root/ipc/ipc_sync_channel.cc

DEFINITIONS

1. AddContext
2. QueueMessage
3. QueueReply
4. DispatchMessagesTask
5. DispatchMessages
6. RemoveContext
7. dispatch_event
8. listener_task_runner
9. DispatchReplies
10. top_send_done_watcher
11. set_top_send_done_watcher
12. ReceivedSyncMsgQueue
13. restrict_dispatch_group_
14. Push
15. Pop
16. GetSendDoneEvent
17. GetDispatchEvent
18. DispatchMessages
19. TryToUnblockListener
20. Clear
21. OnMessageReceived
22. OnChannelError
23. OnChannelOpened
24. OnChannelClosed
25. OnSendTimeout
26. CancelPendingSends
27. OnWaitableEventSignaled
28. MakeWaitableEventCallback
29. sync_messages_with_no_timeout_allowed_
30. sync_messages_with_no_timeout_allowed_
31. SetRestrictDispatchChannelGroup
32. Send
33. SendWithTimeout
34. WaitForReply
35. WaitForReplyWithNestedMessageLoop
36. OnWaitableEventSignaled
37. StartWatching

// 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 "ipc/ipc_sync_channel.h"

#include "base/bind.h"
#include "base/debug/trace_event.h"
#include "base/lazy_instance.h"
#include "base/location.h"
#include "base/logging.h"
#include "base/synchronization/waitable_event.h"
#include "base/synchronization/waitable_event_watcher.h"
#include "base/thread_task_runner_handle.h"
#include "base/threading/thread_local.h"
#include "ipc/ipc_logging.h"
#include "ipc/ipc_message_macros.h"
#include "ipc/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;
  }

  // Called on IPC thread when a synchronous message or reply arrives.
  void QueueMessage(const Message& msg, SyncChannel::SyncContext* context) {
    bool was_task_pending;
    {
      base::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));
      message_queue_version_++;
    }

    dispatch_event_.Signal();
    if (!was_task_pending) {
      listener_task_runner_->PostTask(
          FROM_HERE, base::Bind(&ReceivedSyncMsgQueue::DispatchMessagesTask,
                                this, scoped_refptr<SyncContext>(context)));
    }
  }

  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(SyncContext* context) {
    {
      base::AutoLock auto_lock(message_lock_);
      task_pending_ = false;
    }
    context->DispatchMessages();
  }

  void DispatchMessages(SyncContext* dispatching_context) {
    bool first_time = true;
    uint32 expected_version = 0;
    SyncMessageQueue::iterator it;
    while (true) {
      Message* message = NULL;
      scoped_refptr<SyncChannel::SyncContext> context;
      {
        base::AutoLock auto_lock(message_lock_);
        if (first_time || message_queue_version_ != expected_version) {
          it = message_queue_.begin();
          first_time = false;
        }
        for (; it != message_queue_.end(); it++) {
          int message_group = it->context->restrict_dispatch_group();
          if (message_group == kRestrictDispatchGroup_None ||
              message_group == dispatching_context->restrict_dispatch_group()) {
            message = it->message;
            context = it->context;
            it = message_queue_.erase(it);
            message_queue_version_++;
            expected_version = message_queue_version_;
            break;
          }
        }
      }

      if (message == NULL)
        break;
      context->OnDispatchMessage(*message);
      delete message;
    }
  }

  // SyncChannel calls this in its destructor.
  void RemoveContext(SyncContext* context) {
    base::AutoLock auto_lock(message_lock_);

    SyncMessageQueue::iterator iter = message_queue_.begin();
    while (iter != message_queue_.end()) {
      if (iter->context.get() == context) {
        delete iter->message;
        iter = message_queue_.erase(iter);
        message_queue_version_++;
      } else {
        iter++;
      }
    }

    if (--listener_count_ == 0) {
      DCHECK(lazy_tls_ptr_.Pointer()->Get());
      lazy_tls_ptr_.Pointer()->Set(NULL);
    }
  }

