The Tor Browser: ipc/chromium/src/chrome/common/ipc_sync

ipc/chromium/src/chrome/common/ipc_sync_channel.cc@8bccb770b82d (annotated)

ipc/chromium/src/chrome/common/ipc_sync_channel.cc

Wed, 31 Dec 2014 13:27:57 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Wed, 31 Dec 2014 13:27:57 +0100
branch: TOR_BUG_3246
changeset 6: 8bccb770b82d
permissions: -rw-r--r--

Ignore runtime configuration files generated during quality assurance.

 // Copyright (c) 2006-2008 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/common/ipc_sync_channel.h"
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/thread_local.h"
 #include "base/message_loop.h"
 #include "base/waitable_event.h"
 #include "base/waitable_event_watcher.h"
 #include "chrome/common/ipc_sync_message.h"
 using base::TimeDelta;
 using base::TimeTicks;
 using base::WaitableEvent;
 namespace IPC {
 // When we're blocked in a Send(), we need to process incoming synchronous
 // messages right away because it could be blocking our reply (either
 // directly from the same object we're calling, or indirectly through one or
 // more other channels).  That means that in SyncContext's OnMessageReceived,
 // we need to process sync message right away if we're blocked.  However a
 // simple check isn't sufficient, because the listener thread can be in the
 // process of calling Send.
 // To work around this, when SyncChannel filters a sync message, it sets
 // an event that the listener thread waits on during its Send() call.  This
 // allows us to dispatch incoming sync messages when blocked.  The race
 // condition is handled because if Send is in the process of being called, it
 // will check the event.  In case the listener thread isn't sending a message,
 // we queue a task on the listener thread to dispatch the received messages.
 // The messages are stored in this queue object that's shared among all
 // SyncChannel objects on the same thread (since one object can receive a
 // sync message while another one is blocked).
 class SyncChannel::ReceivedSyncMsgQueue :
     public base::RefCountedThreadSafe<ReceivedSyncMsgQueue> {
  public:
   // Returns the ReceivedSyncMsgQueue instance for this thread, creating one
   // if necessary.  Call RemoveContext on the same thread when done.
   static ReceivedSyncMsgQueue* AddContext() {
     // We want one ReceivedSyncMsgQueue per listener thread (i.e. since multiple
     // SyncChannel objects can block the same thread).
     ReceivedSyncMsgQueue* rv = lazy_tls_ptr_.Pointer()->Get();
     if (!rv) {
       rv = new ReceivedSyncMsgQueue();
       ReceivedSyncMsgQueue::lazy_tls_ptr_.Pointer()->Set(rv);
     }
     rv->listener_count_++;
     return rv;
   }
   ~ReceivedSyncMsgQueue() {
   }
   // Called on IPC thread when a synchronous message or reply arrives.
   void QueueMessage(const Message& msg, SyncChannel::SyncContext* context) {
     bool was_task_pending;
     {
       AutoLock auto_lock(message_lock_);
       was_task_pending = task_pending_;
       task_pending_ = true;
       // We set the event in case the listener thread is blocked (or is about
       // to). In case it's not, the PostTask dispatches the messages.
       message_queue_.push_back(QueuedMessage(new Message(msg), context));
     }
     dispatch_event_.Signal();
     if (!was_task_pending) {
       listener_message_loop_->PostTask(FROM_HERE, NewRunnableMethod(
           this, &ReceivedSyncMsgQueue::DispatchMessagesTask));
     }
   }
   void QueueReply(const Message &msg, SyncChannel::SyncContext* context) {
     received_replies_.push_back(QueuedMessage(new Message(msg), context));
   }
   // Called on the listener's thread to process any queues synchronous
   // messages.
   void DispatchMessagesTask() {
     {
       AutoLock auto_lock(message_lock_);
       task_pending_ = false;
     }
     DispatchMessages();
   }
   void DispatchMessages() {
     while (true) {
       Message* message;
       scoped_refptr<SyncChannel::SyncContext> context;
       {
