><div class="line"> <span class="keyword">else</span></div><div class="line"> hn = <span class="keyword">new</span> Node<K,V>(ph, pk, pv, hn);</div><div class="line"> }</div><div class="line"> setTabAt(nextTab, i, ln);</div><div class="line"> setTabAt(nextTab, i + n, hn);</div><div class="line"> setTabAt(tab, i, fwd);</div><div class="line"> advance = <span class="keyword">true</span>;</div><div class="line"> }</div><div class="line"> <span class="keyword">else</span> <span class="keyword">if</span> (f <span class="keyword">instanceof</span> TreeBin) {</div><div class="line"> TreeBin<K,V> t = (TreeBin<K,V>)f;</div><div class="line"> TreeNode<K,V> lo = <span class="keyword">null</span>, loTail = <span class="keyword">null</span>;</div><div class="line"> TreeNode<K,V> hi = <span class="keyword">null</span>, hiTail = <span class="keyword">null</span>;</div><div class="line"> <span class="keyword">int</span> lc = <span class="number">0</span>, hc = <span class="number">0</span>;</div><div class="line"> <span class="keyword">for</span> (Node<K,V> e = t.first; e != <span class="keyword">null</span>; e = e.next) {</div><div class="line"> <span class="keyword">int</span> h = e.hash;</div><div class="line"> TreeNode<K,V> p = <span class="keyword">new</span> TreeNode<K,V></div><div class="line"> (h, e.key, e.val, <span class="keyword">null</span>, <span class="keyword">null</span>);</div><div class="line"> <span class="keyword">if</span> ((h & n) == <span class="number">0</span>) {</div><div class="line"> <span class="keyword">if</span> ((p.prev = loTail) == <span class="keyword">null</span>)</div><div class="line"> lo = p;</div><div class="line"> <span class="keyword">else</span></div><div class="line"> loTail.next = p;</div><div class="line"> loTail = p;</div><div class="line"> ++lc;</div><div class="line"> }</div><div class="line"> <span class="keyword">else</span> {</div><div class="line"> <span class="keyword">if</span> ((p.prev = hiTail) == <span class="keyword">null</span>)</div><div class="line"> hi = p;</div><div class="line"> <span class="keyword">else</span></div><div class="line"> hiTail.next = p;</div><div class="line"> hiTail = p;</div><div class="line"> ++hc;</div><div class="line"> }</div><div class="line"> }</div><div class="line"> ln = (lc <= UNTREEIFY_THRESHOLD) ? untreeify(lo) :</div><div class="line"> (hc != <span class="number">0</span>) ? <span class="keyword">new</span> TreeBin<K,V>(lo) : t;</div><div class="line"> hn = (hc <= UNTREEIFY_THRESHOLD) ? untreeify(hi) :</div><div class="line"> (lc != <span class="number">0</span>) ? <span class="keyword">new</span> TreeBin<K,V>(hi) : t;</div><div class="line"> setTabAt(nextTab, i, ln);</div><div class="line"> setTabAt(nextTab, i + n, hn);</div><div class="line"> setTabAt(tab, i, fwd);</div><div class="line"> advance = <span class="keyword">true</span>;</div><div class="line"> }</div><div class="line"> }</div><div class="line"> }</div><div class="line"> }</div><div class="line"> }</div><div class="line"> }</div></pre></td></tr></table></figure>
<p>transfer方法总结：<br>></p>
<p>addCount方法</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div><div class="line">31</div><div class="line">32</div><div class="line">33</div><div class="line">34</div><div class="line">35</div><div class="line">36</div><div class="line">37</div><div class="line">38</div><div class="line">39</div><div class="line">40</div></pre></td><td class="code"><pre><div class="line"><span class="function"><span class="keyword">private</span> <span class="keyword">final</span> <span class="keyword">void</span> <span class="title">addCount</span><span class="params">(<span class="keyword">long</span> x, <span class="keyword">int</span> check)</span> </span>{</div><div class="line"> CounterCell[] as; <span class="keyword">long</span> b, s;</div><div class="line"> <span class="comment">//使as等于counterCells 并且不等于null </span></div><div class="line"> <span class="comment">//或者在修改baseCount时失败，才会进入此方法</span></div><div class="line"> <span class="comment">//这里的x值，我个人理解的也就是此次增加了几个元素。