runtime/vm/message_handler.cc - sdk.git - Git at Google

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.

 #include <utility>

 #include "vm/message_handler.h"

 #include "vm/dart.h"
 #include "vm/heap/safepoint.h"
 #include "vm/isolate.h"
 #include "vm/lockers.h"
 #include "vm/object.h"
 #include "vm/object_store.h"
 #include "vm/os.h"
 #include "vm/port.h"
 #include "vm/thread_interrupter.h"

 namespace dart {

 DECLARE_FLAG(bool, trace_service_pause_events);

 class MessageHandlerTask : public ThreadPool::Task {
  public:
   explicit MessageHandlerTask(MessageHandler* handler) : handler_(handler) {
     ASSERT(handler != NULL);
   }

   virtual void Run() {
     ASSERT(handler_ != NULL);
     handler_->TaskCallback();
   }

  private:
   MessageHandler* handler_;

   DISALLOW_COPY_AND_ASSIGN(MessageHandlerTask);
 };

 // static
 const char* MessageHandler::MessageStatusString(MessageStatus status) {
   switch (status) {
     case kOK:
       return "OK";
     case kError:
       return "Error";
     case kRestart:
       return "Restart";
     case kShutdown:
       return "Shutdown";
     default:
       UNREACHABLE();
       return "Illegal";
   }
 }

 MessageHandler::MessageHandler()
     : queue_(new MessageQueue()),
       oob_queue_(new MessageQueue()),
       oob_message_handling_allowed_(true),
       paused_for_messages_(false),
       live_ports_(0),
       paused_(0),
 #if !defined(PRODUCT)
       should_pause_on_start_(false),
       should_pause_on_exit_(false),
       is_paused_on_start_(false),
       is_paused_on_exit_(false),
       paused_timestamp_(-1),
 #endif
       task_running_(false),
       delete_me_(false),
       pool_(NULL),
       start_callback_(NULL),
       end_callback_(NULL),
       callback_data_(0) {
   ASSERT(queue_ != NULL);
   ASSERT(oob_queue_ != NULL);
 }

 MessageHandler::~MessageHandler() {
   delete queue_;
   delete oob_queue_;
   queue_ = NULL;
   oob_queue_ = NULL;
   pool_ = NULL;
 }

 const char* MessageHandler::name() const {
   return "<unnamed>";
 }

 #if defined(DEBUG)
 void MessageHandler::CheckAccess() {
   // By default there is no checking.
 }
 #endif

 void MessageHandler::MessageNotify(Message::Priority priority) {
   // By default, there is no custom message notification.
 }

 void MessageHandler::Run(ThreadPool* pool,
                          StartCallback start_callback,
                          EndCallback end_callback,
                          CallbackData data) {
   MonitorLocker ml(&monitor_);
   if (FLAG_trace_isolates) {
     OS::PrintErr(
         "[+] Starting message handler:\n"
         "\thandler:    %s\n",
         name());
   }
   ASSERT(pool_ == NULL);
   ASSERT(!delete_me_);
   pool_ = pool;
   start_callback_ = start_callback;
   end_callback_ = end_callback;
   callback_data_ = data;
   task_running_ = true;
   const bool launched_successfully = pool_->Run<MessageHandlerTask>(this);
   ASSERT(launched_successfully);
 }

 void MessageHandler::PostMessage(std::unique_ptr<Message> message,
                                  bool before_events) {
   Message::Priority saved_priority;

   {
     MonitorLocker ml(&monitor_);
     if (FLAG_trace_isolates) {
       Isolate* source_isolate = Isolate::Current();
       if (source_isolate != nullptr) {
         OS::PrintErr(
             "[>] Posting message:\n"
             "\tlen:        %" Pd "\n\tsource:     (%" Pd64
             ") %s\n\tdest:       %s\n"
             "\tdest_port:  %" Pd64 "\n",
             message->Size(), static_cast<int64_t>(source_isolate->main_port()),
             source_isolate->name(), name(), message->dest_port());
       } else {
         OS::PrintErr(
             "[>] Posting message:\n"
             "\tlen:        %" Pd
             "\n\tsource:     <native code>\n"
             "\tdest:       %s\n"
             "\tdest_port:  %" Pd64 "\n",
             message->Size(), name(), message->dest_port());
       }
     }

     saved_priority = message->priority();
     if (message->IsOOB()) {
       oob_queue_->Enqueue(std::move(message), before_events);
     } else {
       queue_->Enqueue(std::move(message), before_events);
     }
     if (paused_for_messages_) {
       ml.Notify();
     }

     if (pool_ != nullptr && !task_running_) {
       ASSERT(!delete_me_);
       task_running_ = true;
       const bool launched_successfully = pool_->Run<MessageHandlerTask>(this);
       ASSERT(launched_successfully);
     }
   }

