ipc/ipc_sync_channel.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "ipc/ipc_sync_channel.h"
   6
   7 #include "base/bind.h"
   8 #include "base/debug/trace_event.h"
   9 #include "base/lazy_instance.h"
  10 #include "base/location.h"
  11 #include "base/logging.h"
  12 #include "base/synchronization/waitable_event.h"
  13 #include "base/synchronization/waitable_event_watcher.h"
  14 #include "base/thread_task_runner_handle.h"
  15 #include "base/threading/thread_local.h"
  16 #include "ipc/ipc_logging.h"
  17 #include "ipc/ipc_message_macros.h"
  18 #include "ipc/ipc_sync_message.h"
  19
  20 using base::TimeDelta;
  21 using base::TimeTicks;
  22 using base::WaitableEvent;
  23
  24 namespace IPC {
  25 // When we're blocked in a Send(), we need to process incoming synchronous
  26 // messages right away because it could be blocking our reply (either
  27 // directly from the same object we're calling, or indirectly through one or
  28 // more other channels).  That means that in SyncContext's OnMessageReceived,
  29 // we need to process sync message right away if we're blocked.  However a
  30 // simple check isn't sufficient, because the listener thread can be in the
  31 // process of calling Send.
  32 // To work around this, when SyncChannel filters a sync message, it sets
  33 // an event that the listener thread waits on during its Send() call.  This
  34 // allows us to dispatch incoming sync messages when blocked.  The race
  35 // condition is handled because if Send is in the process of being called, it
  36 // will check the event.  In case the listener thread isn't sending a message,
  37 // we queue a task on the listener thread to dispatch the received messages.
  38 // The messages are stored in this queue object that's shared among all
  39 // SyncChannel objects on the same thread (since one object can receive a
  40 // sync message while another one is blocked).
  41
  42 class SyncChannel::ReceivedSyncMsgQueue :
  43     public base::RefCountedThreadSafe<ReceivedSyncMsgQueue> {
  44  public:
  45   // Returns the ReceivedSyncMsgQueue instance for this thread, creating one
  46   // if necessary.  Call RemoveContext on the same thread when done.
  47   static ReceivedSyncMsgQueue* AddContext() {
  48     // We want one ReceivedSyncMsgQueue per listener thread (i.e. since multiple
  49     // SyncChannel objects can block the same thread).
  50     ReceivedSyncMsgQueue* rv = lazy_tls_ptr_.Pointer()->Get();
  51     if (!rv) {
  52       rv = new ReceivedSyncMsgQueue();
  53       ReceivedSyncMsgQueue::lazy_tls_ptr_.Pointer()->Set(rv);
  54     }
  55     rv->listener_count_++;
  56     return rv;
  57   }
  58
  59   // Called on IPC thread when a synchronous message or reply arrives.
  60   void QueueMessage(const Message& msg, SyncChannel::SyncContext* context) {
  61     bool was_task_pending;
  62     {
  63       base::AutoLock auto_lock(message_lock_);
  64
  65       was_task_pending = task_pending_;
  66       task_pending_ = true;
  67
  68       // We set the event in case the listener thread is blocked (or is about
  69       // to). In case it's not, the PostTask dispatches the messages.
  70       message_queue_.push_back(QueuedMessage(new Message(msg), context));
  71       message_queue_version_++;
  72     }
  73
  74     dispatch_event_.Signal();
  75     if (!was_task_pending) {
  76       listener_task_runner_->PostTask(
  77           FROM_HERE, base::Bind(&ReceivedSyncMsgQueue::DispatchMessagesTask,
  78                                 this, scoped_refptr<SyncContext>(context)));
  79     }
  80   }
  81
  82   void QueueReply(const Message &msg, SyncChannel::SyncContext* context) {
  83     received_replies_.push_back(QueuedMessage(new Message(msg), context));
  84   }
  85
  86   // Called on the listener's thread to process any queues synchronous
  87   // messages.