</span></div><div class="line"> <span class="keyword">if</span> ((as = counterCells) != <span class="keyword">null</span> ||</div><div class="line"> !U.compareAndSwapLong(<span class="keyword">this</span>, BASECOUNT, b = baseCount, s = b + x)) {</div><div class="line"> CounterCell a; <span class="keyword">long</span> v; <span class="keyword">int</span> m;</div><div class="line"> <span class="keyword">boolean</span> uncontended = <span class="keyword">true</span>;</div><div class="line"> <span class="keyword">if</span> (as == <span class="keyword">null</span> || (m = as.length - <span class="number">1</span>) < <span class="number">0</span> ||</div><div class="line"> (a = as[ThreadLocalRandom.getProbe() & m]) == <span class="keyword">null</span> ||</div><div class="line"> !(uncontended =</div><div class="line"> U.compareAndSwapLong(a, CELLVALUE, v = a.value, v + x))) {</div><div class="line"> fullAddCount(x, uncontended);</div><div class="line"> <span class="keyword">return</span>;</div><div class="line"> }</div><div class="line"> <span class="keyword">if</span> (check <= <span class="number">1</span>)</div><div class="line"> <span class="keyword">return</span>;</div><div class="line"> s = sumCount();</div><div class="line"> }</div><div class="line"> <span class="keyword">if</span> (check >= <span class="number">0</span>) {</div><div class="line"> Node<K,V>[] tab, nt; <span class="keyword">int</span> n, sc;</div><div class="line"> <span class="keyword">while</span> (s >= (<span class="keyword">long</span>)(sc = sizeCtl) && (tab = table) != <span class="keyword">null</span> &&</div><div class="line"> (n = tab.length) < MAXIMUM_CAPACITY) {</div><div class="line"> <span class="keyword">int</span> rs = resizeStamp(n);</div><div class="line"> <span class="keyword">if</span> (sc < <span class="number">0</span>) {</div><div class="line"> <span class="keyword">if</span> ((sc >>> RESIZE_STAMP_SHIFT) != rs || sc == rs + <span class="number">1</span> ||</div><div class="line"> sc == rs + MAX_RESIZERS || (nt = nextTable) == <span class="keyword">null</span> ||</div><div class="line"> transferIndex <= <span class="number">0</span>)</div><div class="line"> <span class="keyword">break</span>;</div><div class="line"> <span class="keyword">if</span> (U.compareAndSwapInt(<span class="keyword">this</span>, SIZECTL, sc, sc + <span class="number">1</span>))</div><div class="line"> transfer(tab, nt);</div><div class="line"> }</div><div class="line"> <span class="keyword">else</span> <span class="keyword">if</span> (U.compareAndSwapInt(<span class="keyword">this</span>, SIZECTL, sc,</div><div class="line"> (rs << RESIZE_STAMP_SHIFT) + <span class="number">2</span>))</div><div class="line"> transfer(tab, <span class="keyword">null</span>);</div><div class="line"> s = sumCount();</div><div class="line"> }</div><div class="line"> }</div><div class="line"> }</div></pre></td></tr></table></figure>
<h4 id="remove方法"><a href="#remove方法" class="headerlink" title="remove方法"></a>remove方法</h4><h4 id="get方法"><a href="#get方法" class="headerlink" title="get方法"></a>get方法</h4><h4 id="其他相关"><a href="#其他相关" class="headerlink" title="其他相关"></a>其他相关</h4><h3 id="总结"><a href="#总结" class="headerlink" title="总结"></a>总结</h3>
</div>
<div>
</div>
<div>