   // Invoke any custom message notification.
   MessageNotify(saved_priority);
 }

 std::unique_ptr<Message> MessageHandler::DequeueMessage(
     Message::Priority min_priority) {
   // TODO(turnidge): Add assert that monitor_ is held here.
   std::unique_ptr<Message> message = oob_queue_->Dequeue();
   if ((message == nullptr) && (min_priority < Message::kOOBPriority)) {
     message = queue_->Dequeue();
   }
   return message;
 }

 void MessageHandler::ClearOOBQueue() {
   oob_queue_->Clear();
 }

 MessageHandler::MessageStatus MessageHandler::HandleMessages(
     MonitorLocker* ml,
     bool allow_normal_messages,
     bool allow_multiple_normal_messages) {
   ASSERT(monitor_.IsOwnedByCurrentThread());

   // Scheduling of the mutator thread during the isolate start can cause this
   // thread to safepoint.
   // We want to avoid holding the message handler monitor during the safepoint
   // operation to avoid possible deadlocks, which can occur if other threads are
   // sending messages to this message handler.
   //
   // If isolate() returns nullptr [StartIsolateScope] does nothing.
   ml->Exit();
   StartIsolateScope start_isolate(isolate());
   ml->Enter();

   auto idle_time_handler =
       isolate() != nullptr ? isolate()->group()->idle_time_handler() : nullptr;

   MessageStatus max_status = kOK;
   Message::Priority min_priority =
       ((allow_normal_messages && !paused()) ? Message::kNormalPriority
                                             : Message::kOOBPriority);
   std::unique_ptr<Message> message = DequeueMessage(min_priority);
   while (message != nullptr) {
     intptr_t message_len = message->Size();
     if (FLAG_trace_isolates) {
       OS::PrintErr(
           "[<] Handling message:\n"
           "\tlen:        %" Pd
           "\n"
           "\thandler:    %s\n"
           "\tport:       %" Pd64 "\n",
           message_len, name(), message->dest_port());
     }

     // Release the monitor_ temporarily while we handle the message.
     // The monitor was acquired in MessageHandler::TaskCallback().
     ml->Exit();
     Message::Priority saved_priority = message->priority();
     Dart_Port saved_dest_port = message->dest_port();
     MessageStatus status = kOK;
     {
       DisableIdleTimerScope disable_idle_timer(idle_time_handler);
       status = HandleMessage(std::move(message));
     }
     if (status > max_status) {
       max_status = status;
     }
     ml->Enter();
     if (FLAG_trace_isolates) {
       OS::PrintErr(
           "[.] Message handled (%s):\n"
           "\tlen:        %" Pd
           "\n"
           "\thandler:    %s\n"
           "\tport:       %" Pd64 "\n",
           MessageStatusString(status), message_len, name(), saved_dest_port);
     }
     // If we are shutting down, do not process any more messages.
     if (status == kShutdown) {
       ClearOOBQueue();
       break;
     }

     // Remember time since the last message. Don't consider OOB messages so
     // using Observatory doesn't trigger additional idle tasks.
     if ((FLAG_idle_timeout_micros != 0) &&
         (saved_priority == Message::kNormalPriority)) {
       if (idle_time_handler != nullptr) {
         idle_time_handler->UpdateStartIdleTime();
       }
     }

     // Some callers want to process only one normal message and then quit. At
     // the same time it is OK to process multiple OOB messages.
     if ((saved_priority == Message::kNormalPriority) &&
         !allow_multiple_normal_messages) {
       // We processed one normal message.  Allow no more.
       allow_normal_messages = false;
     }

     // Reevaluate the minimum allowable priority.  The paused state
     // may have changed as part of handling the message.  We may also
     // have encountered an error during message processing.
     //
     // Even if we encounter an error, we still process pending OOB
     // messages so that we don't lose the message notification.
     min_priority = (((max_status == kOK) && allow_normal_messages && !paused())
                         ? Message::kNormalPriority
                         : Message::kOOBPriority);
     message = DequeueMessage(min_priority);
   }
   return max_status;
 }

 MessageHandler::MessageStatus MessageHandler::HandleNextMessage() {
   // We can only call HandleNextMessage when this handler is not
   // assigned to a thread pool.
   MonitorLocker ml(&monitor_);
   ASSERT(pool_ == NULL);
   ASSERT(!delete_me_);
 #if defined(DEBUG)
   CheckAccess();
 #endif
   return HandleMessages(&ml, true, false);
 }

 MessageHandler::MessageStatus MessageHandler::PauseAndHandleAllMessages(
     int64_t timeout_millis) {
   MonitorLocker ml(&monitor_, /*no_safepoint_scope=*/false);
   ASSERT(task_running_);
   ASSERT(!delete_me_);
 #if defined(DEBUG)
   CheckAccess();
 #endif
   paused_for_messages_ = true;
   while (queue_->IsEmpty() && oob_queue_->IsEmpty()) {
     Monitor::WaitResult wr;
     {
       // Ensure this thread is at a safepoint while we wait for new messages to
       // arrive.
       TransitionVMToNative transition(Thread::Current());
       wr = ml.Wait(timeout_millis);
     }
     ASSERT(task_running_);
     ASSERT(!delete_me_);
     if (wr == Monitor::kTimedOut) {
       break;
     }
     if (queue_->IsEmpty()) {
       // There are only OOB messages. Handle them and then continue waiting for
       // normal messages unless there is an error.
       MessageStatus status = HandleMessages(&ml, false, false);
       if (status != kOK) {
         paused_for_messages_ = false;
         return status;
       }
     }
   }
   paused_for_messages_ = false;
   return HandleMessages(&ml, true, true);
 }