  88   void DispatchMessagesTask(SyncContext* context) {
  89     {
  90       base::AutoLock auto_lock(message_lock_);
  91       task_pending_ = false;
  92     }
  93     context->DispatchMessages();
  94   }
  95
  96   void DispatchMessages(SyncContext* dispatching_context) {
  97     bool first_time = true;
  98     uint32 expected_version = 0;
  99     SyncMessageQueue::iterator it;
 100     while (true) {
 101       Message* message = NULL;
 102       scoped_refptr<SyncChannel::SyncContext> context;
 103       {
 104         base::AutoLock auto_lock(message_lock_);
 105         if (first_time || message_queue_version_ != expected_version) {
 106           it = message_queue_.begin();
 107           first_time = false;
 108         }
 109         for (; it != message_queue_.end(); it++) {
 110           int message_group = it->context->restrict_dispatch_group();
 111           if (message_group == kRestrictDispatchGroup_None ||
 112               message_group == dispatching_context->restrict_dispatch_group()) {
 113             message = it->message;
 114             context = it->context;
 115             it = message_queue_.erase(it);
 116             message_queue_version_++;
 117             expected_version = message_queue_version_;
 118             break;
 119           }
 120         }
 121       }
 122
 123       if (message == NULL)
 124         break;
 125       context->OnDispatchMessage(*message);
 126       delete message;
 127     }
 128   }
 129
 130   // SyncChannel calls this in its destructor.
 131   void RemoveContext(SyncContext* context) {
 132     base::AutoLock auto_lock(message_lock_);
 133
 134     SyncMessageQueue::iterator iter = message_queue_.begin();
 135     while (iter != message_queue_.end()) {
 136       if (iter->context.get() == context) {
 137         delete iter->message;
 138         iter = message_queue_.erase(iter);
 139         message_queue_version_++;
 140       } else {
 141         iter++;
 142       }
 143     }
 144
 145     if (--listener_count_ == 0) {
 146       DCHECK(lazy_tls_ptr_.Pointer()->Get());
 147       lazy_tls_ptr_.Pointer()->Set(NULL);
 148     }
 149   }
 150
 151   WaitableEvent* dispatch_event() { return &dispatch_event_; }
 152   base::SingleThreadTaskRunner* listener_task_runner() {
 153     return listener_task_runner_.get();
 154   }
 155
 156   // Holds a pointer to the per-thread ReceivedSyncMsgQueue object.
 157   static base::LazyInstance<base::ThreadLocalPointer<ReceivedSyncMsgQueue> >
 158       lazy_tls_ptr_;
 159
 160   // Called on the ipc thread to check if we can unblock any current Send()
 161   // calls based on a queued reply.
 162   void DispatchReplies() {
 163     for (size_t i = 0; i < received_replies_.size(); ++i) {
 164       Message* message = received_replies_[i].message;
 165       if (received_replies_[i].context->TryToUnblockListener(message)) {
 166         delete message;
 167         received_replies_.erase(received_replies_.begin() + i);
 168         return;
 169       }
 170     }
 171   }
 172
 173   base::WaitableEventWatcher* top_send_done_watcher() {
 174     return top_send_done_watcher_;
 175   }
 176
 177   void set_top_send_done_watcher(base::WaitableEventWatcher* watcher) {
 178     top_send_done_watcher_ = watcher;
 179   }
 180
 181  private:
 182   friend class base::RefCountedThreadSafe<ReceivedSyncMsgQueue>;
 183
 184   // See the comment in SyncChannel::SyncChannel for why this event is created
 185   // as manual reset.
 186   ReceivedSyncMsgQueue() :
 187       message_queue_version_(0),
 188       dispatch_event_(true, false),
 189       listener_task_runner_(base::ThreadTaskRunnerHandle::Get()),
 190       task_pending_(false),
 191       listener_count_(0),
 192       top_send_done_watcher_(NULL) {
 193   }
 194
 195   ~ReceivedSyncMsgQueue() {}
 196
 197   // Holds information about a queued synchronous message or reply.
