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      1 // Copyright 2013 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 "base/message_loop/message_loop.h"
      6 
      7 #include <algorithm>
      8 #include <memory>
      9 #include <utility>
     10 
     11 #include "base/bind.h"
     12 #include "base/compiler_specific.h"
     13 #include "base/lazy_instance.h"
     14 #include "base/logging.h"
     15 #include "base/memory/ptr_util.h"
     16 #include "base/message_loop/message_pump_default.h"
     17 #include "base/metrics/histogram.h"
     18 #include "base/metrics/statistics_recorder.h"
     19 #include "base/run_loop.h"
     20 #include "base/third_party/dynamic_annotations/dynamic_annotations.h"
     21 #include "base/threading/thread_id_name_manager.h"
     22 #include "base/threading/thread_local.h"
     23 #include "base/threading/thread_task_runner_handle.h"
     24 #include "base/time/time.h"
     25 #include "base/trace_event/trace_event.h"
     26 #include "base/tracked_objects.h"
     27 #include "build/build_config.h"
     28 
     29 #if defined(OS_MACOSX)
     30 #include "base/message_loop/message_pump_mac.h"
     31 #endif
     32 #if defined(OS_POSIX) && !defined(OS_IOS)
     33 #include "base/message_loop/message_pump_libevent.h"
     34 #endif
     35 #if defined(OS_ANDROID)
     36 #include "base/message_loop/message_pump_android.h"
     37 #endif
     38 #if defined(USE_GLIB)
     39 #include "base/message_loop/message_pump_glib.h"
     40 #endif
     41 
     42 namespace base {
     43 
     44 namespace {
     45 
     46 // A lazily created thread local storage for quick access to a thread's message
     47 // loop, if one exists.  This should be safe and free of static constructors.
     48 LazyInstance<base::ThreadLocalPointer<MessageLoop> >::Leaky lazy_tls_ptr =
     49     LAZY_INSTANCE_INITIALIZER;
     50 
     51 // Logical events for Histogram profiling. Run with --message-loop-histogrammer
     52 // to get an accounting of messages and actions taken on each thread.
     53 const int kTaskRunEvent = 0x1;
     54 #if !defined(OS_NACL)
     55 const int kTimerEvent = 0x2;
     56 
     57 // Provide range of message IDs for use in histogramming and debug display.
     58 const int kLeastNonZeroMessageId = 1;
     59 const int kMaxMessageId = 1099;
     60 const int kNumberOfDistinctMessagesDisplayed = 1100;
     61 
     62 // Provide a macro that takes an expression (such as a constant, or macro
     63 // constant) and creates a pair to initialize an array of pairs.  In this case,
     64 // our pair consists of the expressions value, and the "stringized" version
     65 // of the expression (i.e., the expression put in quotes).  For example, if
     66 // we have:
     67 //    #define FOO 2
     68 //    #define BAR 5
     69 // then the following:
     70 //    VALUE_TO_NUMBER_AND_NAME(FOO + BAR)
     71 // will expand to:
     72 //   {7, "FOO + BAR"}
     73 // We use the resulting array as an argument to our histogram, which reads the
     74 // number as a bucket identifier, and proceeds to use the corresponding name
     75 // in the pair (i.e., the quoted string) when printing out a histogram.
     76 #define VALUE_TO_NUMBER_AND_NAME(name) {name, #name},
     77 
     78 const LinearHistogram::DescriptionPair event_descriptions_[] = {
     79   // Provide some pretty print capability in our histogram for our internal
     80   // messages.
     81 
     82   // A few events we handle (kindred to messages), and used to profile actions.
     83   VALUE_TO_NUMBER_AND_NAME(kTaskRunEvent)
     84   VALUE_TO_NUMBER_AND_NAME(kTimerEvent)
     85 
     86   {-1, NULL}  // The list must be null-terminated, per API to histogram.