 MessageHandler::MessageStatus MessageHandler::HandleOOBMessages() {
   if (!oob_message_handling_allowed_) {
     return kOK;
   }
   MonitorLocker ml(&monitor_);
   ASSERT(!delete_me_);
 #if defined(DEBUG)
   CheckAccess();
 #endif
   return HandleMessages(&ml, false, false);
 }

 #if !defined(PRODUCT)
 bool MessageHandler::ShouldPauseOnStart(MessageStatus status) const {
   Isolate* owning_isolate = isolate();
   if (owning_isolate == NULL) {
     return false;
   }
   // If we are restarting or shutting down, we do not want to honor
   // should_pause_on_start or should_pause_on_exit.
   return (status != MessageHandler::kRestart &&
           status != MessageHandler::kShutdown) &&
          should_pause_on_start() && owning_isolate->is_runnable();
 }

 bool MessageHandler::ShouldPauseOnExit(MessageStatus status) const {
   Isolate* owning_isolate = isolate();
   if (owning_isolate == NULL) {
     return false;
   }
   return (status != MessageHandler::kRestart &&
           status != MessageHandler::kShutdown) &&
          should_pause_on_exit() && owning_isolate->is_runnable();
 }
 #endif

 bool MessageHandler::HasOOBMessages() {
   MonitorLocker ml(&monitor_);
   return !oob_queue_->IsEmpty();
 }

 bool MessageHandler::HasMessages() {
   MonitorLocker ml(&monitor_);
   return !queue_->IsEmpty();
 }

 void MessageHandler::TaskCallback() {
   ASSERT(Isolate::Current() == NULL);
   MessageStatus status = kOK;
   bool run_end_callback = false;
   bool delete_me = false;
   EndCallback end_callback = NULL;
   CallbackData callback_data = 0;
   {
     // We will occasionally release and reacquire this monitor in this
     // function. Whenever we reacquire the monitor we *must* process
     // all pending OOB messages, or we may miss a request for vm
     // shutdown.
     MonitorLocker ml(&monitor_);

     // This method is running on the message handler task. Which means no
     // other message handler tasks will be started until this one sets
     // [task_running_] to false.
     ASSERT(task_running_);

 #if !defined(PRODUCT)
     if (ShouldPauseOnStart(kOK)) {
       if (!is_paused_on_start()) {
         PausedOnStartLocked(&ml, true);
       }
       // More messages may have come in before we (re)acquired the monitor.
       status = HandleMessages(&ml, false, false);
       if (ShouldPauseOnStart(status)) {
         // Still paused.
         ASSERT(oob_queue_->IsEmpty());
         task_running_ = false;  // No task in queue.
         return;
       } else {
         PausedOnStartLocked(&ml, false);
       }
     }
     if (is_paused_on_exit()) {
       status = HandleMessages(&ml, false, false);
       if (ShouldPauseOnExit(status)) {
         // Still paused.
         ASSERT(oob_queue_->IsEmpty());
         task_running_ = false;  // No task in queue.
         return;
       } else {
         PausedOnExitLocked(&ml, false);
       }
     }
 #endif  // !defined(PRODUCT)

     if (status == kOK) {
       if (start_callback_ != nullptr) {
         // Initialize the message handler by running its start function,
         // if we have one.  For an isolate, this will run the isolate's
         // main() function.
         //
         // Release the monitor_ temporarily while we call the start callback.
         ml.Exit();
         status = start_callback_(callback_data_);
         ASSERT(Isolate::Current() == NULL);
         start_callback_ = NULL;
         ml.Enter();
       }

       // Handle any pending messages for this message handler.
       if (status != kShutdown) {
         status = HandleMessages(&ml, (status == kOK), true);
       }
     }

     // The isolate exits when it encounters an error or when it no
     // longer has live ports.
     if (status != kOK || !HasLivePorts()) {
 #if !defined(PRODUCT)
       if (ShouldPauseOnExit(status)) {
         if (FLAG_trace_service_pause_events) {
           OS::PrintErr(
               "Isolate %s paused before exiting. "
               "Use the Observatory to release it.\n",
               name());
         }
         PausedOnExitLocked(&ml, true);
         // More messages may have come in while we released the monitor.
         status = HandleMessages(&ml, false, false);
         if (ShouldPauseOnExit(status)) {
           // Still paused.
           ASSERT(oob_queue_->IsEmpty());
           task_running_ = false;  // No task in queue.
           return;
         } else {
           PausedOnExitLocked(&ml, false);
         }
       }
 #endif  // !defined(PRODUCT)
       if (FLAG_trace_isolates) {
         if (status != kOK && thread() != NULL) {
           const Error& error = Error::Handle(thread()->sticky_error());
           OS::PrintErr(
               "[-] Stopping message handler (%s):\n"
               "\thandler:    %s\n"
               "\terror:    %s\n",
               MessageStatusString(status), name(), error.ToCString());
         } else {
           OS::PrintErr(
               "[-] Stopping message handler (%s):\n"
               "\thandler:    %s\n",
               MessageStatusString(status), name());
         }
       }
       pool_ = NULL;
       // Decide if we have a callback before releasing the monitor.
       end_callback = end_callback_;
       callback_data = callback_data_;
       run_end_callback = end_callback_ != NULL;
       delete_me = delete_me_;
     }

     // Clear task_running_ last.  This allows other tasks to potentially start
     // for this message handler.
     ASSERT(oob_queue_->IsEmpty());
     task_running_ = false;
   }

   // The handler may have been deleted by another thread here if it is a native
   // message handler.