 198   struct QueuedMessage {
 199     QueuedMessage(Message* m, SyncContext* c) : message(m), context(c) { }
 200     Message* message;
 201     scoped_refptr<SyncChannel::SyncContext> context;
 202   };
 203
 204   typedef std::list<QueuedMessage> SyncMessageQueue;
 205   SyncMessageQueue message_queue_;
 206   uint32 message_queue_version_;  // Used to signal DispatchMessages to rescan
 207
 208   std::vector<QueuedMessage> received_replies_;
 209
 210   // Set when we got a synchronous message that we must respond to as the
 211   // sender needs its reply before it can reply to our original synchronous
 212   // message.
 213   WaitableEvent dispatch_event_;
 214   scoped_refptr<base::SingleThreadTaskRunner> listener_task_runner_;
 215   base::Lock message_lock_;
 216   bool task_pending_;
 217   int listener_count_;
 218
 219   // The current send done event watcher for this thread. Used to maintain
 220   // a local global stack of send done watchers to ensure that nested sync
 221   // message loops complete correctly.
 222   base::WaitableEventWatcher* top_send_done_watcher_;
 223 };
 224
 225 base::LazyInstance<base::ThreadLocalPointer<SyncChannel::ReceivedSyncMsgQueue> >
 226     SyncChannel::ReceivedSyncMsgQueue::lazy_tls_ptr_ =
 227         LAZY_INSTANCE_INITIALIZER;
 228
 229 SyncChannel::SyncContext::SyncContext(
 230     Listener* listener,
 231     base::SingleThreadTaskRunner* ipc_task_runner,
 232     WaitableEvent* shutdown_event)
 233     : ChannelProxy::Context(listener, ipc_task_runner),
 234       received_sync_msgs_(ReceivedSyncMsgQueue::AddContext()),
 235       shutdown_event_(shutdown_event),
 236       restrict_dispatch_group_(kRestrictDispatchGroup_None) {
 237 }
 238
 239 SyncChannel::SyncContext::~SyncContext() {
 240   while (!deserializers_.empty())
 241     Pop();
 242 }
 243
 244 // Adds information about an outgoing sync message to the context so that
 245 // we know how to deserialize the reply.  Returns a handle that's set when
 246 // the reply has arrived.
 247 void SyncChannel::SyncContext::Push(SyncMessage* sync_msg) {
 248   // Create the tracking information for this message. This object is stored
 249   // by value since all members are pointers that are cheap to copy. These
 250   // pointers are cleaned up in the Pop() function.
 251   //
 252   // The event is created as manual reset because in between Signal and
 253   // OnObjectSignalled, another Send can happen which would stop the watcher
 254   // from being called.  The event would get watched later, when the nested
 255   // Send completes, so the event will need to remain set.
 256   PendingSyncMsg pending(SyncMessage::GetMessageId(*sync_msg),
 257                          sync_msg->GetReplyDeserializer(),
 258                          new WaitableEvent(true, false));
 259   base::AutoLock auto_lock(deserializers_lock_);
 260   deserializers_.push_back(pending);
 261 }
 262
 263 bool SyncChannel::SyncContext::Pop() {
 264   bool result;
 265   {
 266     base::AutoLock auto_lock(deserializers_lock_);
 267     PendingSyncMsg msg = deserializers_.back();
 268     delete msg.deserializer;
 269     delete msg.done_event;
 270     msg.done_event = NULL;
 271     deserializers_.pop_back();
 272     result = msg.send_result;
 273   }
 274
 275   // We got a reply to a synchronous Send() call that's blocking the listener
 276   // thread.  However, further down the call stack there could be another
 277   // blocking Send() call, whose reply we received after we made this last
 278   // Send() call.  So check if we have any queued replies available that
 279   // can now unblock the listener thread.
