Worker changes to prepare for lock-free shutdown.

chrome/browser/sync/glue/ui_model_worker.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/sync/glue/ui_model_worker.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/message_loop.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/third_party/dynamic_annotations/dynamic_annotations.h"
 #include "base/threading/thread_restrictions.h"
 #include "content/public/browser/browser_thread.h"
 
 using content::BrowserThread;
 
 namespace browser_sync {
 
-namespace {
-
-// A simple callback to signal a waitable event after running a closure.
-void CallDoWorkAndSignalCallback(const syncer::WorkCallback& work,
-                                 base::WaitableEvent* work_done,
-                                 UIModelWorker* const scheduler,
-                                 syncer::SyncerError* error_info) {
-  if (work.is_null()) {
-    // This can happen during tests or cases where there are more than just the
-    // default UIModelWorker in existence and it gets destroyed before
-    // the main UI loop has terminated.  There is no easy way to assert the
-    // loop is running / not running at the moment, so we just provide cancel
-    // semantics here and short-circuit.
-    // TODO(timsteele): Maybe we should have the message loop destruction
-    // observer fire when the loop has ended, just a bit before it
-    // actually gets destroyed.
-    return;
-  }
-
-  *error_info = work.Run();
-
-  // Notify the UIModelWorker that scheduled us that we have run
-  // successfully.
-  scheduler->OnTaskCompleted();
-  work_done->Signal();  // Unblock the syncer thread that scheduled us.
+UIModelWorker::UIModelWorker(syncer::WorkerObserver* observer)
+    : syncer::ModelSafeWorker(observer),
+      state_(WORKING),
+      syncapi_has_shutdown_(false),
+      syncapi_event_(&lock_) {
 }
 
-}  // namespace
-
-UIModelWorker::UIModelWorker()
-    : state_(WORKING),
-      syncapi_has_shutdown_(false),
-      syncapi_event_(&lock_) {
+void UIModelWorker::RegisterForLoopDestruction() {
+  CHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  MessageLoop::current()->AddDestructionObserver(this);
 }
 
 void UIModelWorker::Stop() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
   base::AutoLock lock(lock_);
   DCHECK_EQ(state_, WORKING);
 
   // We're on our own now, the beloved UI MessageLoop is no longer running.
   // Any tasks scheduled or to be scheduled on the UI MessageLoop will not run.
   state_ = RUNNING_MANUAL_SHUTDOWN_PUMP;
 
   // Drain any final tasks manually until the SyncerThread tells us it has
   // totally finished. There should only ever be 0 or 1 tasks Run() here.
   while (!syncapi_has_shutdown_) {
     if (!pending_work_.is_null())
       pending_work_.Run();  // OnTaskCompleted will set reset |pending_work_|.
 
     // http://crbug.com/19757
     base::ThreadRestrictions::ScopedAllowWait allow_wait;
     // Wait for either a new task or SyncerThread termination.
     syncapi_event_.Wait();
   }
 
   state_ = STOPPED;
 }
 
 syncer::SyncerError UIModelWorker::DoWorkAndWaitUntilDone(
-    const syncer::WorkCallback& work) {
+    const syncer::WorkCallback& work, base::WaitableEvent* done) {
   // In most cases, this method is called in WORKING state. It is possible this
   // gets called when we are in the RUNNING_MANUAL_SHUTDOWN_PUMP state, because
   // the UI loop has initiated shutdown but the syncer hasn't got the memo yet.
   // This is fine, the work will get scheduled and run normally or run by our
   // code handling this case in Stop(). Note there _no_ way we can be in here
   // with state_ = STOPPED, so it is safe to read / compare in this case.
   CHECK_NE(ANNOTATE_UNPROTECTED_READ(state_), STOPPED);
   syncer::SyncerError error_info;
   if (BrowserThread::CurrentlyOn(BrowserThread::UI)) {
     DLOG(WARNING) << "DoWorkAndWaitUntilDone called from "
       << "ui_loop_. Probably a nested invocation?";
     return work.Run();
   }
 
-  // Create an unsignaled event to wait on.
-  base::WaitableEvent work_done(false, false);
   {
     // We lock only to avoid PostTask'ing a NULL pending_work_ (because it
     // could get Run() in Stop() and call OnTaskCompleted before we post).
     // The task is owned by the message loop as per usual.
     base::AutoLock lock(lock_);
     DCHECK(pending_work_.is_null());
-    pending_work_ = base::Bind(&CallDoWorkAndSignalCallback, work, &work_done,
-                               base::Unretained(this), &error_info);
+    pending_work_ = base::Bind(&UIModelWorker::CallDoWorkAndSignalCallback,
+                               this, work, done, &error_info);
     if (!BrowserThread::PostTask(BrowserThread::UI, FROM_HERE, pending_work_)) {
       DLOG(WARNING) << "Could not post work to UI loop.";
       error_info = syncer::CANNOT_DO_WORK;
       pending_work_.Reset();
       syncapi_event_.Signal();
       return error_info;
     }
   }
   syncapi_event_.Signal();  // Notify that the syncapi produced work for us.
-  work_done.Wait();
+  done->Wait();
   return error_info;
 }
 
+void UIModelWorker::CallDoWorkAndSignalCallback(
+    const syncer::WorkCallback& work,
+    base::WaitableEvent* work_done,
+    syncer::SyncerError* error_info) {
+  if (work.is_null()) {
+    // This can happen during tests or cases where there are more than just the
+    // default UIModelWorker in existence and it gets destroyed before
+    // the main UI loop has terminated.  There is no easy way to assert the
+    // loop is running / not running at the moment, so we just provide cancel
+    // semantics here and short-circuit.
+    // TODO(timsteele): Maybe we should have the message loop destruction
+    // observer fire when the loop has ended, just a bit before it
+    // actually gets destroyed.
+    return;
+  }
+
+  if (!Stopped())
+    *error_info = work.Run();
+  else
+    *error_info = syncer::CANNOT_DO_WORK;
+
+  // Notify the UIModelWorker that scheduled us that we have run
+  // successfully.
+  OnTaskCompleted();
+  work_done->Signal();  // Unblock the syncer thread that scheduled us.
+}
+
 syncer::ModelSafeGroup UIModelWorker::GetModelSafeGroup() {
   return syncer::GROUP_UI;
 }
 
 void UIModelWorker::OnSyncerShutdownComplete() {
   base::AutoLock lock(lock_);
   // The SyncerThread has terminated and we are no longer needed by syncapi.
   // The UI loop initiated shutdown and is (or will be) waiting in Stop().
   // We could either be WORKING or RUNNING_MANUAL_SHUTDOWN_PUMP, depending
   // on where we timeslice the UI thread in Stop; but we can't be STOPPED,
   // because that would imply OnSyncerShutdownComplete already signaled.
   DCHECK_NE(state_, STOPPED);
 
   syncapi_has_shutdown_ = true;
   syncapi_event_.Signal();
 }
 
 UIModelWorker::~UIModelWorker() {
   DCHECK_EQ(state_, STOPPED);
 }
 
 }  // namespace browser_sync