   // Message handlers either use delete_me or end_callback but not both.
   ASSERT(!delete_me || !run_end_callback);

   if (run_end_callback) {
     ASSERT(end_callback != NULL);
     end_callback(callback_data);
     // The handler may have been deleted after this point.
   }
   if (delete_me) {
     delete this;
   }
 }

 void MessageHandler::ClosePort(Dart_Port port) {
   MonitorLocker ml(&monitor_);
   if (FLAG_trace_isolates) {
     OS::PrintErr(
         "[-] Closing port:\n"
         "\thandler:    %s\n"
         "\tport:       %" Pd64
         "\n"
         "\tports:      live(%" Pd ")\n",
         name(), port, live_ports_);
   }
 }

 void MessageHandler::CloseAllPorts() {
   MonitorLocker ml(&monitor_);
   if (FLAG_trace_isolates) {
     OS::PrintErr(
         "[-] Closing all ports:\n"
         "\thandler:    %s\n",
         name());
   }
   queue_->Clear();
   oob_queue_->Clear();
 }

 void MessageHandler::RequestDeletion() {
   ASSERT(OwnedByPortMap());
   {
     MonitorLocker ml(&monitor_);
     if (task_running_) {
       // This message handler currently has a task running on the thread pool.
       delete_me_ = true;
       return;
     }
   }

   // This message handler has no current task.  Delete it.
   delete this;
 }

 void MessageHandler::increment_live_ports() {
   MonitorLocker ml(&monitor_);
 #if defined(DEBUG)
   CheckAccess();
 #endif
   live_ports_++;
 }

 void MessageHandler::decrement_live_ports() {
   MonitorLocker ml(&monitor_);
 #if defined(DEBUG)
   CheckAccess();
 #endif
   live_ports_--;
 }

 #if !defined(PRODUCT)
 void MessageHandler::DebugDump() {
   PortMap::DebugDumpForMessageHandler(this);
 }

 void MessageHandler::PausedOnStart(bool paused) {
   MonitorLocker ml(&monitor_);
   PausedOnStartLocked(&ml, paused);
 }

 void MessageHandler::PausedOnStartLocked(MonitorLocker* ml, bool paused) {
   if (paused) {
     ASSERT(!is_paused_on_start_);
     ASSERT(paused_timestamp_ == -1);
     paused_timestamp_ = OS::GetCurrentTimeMillis();
     // Temporarily release the monitor when calling out to
     // NotifyPauseOnStart.  This avoids a dead lock that can occur
     // when this message handler tries to post a message while a
     // message is being posted to it.
     ml->Exit();
     NotifyPauseOnStart();
     ml->Enter();
     is_paused_on_start_ = true;
   } else {
     ASSERT(is_paused_on_start_);
     ASSERT(paused_timestamp_ != -1);
     paused_timestamp_ = -1;
     // Resumed. Clear the resume request of the owning isolate.
     Isolate* owning_isolate = isolate();
     if (owning_isolate != NULL) {
       owning_isolate->GetAndClearResumeRequest();
     }
     is_paused_on_start_ = false;
   }
 }

 void MessageHandler::PausedOnExit(bool paused) {
   MonitorLocker ml(&monitor_);
   PausedOnExitLocked(&ml, paused);
 }

 void MessageHandler::PausedOnExitLocked(MonitorLocker* ml, bool paused) {
   if (paused) {
     ASSERT(!is_paused_on_exit_);
     ASSERT(paused_timestamp_ == -1);
     paused_timestamp_ = OS::GetCurrentTimeMillis();
     // Temporarily release the monitor when calling out to
     // NotifyPauseOnExit.  This avoids a dead lock that can
     // occur when this message handler tries to post a message
     // while a message is being posted to it.
     ml->Exit();
     NotifyPauseOnExit();
     ml->Enter();
     is_paused_on_exit_ = true;
   } else {
     ASSERT(is_paused_on_exit_);
     ASSERT(paused_timestamp_ != -1);
     paused_timestamp_ = -1;
     // Resumed. Clear the resume request of the owning isolate.
     Isolate* owning_isolate = isolate();
     if (owning_isolate != NULL) {
       owning_isolate->GetAndClearResumeRequest();
     }
     is_paused_on_exit_ = false;
   }
 }
 #endif  // !defined(PRODUCT)

 MessageHandler::AcquiredQueues::AcquiredQueues(MessageHandler* handler)
     : handler_(handler), ml_(&handler->monitor_) {
   ASSERT(handler != NULL);
   handler_->oob_message_handling_allowed_ = false;
 }

 MessageHandler::AcquiredQueues::~AcquiredQueues() {
   ASSERT(handler_ != NULL);
   handler_->oob_message_handling_allowed_ = true;
 }

 }  // namespace dart
	// Copyright (c) 2011, the Dart project authors. Please see the AUTHORS file
	// for details. All rights reserved. Use of this source code is governed by a
	// BSD-style license that can be found in the LICENSE file.