 280   ipc_task_runner()->PostTask(
 281       FROM_HERE, base::Bind(&ReceivedSyncMsgQueue::DispatchReplies,
 282                             received_sync_msgs_.get()));
 283
 284   return result;
 285 }
 286
 287 WaitableEvent* SyncChannel::SyncContext::GetSendDoneEvent() {
 288   base::AutoLock auto_lock(deserializers_lock_);
 289   return deserializers_.back().done_event;
 290 }
 291
 292 WaitableEvent* SyncChannel::SyncContext::GetDispatchEvent() {
 293   return received_sync_msgs_->dispatch_event();
 294 }
 295
 296 void SyncChannel::SyncContext::DispatchMessages() {
 297   received_sync_msgs_->DispatchMessages(this);
 298 }
 299
 300 bool SyncChannel::SyncContext::TryToUnblockListener(const Message* msg) {
 301   base::AutoLock auto_lock(deserializers_lock_);
 302   if (deserializers_.empty() ||
 303       !SyncMessage::IsMessageReplyTo(*msg, deserializers_.back().id)) {
 304     return false;
 305   }
 306
 307   // TODO(bauerb): Remove logging once investigation of http://crbug.com/141055
 308   // has finished.
 309   if (!msg->is_reply_error()) {
 310     bool send_result = deserializers_.back().deserializer->
 311         SerializeOutputParameters(*msg);
 312     deserializers_.back().send_result = send_result;
 313     VLOG_IF(1, !send_result) << "Couldn't deserialize reply message";
 314   } else {
 315     VLOG(1) << "Received error reply";
 316   }
 317   deserializers_.back().done_event->Signal();
 318
 319   return true;
 320 }
 321
 322 void SyncChannel::SyncContext::Clear() {
 323   CancelPendingSends();
 324   received_sync_msgs_->RemoveContext(this);
 325   Context::Clear();
 326 }
 327
 328 bool SyncChannel::SyncContext::OnMessageReceived(const Message& msg) {
 329   // Give the filters a chance at processing this message.
 330   if (TryFilters(msg))
 331     return true;
 332
 333   if (TryToUnblockListener(&msg))
 334     return true;
 335
 336   if (msg.is_reply()) {
 337     received_sync_msgs_->QueueReply(msg, this);
 338     return true;
 339   }
 340
 341   if (msg.should_unblock()) {
 342     received_sync_msgs_->QueueMessage(msg, this);
 343     return true;
 344   }
 345
 346   return Context::OnMessageReceivedNoFilter(msg);
 347 }
 348
 349 void SyncChannel::SyncContext::OnChannelError() {
 350   CancelPendingSends();
 351   shutdown_watcher_.StopWatching();
 352   Context::OnChannelError();
 353 }
 354
 355 void SyncChannel::SyncContext::OnChannelOpened() {
 356   shutdown_watcher_.StartWatching(
 357       shutdown_event_,
 358       base::Bind(&SyncChannel::SyncContext::OnWaitableEventSignaled,
 359                  base::Unretained(this)));
 360   Context::OnChannelOpened();
 361 }
 362
 363 void SyncChannel::SyncContext::OnChannelClosed() {
 364   CancelPendingSends();
 365   shutdown_watcher_.StopWatching();
 366   Context::OnChannelClosed();
 367 }
 368
 369 void SyncChannel::SyncContext::OnSendTimeout(int message_id) {
 370   base::AutoLock auto_lock(deserializers_lock_);
 371   PendingSyncMessageQueue::iterator iter;
 372   VLOG(1) << "Send timeout";
 373   for (iter = deserializers_.begin(); iter != deserializers_.end(); iter++) {
 374     if (iter->id == message_id) {
 375       iter->done_event->Signal();
 376       break;
 377     }
 378   }
 379 }
 380
 381 void SyncChannel::SyncContext::CancelPendingSends() {
 382   base::AutoLock auto_lock(deserializers_lock_);
 383   PendingSyncMessageQueue::iterator iter;
 384   // TODO(bauerb): Remove once http://crbug/141055 is fixed.