     87 };
     88 #endif  // !defined(OS_NACL)
     89 
     90 bool enable_histogrammer_ = false;
     91 
     92 MessageLoop::MessagePumpFactory* message_pump_for_ui_factory_ = NULL;
     93 
     94 #if defined(OS_IOS)
     95 typedef MessagePumpIOSForIO MessagePumpForIO;
     96 #elif defined(OS_NACL_SFI)
     97 typedef MessagePumpDefault MessagePumpForIO;
     98 #elif defined(OS_POSIX)
     99 typedef MessagePumpLibevent MessagePumpForIO;
    100 #endif
    101 
    102 #if !defined(OS_NACL_SFI)
    103 MessagePumpForIO* ToPumpIO(MessagePump* pump) {
    104   return static_cast<MessagePumpForIO*>(pump);
    105 }
    106 #endif  // !defined(OS_NACL_SFI)
    107 
    108 std::unique_ptr<MessagePump> ReturnPump(std::unique_ptr<MessagePump> pump) {
    109   return pump;
    110 }
    111 
    112 }  // namespace
    113 
    114 //------------------------------------------------------------------------------
    115 
    116 MessageLoop::TaskObserver::TaskObserver() {
    117 }
    118 
    119 MessageLoop::TaskObserver::~TaskObserver() {
    120 }
    121 
    122 MessageLoop::DestructionObserver::~DestructionObserver() {
    123 }
    124 
    125 MessageLoop::NestingObserver::~NestingObserver() {}
    126 
    127 //------------------------------------------------------------------------------
    128 
    129 MessageLoop::MessageLoop(Type type)
    130     : MessageLoop(type, MessagePumpFactoryCallback()) {
    131   BindToCurrentThread();
    132 }
    133 
    134 MessageLoop::MessageLoop(std::unique_ptr<MessagePump> pump)
    135     : MessageLoop(TYPE_CUSTOM, Bind(&ReturnPump, Passed(&pump))) {
    136   BindToCurrentThread();
    137 }
    138 
    139 MessageLoop::~MessageLoop() {
    140   // If |pump_| is non-null, this message loop has been bound and should be the
    141   // current one on this thread. Otherwise, this loop is being destructed before
    142   // it was bound to a thread, so a different message loop (or no loop at all)
    143   // may be current.
    144   DCHECK((pump_ && current() == this) || (!pump_ && current() != this));
    145 
    146   // iOS just attaches to the loop, it doesn't Run it.
    147   // TODO(stuartmorgan): Consider wiring up a Detach().
    148 #if !defined(OS_IOS)
    149   DCHECK(!run_loop_);
    150 #endif
    151 
    152 #if defined(OS_WIN)
    153   if (in_high_res_mode_)
    154     Time::ActivateHighResolutionTimer(false);
    155 #endif
    156   // Clean up any unprocessed tasks, but take care: deleting a task could
    157   // result in the addition of more tasks (e.g., via DeleteSoon).  We set a
    158   // limit on the number of times we will allow a deleted task to generate more
    159   // tasks.  Normally, we should only pass through this loop once or twice.  If
    160   // we end up hitting the loop limit, then it is probably due to one task that
    161   // is being stubborn.  Inspect the queues to see who is left.
    162   bool did_work;
    163   for (int i = 0; i < 100; ++i) {
    164     DeletePendingTasks();
    165     ReloadWorkQueue();
    166     // If we end up with empty queues, then break out of the loop.
    167     did_work = DeletePendingTasks();
    168     if (!did_work)
    169       break;
    170   }
    171   DCHECK(!did_work);
    172 
    173   // Let interested parties have one last shot at accessing this.
    174   FOR_EACH_OBSERVER(DestructionObserver, destruction_observers_,
    175                     WillDestroyCurrentMessageLoop());
    176 
    177   thread_task_runner_handle_.reset();
    178 
    179   // Tell the incoming queue that we are dying.
    180   incoming_task_queue_->WillDestroyCurrentMessageLoop();
    181   incoming_task_queue_ = NULL;
    182   unbound_task_runner_ = NULL;
    183   task_runner_ = NULL;
    184 
    185   // OK, now make it so that no one can find us.