	#include <utility>

	#include "vm/message_handler.h"

	#include "vm/dart.h"
	#include "vm/heap/safepoint.h"
	#include "vm/isolate.h"
	#include "vm/lockers.h"
	#include "vm/object.h"
	#include "vm/object_store.h"
	#include "vm/os.h"
	#include "vm/port.h"
	#include "vm/thread_interrupter.h"

	namespace dart {

	DECLARE_FLAG(bool, trace_service_pause_events);

	class MessageHandlerTask : public ThreadPool::Task {
	public:
	explicit MessageHandlerTask(MessageHandler* handler) : handler_(handler) {
	ASSERT(handler != NULL);
	}

	virtual void Run() {
	ASSERT(handler_ != NULL);
	handler_->TaskCallback();
	}

	private:
	MessageHandler* handler_;

	DISALLOW_COPY_AND_ASSIGN(MessageHandlerTask);
	};

	// static
	const char* MessageHandler::MessageStatusString(MessageStatus status) {
	switch (status) {
	case kOK:
	return "OK";
	case kError:
	return "Error";
	case kRestart:
	return "Restart";
	case kShutdown:
	return "Shutdown";
	default:
	UNREACHABLE();
	return "Illegal";
	}
	}

	MessageHandler::MessageHandler()
	: queue_(new MessageQueue()),
	oob_queue_(new MessageQueue()),
	oob_message_handling_allowed_(true),
	paused_for_messages_(false),
	live_ports_(0),
	paused_(0),
	#if !defined(PRODUCT)
	should_pause_on_start_(false),
	should_pause_on_exit_(false),
	is_paused_on_start_(false),
	is_paused_on_exit_(false),
	paused_timestamp_(-1),
	#endif
	task_running_(false),
	delete_me_(false),
	pool_(NULL),
	start_callback_(NULL),
	end_callback_(NULL),
	callback_data_(0) {
	ASSERT(queue_ != NULL);
	ASSERT(oob_queue_ != NULL);
	}

	MessageHandler::~MessageHandler() {
	delete queue_;
	delete oob_queue_;
	queue_ = NULL;
	oob_queue_ = NULL;
	pool_ = NULL;
	}

	const char* MessageHandler::name() const {
	return "<unnamed>";
	}

	#if defined(DEBUG)
	void MessageHandler::CheckAccess() {
	// By default there is no checking.
	}
	#endif

	void MessageHandler::MessageNotify(Message::Priority priority) {
	// By default, there is no custom message notification.
	}

	void MessageHandler::Run(ThreadPool* pool,
	StartCallback start_callback,
	EndCallback end_callback,
	CallbackData data) {
	MonitorLocker ml(&monitor_);
	if (FLAG_trace_isolates) {
	OS::PrintErr(
	"[+] Starting message handler:\n"
	"\thandler: %s\n",
	name());
	}
	ASSERT(pool_ == NULL);
	ASSERT(!delete_me_);
	pool_ = pool;
	start_callback_ = start_callback;
	end_callback_ = end_callback;
	callback_data_ = data;
	task_running_ = true;
	const bool launched_successfully = pool_->Run<MessageHandlerTask>(this);
	ASSERT(launched_successfully);
	}

	void MessageHandler::PostMessage(std::unique_ptr<Message> message,
	bool before_events) {
	Message::Priority saved_priority;

	{
	MonitorLocker ml(&monitor_);
	if (FLAG_trace_isolates) {
	Isolate* source_isolate = Isolate::Current();
	if (source_isolate != nullptr) {
	OS::PrintErr(
	"[>] Posting message:\n"
	"\tlen: %" Pd "\n\tsource: (%" Pd64
	") %s\n\tdest: %s\n"
	"\tdest_port: %" Pd64 "\n",
	message->Size(), static_cast<int64_t>(source_isolate->main_port()),
	source_isolate->name(), name(), message->dest_port());
	} else {
	OS::PrintErr(
	"[>] Posting message:\n"
	"\tlen: %" Pd
	"\n\tsource: <native code>\n"
	"\tdest: %s\n"
	"\tdest_port: %" Pd64 "\n",
	message->Size(), name(), message->dest_port());
	}
	}

	saved_priority = message->priority();
	if (message->IsOOB()) {
	oob_queue_->Enqueue(std::move(message), before_events);
	} else {
	queue_->Enqueue(std::move(message), before_events);
	}
	if (paused_for_messages_) {
	ml.Notify();
	}

	if (pool_ != nullptr && !task_running_) {
	ASSERT(!delete_me_);
	task_running_ = true;
	const bool launched_successfully = pool_->Run<MessageHandlerTask>(this);
	ASSERT(launched_successfully);
	}
	}

