Allow synchronous messages to be sent from threads other than the main thread...

chrome/common/db_message_filter.h

Index: chrome/common/db_message_filter.h
===================================================================
--- chrome/common/db_message_filter.h	(revision 43588)
+++ chrome/common/db_message_filter.h	(working copy)
@@ -1,143 +1,27 @@
-// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Copyright (c) 2010 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 CHROME_COMMON_DB_MESSAGE_FILTER_H_
 #define CHROME_COMMON_DB_MESSAGE_FILTER_H_
 
-#include "base/atomic_sequence_num.h"
-#include "base/id_map.h"
-#include "base/lock.h"
-#include "base/scoped_ptr.h"
-#include "base/waitable_event.h"
 #include "ipc/ipc_channel_proxy.h"
 
-class Lock;
-class MessageLoop;
-
-namespace IPC {
-class Channel;
-}
-
-// A thread-safe message filter used to send IPCs from DB threads and process
-// replies from the browser process.
-//
-// This class should not be instantianted anywhere but RenderThread::Init().  It
-// is meant to be a singleton in each renderer process. To access the singleton,
-// use GetInstance().
+// Receives database messages from the browser process and processes them on the
+// IO thread.
 class DBMessageFilter : public IPC::ChannelProxy::MessageFilter {
  public:
-  // Returns the DBMessageFilter singleton created in this renderer process.
-  static DBMessageFilter* GetInstance() { return instance_; }
-
-  // Creates a new DBMessageFilter instance.
   DBMessageFilter();
 
-  // Returns a unique ID for use when calling the SendAndWait() method.
-  virtual int GetUniqueID();
-
-  // Posts a task to the IO thread to send |message| to the browser.
-  virtual void Send(IPC::Message* message);
-
-  // Sends |message| and blocks the current thread.  Returns the result from the
-  // reply message, or |default_result| if the renderer process is being
-  // destroyed or the message could not be sent.
-  template<class ResultType>
-  ResultType SendAndWait(IPC::Message* message,
-                         int message_id,
-                         ResultType default_result) {
-    ResultType result = default_result;
-    base::WaitableEvent waitable_event(false, false);
-    DBMessageState state =
-        { reinterpret_cast<intptr_t>(&result), &waitable_event };
-    {
-      AutoLock msgs_awaiting_replies_autolock(messages_awaiting_replies_lock_);
-      messages_awaiting_replies_->AddWithID(&state, message_id);
-    }
-
-    Send(message);
-
-    base::WaitableEvent* events[2] = { shutdown_event_, &waitable_event };
-    base::WaitableEvent::WaitMany(events, 2);
-
-    // Locking on messages_awaiting_replies_ guarantees that either the IO
-    // thread won't enter OnResponse(), or if it's already in OnResponse(),
-    // then WaitableEvent::Signal() will get a chance to do all its work
-    // before waitable_event is deleted.
-    AutoLock msgs_awaiting_replies_autolock(messages_awaiting_replies_lock_);
-    messages_awaiting_replies_->Remove(message_id);
-    return result;
-  }
-
-  // Processes incoming message |message| from the browser process.
+ private:
   virtual bool OnMessageReceived(const IPC::Message& message);
 
- private:
-  // The state we store for each message we send.
-  struct DBMessageState {
-    intptr_t result_address_;
-    base::WaitableEvent* waitable_event_;
-  };
-
-  // This is a RefCounted class, do not allow anybody to destroy it directly.
-  virtual ~DBMessageFilter() { instance_ = NULL; }
-
-  // Invoked when this filter is added to |channel|.
-  virtual void OnFilterAdded(IPC::Channel* channel);
-
-  // Called when the channel encounters a problem. The filter should clean up
-  // its internal data and not accept any more messages.
-  virtual void OnChannelError();
-
-  // Called when the channel is closing. The filter should clean up its internal
-  // and not accept any more messages.
-  virtual void OnChannelClosing();
-
-  // Processes the reply to a sync DB request.
-  template<class ResultType>
-  void OnResponse(int32 message_id, ResultType result) {
-    AutoLock msgs_awaiting_replies_autolock(messages_awaiting_replies_lock_);
-    DBMessageState *state = messages_awaiting_replies_->Lookup(message_id);
-    if (state) {
-      *reinterpret_cast<ResultType*>(state->result_address_) = result;
-      state->waitable_event_->Signal();
-    }
-  }
-
-  // Processes IPCs that indicate a change in the size of a DB file.
   void OnDatabaseUpdateSize(const string16& origin_identifier,
                             const string16& database_name,
                             int64 database_size,
                             int64 space_available);
-
-  // Processes IPCs that ask for a DB to be closed immediately.
   void OnDatabaseCloseImmediately(const string16& origin_identifier,
                                   const string16& database_name);
-
-  // The message loop for the IO thread.
-  MessageLoop* io_thread_message_loop_;
-
-  // The channel to which this filter was added.
-  IPC::Channel* channel_;
-
-  // A lock around the channel.
-  Lock channel_lock_;
-
-  // The shutdown event.
-  base::WaitableEvent* shutdown_event_;
-
-  // The list of messages awaiting replies. For each such message we store a
-  // DBMessageState instance.
-  scoped_ptr<IDMap<DBMessageState> > messages_awaiting_replies_;
-
-  // The lock for 'messages_awaiting_replies_'.
-  Lock messages_awaiting_replies_lock_;
-
-  // A thread-safe unique number generator.
-  scoped_ptr<base::AtomicSequenceNumber> unique_id_generator_;
-
-  // The singleton.
-  static DBMessageFilter* instance_;
 };
 
 #endif  // CHROME_COMMON_DB_MESSAGE_FILTER_H_