Flush SequenceWorkerPool tasks after each unit test.

base/threading/sequenced_worker_pool.cc

Index: base/threading/sequenced_worker_pool.cc
===================================================================
--- base/threading/sequenced_worker_pool.cc	(revision 174239)
+++ base/threading/sequenced_worker_pool.cc	(working copy)
@@ -389,7 +389,7 @@
   ConditionVariable has_work_cv_;
 
   // Condition variable that is waited on by non-worker threads (in
-  // FlushForTesting()) until IsIdle() goes to true.
+  // FlushForTesting()) until IsIdle() goes to true or Shutdown completes.

[michaeln, 2012/12/21 03:17:55]

I might be able to better normalize things by introducing a shutdown_complete_
bool + cv pair but I think the smaller changes here are enough to break the
deadlock... i'll see what the trybots think.

   ConditionVariable is_idle_cv_;
 
   // Condition variable that is waited on by non-worker threads (in
@@ -610,8 +610,9 @@
 }
 
 void SequencedWorkerPool::Inner::FlushForTesting() {
+  base::ThreadRestrictions::ScopedAllowWait allow_wait;
   AutoLock lock(lock_);
-  while (!IsIdle())
+  while (!IsIdle() && !shutdown_called_)
     is_idle_cv_.Wait();
 }
 
@@ -635,8 +636,10 @@
     SignalHasWork();
 
     // There are no pending or running tasks blocking shutdown, we're done.
-    if (CanShutdown())
+    if (CanShutdown()) {
+      is_idle_cv_.Signal();

[michaeln, 2012/12/21 02:50:47]

FlushForTesting can wait forever if Shutdown happens after its wait has begun.
So we signal upon return to wake them.

Some existing tests are disabled due to this problem, and when adding my
additional calls to FlushForTesting more test timeouts show up.

       return;
+    }
   }
 
   // If we're here, then something is blocking shutdown.  So wait for
@@ -652,6 +655,7 @@
     AutoLock lock(lock_);
     while (!CanShutdown())
       can_shutdown_cv_.Wait();
+    is_idle_cv_.Signal();
   }
   UMA_HISTOGRAM_TIMES("SequencedWorkerPool.ShutdownDelayTime",
                       TimeTicks::Now() - shutdown_wait_begin);