	// Invoke any custom message notification.
	MessageNotify(saved_priority);
	}

	std::unique_ptr<Message> MessageHandler::DequeueMessage(
	Message::Priority min_priority) {
	// TODO(turnidge): Add assert that monitor_ is held here.
	std::unique_ptr<Message> message = oob_queue_->Dequeue();
	if ((message == nullptr) && (min_priority < Message::kOOBPriority)) {
	message = queue_->Dequeue();
	}
	return message;
	}

	void MessageHandler::ClearOOBQueue() {
	oob_queue_->Clear();
	}

	MessageHandler::MessageStatus MessageHandler::HandleMessages(
	MonitorLocker* ml,
	bool allow_normal_messages,
	bool allow_multiple_normal_messages) {
	ASSERT(monitor_.IsOwnedByCurrentThread());

	// Scheduling of the mutator thread during the isolate start can cause this
	// thread to safepoint.
	// We want to avoid holding the message handler monitor during the safepoint
	// operation to avoid possible deadlocks, which can occur if other threads are
	// sending messages to this message handler.
	//
	// If isolate() returns nullptr [StartIsolateScope] does nothing.
	ml->Exit();
	StartIsolateScope start_isolate(isolate());
	ml->Enter();

	auto idle_time_handler =
	isolate() != nullptr ? isolate()->group()->idle_time_handler() : nullptr;

	MessageStatus max_status = kOK;
	Message::Priority min_priority =
	((allow_normal_messages && !paused()) ? Message::kNormalPriority
	: Message::kOOBPriority);
	std::unique_ptr<Message> message = DequeueMessage(min_priority);
	while (message != nullptr) {
	intptr_t message_len = message->Size();
	if (FLAG_trace_isolates) {
	OS::PrintErr(
	"[<] Handling message:\n"
	"\tlen: %" Pd
	"\n"
	"\thandler: %s\n"
	"\tport: %" Pd64 "\n",
	message_len, name(), message->dest_port());
	}

	// Release the monitor_ temporarily while we handle the message.
	// The monitor was acquired in MessageHandler::TaskCallback().
	ml->Exit();
	Message::Priority saved_priority = message->priority();
	Dart_Port saved_dest_port = message->dest_port();
	MessageStatus status = kOK;
	{
	DisableIdleTimerScope disable_idle_timer(idle_time_handler);
	status = HandleMessage(std::move(message));
	}
	if (status > max_status) {
	max_status = status;
	}
	ml->Enter();
	if (FLAG_trace_isolates) {
	OS::PrintErr(
	"[.] Message handled (%s):\n"
	"\tlen: %" Pd
	"\n"
	"\thandler: %s\n"
	"\tport: %" Pd64 "\n",
	MessageStatusString(status), message_len, name(), saved_dest_port);
	}
	// If we are shutting down, do not process any more messages.
	if (status == kShutdown) {
	ClearOOBQueue();
	break;
	}

	// Remember time since the last message. Don't consider OOB messages so
	// using Observatory doesn't trigger additional idle tasks.
	if ((FLAG_idle_timeout_micros != 0) &&
	(saved_priority == Message::kNormalPriority)) {
	if (idle_time_handler != nullptr) {
	idle_time_handler->UpdateStartIdleTime();
	}
	}

	// Some callers want to process only one normal message and then quit. At
	// the same time it is OK to process multiple OOB messages.
	if ((saved_priority == Message::kNormalPriority) &&
	!allow_multiple_normal_messages) {
	// We processed one normal message. Allow no more.
	allow_normal_messages = false;
	}

	// Reevaluate the minimum allowable priority. The paused state
	// may have changed as part of handling the message. We may also
	// have encountered an error during message processing.
	//
	// Even if we encounter an error, we still process pending OOB
	// messages so that we don't lose the message notification.
	min_priority = (((max_status == kOK) && allow_normal_messages && !paused())
	? Message::kNormalPriority
	: Message::kOOBPriority);
	message = DequeueMessage(min_priority);
	}
	return max_status;
	}

	MessageHandler::MessageStatus MessageHandler::HandleNextMessage() {
	// We can only call HandleNextMessage when this handler is not
	// assigned to a thread pool.
	MonitorLocker ml(&monitor_);
	ASSERT(pool_ == NULL);
	ASSERT(!delete_me_);
	#if defined(DEBUG)
	CheckAccess();
	#endif
	return HandleMessages(&ml, true, false);
	}

	MessageHandler::MessageStatus MessageHandler::PauseAndHandleAllMessages(
	int64_t timeout_millis) {
	MonitorLocker ml(&monitor_, /no_safepoint_scope=/false);
	ASSERT(task_running_);
	ASSERT(!delete_me_);
	#if defined(DEBUG)
	CheckAccess();
	#endif
	paused_for_messages_ = true;
	while (queue_->IsEmpty() && oob_queue_->IsEmpty()) {
	Monitor::WaitResult wr;
	{
	// Ensure this thread is at a safepoint while we wait for new messages to
	// arrive.
	TransitionVMToNative transition(Thread::Current());
	wr = ml.Wait(timeout_millis);
	}
	ASSERT(task_running_);
	ASSERT(!delete_me_);
	if (wr == Monitor::kTimedOut) {
	break;
	}
	if (queue_->IsEmpty()) {
	// There are only OOB messages. Handle them and then continue waiting for
	// normal messages unless there is an error.
	MessageStatus status = HandleMessages(&ml, false, false);
	if (status != kOK) {
	paused_for_messages_ = false;
	return status;
	}
	}
	}
	paused_for_messages_ = false;
	return HandleMessages(&ml, true, true);
	}

