Add a final event on the event bus

Add an event to the event bus that is guaranteed to come after the
completion of the command. Listeners can use this event to clean up
any resources that still need to be cleaned up. As first customer, add
the ExperimentalEventHandler so that it is guaranteed not to leak the
update thread.

--
Change-Id: Ia20bae8a00541aa1338e49f74a7320ac098ab71d
Reviewed-on: https://bazel-review.googlesource.com/#/c/4011
MOS_MIGRATED_REVID=126909844

3 files changed, 28 insertions, 0 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/runtime/AfterCommandEvent.java b/src/main/java/com/google/devtools/build/lib/runtime/AfterCommandEvent.java
new file mode 100644
index 0000000000..0cc630211f
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/runtime/AfterCommandEvent.java
@@ -0,0 +1,21 @@
+// Copyright 2016 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package com.google.devtools.build.lib.runtime;
+
+/**
+ * An event that is guaranteed to be posted after every command, no matter what the command was and
+ * how it terminated. Listeneres on the event bus can use this event to do any final resource clean
+ * up.
+ */
+public class AfterCommandEvent {}
diff --git a/src/main/java/com/google/devtools/build/lib/runtime/BlazeCommandDispatcher.java b/src/main/java/com/google/devtools/build/lib/runtime/BlazeCommandDispatcher.java
index 48a4898545..ebb512df09 100644
--- a/src/main/java/com/google/devtools/build/lib/runtime/BlazeCommandDispatcher.java
+++ b/src/main/java/com/google/devtools/build/lib/runtime/BlazeCommandDispatcher.java
@@ -501,6 +501,7 @@ public class BlazeCommandDispatcher {
           : ExitCode.BLAZE_INTERNAL_ERROR.getNumericExitCode();
       throw new ShutdownBlazeServerException(numericExitCode, ShutdownMethod.CLEAN, e);
     } finally {
+      env.getEventBus().post(new AfterCommandEvent());
       runtime.afterCommand(env, numericExitCode);
       // Swallow IOException, as we are already in a finally clause
       Flushables.flushQuietly(outErr.getOutputStream());
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
index fb0822acc7..dbc0dbffd5 100644
--- a/src/main/java/com/google/devtools/build/lib/runtime/ExperimentalEventHandler.java
+++ b/src/main/java/com/google/devtools/build/lib/runtime/ExperimentalEventHandler.java
@@ -334,6 +334,12 @@ public class ExperimentalEventHandler implements EventHandler {
   }
 
   @Subscribe
+  public synchronized void afterCommand(AfterCommandEvent event) {
+    buildComplete = true;
+    stopUpdateThread();
+  }
+
+  @Subscribe
   public void actionStarted(ActionStartedEvent event) {
     stateTracker.actionStarted(event);
     refresh();