 385   VLOG(1) << "Canceling pending sends";
 386   for (iter = deserializers_.begin(); iter != deserializers_.end(); iter++)
 387     iter->done_event->Signal();
 388 }
 389
 390 void SyncChannel::SyncContext::OnWaitableEventSignaled(WaitableEvent* event) {
 391   if (event == shutdown_event_) {
 392     // Process shut down before we can get a reply to a synchronous message.
 393     // Cancel pending Send calls, which will end up setting the send done event.
 394     CancelPendingSends();
 395   } else {
 396     // We got the reply, timed out or the process shutdown.
 397     DCHECK_EQ(GetSendDoneEvent(), event);
 398     base::MessageLoop::current()->QuitNow();
 399   }
 400 }
 401
 402 base::WaitableEventWatcher::EventCallback
 403     SyncChannel::SyncContext::MakeWaitableEventCallback() {
 404   return base::Bind(&SyncChannel::SyncContext::OnWaitableEventSignaled, this);
 405 }
 406
 407 SyncChannel::SyncChannel(
 408     const IPC::ChannelHandle& channel_handle,
 409     Channel::Mode mode,
 410     Listener* listener,
 411     base::SingleThreadTaskRunner* ipc_task_runner,
 412     bool create_pipe_now,
 413     WaitableEvent* shutdown_event)
 414     : ChannelProxy(new SyncContext(listener, ipc_task_runner, shutdown_event)) {
 415   // The current (listener) thread must be distinct from the IPC thread, or else
 416   // sending synchronous messages will deadlock.
 417   DCHECK_NE(ipc_task_runner, base::ThreadTaskRunnerHandle::Get());
 418   ChannelProxy::Init(channel_handle, mode, create_pipe_now);
 419   StartWatching();
 420 }
 421
 422 SyncChannel::SyncChannel(
 423     Listener* listener,
 424     base::SingleThreadTaskRunner* ipc_task_runner,
 425     WaitableEvent* shutdown_event)
 426     : ChannelProxy(new SyncContext(listener, ipc_task_runner, shutdown_event)) {
 427   // The current (listener) thread must be distinct from the IPC thread, or else
 428   // sending synchronous messages will deadlock.
 429   DCHECK_NE(ipc_task_runner, base::ThreadTaskRunnerHandle::Get());
 430   StartWatching();
 431 }
 432
 433 SyncChannel::~SyncChannel() {
 434 }
 435
 436 void SyncChannel::SetRestrictDispatchChannelGroup(int group) {
 437   sync_context()->set_restrict_dispatch_group(group);
 438 }
 439
 440 bool SyncChannel::Send(Message* message) {
 441 #ifdef IPC_MESSAGE_LOG_ENABLED
 442   Logging* logger = Logging::GetInstance();
 443   std::string name;
 444   logger->GetMessageText(message->type(), &name, message, NULL);
 445   TRACE_EVENT1("toplevel", "SyncChannel::Send", "name", name);
 446 #else
 447   TRACE_EVENT2("toplevel", "SyncChannel::Send",
 448                "class", IPC_MESSAGE_ID_CLASS(message->type()),
 449                "line", IPC_MESSAGE_ID_LINE(message->type()));
 450 #endif
 451   if (!message->is_sync()) {
 452     ChannelProxy::Send(message);
 453     return true;
 454   }
 455
 456   // *this* might get deleted in WaitForReply.
 457   scoped_refptr<SyncContext> context(sync_context());
 458   if (context->shutdown_event()->IsSignaled()) {
 459     VLOG(1) << "shutdown event is signaled";
 460     delete message;
 461     return false;
 462   }
 463
 464   SyncMessage* sync_msg = static_cast<SyncMessage*>(message);
 465   context->Push(sync_msg);
 466   WaitableEvent* pump_messages_event = sync_msg->pump_messages_event();
 467
 468   ChannelProxy::Send(message);
 469
 470   // Wait for reply, or for any other incoming synchronous messages.
 471   // *this* might get deleted, so only call static functions at this point.