	MessageHandler::MessageStatus MessageHandler::HandleOOBMessages() {
	if (!oob_message_handling_allowed_) {
	return kOK;
	}
	MonitorLocker ml(&monitor_);
	ASSERT(!delete_me_);
	#if defined(DEBUG)
	CheckAccess();
	#endif
	return HandleMessages(&ml, false, false);
	}

	#if !defined(PRODUCT)
	bool MessageHandler::ShouldPauseOnStart(MessageStatus status) const {
	Isolate* owning_isolate = isolate();
	if (owning_isolate == NULL) {
	return false;
	}
	// If we are restarting or shutting down, we do not want to honor
	// should_pause_on_start or should_pause_on_exit.
	return (status != MessageHandler::kRestart &&
	status != MessageHandler::kShutdown) &&
	should_pause_on_start() && owning_isolate->is_runnable();
	}

	bool MessageHandler::ShouldPauseOnExit(MessageStatus status) const {
	Isolate* owning_isolate = isolate();
	if (owning_isolate == NULL) {
	return false;
	}
	return (status != MessageHandler::kRestart &&
	status != MessageHandler::kShutdown) &&
	should_pause_on_exit() && owning_isolate->is_runnable();
	}
	#endif

	bool MessageHandler::HasOOBMessages() {
	MonitorLocker ml(&monitor_);
	return !oob_queue_->IsEmpty();
	}

	bool MessageHandler::HasMessages() {
	MonitorLocker ml(&monitor_);
	return !queue_->IsEmpty();
	}

	void MessageHandler::TaskCallback() {
	ASSERT(Isolate::Current() == NULL);
	MessageStatus status = kOK;
	bool run_end_callback = false;
	bool delete_me = false;
	EndCallback end_callback = NULL;
	CallbackData callback_data = 0;
	{
	// We will occasionally release and reacquire this monitor in this
	// function. Whenever we reacquire the monitor we must process
	// all pending OOB messages, or we may miss a request for vm
	// shutdown.
	MonitorLocker ml(&monitor_);

	// This method is running on the message handler task. Which means no
	// other message handler tasks will be started until this one sets
	// [task_running_] to false.
	ASSERT(task_running_);

	#if !defined(PRODUCT)
	if (ShouldPauseOnStart(kOK)) {
	if (!is_paused_on_start()) {
	PausedOnStartLocked(&ml, true);
	}
	// More messages may have come in before we (re)acquired the monitor.
	status = HandleMessages(&ml, false, false);
	if (ShouldPauseOnStart(status)) {
	// Still paused.
	ASSERT(oob_queue_->IsEmpty());
	task_running_ = false; // No task in queue.
	return;
	} else {
	PausedOnStartLocked(&ml, false);
	}
	}
	if (is_paused_on_exit()) {
	status = HandleMessages(&ml, false, false);
	if (ShouldPauseOnExit(status)) {
	// Still paused.
	ASSERT(oob_queue_->IsEmpty());
	task_running_ = false; // No task in queue.
	return;
	} else {
	PausedOnExitLocked(&ml, false);
	}
	}
	#endif // !defined(PRODUCT)

	if (status == kOK) {
	if (start_callback_ != nullptr) {
	// Initialize the message handler by running its start function,
	// if we have one. For an isolate, this will run the isolate's
	// main() function.
	//
	// Release the monitor_ temporarily while we call the start callback.
	ml.Exit();
	status = start_callback_(callback_data_);
	ASSERT(Isolate::Current() == NULL);
	start_callback_ = NULL;
	ml.Enter();
	}

	// Handle any pending messages for this message handler.
	if (status != kShutdown) {
	status = HandleMessages(&ml, (status == kOK), true);
	}
	}

	// The isolate exits when it encounters an error or when it no
	// longer has live ports.
	if (status != kOK \|\| !HasLivePorts()) {
	#if !defined(PRODUCT)
	if (ShouldPauseOnExit(status)) {
	if (FLAG_trace_service_pause_events) {
	OS::PrintErr(
	"Isolate %s paused before exiting. "
	"Use the Observatory to release it.\n",
	name());
	}
	PausedOnExitLocked(&ml, true);
	// More messages may have come in while we released the monitor.
	status = HandleMessages(&ml, false, false);
	if (ShouldPauseOnExit(status)) {
	// Still paused.
	ASSERT(oob_queue_->IsEmpty());
	task_running_ = false; // No task in queue.
	return;
	} else {
	PausedOnExitLocked(&ml, false);
	}
	}
	#endif // !defined(PRODUCT)
	if (FLAG_trace_isolates) {
	if (status != kOK && thread() != NULL) {
	const Error& error = Error::Handle(thread()->sticky_error());
	OS::PrintErr(
	"[-] Stopping message handler (%s):\n"
	"\thandler: %s\n"
	"\terror: %s\n",
	MessageStatusString(status), name(), error.ToCString());
	} else {
	OS::PrintErr(
	"[-] Stopping message handler (%s):\n"
	"\thandler: %s\n",
	MessageStatusString(status), name());
	}
	}
	pool_ = NULL;
	// Decide if we have a callback before releasing the monitor.
	end_callback = end_callback_;
	callback_data = callback_data_;
	run_end_callback = end_callback_ != NULL;
	delete_me = delete_me_;
	}

	// Clear task_running_ last. This allows other tasks to potentially start
	// for this message handler.
	ASSERT(oob_queue_->IsEmpty());
	task_running_ = false;
	}

	// The handler may have been deleted by another thread here if it is a native
	// message handler.