</div>
<footer class="post-footer">
<div class="post-eof"></div>
</footer>
</article>
<article class="post post-type-normal " itemscope itemtype="//schema.org/Article">
<header class="post-header">
<h1 class="post-title" itemprop="name headline">
<a class="post-title-link" href="/posts/java/JDK源码之LinkedHashMap.html" itemprop="url">
JDK源码之LinkedHashMap
</a>
</h1>
<div class="post-meta">
<span class="post-time">
<span class="post-meta-item-icon">
<i class="fa fa-calendar-o"></i>
</span>
<span class="post-meta-item-text">发表于</span>
<time itemprop="dateCreated" datetime="2016-12-04T13:18:58+08:00" content="2016-12-04">
2016-12-04
</time>
</span>
<span class="post-category" >
|
<span class="post-meta-item-icon">
<i class="fa fa-folder-o"></i>
</span>
<span class="post-meta-item-text">分类于</span>
<span itemprop="about" itemscope itemtype="https://schema.org/Thing">
<a href="/categories/java/" itemprop="url" rel="index">
<span itemprop="name">java</span>
</a>
</span>
</span>
<span class="post-comments-count">
|
<a href="/posts/java/JDK源码之LinkedHashMap.html#comments" itemprop="discussionUrl">
<span class="post-comments-count ds-thread-count" data-thread-key="posts/java/JDK源码之LinkedHashMap.html" itemprop="commentsCount"></span>
</a>
</span>
<span id="/posts/java/JDK源码之LinkedHashMap.html" class="leancloud_visitors" data-flag-title="JDK源码之LinkedHashMap">
|
<span class="post-meta-item-icon">
<i class="fa fa-eye"></i>
</span>
<span class="post-meta-item-text">阅读次数 </span>
<span class="leancloud-visitors-count"></span>
</span>
</div>
</header>
<div class="post-body" itemprop="articleBody">
<h2 id="LinkedHashMap使用场景"><a href="#LinkedHashMap使用场景" class="headerlink" title="LinkedHashMap使用场景"></a>LinkedHashMap使用场景</h2><p>我们都知道平常使用的HashMap是存放无顺序的，但当我们需要有顺序的HashMap的时候呢？所以JDK提供了<code>LinkedHashMap</code>和<code>TreeMap</code>2种有序的Map供我们使用。虽然以前一直都看过说<code>LinkedHashMap</code>是通过链表实现的，但一直没有去源码里探索究竟，今天看了之后原来和自己理解的不完全一样，理论的这些东西，还是自己真正去研究过才有底气。<br><code>LinkedHashMap</code>还支持插入顺序和访问顺序2种方式，默认的就是按照插入顺序排序的，如果需要按照访问顺序排序，在初始化时设置<code>accessOrder</code>为true即可。通过这个访问顺序我们也可以实现简单的LRU算法。</p>
<h2 id="源码概要"><a href="#源码概要" class="headerlink" title="源码概要"></a>源码概要</h2><p><code>LinkedHashMap</code>继承了<code>HashMap</code>，所以好多方法都是直接用的<code>HashMap</code>中的，在控制底层数据这方面，并没有选择自己去实现，而是通过重写了<code>HashMap</code>中的某些节点方法，来完成相应的功能。</p>
<p>比如通过重写一些对节点的操作来实现了自己的链表结构，增，删，改，查，几乎都是用的<code>HashMap</code>中的方法，但是在遍历的时候，以及在需要对象顺序的地方都重写了自己有序实现，这样即保持了功能性，又避免了开发重复的功能。</p>
<div class="post-more-link text-center">
<a class="btn" href="/posts/java/JDK源码之LinkedHashMap.html#more" rel="contents">
阅读全文 »
</a>
</div>
</div>
<div>
</div>
<div>
</div>
<footer class="post-footer">
<div class="post-eof"></div>
</footer>
</article>
<article class="post post-type-normal " itemscope itemtype="//schema.org/Article">
<header class="post-header">
<h1 class="post-title" itemprop="name headline">
<a class="post-title-link" href="/posts/java/JDK源码之ThreadLocal.html" itemprop="url">
JDK源码之ThreadLocal
</a>
</h1>
<div class="post-meta">
<span class="post-time">
<span class="post-meta-item-icon">
<i class="fa fa-calendar-o"></i>
</span>
<span class="post-meta-item-text">发表于</span>
<time itemprop="dateCreated" datetime="2016-11-26T21:07:05+08:00" content="2016-11-26">
2016-11-26
</time>
</span>
<span class="post-category" >
|
<span class="post-meta-item-icon">
<i class="fa fa-folder-o"></i>
</span>
<span class="post-meta-item-text">分类于</span>
<span itemprop="about" itemscope itemtype="https://schema.org/Thing">
<a href="/categories/java/" itemprop="url" rel="index">
<span itemprop="name">java</span>
</a>
</span>
</span>
<span class="post-comments-count">
|