  WaitableEvent* dispatch_event() { return &dispatch_event_; }
  base::SingleThreadTaskRunner* listener_task_runner() {
    return listener_task_runner_.get();
  }

  // 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;
      }
    }
  }

  base::WaitableEventWatcher* top_send_done_watcher() {
    return top_send_done_watcher_;
  }

  void set_top_send_done_watcher(base::WaitableEventWatcher* watcher) {
    top_send_done_watcher_ = watcher;
  }

 private:
  friend class base::RefCountedThreadSafe<ReceivedSyncMsgQueue>;

  // See the comment in SyncChannel::SyncChannel for why this event is created
  // as manual reset.
  ReceivedSyncMsgQueue() :
      message_queue_version_(0),
      dispatch_event_(true, false),
      listener_task_runner_(base::ThreadTaskRunnerHandle::Get()),
      task_pending_(false),
      listener_count_(0),
      top_send_done_watcher_(NULL) {
  }

  ~ReceivedSyncMsgQueue() {}

  // 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::list<QueuedMessage> SyncMessageQueue;
  SyncMessageQueue message_queue_;
  uint32 message_queue_version_;  // Used to signal DispatchMessages to rescan

  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_;
  scoped_refptr<base::SingleThreadTaskRunner> listener_task_runner_;
  base::Lock message_lock_;
  bool task_pending_;
  int listener_count_;

  // The current send done event watcher for this thread. Used to maintain
  // a local global stack of send done watchers to ensure that nested sync
  // message loops complete correctly.
  base::WaitableEventWatcher* top_send_done_watcher_;
};

base::LazyInstance<base::ThreadLocalPointer<SyncChannel::ReceivedSyncMsgQueue> >
    SyncChannel::ReceivedSyncMsgQueue::lazy_tls_ptr_ =
        LAZY_INSTANCE_INITIALIZER;

SyncChannel::SyncContext::SyncContext(
    Listener* listener,
    base::SingleThreadTaskRunner* ipc_task_runner,
    WaitableEvent* shutdown_event)
    : ChannelProxy::Context(listener, ipc_task_runner),
      received_sync_msgs_(ReceivedSyncMsgQueue::AddContext()),
      shutdown_event_(shutdown_event),
      restrict_dispatch_group_(kRestrictDispatchGroup_None) {
}

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) {
  // Create the tracking information for this message. This object is stored
  // by value since all members are pointers that are cheap to copy. These
  // pointers are cleaned up in the Pop() function.
  //
  // 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));
  base::AutoLock auto_lock(deserializers_lock_);
  deserializers_.push_back(pending);
}

bool SyncChannel::SyncContext::Pop() {
  bool result;
  {
    base::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_task_runner()->PostTask(
      FROM_HERE, base::Bind(&ReceivedSyncMsgQueue::DispatchReplies,
                            received_sync_msgs_.get()));

  return result;
}

WaitableEvent* SyncChannel::SyncContext::GetSendDoneEvent() {
  base::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(this);
}

bool SyncChannel::SyncContext::TryToUnblockListener(const Message* msg) {
  base::AutoLock auto_lock(deserializers_lock_);
  if (deserializers_.empty() ||
      !SyncMessage::IsMessageReplyTo(*msg, deserializers_.back().id)) {
    return false;
  }