	// Message handlers either use delete_me or end_callback but not both.
	ASSERT(!delete_me \|\| !run_end_callback);

	if (run_end_callback) {
	ASSERT(end_callback != NULL);
	end_callback(callback_data);
	// The handler may have been deleted after this point.
	}
	if (delete_me) {
	delete this;
	}
	}

	void MessageHandler::ClosePort(Dart_Port port) {
	MonitorLocker ml(&monitor_);
	if (FLAG_trace_isolates) {
	OS::PrintErr(
	"[-] Closing port:\n"
	"\thandler: %s\n"
	"\tport: %" Pd64
	"\n"
	"\tports: live(%" Pd ")\n",
	name(), port, live_ports_);
	}
	}

	void MessageHandler::CloseAllPorts() {
	MonitorLocker ml(&monitor_);
	if (FLAG_trace_isolates) {
	OS::PrintErr(
	"[-] Closing all ports:\n"
	"\thandler: %s\n",
	name());
	}
	queue_->Clear();
	oob_queue_->Clear();
	}

	void MessageHandler::RequestDeletion() {
	ASSERT(OwnedByPortMap());
	{
	MonitorLocker ml(&monitor_);
	if (task_running_) {
	// This message handler currently has a task running on the thread pool.
	delete_me_ = true;
	return;
	}
	}

	// This message handler has no current task. Delete it.
	delete this;
	}

	void MessageHandler::increment_live_ports() {
	MonitorLocker ml(&monitor_);
	#if defined(DEBUG)
	CheckAccess();
	#endif
	live_ports_++;
	}

	void MessageHandler::decrement_live_ports() {
	MonitorLocker ml(&monitor_);
	#if defined(DEBUG)
	CheckAccess();
	#endif
	live_ports_--;
	}

	#if !defined(PRODUCT)
	void MessageHandler::DebugDump() {
	PortMap::DebugDumpForMessageHandler(this);
	}

	void MessageHandler::PausedOnStart(bool paused) {
	MonitorLocker ml(&monitor_);
	PausedOnStartLocked(&ml, paused);
	}

	void MessageHandler::PausedOnStartLocked(MonitorLocker* ml, bool paused) {
	if (paused) {
	ASSERT(!is_paused_on_start_);
	ASSERT(paused_timestamp_ == -1);
	paused_timestamp_ = OS::GetCurrentTimeMillis();
	// Temporarily release the monitor when calling out to
	// NotifyPauseOnStart. This avoids a dead lock that can occur
	// when this message handler tries to post a message while a
	// message is being posted to it.
	ml->Exit();
	NotifyPauseOnStart();
	ml->Enter();
	is_paused_on_start_ = true;
	} else {
	ASSERT(is_paused_on_start_);
	ASSERT(paused_timestamp_ != -1);
	paused_timestamp_ = -1;
	// Resumed. Clear the resume request of the owning isolate.
	Isolate* owning_isolate = isolate();
	if (owning_isolate != NULL) {
	owning_isolate->GetAndClearResumeRequest();
	}
	is_paused_on_start_ = false;
	}
	}

	void MessageHandler::PausedOnExit(bool paused) {
	MonitorLocker ml(&monitor_);
	PausedOnExitLocked(&ml, paused);
	}

	void MessageHandler::PausedOnExitLocked(MonitorLocker* ml, bool paused) {
	if (paused) {
	ASSERT(!is_paused_on_exit_);
	ASSERT(paused_timestamp_ == -1);
	paused_timestamp_ = OS::GetCurrentTimeMillis();
	// Temporarily release the monitor when calling out to
	// NotifyPauseOnExit. This avoids a dead lock that can
	// occur when this message handler tries to post a message
	// while a message is being posted to it.
	ml->Exit();
	NotifyPauseOnExit();
	ml->Enter();
	is_paused_on_exit_ = true;
	} else {
	ASSERT(is_paused_on_exit_);
	ASSERT(paused_timestamp_ != -1);
	paused_timestamp_ = -1;
	// Resumed. Clear the resume request of the owning isolate.
	Isolate* owning_isolate = isolate();
	if (owning_isolate != NULL) {
	owning_isolate->GetAndClearResumeRequest();
	}
	is_paused_on_exit_ = false;
	}
	}
	#endif // !defined(PRODUCT)

	MessageHandler::AcquiredQueues::AcquiredQueues(MessageHandler* handler)
	: handler_(handler), ml_(&handler->monitor_) {
	ASSERT(handler != NULL);
	handler_->oob_message_handling_allowed_ = false;
	}

	MessageHandler::AcquiredQueues::~AcquiredQueues() {
	ASSERT(handler_ != NULL);
	handler_->oob_message_handling_allowed_ = true;
	}

	} // namespace dart