Track webcore worker message loops in chromium.

content/common/worker_task_runner.cc

+// Copyright (c) 2011 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 "base/callback.h"
+#include "base/lazy_instance.h"
+#include "base/logging.h"
+#include "content/common/worker_task_runner.h"
+
+using WebKit::WebWorkerRunLoop;
+
+namespace {
+
+class RunClosureTask : public WebKit::WebWorkerRunLoop::Task {
+ public:
+  RunClosureTask(const base::Closure& task) : task_(task) { }
+  virtual ~RunClosureTask() { }
+  virtual void Run() {
+    task_.Run();
+  }
+ private:
+  base::Closure task_;
+};
+
+}
+
+WorkerTaskRunner::WorkerTaskRunner() : id_sequence_(0) {
+}
+
+void WorkerTaskRunner::PostTask(
+    int id, const base::Closure& closure) {
+  DCHECK(id > 0);
+  base::AutoLock locker_(lock_);
+  IDToLoopMap::iterator found = loop_map_.find(id);
+  if (found != loop_map_.end())
+    found->second.postTask(new RunClosureTask(closure));
+}
+
+int WorkerTaskRunner::CurrentWorkerId() {
+  if (!current_tls_.Get())
+    return 0;
+  return current_tls_.Get()->first;
+}
+
+WorkerTaskRunner* WorkerTaskRunner::Instance() {
+  static base::LazyInstance<WorkerTaskRunner,
+      base::LeakyLazyInstanceTraits<WorkerTaskRunner> >
+      worker_task_runner_;

[michaeln, 2011/12/08 03:10:47]

other usages of LazyInstance assign the LAZY_INSTANCE_INITIALIZER value to it,
can you do that here too unless there's reason not to.

  static base::LazyInstance<WorkerTaskRunner,
                            base::LeakyLazyInstanceTraits<WorkerTaskRunner> >
      instance = LAZY_INSTANCE_INITIALIZER;

[dgrogan, 2011/12/09 03:20:41]

You're right.  Changed.

+  return worker_task_runner_.Pointer();
+}
+
+void WorkerTaskRunner::AddObserver(Observer* obs) {
+  base::AutoLock locker(observer_lock_);
+  observer_list_.insert(obs);
+}
+
+int WorkerTaskRunner::RemoveObserver(Observer* obs) {
+  base::AutoLock locker(observer_lock_);
+  return observer_list_.erase(obs);
+}
+
+WorkerTaskRunner::~WorkerTaskRunner() {
+}
+
+void WorkerTaskRunner::OnWorkerRunLoopStarted(const WebWorkerRunLoop& loop) {
+  DCHECK(!current_tls_.Get());
+  {
+    base::AutoLock locker_(lock_);
+    int id = ++id_sequence_;
+    current_tls_.Set(new std::pair<int, WebWorkerRunLoop>(id, loop));
+    loop_map_[id] = loop;
+  }
+  base::AutoLock locker(observer_lock_);
+  for(ObserverList::iterator iter = observer_list_.begin();
+      iter != observer_list_.end(); iter++) {
+    (*iter)->OnWorkerRunLoopStarted();

[darin (slow to review), 2011/12/08 22:41:21]

It is usually bad design to hold locks while calling out to foreign code.  It
can lead to dead-locks.

[michaeln, 2011/12/09 00:43:32]

This is generally true, but also not much an issue for the first consumer of
this class and i don't expect it to be for any other consumers either.

Observers can reasonably be expected to be added/removed on either the 'main' or
'io' threads and never added/removed on the 'worker' threads. Maybe we could
make an assertion in Add/Remove observer to codify this...
    DCHECK(!CurrentWorkerId());
... which eliminates the possibility of mutex recursion.

[dgrogan, 2011/12/09 03:20:41]

Darin and I talked about this today, mostly in the context of the larger problem
of chromium not waiting around for the webcore worker threads to die.  I added a
snapshot here to avoid the narrow problem of mutex recursion.

+  }
+}
+
+void WorkerTaskRunner::OnWorkerRunLoopStopped(
+    const WebWorkerRunLoop& loop) {
+  DCHECK(CurrentWorkerId() > 0);
+  DCHECK(current_tls_.Get());
+  {
+    base::AutoLock lock(observer_lock_);
+    for(ObserverList::iterator iter = observer_list_.begin();
+        iter != observer_list_.end(); iter++) {
+      (*iter)->OnWorkerRunLoopStopped();
+    }
+  }
+  base::AutoLock locker_(lock_);
+  DCHECK(loop_map_[CurrentWorkerId()] == loop);
+  loop_map_.erase(CurrentWorkerId());
+  delete current_tls_.Get();
+  current_tls_.Set(NULL);
+}