  // TODO(bauerb): Remove logging once investigation of http://crbug.com/141055
  // has finished.
  if (!msg->is_reply_error()) {
    bool send_result = deserializers_.back().deserializer->
        SerializeOutputParameters(*msg);
    deserializers_.back().send_result = send_result;
    VLOG_IF(1, !send_result) << "Couldn't deserialize reply message";
  } else {
    VLOG(1) << "Received error reply";
  }
  deserializers_.back().done_event->Signal();

  return true;
}

void SyncChannel::SyncContext::Clear() {
  CancelPendingSends();
  received_sync_msgs_->RemoveContext(this);
  Context::Clear();
}

bool SyncChannel::SyncContext::OnMessageReceived(const Message& msg) {
  // Give the filters a chance at processing this message.
  if (TryFilters(msg))
    return true;

  if (TryToUnblockListener(&msg))
    return true;

  if (msg.is_reply()) {
    received_sync_msgs_->QueueReply(msg, this);
    return true;
  }

  if (msg.should_unblock()) {
    received_sync_msgs_->QueueMessage(msg, this);
    return true;
  }

  return Context::OnMessageReceivedNoFilter(msg);
}

void SyncChannel::SyncContext::OnChannelError() {
  CancelPendingSends();
  shutdown_watcher_.StopWatching();
  Context::OnChannelError();
}

void SyncChannel::SyncContext::OnChannelOpened() {
  shutdown_watcher_.StartWatching(
      shutdown_event_,
      base::Bind(&SyncChannel::SyncContext::OnWaitableEventSignaled,
                 base::Unretained(this)));
  Context::OnChannelOpened();
}

void SyncChannel::SyncContext::OnChannelClosed() {
  CancelPendingSends();
  shutdown_watcher_.StopWatching();
  Context::OnChannelClosed();
}

void SyncChannel::SyncContext::OnSendTimeout(int message_id) {
  base::AutoLock auto_lock(deserializers_lock_);
  PendingSyncMessageQueue::iterator iter;
  VLOG(1) << "Send timeout";
  for (iter = deserializers_.begin(); iter != deserializers_.end(); iter++) {
    if (iter->id == message_id) {
      iter->done_event->Signal();
      break;
    }
  }
}

void SyncChannel::SyncContext::CancelPendingSends() {
  base::AutoLock auto_lock(deserializers_lock_);
  PendingSyncMessageQueue::iterator iter;
  // TODO(bauerb): Remove once http://crbug/141055 is fixed.
  VLOG(1) << "Canceling pending sends";
  for (iter = deserializers_.begin(); iter != deserializers_.end(); iter++)
    iter->done_event->Signal();
}

void SyncChannel::SyncContext::OnWaitableEventSignaled(WaitableEvent* event) {
  if (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();
  } else {
    // We got the reply, timed out or the process shutdown.
    DCHECK_EQ(GetSendDoneEvent(), event);
    base::MessageLoop::current()->QuitNow();
  }
}

base::WaitableEventWatcher::EventCallback
    SyncChannel::SyncContext::MakeWaitableEventCallback() {
  return base::Bind(&SyncChannel::SyncContext::OnWaitableEventSignaled, this);
}

SyncChannel::SyncChannel(
    const IPC::ChannelHandle& channel_handle,
    Channel::Mode mode,
    Listener* listener,
    base::SingleThreadTaskRunner* ipc_task_runner,
    bool create_pipe_now,
    WaitableEvent* shutdown_event)
    : ChannelProxy(new SyncContext(listener, ipc_task_runner, shutdown_event)),
      sync_messages_with_no_timeout_allowed_(true) {
  ChannelProxy::Init(channel_handle, mode, create_pipe_now);
  StartWatching();
}

SyncChannel::SyncChannel(
    Listener* listener,
    base::SingleThreadTaskRunner* ipc_task_runner,
    WaitableEvent* shutdown_event)
    : ChannelProxy(new SyncContext(listener, ipc_task_runner, shutdown_event)),
      sync_messages_with_no_timeout_allowed_(true) {
  StartWatching();
}