         AutoLock auto_lock(message_lock_);
         if (message_queue_.empty())
           break;
         message = message_queue_.front().message;
         context = message_queue_.front().context;
         message_queue_.pop_front();
       }
       context->OnDispatchMessage(*message);
       delete message;
     }
   }
   // SyncChannel calls this in its destructor.
   void RemoveContext(SyncContext* context) {
     AutoLock auto_lock(message_lock_);
     SyncMessageQueue::iterator iter = message_queue_.begin();
     while (iter != message_queue_.end()) {
       if (iter->context == context) {
         delete iter->message;
         iter = message_queue_.erase(iter);
       } else {
         iter++;
       }
     }
     if (--listener_count_ == 0) {
       DCHECK(lazy_tls_ptr_.Pointer()->Get());
       lazy_tls_ptr_.Pointer()->Set(NULL);
     }
   }
   WaitableEvent* dispatch_event() { return &dispatch_event_; }
   MessageLoop* listener_message_loop() { return listener_message_loop_; }
   // Holds a pointer to the per-thread ReceivedSyncMsgQueue object.
   static base::LazyInstance<base::ThreadLocalPointer<ReceivedSyncMsgQueue> >
       lazy_tls_ptr_;
   // Called on the ipc thread to check if we can unblock any current Send()
   // calls based on a queued reply.
   void DispatchReplies() {
     for (size_t i = 0; i < received_replies_.size(); ++i) {
       Message* message = received_replies_[i].message;
       if (received_replies_[i].context->TryToUnblockListener(message)) {
         delete message;
         received_replies_.erase(received_replies_.begin() + i);
         return;
       }
     }
   }
  private:
   // See the comment in SyncChannel::SyncChannel for why this event is created
   // as manual reset.
   ReceivedSyncMsgQueue() :
       dispatch_event_(true, false),
       listener_message_loop_(MessageLoop::current()),
       task_pending_(false),
       listener_count_(0) {
   }
   // Holds information about a queued synchronous message or reply.
   struct QueuedMessage {
     QueuedMessage(Message* m, SyncContext* c) : message(m), context(c) { }
     Message* message;
     scoped_refptr<SyncChannel::SyncContext> context;
   };
   typedef std::deque<QueuedMessage> SyncMessageQueue;
   SyncMessageQueue message_queue_;
   std::vector<QueuedMessage> received_replies_;
   // Set when we got a synchronous message that we must respond to as the
   // sender needs its reply before it can reply to our original synchronous
   // message.
   WaitableEvent dispatch_event_;
   MessageLoop* listener_message_loop_;
   Lock message_lock_;
   bool task_pending_;
   int listener_count_;
 };
 base::LazyInstance<base::ThreadLocalPointer<SyncChannel::ReceivedSyncMsgQueue> >
     SyncChannel::ReceivedSyncMsgQueue::lazy_tls_ptr_(base::LINKER_INITIALIZED);
 SyncChannel::SyncContext::SyncContext(
     Channel::Listener* listener,
     MessageFilter* filter,
     MessageLoop* ipc_thread,
     WaitableEvent* shutdown_event)
     : ChannelProxy::Context(listener, filter, ipc_thread),
       received_sync_msgs_(ReceivedSyncMsgQueue::AddContext()),
       shutdown_event_(shutdown_event) {
 }
 SyncChannel::SyncContext::~SyncContext() {
   while (!deserializers_.empty())
     Pop();
 }
 // Adds information about an outgoing sync message to the context so that
 // we know how to deserialize the reply.  Returns a handle that's set when
 // the reply has arrived.
 void SyncChannel::SyncContext::Push(SyncMessage* sync_msg) {
   // The event is created as manual reset because in between Signal and
   // OnObjectSignalled, another Send can happen which would stop the watcher
   // from being called.  The event would get watched later, when the nested
   // Send completes, so the event will need to remain set.
   PendingSyncMsg pending(SyncMessage::GetMessageId(*sync_msg),
                          sync_msg->GetReplyDeserializer(),
                          new WaitableEvent(true, false));
   AutoLock auto_lock(deserializers_lock_);
   deserializers_.push_back(pending);
 }
