experimental UI: move stopUpdateThread() out of synchronized, again

aehlig · katre · commit 68028317c1d3 · 2017-06-09T14:07:39.000-04:00
The experimental UI uses a thread to regularly update itself to reflect time-based changes. As that that thread has to call synchronized methods any waiting for it to finish has to happen outside any synchronized block. Unfortunately, 9e0308e accidentally moved the stopUpdateThread() in buildComplete() into the synchronized block, thus giving an opportunity for deadlocks. Move it out again. Also, as the accounting for pending transports now happens in synchronized methods in the state tracker, the buildEventTransportClosed() method does not have to be synchronized any more---thus eliminating the second deadlock opportunity. Change-Id: Icacb2ee70f4bedde1c1aac2bcfefc6fabf42fdd3 PiperOrigin-RevId: 158537844
diff --git a/src/main/java/com/google/devtools/build/lib/runtime/ExperimentalEventHandler.java b/src/main/java/com/google/devtools/build/lib/runtime/ExperimentalEventHandler.java
@@ -446,6 +446,7 @@ public void progressReceiverAvailable(ExecutionProgressReceiverAvailableEvent ev
   public void buildComplete(BuildCompleteEvent event) {
     // The final progress bar will flow into the scroll-back buffer, to if treat
     // it as an event and add a timestamp, if events are supposed to have a timestmap.
+    boolean done = false;
     synchronized (this) {
       stateTracker.buildComplete(event);
       ignoreRefreshLimitOnce();
@@ -455,10 +456,13 @@ public void buildComplete(BuildCompleteEvent event) {
       // upload happening.
       if (stateTracker.pendingTransports() == 0) {
         buildComplete = true;
-        stopUpdateThread();
-        flushStdOutStdErrBuffers();
+        done = true;
       }
     }
+    if (done) {
+      stopUpdateThread();
+      flushStdOutStdErrBuffers();
+    }
   }
 
   @Subscribe
@@ -574,7 +578,7 @@ public synchronized void buildEventTransportsAnnounced(AnnounceBuildEventTranspo
   }
 
   @Subscribe
-  public synchronized void buildEventTransportClosed(BuildEventTransportClosedEvent event) {
+  public void buildEventTransportClosed(BuildEventTransportClosedEvent event) {
     stateTracker.buildEventTransportClosed(event);
     if (debugAllEvents) {
       this.handle(Event.info(null, "Transport " + event.transport().name() + " closed"));
@@ -721,6 +725,11 @@ public void run() {
     }
   }
 
+  /**
+   * Stop the update thread and wait for it to terminate. As the update thread, which is a separate
+   * thread, might have to call a synchronized method between being interrupted and terminating, DO
+   * NOT CALL from a SYNCHRONIZED block, as this will give the opportunity for dead locks.
+   */
   private void stopUpdateThread() {
     Thread threadToWaitFor = null;
     synchronized (this) {
