Sync: Check that the current thread is a ModelSafeWorker's home thread.

Use this in sync_backend_host.cc to avoid dispatching to a data type
controller except when we're on the DTC's home thread.

BUG=41824
TEST=during manual testing of 2-client sync; this code is never active
during add/deletes and associates/disassociates.

Review URL: http://codereview.chromium.org/1741001

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@45201 0039d316-1c4b-4281-b951-d872f2087c98

11 files changed, 58 insertions, 2 deletions

diff --git a/chrome/browser/sync/engine/mock_model_safe_workers.h b/chrome/browser/sync/engine/mock_model_safe_workers.h
index e776596..13d66aa 100644
--- a/chrome/browser/sync/engine/mock_model_safe_workers.h
+++ b/chrome/browser/sync/engine/mock_model_safe_workers.h
@@ -12,11 +12,13 @@ namespace browser_sync {
 class MockUIModelWorker : public ModelSafeWorker {
  public:
   virtual ModelSafeGroup GetModelSafeGroup() { return GROUP_UI; }
+  virtual bool CurrentThreadIsWorkThread() { return true; }
 };
 
 class MockDBModelWorker : public ModelSafeWorker {
  public:
   virtual ModelSafeGroup GetModelSafeGroup() { return GROUP_DB; }
+  virtual bool CurrentThreadIsWorkThread() { return true; }
 };
 
 }  // namespace browser_sync
diff --git a/chrome/browser/sync/engine/model_safe_worker.h b/chrome/browser/sync/engine/model_safe_worker.h
index df2edae..7d7461a 100644
--- a/chrome/browser/sync/engine/model_safe_worker.h
+++ b/chrome/browser/sync/engine/model_safe_worker.h
@@ -49,9 +49,18 @@ class ModelSafeWorker : public base::RefCountedThreadSafe<ModelSafeWorker> {
     return GROUP_PASSIVE;
   }
 
+  // Check the current thread and see if it's the thread associated with
+  // this worker.  If this returns true, then it should be safe to operate
+  // on models that are in this worker's group.  If this returns false,
+  // such work should not be attempted.
+  virtual bool CurrentThreadIsWorkThread() {
+    // The passive group is not the work thread for any browser model.
+    return false;
+  }
+
  private:
   friend class base::RefCountedThreadSafe<ModelSafeWorker>;
-
+ 
   DISALLOW_COPY_AND_ASSIGN(ModelSafeWorker);
 };
 
diff --git a/chrome/browser/sync/glue/database_model_worker.cc b/chrome/browser/sync/glue/database_model_worker.cc
index 02516c7..95c49a6 100644
--- a/chrome/browser/sync/glue/database_model_worker.cc
+++ b/chrome/browser/sync/glue/database_model_worker.cc
@@ -33,4 +33,8 @@ void DatabaseModelWorker::CallDoWorkAndSignalTask(Closure* work,
   done->Signal();
 }
 
+bool DatabaseModelWorker::CurrentThreadIsWorkThread() {
+  return ChromeThread::CurrentlyOn(ChromeThread::DB);
+}
+
 }  // namespace browser_sync
diff --git a/chrome/browser/sync/glue/database_model_worker.h b/chrome/browser/sync/glue/database_model_worker.h
index 64f53ed..fbaf2bd 100644
--- a/chrome/browser/sync/glue/database_model_worker.h
+++ b/chrome/browser/sync/glue/database_model_worker.h
@@ -21,6 +21,7 @@ class DatabaseModelWorker : public browser_sync::ModelSafeWorker {
   // ModelSafeWorker implementation. Called on syncapi SyncerThread.
   void DoWorkAndWaitUntilDone(Closure* work);
   virtual ModelSafeGroup GetModelSafeGroup() { return GROUP_DB; }
+  virtual bool CurrentThreadIsWorkThread();
 
  private:
   void CallDoWorkAndSignalTask(Closure* work, base::WaitableEvent* done);
diff --git a/chrome/browser/sync/glue/history_model_worker.cc b/chrome/browser/sync/glue/history_model_worker.cc
index cab697c..74b914b 100644
--- a/chrome/browser/sync/glue/history_model_worker.cc
+++ b/chrome/browser/sync/glue/history_model_worker.cc
@@ -50,4 +50,9 @@ void HistoryModelWorker::DoWorkAndWaitUntilDone(Closure* work) {
   done.Wait();
 }
 
+bool HistoryModelWorker::CurrentThreadIsWorkThread() {
+  // TODO(ncarter): How to determine this?
+  return true;
+}
+
 }  // namespace browser_sync
diff --git a/chrome/browser/sync/glue/history_model_worker.h b/chrome/browser/sync/glue/history_model_worker.h
index d9fa5ed..6fd65e8 100644
--- a/chrome/browser/sync/glue/history_model_worker.h
+++ b/chrome/browser/sync/glue/history_model_worker.h
@@ -30,6 +30,7 @@ class HistoryModelWorker : public browser_sync::ModelSafeWorker,
   // ModelSafeWorker implementation. Called on syncapi SyncerThread.
   void DoWorkAndWaitUntilDone(Closure* work);
   virtual ModelSafeGroup GetModelSafeGroup() { return GROUP_HISTORY; }
+  virtual bool CurrentThreadIsWorkThread();
 
