Null ModelSafeWorker's working_loop_ if loop is destructed and synchronize access to workiing_loop_. Otherwise ModelSafeWorker could try to unregister for dead loop.

BUG=274729

Review URL: https://chromiumcodereview.appspot.com/22985008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@218648 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 25 insertions, 8 deletions

diff --git a/sync/internal_api/public/engine/model_safe_worker.cc b/sync/internal_api/public/engine/model_safe_worker.cc
index 7179ed5..5c91715 100644
--- a/sync/internal_api/public/engine/model_safe_worker.cc
+++ b/sync/internal_api/public/engine/model_safe_worker.cc
@@ -134,11 +134,17 @@ void ModelSafeWorker::WillDestroyCurrentMessageLoop() {
         << " worker stops on destruction of its working thread.";
   }
 
+  {
+    base::AutoLock l(working_loop_lock_);
+    working_loop_ = NULL;
+  }
+
   if (observer_)
     observer_->OnWorkerLoopDestroyed(GetModelSafeGroup());
 }
 
 void ModelSafeWorker::SetWorkingLoopToCurrent() {
+  base::AutoLock l(working_loop_lock_);
   DCHECK(!working_loop_);
   working_loop_ = base::MessageLoop::current();
   working_loop_set_wait_.Signal();
@@ -150,19 +156,29 @@ void ModelSafeWorker::UnregisterForLoopDestruction(
   // loop.
   working_loop_set_wait_.Wait();
 
-  // Should be called on sync loop.
-  DCHECK_NE(base::MessageLoop::current(), working_loop_);
-  DCHECK(working_loop_);
-  working_loop_->PostTask(
-      FROM_HERE,
-      base::Bind(&ModelSafeWorker::UnregisterForLoopDestructionAsync,
-                 this, unregister_done_callback));
+  {
+    base::AutoLock l(working_loop_lock_);
+    if (working_loop_ != NULL) {
+      // Should be called on sync loop.
+      DCHECK_NE(base::MessageLoop::current(), working_loop_);
+      working_loop_->PostTask(
+          FROM_HERE,
+          base::Bind(&ModelSafeWorker::UnregisterForLoopDestructionAsync,
+                     this, unregister_done_callback));
+    }
+  }
 }
 
 void ModelSafeWorker::UnregisterForLoopDestructionAsync(
     base::Callback<void(ModelSafeGroup)> unregister_done_callback) {
+  {
+    base::AutoLock l(working_loop_lock_);
+    if (!working_loop_)
+      return;
+    DCHECK_EQ(base::MessageLoop::current(), working_loop_);
+  }
+
   DCHECK(stopped_);
-  DCHECK_EQ(base::MessageLoop::current(), working_loop_);
   base::MessageLoop::current()->RemoveDestructionObserver(this);
   unregister_done_callback.Run(GetModelSafeGroup());
 }
diff --git a/sync/internal_api/public/engine/model_safe_worker.h b/sync/internal_api/public/engine/model_safe_worker.h
index f6b7ea6..0f41594 100644
--- a/sync/internal_api/public/engine/model_safe_worker.h
+++ b/sync/internal_api/public/engine/model_safe_worker.h
@@ -132,6 +132,7 @@ class SYNC_EXPORT ModelSafeWorker
 
   // Remember working loop for posting task to unregister destruction
   // observation from sync thread when shutting down sync.
+  base::Lock working_loop_lock_;
   base::MessageLoop* working_loop_;
   base::WaitableEvent working_loop_set_wait_;
 };