 bool SyncChannel::SyncContext::Pop() {
   bool result;
   {
     AutoLock auto_lock(deserializers_lock_);
     PendingSyncMsg msg = deserializers_.back();
     delete msg.deserializer;
     delete msg.done_event;
     msg.done_event = NULL;
     deserializers_.pop_back();
     result = msg.send_result;
   }
   // We got a reply to a synchronous Send() call that's blocking the listener
   // thread.  However, further down the call stack there could be another
   // blocking Send() call, whose reply we received after we made this last
   // Send() call.  So check if we have any queued replies available that
   // can now unblock the listener thread.
   ipc_message_loop()->PostTask(FROM_HERE, NewRunnableMethod(
       received_sync_msgs_.get(), &ReceivedSyncMsgQueue::DispatchReplies));
   return result;
 }
 WaitableEvent* SyncChannel::SyncContext::GetSendDoneEvent() {
   AutoLock auto_lock(deserializers_lock_);
   return deserializers_.back().done_event;
 }
 WaitableEvent* SyncChannel::SyncContext::GetDispatchEvent() {
   return received_sync_msgs_->dispatch_event();
 }
 void SyncChannel::SyncContext::DispatchMessages() {
   received_sync_msgs_->DispatchMessages();
 }
 bool SyncChannel::SyncContext::TryToUnblockListener(const Message* msg) {
   AutoLock auto_lock(deserializers_lock_);
   if (deserializers_.empty() ||
       !SyncMessage::IsMessageReplyTo(*msg, deserializers_.back().id)) {
     return false;
   }
   if (!msg->is_reply_error()) {
     deserializers_.back().send_result = deserializers_.back().deserializer->
         SerializeOutputParameters(*msg);
   }
   deserializers_.back().done_event->Signal();
   return true;
 }
 void SyncChannel::SyncContext::Clear() {
   CancelPendingSends();
   received_sync_msgs_->RemoveContext(this);
   Context::Clear();
 }
 void SyncChannel::SyncContext::OnMessageReceived(const Message& msg) {
   // Give the filters a chance at processing this message.
   if (TryFilters(msg))
     return;
   if (TryToUnblockListener(&msg))
     return;
   if (msg.should_unblock()) {
     received_sync_msgs_->QueueMessage(msg, this);
     return;
   }
   if (msg.is_reply()) {
     received_sync_msgs_->QueueReply(msg, this);
     return;
   }
   return Context::OnMessageReceivedNoFilter(msg);
 }
 void SyncChannel::SyncContext::OnChannelError() {
   CancelPendingSends();
   shutdown_watcher_.StopWatching();
   Context::OnChannelError();
 }
 void SyncChannel::SyncContext::OnChannelOpened() {
   shutdown_watcher_.StartWatching(shutdown_event_, this);
   Context::OnChannelOpened();
 }
 void SyncChannel::SyncContext::OnChannelClosed() {
   shutdown_watcher_.StopWatching();
   Context::OnChannelClosed();
 }
 void SyncChannel::SyncContext::OnSendTimeout(int message_id) {
   AutoLock auto_lock(deserializers_lock_);
   PendingSyncMessageQueue::iterator iter;
   for (iter = deserializers_.begin(); iter != deserializers_.end(); iter++) {
     if (iter->id == message_id) {
       iter->done_event->Signal();
       break;
     }
   }
 }
 void SyncChannel::SyncContext::CancelPendingSends() {
   AutoLock auto_lock(deserializers_lock_);
   PendingSyncMessageQueue::iterator iter;
   for (iter = deserializers_.begin(); iter != deserializers_.end(); iter++)
     iter->done_event->Signal();
 }
 void SyncChannel::SyncContext::OnWaitableEventSignaled(WaitableEvent* event) {
   DCHECK(event == shutdown_event_);
   // Process shut down before we can get a reply to a synchronous message.
   // Cancel pending Send calls, which will end up setting the send done event.
   CancelPendingSends();
 }
 SyncChannel::SyncChannel(
     const std::wstring& channel_id, Channel::Mode mode,
     Channel::Listener* listener, MessageFilter* filter,
     MessageLoop* ipc_message_loop, bool create_pipe_now,
     WaitableEvent* shutdown_event)
     : ChannelProxy(
           channel_id, mode, ipc_message_loop,
           new SyncContext(listener, filter, ipc_message_loop, shutdown_event),
           create_pipe_now),
       sync_messages_with_no_timeout_allowed_(true) {