 472   WaitForReply(context.get(), pump_messages_event);
 473
 474   return context->Pop();
 475 }
 476
 477 void SyncChannel::WaitForReply(
 478     SyncContext* context, WaitableEvent* pump_messages_event) {
 479   context->DispatchMessages();
 480   while (true) {
 481     WaitableEvent* objects[] = {
 482       context->GetDispatchEvent(),
 483       context->GetSendDoneEvent(),
 484       pump_messages_event
 485     };
 486
 487     unsigned count = pump_messages_event ? 3: 2;
 488     size_t result = WaitableEvent::WaitMany(objects, count);
 489     if (result == 0 /* dispatch event */) {
 490       // We're waiting for a reply, but we received a blocking synchronous
 491       // call.  We must process it or otherwise a deadlock might occur.
 492       context->GetDispatchEvent()->Reset();
 493       context->DispatchMessages();
 494       continue;
 495     }
 496
 497     if (result == 2 /* pump_messages_event */)
 498       WaitForReplyWithNestedMessageLoop(context);  // Run a nested message loop.
 499
 500     break;
 501   }
 502 }
 503
 504 void SyncChannel::WaitForReplyWithNestedMessageLoop(SyncContext* context) {
 505   base::WaitableEventWatcher send_done_watcher;
 506
 507   ReceivedSyncMsgQueue* sync_msg_queue = context->received_sync_msgs();
 508   DCHECK(sync_msg_queue != NULL);
 509
 510   base::WaitableEventWatcher* old_send_done_event_watcher =
 511       sync_msg_queue->top_send_done_watcher();
 512
 513   base::WaitableEventWatcher::EventCallback old_callback;
 514   base::WaitableEvent* old_event = NULL;
 515
 516   // Maintain a local global stack of send done delegates to ensure that
 517   // nested sync calls complete in the correct sequence, i.e. the
 518   // outermost call completes first, etc.
 519   if (old_send_done_event_watcher) {
 520     old_callback = old_send_done_event_watcher->callback();
 521     old_event = old_send_done_event_watcher->GetWatchedEvent();
 522     old_send_done_event_watcher->StopWatching();
 523   }
 524
 525   sync_msg_queue->set_top_send_done_watcher(&send_done_watcher);
 526
 527   send_done_watcher.StartWatching(context->GetSendDoneEvent(),
 528                                   context->MakeWaitableEventCallback());
 529
 530   {
 531     base::MessageLoop::ScopedNestableTaskAllower allow(
 532         base::MessageLoop::current());
 533     base::MessageLoop::current()->Run();
 534   }
 535
 536   sync_msg_queue->set_top_send_done_watcher(old_send_done_event_watcher);
 537   if (old_send_done_event_watcher && old_event) {
 538     old_send_done_event_watcher->StartWatching(old_event, old_callback);
 539   }
 540 }
 541
 542 void SyncChannel::OnWaitableEventSignaled(WaitableEvent* event) {
 543   DCHECK(event == sync_context()->GetDispatchEvent());
 544   // The call to DispatchMessages might delete this object, so reregister
 545   // the object watcher first.
 546   event->Reset();
 547   dispatch_watcher_.StartWatching(event, dispatch_watcher_callback_);
 548   sync_context()->DispatchMessages();
 549 }
 550
 551 void SyncChannel::StartWatching() {
 552   // Ideally we only want to watch this object when running a nested message
 553   // loop.  However, we don't know when it exits if there's another nested
 554   // message loop running under it or not, so we wouldn't know whether to
 555   // stop or keep watching.  So we always watch it, and create the event as
 556   // manual reset since the object watcher might otherwise reset the event
 557   // when we're doing a WaitMany.
 558   dispatch_watcher_callback_ =
 559       base::Bind(&SyncChannel::OnWaitableEventSignaled,
 560                   base::Unretained(this));
 561   dispatch_watcher_.StartWatching(sync_context()->GetDispatchEvent(),
 562                                   dispatch_watcher_callback_);
 563 }
 564
 565 }  // namespace IPC