Dispatch IndexedDB IPC messages to worker threads

content/common/worker_task_runner.h

+// 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.
+
+#ifndef CONTENT_COMMON_WORKER_TASK_RUNNER_H_
+#define CONTENT_COMMON_WORKER_TASK_RUNNER_H_
+#pragma once
+
+#include "base/memory/ref_counted.h"
+#include "base/observer_list.h"
+#include "base/synchronization/lock.h"
+#include "base/threading/thread_local.h"
+#include "content/renderer/renderer_webkitplatformsupport_impl.h"
+#include "third_party/WebKit/Source/WebKit/chromium/public/WebWorkerRunLoop.h"
+
+#include <map>
+
+using WebKit::WebWorkerRunLoop;
+
+class WorkerTaskRunner : public base::RefCountedThreadSafe<WorkerTaskRunner> {

[michaeln, 2011/12/01 21:42:05]

why refcounted?

[dgrogan, 2011/12/01 22:49:00]

I was imagining that ChildThread would be handing this out, possibly to threads
that would outlive the main thread.  In my case it's just the IO thread.  Do you
know if there is a well-defined shutdown order between the main and IO threads?

[michaeln, 2011/12/02 00:15:03]

Take a look a renderer_main.cc, worker_main.cc, ChildThread, and ChildProcess.

Looks like the the 'main' thread is the primary thread of the process, the
ChildThread class does not really start it, it just gloms onto it and putting a
MessageLoop and ChildProcess on the stack and heap alloc'ing the ChildThread
object. The seperate io thread is started/stopped by the ChildProcess class. The
ChildThread object is killed in the ChildProcess dtor (prior to io_thread_'s
dtor being run).

[dgrogan, 2011/12/02 11:57:44]

I interpret this to mean that the ref counting is needed, to protect the io
thread's continued access to this class after the child thread is destroyed. 
Are we on the same page?

+ public:
+  // Change this to a real closure.
+  void PostTask(int id, WebKit::WebWorkerRunLoop::Task* closure) {
+    DCHECK(id > 0);
+    base::AutoLock locker_(lock_);
+    IDToLoopMap::iterator found = loop_map_.find(id);
+    if (found != loop_map_.end())
+      found->second.postTask(closure);
+    else
+      delete closure;
+  }
+  int CurrentWorkerId() {
+    if (!current_tls_.Get())
+      return 0;
+    return current_tls_.Get()->first;
+  }
+  class Observer {
+   public:
+    virtual ~Observer() { }
+    virtual void onLoopRegistered() { }
+    virtual void onLoopUnregistered() { }
+  };
+  void AddObserver(Observer* obs) {
+    observer_list_.AddObserver(obs);
+  }
+  void RemoveObserver(Observer* obs) {
+    observer_list_.RemoveObserver(obs);
+  }
+
+ private:
+  friend RendererWebKitPlatformSupportImpl;
+
+  void RegisterCurrentWorkerLoop(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;
+    }
+    FOR_EACH_OBSERVER(Observer, observer_list_, onLoopRegistered());
+  }
+  void UnRegisterCurrentWorkerLoop(const WebWorkerRunLoop& loop) {

[michaeln, 2011/12/01 21:42:05]

there's probably enough code in here to warrant a .cc file

[dgrogan, 2011/12/01 22:49:00]

Agreed.

+    DCHECK(CurrentWorkerId() > 0);
+    DCHECK(current_tls_.Get());
+    FOR_EACH_OBSERVER(Observer, observer_list_, onLoopUnregistered());
+    base::AutoLock locker_(lock_);
+    DCHECK(loop_map_[CurrentWorkerId()] == loop);
+    loop_map_.erase(CurrentWorkerId());
+    delete current_tls_.Get();
+    current_tls_.Set(NULL);
+  }
+
+  typedef std::map<int, WebWorkerRunLoop> IDToLoopMap;
+  base::ThreadLocalPointer<std::pair<int, WebWorkerRunLoop> > current_tls_;
+  base::Lock lock_;
+  int id_sequence_ = 0;
+  std::map<int, WebWorkerRunLoop> loop_map_;
+
+  ObserverList<Observer> observer_list_;

[michaeln, 2011/12/01 21:42:05]

I think ObserverList is not thread-safe.

[dgrogan, 2011/12/01 22:49:00]

Argh, quite right.  ObserverListThreadSafe doesn't look like it's what I want
either.  I suppose I'll add a lock around this observer_list_ and forbid clients
from removing themselves during iteration to prevent lock reacquisition.

+};
+
+#endif  // CONTENT_COMMON_SOCKET_STREAM_H_