Fix touch crash after X client disconnect

app/src/main/runtime/display/connector/XOutputStream.java

@@ -32,21 +32,25 @@ public void setAncillaryFd(int ancillaryFd) {
   }
 
   public void writeByte(byte value) {
+    if (buffer == null) return;
     ensureSpaceIsAvailable(1);
     buffer.put(value);
   }
 
   public void writeShort(short value) {
+    if (buffer == null) return;
     ensureSpaceIsAvailable(2);
     buffer.putShort(value);
   }
 
   public void writeInt(int value) {
+    if (buffer == null) return;
     ensureSpaceIsAvailable(4);
     buffer.putInt(value);
   }
 
   public void writeLong(long value) {
+    if (buffer == null) return;
     ensureSpaceIsAvailable(8);
     buffer.putLong(value);
   }
@@ -57,6 +61,7 @@ public void writeFP3232(double value) {
   }
 
   public void writeString8(String str) {
+    if (buffer == null) return;
     byte[] bytes = str.getBytes(XServer.LATIN1_CHARSET);
     int length = -bytes.length & 3;
     ensureSpaceIsAvailable(bytes.length + length);
@@ -69,11 +74,13 @@ public void write(byte[] data) {
   }
 
   public void write(byte[] data, int offset, int length) {
+    if (buffer == null) return;
     ensureSpaceIsAvailable(length);
     buffer.put(data, offset, length);
   }
 
   public void write(ByteBuffer data) {
+    if (buffer == null) return;
     ensureSpaceIsAvailable(data.remaining());
     buffer.put(data);
   }
@@ -83,6 +90,7 @@ public void writePad(int length) {
   }
 
   private void flush() throws IOException {
+    if (buffer == null) return;
     if (buffer.position() != 0) {
       buffer.flip();
 
@@ -124,9 +132,19 @@ public void close() throws IOException {
     }
   }
 
+  // Writers hold `lock` for the whole event write; releasing under the same lock
+  // means the buffer can never be freed mid-write, and later writes see null and
+  // discard (dead connection).
   public void release() {
-    XInputStream.freeDirectBuffer(buffer);
-    buffer = null;
+    lock.lock();
+    try {
+      if (buffer != null) {
+        XInputStream.freeDirectBuffer(buffer);
+        buffer = null;
+      }
+    } finally {
+      lock.unlock();
+    }
   }
 
   public void writeSuccessReply(int sequenceNumber, int replyLength) throws IOException {

app/src/main/runtime/display/xserver/XClient.java

@@ -4,6 +4,7 @@
 import com.winlator.cmod.runtime.display.connector.XInputStream;
 import com.winlator.cmod.runtime.display.connector.XOutputStream;
 import com.winlator.cmod.runtime.display.xserver.events.Event;
+import com.winlator.cmod.runtime.display.xserver.extensions.XInput2Extension;
 import com.winlator.cmod.shared.android.RefreshRateUtils;
 import java.io.IOException;
 import java.util.ArrayList;
@@ -92,6 +93,9 @@ public void freeResources() {
         eventListeners.keyAt(i).removeEventListener(eventListeners.removeAt(i));
       }
 
+      XInput2Extension xInput2Extension = xServer.getExtension(XInput2Extension.MAJOR_OPCODE);
+      if (xInput2Extension != null) xInput2Extension.onClientDisconnected(this);
+
       xServer.windowManager.removeOnResourceLifecycleListener(this);
       xServer.pixmapManager.removeOnResourceLifecycleListener(this);
       xServer.graphicsContextManager.removeOnResourceLifecycleListener(this);