<a href="/posts/java/JDK源码之ThreadLocal.html#comments" itemprop="discussionUrl">
<span class="post-comments-count ds-thread-count" data-thread-key="posts/java/JDK源码之ThreadLocal.html" itemprop="commentsCount"></span>
</a>
</span>
<span id="/posts/java/JDK源码之ThreadLocal.html" class="leancloud_visitors" data-flag-title="JDK源码之ThreadLocal">
|
<span class="post-meta-item-icon">
<i class="fa fa-eye"></i>
</span>
<span class="post-meta-item-text">阅读次数 </span>
<span class="leancloud-visitors-count"></span>
</span>
</div>
</header>
<div class="post-body" itemprop="articleBody">
<h4 id="ThreadLocal介绍"><a href="#ThreadLocal介绍" class="headerlink" title="ThreadLocal介绍"></a>ThreadLocal介绍</h4><p>一般我们都是如果发现有资源需要共享的时候，在多个线程之间要互相共享数据的时候，我们可以使用<code>ThreadLocal</code>来实现。因为存入<code>ThreadLocal</code>中的数据是和每个线程绑定的，所以不会存在数据竞争的问题了。</p>
<h4 id="使用场景"><a href="#使用场景" class="headerlink" title="使用场景"></a>使用场景</h4><p>例子如下：</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div></pre></td><td class="code"><pre><div class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">ThreadLocalTest</span> </span>{</div><div class="line"></div><div class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String[] args)</span> </span>{</div><div class="line"> executeThread();</div><div class="line"></div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="function"><span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">executeThread</span><span class="params">()</span> </span>{</div><div class="line"> ExecutorService executor = Executors.newFixedThreadPool(<span class="number">10</span>);</div><div class="line"> executor.submit(<span class="keyword">new</span> MyThread());</div><div class="line"> executor.submit(<span class="keyword">new</span> MyThread());</div><div class="line"> executor.submit(<span class="keyword">new</span> MyThread());</div><div class="line"> executor.shutdown();</div><div class="line"></div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="keyword">static</span> <span class="class"><span class="keyword">class</span> <span class="title">MyThread</span> <span class="keyword">extends</span> <span class="title">Thread</span> </span>{</div><div class="line"> ThreadLocal threadLocal = <span class="keyword">new</span> ThreadLocal();</div><div class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">run</span><span class="params">()</span> </span>{</div><div class="line"> String str = Thread.currentThread() + <span class="string">"_"</span> + Math.random();</div><div class="line"> threadLocal.set(str);</div><div class="line"> <span class="keyword">try</span> {</div><div class="line"> Thread.sleep(<span class="number">2000</span>);</div><div class="line"> } <span class="keyword">catch</span> (InterruptedException e) {</div><div class="line"> e.printStackTrace();</div><div class="line"> }</div><div class="line"> System.out.println(threadLocal.get());</div><div class="line"> }</div><div class="line"> }</div><div class="line">}</div></pre></td></tr></table></figure>
<div class="post-more-link text-center">
<a class="btn" href="/posts/java/JDK源码之ThreadLocal.html#more" rel="contents">
阅读全文 »
</a>
</div>
</div>
<div>
</div>
<div>
</div>
<footer class="post-footer">
<div class="post-eof"></div>
</footer>
</article>
<article class="post post-type-normal " itemscope itemtype="//schema.org/Article">
<header class="post-header">
<h1 class="post-title" itemprop="name headline">
<a class="post-title-link" href="/posts/hexo/hexo博客主动推送到百度站长平台.html" itemprop="url">
hexo博客主动推送到百度站长平台
</a>
</h1>
<div class="post-meta">
<span class="post-time">
<span class="post-meta-item-icon">
<i class="fa fa-calendar-o"></i>
</span>
<span class="post-meta-item-text">发表于</span>
