Error: Cannot start a build if one is already running

[andreyfel]

After upgrading to ember-cli 3.17.1 this error started popping up frequently.

If you have ember s running and editing files quickly it will show up.
Edit one file, save, go to another file, edit and save before the previous incremental build is finished, the "Cannot start a build if one is already running" error pops up and live-reload won't recover. It needs to be restarted.

[nickschot]

Also noticed this on 3.16.4/5.

[andreyfel]

Other references for this issue with cli 3.15 and 3.16
https://discordapp.com/channels/480462759797063690/486548111221719040/690727373875970109
https://discordapp.com/channels/480462759797063690/483601670685720591/690647379736526969

[wagenet]

This has started happening to me very frequently on an app running ember-cli 3.17.

[houfeng0923]

i used ember3.17.0 , it happens frequently when code changed

PLATFORM: darwin x64
  FREEMEM: 186888192
  TOTALMEM: 8589934592
  UPTIME: 8965
  LOADAVG: 6.65380859375,3.20849609375,3.458984375
  CPUS:
  - Intel(R) Core(TM) i5-5257U CPU @ 2.70GHz - 2700
  - Intel(R) Core(TM) i5-5257U CPU @ 2.70GHz - 2700
  - Intel(R) Core(TM) i5-5257U CPU @ 2.70GHz - 2700
  - Intel(R) Core(TM) i5-5257U CPU @ 2.70GHz - 2700
  ENDIANNESS: LE
  VERSIONS:
  - ares: 1.15.0
  - brotli: 1.0.7
  - cldr: 35.1
  - http_parser: 2.9.3
  - icu: 64.2
  - llhttp: 2.0.4
  - modules: 72
  - napi: 5
  - nghttp2: 1.40.0
  - node: 12.16.0
  - openssl: 1.1.1d
  - tz: 2019c
  - unicode: 12.1
  - uv: 1.34.0
  - v8: 7.8.279.23-node.31
  - zlib: 1.2.11

ERROR Summary:

  - broccoliBuilderErrorStack: [undefined]
  - code: [undefined]
  - codeFrame: [undefined]
  - errorMessage: Cannot start a build if one is already running
  - errorType: [undefined]
  - location:
    - column: [undefined]
    - file: [undefined]
    - line: [undefined]
  - message: Cannot start a build if one is already running
  - name: Error
  - nodeAnnotation: [undefined]
  - nodeName: [undefined]
  - originalErrorMessage: [undefined]
  - stack: Error: Cannot start a build if one is already running
    at Builder.build (/Users/ember-test/node_modules/broccoli/dist/builder.js:100:19)
    at /Users/ember-test/node_modules/ember-cli/lib/models/builder.js:200:32

=================================================================================

[jordpo]

Yeah I'm seeing this a lot now. Happens when you do rapid code changes in a row.

[jordpo]

So you don't necessarily have to restart. You can do another change and let the build finish and livereload should recover.

[rwjblue]

This is coming from:

https://github.com/broccolijs/broccoli/blob/30f95811a966233e944a5912f5b2f4be5e157ef1/lib/builder.ts#L128

Which has been around for a while now, but I suspect the actual issue was introduced by broccolijs/broccoli#408.

@gabrielcsapo / @stefanpenner - Either of you have time to poke at this?

[mehulkar]

There might be a better way of doing this too, but I was able to downgrade like this as a workaround:

# remove broccoli from package-lock
npm uninstall --save-dev ember-cli

# install pinned version of broccoli at 3.3
npm install --save-dev broccoli@3.3

# install downgraded ember-cli which won't force
# broccoli 3.4 since current install already meets reqs
npm install --save-dev ember-cli@3.16

# get rid of explicit dep on broccoli from package.json
npm uninstall --save-dev broccoli

Note that simply downgrading ember-cli won't downgrade broccoli, because ^ ranges make npm think that 3.4.0 is a safe upgrade.

I'm sure there's a fancypants way of doing this more easily with yarn too.

Edit: I suppose after downgrading broccoli, you can install ember-cli@3.17 too, since the transitive dep range didn't change.

[gabrielcsapo]

Looking into this now

[gabrielcsapo]

https://github.com/ember-cli/ember-cli/blob/master/lib/models/builder.js#L205, this looks like we need to guard against cancellations because those are expected with this change.

[stefanpenner]

I think we need to:

option 1) Figure out how to hide this in broccoli
option 2) If we cannot, then we must:

1. disable this is broccoli (as the fix may be ember-cli)
2. fix this in ember-cli
3. have ember-cli opt-in to this functionality in broccoli

[stefanpenner]

Ok, I believe the following should be done:

1. disable the existing behavior in broccoli
2. release
   This addresses the concern quickly, allowing us to make appropriate changes in broccoli

Changes in broccoli: Rather then cancelling as is, we need to introduce the concept, using the existing cancellation plumbing, a retryable cancellation.

It will more or less be.

• builder.cancel(new RetryCancellationException('mid-build watch occurred, attempt retry') or simply builder.retry() and use RetryCancellationException internally
• builder.build learns about RetryCancellationException, and if a build fails do to a RetryCancellationException it will internally restart itself
• We could consider an internal limit on retries, to prevent infinite loops here. That threshold needs to be decided.

---

I'm going to disable this in broccoli + release now, then kick the tires on the above solution

[rwjblue]

Reverted the changes in broccolijs/broccoli#459 and released as broccoli@3.4.1.