SyncChannel::~SyncChannel() {
}

void SyncChannel::SetRestrictDispatchChannelGroup(int group) {
  sync_context()->set_restrict_dispatch_group(group);
}

bool SyncChannel::Send(Message* message) {
  return SendWithTimeout(message, base::kNoTimeout);
}

bool SyncChannel::SendWithTimeout(Message* message, int timeout_ms) {
#ifdef IPC_MESSAGE_LOG_ENABLED
  Logging* logger = Logging::GetInstance();
  std::string name;
  logger->GetMessageText(message->type(), &name, message, NULL);
  TRACE_EVENT1("toplevel", "SyncChannel::SendWithTimeout",
               "name", name);
#else
  TRACE_EVENT2("toplevel", "SyncChannel::SendWithTimeout",
               "class", IPC_MESSAGE_ID_CLASS(message->type()),
               "line", IPC_MESSAGE_ID_LINE(message->type()));
#endif
  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()) {
    VLOG(1) << "shutdown event is signaled";
    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_task_runner()->PostDelayedTask(
        FROM_HERE,
        base::Bind(&SyncContext::OnSendTimeout, context.get(), message_id),
        base::TimeDelta::FromMilliseconds(timeout_ms));
  }

  // Wait for reply, or for any other incoming synchronous messages.
  // *this* might get deleted, so only call static functions at this point.
  WaitForReply(context.get(), pump_messages_event);

  return context->Pop();
}

void SyncChannel::WaitForReply(
    SyncContext* context, WaitableEvent* pump_messages_event) {
  context->DispatchMessages();
  while (true) {
    WaitableEvent* objects[] = {
      context->GetDispatchEvent(),
      context->GetSendDoneEvent(),
      pump_messages_event
    };

    unsigned count = pump_messages_event ? 3: 2;
    size_t 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.
      context->GetDispatchEvent()->Reset();
      context->DispatchMessages();
      continue;
    }

    if (result == 2 /* pump_messages_event */)
      WaitForReplyWithNestedMessageLoop(context);  // Run a nested message loop.

    break;
  }
}

void SyncChannel::WaitForReplyWithNestedMessageLoop(SyncContext* context) {
  base::WaitableEventWatcher send_done_watcher;

  ReceivedSyncMsgQueue* sync_msg_queue = context->received_sync_msgs();
  DCHECK(sync_msg_queue != NULL);

  base::WaitableEventWatcher* old_send_done_event_watcher =
      sync_msg_queue->top_send_done_watcher();

  base::WaitableEventWatcher::EventCallback old_callback;
  base::WaitableEvent* old_event = NULL;

  // Maintain a local global stack of send done delegates to ensure that
  // nested sync calls complete in the correct sequence, i.e. the
  // outermost call completes first, etc.
  if (old_send_done_event_watcher) {
    old_callback = old_send_done_event_watcher->callback();
    old_event = old_send_done_event_watcher->GetWatchedEvent();
    old_send_done_event_watcher->StopWatching();
  }

  sync_msg_queue->set_top_send_done_watcher(&send_done_watcher);

  send_done_watcher.StartWatching(context->GetSendDoneEvent(),
                                  context->MakeWaitableEventCallback());

  {
    base::MessageLoop::ScopedNestableTaskAllower allow(
        base::MessageLoop::current());
    base::MessageLoop::current()->Run();
  }

  sync_msg_queue->set_top_send_done_watcher(old_send_done_event_watcher);
  if (old_send_done_event_watcher && old_event) {
    old_send_done_event_watcher->StartWatching(old_event, old_callback);
  }
}

void SyncChannel::OnWaitableEventSignaled(WaitableEvent* event) {
  DCHECK(event == sync_context()->GetDispatchEvent());
  // The call to DispatchMessages might delete this object, so reregister
  // the object watcher first.
  event->Reset();
  dispatch_watcher_.StartWatching(event, dispatch_watcher_callback_);
  sync_context()->DispatchMessages();
}

void SyncChannel::StartWatching() {
  // 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_callback_ =
      base::Bind(&SyncChannel::OnWaitableEventSignaled,
                  base::Unretained(this));
  dispatch_watcher_.StartWatching(sync_context()->GetDispatchEvent(),
                                  dispatch_watcher_callback_);
}

}  // namespace IPC