<time itemprop="dateCreated" datetime="2016-11-26T17:19:09+08:00" content="2016-11-26">
2016-11-26
</time>
</span>
<span class="post-category" >
|
<span class="post-meta-item-icon">
<i class="fa fa-folder-o"></i>
</span>
<span class="post-meta-item-text">分类于</span>
<span itemprop="about" itemscope itemtype="https://schema.org/Thing">
<a href="/categories/hexo/" itemprop="url" rel="index">
<span itemprop="name">hexo</span>
</a>
</span>
</span>
<span class="post-comments-count">
|
<a href="/posts/hexo/hexo博客主动推送到百度站长平台.html#comments" itemprop="discussionUrl">
<span class="post-comments-count ds-thread-count" data-thread-key="posts/hexo/hexo博客主动推送到百度站长平台.html" itemprop="commentsCount"></span>
</a>
</span>
<span id="/posts/hexo/hexo博客主动推送到百度站长平台.html" class="leancloud_visitors" data-flag-title="hexo博客主动推送到百度站长平台">
|
<span class="post-meta-item-icon">
<i class="fa fa-eye"></i>
</span>
<span class="post-meta-item-text">阅读次数 </span>
<span class="leancloud-visitors-count"></span>
</span>
</div>
</header>
<div class="post-body" itemprop="articleBody">
<h4 id="推送百度站长平台"><a href="#推送百度站长平台" class="headerlink" title="推送百度站长平台"></a>推送百度站长平台</h4><p>百度站长平台有几种方式提交自己的链接</p>
<ol>
<li>主动推送(实时)</li>
<li>自动推送</li>
<li>sitemap</li>
</ol>
<p>或者自己手工提交，这里主要说以上三种方式。</p>
<div class="post-more-link text-center">
<a class="btn" href="/posts/hexo/hexo博客主动推送到百度站长平台.html#more" rel="contents">
阅读全文 »
</a>
</div>
</div>
<div>
</div>
<div>
</div>
<footer class="post-footer">
<div class="post-eof"></div>
</footer>
</article>
<article class="post post-type-normal " itemscope itemtype="//schema.org/Article">
<header class="post-header">
<h1 class="post-title" itemprop="name headline">
<a class="post-title-link" href="/posts/hexo/hexo博客next主题修改静态资源为CDN.html" itemprop="url">
hexo博客next主题修改静态资源为CDN
</a>
</h1>
<div class="post-meta">
<span class="post-time">
<span class="post-meta-item-icon">
<i class="fa fa-calendar-o"></i>
</span>
<span class="post-meta-item-text">发表于</span>
<time itemprop="dateCreated" datetime="2016-11-15T23:55:21+08:00" content="2016-11-15">
2016-11-15
</time>
</span>
<span class="post-category" >
|
<span class="post-meta-item-icon">
<i class="fa fa-folder-o"></i>
</span>
<span class="post-meta-item-text">分类于</span>
<span itemprop="about" itemscope itemtype="https://schema.org/Thing">
<a href="/categories/hexo/" itemprop="url" rel="index">
<span itemprop="name">hexo</span>
</a>
</span>
</span>
<span class="post-comments-count">
|
<a href="/posts/hexo/hexo博客next主题修改静态资源为CDN.html#comments" itemprop="discussionUrl">
<span class="post-comments-count ds-thread-count" data-thread-key="posts/hexo/hexo博客next主题修改静态资源为CDN.html" itemprop="commentsCount"></span>
</a>
</span>
<span id="/posts/hexo/hexo博客next主题修改静态资源为CDN.html" class="leancloud_visitors" data-flag-title="hexo博客next主题修改静态资源为CDN">
|
<span class="post-meta-item-icon">
<i class="fa fa-eye"></i>
</span>
<span class="post-meta-item-text">阅读次数 </span>
<span class="leancloud-visitors-count"></span>
</span>
</div>
</header>
<div class="post-body" itemprop="articleBody">
<h2 id="问题"><a href="#问题" class="headerlink" title="问题"></a>问题</h2><p>博主最近看到博客打开速度非常慢，点开chrome的开发者工具查看是由于css,js,图片加载太慢，故<code>css,js</code>换成了国内的cdn，图片换成了<a href="http://www.qiniu.com/">七牛云</a>。<br>打开主题配置文件<code>_config.yml</code>以下为修改方式:<br>
<div class="post-more-link text-center">
<a class="btn" href="/posts/hexo/hexo博客next主题修改静态资源为CDN.html#more" rel="contents">
阅读全文 »
</a>
</div>
</div>
<div>
</div>
<div>
</div>
<footer class="post-footer">
<div class="post-eof"></div>
</footer>
</article>
<article class="post post-type-normal " itemscope itemtype="//schema.org/Article">
<header class="post-header">