[Sync] Signal UIModelWorker to abort on sync shutdown.

components/sync/driver/glue/ui_model_worker.cc

Index: components/sync/driver/glue/ui_model_worker.cc
diff --git a/components/sync/driver/glue/ui_model_worker.cc b/components/sync/driver/glue/ui_model_worker.cc
index c812f9a9b54ed6b95cf0c974a3d07f778f2eac48..bd0ae696ca4b2c02655c1f6a24552cdb27533df7 100644
--- a/components/sync/driver/glue/ui_model_worker.cc
+++ b/components/sync/driver/glue/ui_model_worker.cc
@@ -9,16 +9,24 @@
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/callback.h"
-#include "base/synchronization/waitable_event.h"
 #include "components/sync/base/scoped_event_signal.h"
 
 namespace syncer {
 
 namespace {
 
-void CallDoWorkAndSignalEvent(const WorkCallback& work,
-                              syncer::ScopedEventSignal scoped_event_signal,
-                              SyncerError* error_info) {
+// |worker| owns the event backing |scoped_event_signal|, so it's important that
+// it comes after in the parameter list so it gets destroyed after.
+void DoWorkAndSignalEvent(const WorkCallback& work,
+                          syncer::ScopedEventSignal scoped_event_signal,
+                          scoped_refptr<ModelSafeWorker> worker,
+                          SyncerError* error_info) {
+  DCHECK(worker->IsOnModelThread());
+  if (worker->IsStopped()) {
+    // Don't set the error here; the pointer may no longer be valid.
+    return;
+  }
+
   *error_info = work.Run();
   // The event in |scoped_event_signal| is signaled at the end of this scope.
 }
@@ -27,7 +35,10 @@ void CallDoWorkAndSignalEvent(const WorkCallback& work,
 
 UIModelWorker::UIModelWorker(
     scoped_refptr<base::SingleThreadTaskRunner> ui_thread)
-    : ui_thread_(std::move(ui_thread)) {}
+    : ui_thread_(std::move(ui_thread)),
+      work_done_or_abandoned_(base::WaitableEvent::ResetPolicy::AUTOMATIC,
+                              base::WaitableEvent::InitialState::NOT_SIGNALED) {
+}
 
 SyncerError UIModelWorker::DoWorkAndWaitUntilDoneImpl(
     const WorkCallback& work) {
@@ -38,26 +49,26 @@ SyncerError UIModelWorker::DoWorkAndWaitUntilDoneImpl(
     return work.Run();
   }
 
-  // Signaled when the task is deleted, i.e. after it runs or when it is
-  // abandoned.
-  base::WaitableEvent work_done_or_abandoned(
-      base::WaitableEvent::ResetPolicy::AUTOMATIC,
-      base::WaitableEvent::InitialState::NOT_SIGNALED);
-
-  if (!ui_thread_->PostTask(FROM_HERE,
-                            base::Bind(&CallDoWorkAndSignalEvent, work,
-                                       base::Passed(syncer::ScopedEventSignal(
-                                           &work_done_or_abandoned)),
-                                       &error_info))) {
+  if (!ui_thread_->PostTask(
+          FROM_HERE, base::Bind(&DoWorkAndSignalEvent, work,
+                                base::Passed(syncer::ScopedEventSignal(
+                                    &work_done_or_abandoned_)),
+                                make_scoped_refptr(this), &error_info))) {
     DLOG(WARNING) << "Could not post work to UI loop.";
     error_info = CANNOT_DO_WORK;
     return error_info;
   }
-  work_done_or_abandoned.Wait();
+  work_done_or_abandoned_.Wait();
 
   return error_info;
 }
 
+void UIModelWorker::RequestStop() {
+  DCHECK(ui_thread_->BelongsToCurrentThread());
+  ModelSafeWorker::RequestStop();
+  work_done_or_abandoned_.Signal();
+}
+
 ModelSafeGroup UIModelWorker::GetModelSafeGroup() {
   return GROUP_UI;
 }