   // CancelableRequestConsumerBase implementation.
   virtual void OnRequestAdded(CancelableRequestProvider* provider,
diff --git a/chrome/browser/sync/glue/sync_backend_host.cc b/chrome/browser/sync/glue/sync_backend_host.cc
index 1d49bc6..647dbb1 100644
--- a/chrome/browser/sync/glue/sync_backend_host.cc
+++ b/chrome/browser/sync/glue/sync_backend_host.cc
@@ -420,6 +420,14 @@ void SyncBackendHost::Core::OnChangesApplied(
   // association.
   if (it == host_->processors_.end())
     return;
+
+  if (!IsCurrentThreadSafeForModel(model_type)) {
+    NOTREACHED() << "Changes applied on wrong thread.";
+    return;
+  }
+
+  // Now that we're sure we're on the correct thread, we can access the
+  // ChangeProcessor.
   ChangeProcessor* processor = it->second;
 
   // Ensure the change processor is willing to accept changes.
@@ -484,6 +492,24 @@ void SyncBackendHost::Core::HandleInitalizationCompletedOnFrontendLoop() {
   host_->frontend_->OnBackendInitialized();
 }
 
+
+bool SyncBackendHost::Core::IsCurrentThreadSafeForModel(
+    syncable::ModelType model_type) {
+  AutoLock lock(host_->registrar_lock_);
+
+  browser_sync::ModelSafeRoutingInfo::const_iterator routing_it =
+      host_->registrar_.routing_info.find(model_type);
+  if (routing_it == host_->registrar_.routing_info.end())
+    return false;
+  browser_sync::ModelSafeGroup group = routing_it->second;
+  WorkerMap::const_iterator worker_it = host_->registrar_.workers.find(group);
+  if (worker_it == host_->registrar_.workers.end())
+    return false;
+  ModelSafeWorker* worker = worker_it->second;
+  return worker->CurrentThreadIsWorkThread();
+}
+
+
 void SyncBackendHost::Core::OnAuthError(const AuthError& auth_error) {
   // We could be on SyncEngine_AuthWatcherThread.  Post to our core loop so
   // we can modify state.
diff --git a/chrome/browser/sync/glue/sync_backend_host.h b/chrome/browser/sync/glue/sync_backend_host.h
index 574f299..4704f85 100644
--- a/chrome/browser/sync/glue/sync_backend_host.h
+++ b/chrome/browser/sync/glue/sync_backend_host.h
@@ -343,6 +343,9 @@ class SyncBackendHost : public browser_sync::ModelSafeWorkerRegistrar {
     // frontend thread components.
     void HandleInitalizationCompletedOnFrontendLoop();
 
+    // Return true if a model lives on the current thread.
+    bool IsCurrentThreadSafeForModel(syncable::ModelType model_type);
+
     // Our parent SyncBackendHost
     SyncBackendHost* host_;
 
diff --git a/chrome/browser/sync/glue/ui_model_worker.cc b/chrome/browser/sync/glue/ui_model_worker.cc
index 89a9c43..d1a12b6 100644
--- a/chrome/browser/sync/glue/ui_model_worker.cc
+++ b/chrome/browser/sync/glue/ui_model_worker.cc
@@ -81,6 +81,10 @@ void UIModelWorker::Stop() {
   state_ = STOPPED;
 }
 
+bool UIModelWorker::CurrentThreadIsWorkThread() {
+  return MessageLoop::current() == ui_loop_;
+}
+
 void UIModelWorker::CallDoWorkAndSignalTask::Run() {
   if (!work_) {
     // This can happen during tests or cases where there are more than just the
diff --git a/chrome/browser/sync/glue/ui_model_worker.h b/chrome/browser/sync/glue/ui_model_worker.h
index 84833d5..f7d9188 100644
--- a/chrome/browser/sync/glue/ui_model_worker.h
+++ b/chrome/browser/sync/glue/ui_model_worker.h
@@ -70,6 +70,7 @@ class UIModelWorker : public browser_sync::ModelSafeWorker {
   // ModelSafeWorker implementation. Called on syncapi SyncerThread.
   virtual void DoWorkAndWaitUntilDone(Closure* work);
   virtual ModelSafeGroup GetModelSafeGroup() { return GROUP_UI; }
+  virtual bool CurrentThreadIsWorkThread();
 
   // Upon receiving this idempotent call, the ModelSafeWorker can
   // assume no work will ever be scheduled again from now on. If it has any work
diff --git a/chrome/browser/sync/glue/ui_model_worker_unittest.cc b/chrome/browser/sync/glue/ui_model_worker_unittest.cc
index a61832b..e0ad82f 100644
--- a/chrome/browser/sync/glue/ui_model_worker_unittest.cc
+++ b/chrome/browser/sync/glue/ui_model_worker_unittest.cc
@@ -55,7 +55,7 @@ class Syncer {
 };
 
 // A task run from the SyncerThread to "sync share", ie tell the Syncer to
-// ask it's ModelSafeWorker to do something.
+// ask its ModelSafeWorker to do something.
 class FakeSyncShareTask : public Task {
  public:
   FakeSyncShareTask(Syncer* syncer, UIModelWorkerVisitor* visitor)