   // Ideally we only want to watch this object when running a nested message
   // loop.  However, we don't know when it exits if there's another nested
   // message loop running under it or not, so we wouldn't know whether to
   // stop or keep watching.  So we always watch it, and create the event as
   // manual reset since the object watcher might otherwise reset the event
   // when we're doing a WaitMany.
   dispatch_watcher_.StartWatching(sync_context()->GetDispatchEvent(), this);
 }
 SyncChannel::~SyncChannel() {
 }
 bool SyncChannel::Send(Message* message) {
   return SendWithTimeout(message, base::kNoTimeout);
 }
 bool SyncChannel::SendWithTimeout(Message* message, int timeout_ms) {
   if (!message->is_sync()) {
     ChannelProxy::Send(message);
     return true;
   }
   // *this* might get deleted in WaitForReply.
   scoped_refptr<SyncContext> context(sync_context());
   if (context->shutdown_event()->IsSignaled()) {
     delete message;
     return false;
   }
   DCHECK(sync_messages_with_no_timeout_allowed_ ||
          timeout_ms != base::kNoTimeout);
   SyncMessage* sync_msg = static_cast<SyncMessage*>(message);
   context->Push(sync_msg);
   int message_id = SyncMessage::GetMessageId(*sync_msg);
   WaitableEvent* pump_messages_event = sync_msg->pump_messages_event();
   ChannelProxy::Send(message);
   if (timeout_ms != base::kNoTimeout) {
     // We use the sync message id so that when a message times out, we don't
     // confuse it with another send that is either above/below this Send in
     // the call stack.
     context->ipc_message_loop()->PostDelayedTask(FROM_HERE,
         NewRunnableMethod(context.get(),
             &SyncContext::OnSendTimeout, message_id), timeout_ms);
   }
   // Wait for reply, or for any other incoming synchronous messages.
   WaitForReply(pump_messages_event);
   return context->Pop();
 }
 void SyncChannel::WaitForReply(WaitableEvent* pump_messages_event) {
   while (true) {
     WaitableEvent* objects[] = {
       sync_context()->GetDispatchEvent(),
       sync_context()->GetSendDoneEvent(),
       pump_messages_event
     };
     unsigned count = pump_messages_event ? 3: 2;
     unsigned result = WaitableEvent::WaitMany(objects, count);
     if (result == 0 /* dispatch event */) {
       // We're waiting for a reply, but we received a blocking synchronous
       // call.  We must process it or otherwise a deadlock might occur.
       sync_context()->GetDispatchEvent()->Reset();
       sync_context()->DispatchMessages();
       continue;
     }
     if (result == 2 /* pump_messages_event */)
       WaitForReplyWithNestedMessageLoop();  // Start a nested message loop.
     break;
   }
 }
 void SyncChannel::WaitForReplyWithNestedMessageLoop() {
   WaitableEvent* old_done_event = send_done_watcher_.GetWatchedEvent();
   send_done_watcher_.StopWatching();
   send_done_watcher_.StartWatching(sync_context()->GetSendDoneEvent(), this);
   bool old_state = MessageLoop::current()->NestableTasksAllowed();
   MessageLoop::current()->SetNestableTasksAllowed(true);
   MessageLoop::current()->Run();
   MessageLoop::current()->SetNestableTasksAllowed(old_state);
   if (old_done_event)
     send_done_watcher_.StartWatching(old_done_event, this);
 }
 void SyncChannel::OnWaitableEventSignaled(WaitableEvent* event) {
   WaitableEvent* dispatch_event = sync_context()->GetDispatchEvent();
   if (event == dispatch_event) {
     // The call to DispatchMessages might delete this object, so reregister
     // the object watcher first.
     dispatch_event->Reset();
     dispatch_watcher_.StartWatching(dispatch_event, this);
     sync_context()->DispatchMessages();
   } else {
     // We got the reply, timed out or the process shutdown.
     DCHECK(event == sync_context()->GetSendDoneEvent());
     MessageLoop::current()->Quit();
   }
 }
 }  // namespace IPC

The Tor Browser / annotate

ipc/chromium/src/chrome/common/ipc_sync_channel.cc@8bccb770b82d (annotated)

ipc/chromium/src/chrome/common/ipc_sync_channel.cc