    186   if (current() == this)
    187     lazy_tls_ptr.Pointer()->Set(nullptr);
    188 }
    189 
    190 // static
    191 MessageLoop* MessageLoop::current() {
    192   // TODO(darin): sadly, we cannot enable this yet since people call us even
    193   // when they have no intention of using us.
    194   // DCHECK(loop) << "Ouch, did you forget to initialize me?";
    195   return lazy_tls_ptr.Pointer()->Get();
    196 }
    197 
    198 // static
    199 void MessageLoop::EnableHistogrammer(bool enable) {
    200   enable_histogrammer_ = enable;
    201 }
    202 
    203 // static
    204 bool MessageLoop::InitMessagePumpForUIFactory(MessagePumpFactory* factory) {
    205   if (message_pump_for_ui_factory_)
    206     return false;
    207 
    208   message_pump_for_ui_factory_ = factory;
    209   return true;
    210 }
    211 
    212 // static
    213 std::unique_ptr<MessagePump> MessageLoop::CreateMessagePumpForType(Type type) {
    214 // TODO(rvargas): Get rid of the OS guards.
    215 #if defined(USE_GLIB) && !defined(OS_NACL)
    216   typedef MessagePumpGlib MessagePumpForUI;
    217 #elif defined(OS_LINUX) && !defined(OS_NACL)
    218   typedef MessagePumpLibevent MessagePumpForUI;
    219 #endif
    220 
    221 #if defined(OS_IOS) || defined(OS_MACOSX)
    222 #define MESSAGE_PUMP_UI std::unique_ptr<MessagePump>(MessagePumpMac::Create())
    223 #elif defined(OS_NACL)
    224 // Currently NaCl doesn't have a UI MessageLoop.
    225 // TODO(abarth): Figure out if we need this.
    226 #define MESSAGE_PUMP_UI std::unique_ptr<MessagePump>()
    227 #else
    228 #define MESSAGE_PUMP_UI std::unique_ptr<MessagePump>(new MessagePumpForUI())
    229 #endif
    230 
    231 #if defined(OS_MACOSX)
    232   // Use an OS native runloop on Mac to support timer coalescing.
    233 #define MESSAGE_PUMP_DEFAULT \
    234   std::unique_ptr<MessagePump>(new MessagePumpCFRunLoop())
    235 #else
    236 #define MESSAGE_PUMP_DEFAULT \
    237   std::unique_ptr<MessagePump>(new MessagePumpDefault())
    238 #endif
    239 
    240   if (type == MessageLoop::TYPE_UI) {
    241     if (message_pump_for_ui_factory_)
    242       return message_pump_for_ui_factory_();
    243     return MESSAGE_PUMP_UI;
    244   }
    245   if (type == MessageLoop::TYPE_IO)
    246     return std::unique_ptr<MessagePump>(new MessagePumpForIO());
    247 
    248 #if defined(OS_ANDROID)
    249   if (type == MessageLoop::TYPE_JAVA)
    250     return std::unique_ptr<MessagePump>(new MessagePumpForUI());
    251 #endif
    252 
    253   DCHECK_EQ(MessageLoop::TYPE_DEFAULT, type);
    254   return MESSAGE_PUMP_DEFAULT;
    255 }
    256 
    257 void MessageLoop::AddDestructionObserver(
    258     DestructionObserver* destruction_observer) {
    259   DCHECK_EQ(this, current());
    260   destruction_observers_.AddObserver(destruction_observer);
    261 }
    262 
    263 void MessageLoop::RemoveDestructionObserver(
    264     DestructionObserver* destruction_observer) {
    265   DCHECK_EQ(this, current());
    266   destruction_observers_.RemoveObserver(destruction_observer);
    267 }
    268 
    269 void MessageLoop::AddNestingObserver(NestingObserver* observer) {
    270   DCHECK_EQ(this, current());
    271   nesting_observers_.AddObserver(observer);
    272 }
    273 
    274 void MessageLoop::RemoveNestingObserver(NestingObserver* observer) {
    275   DCHECK_EQ(this, current());
    276   nesting_observers_.RemoveObserver(observer);
    277 }
    278 
    279 void MessageLoop::PostTask(
    280     const tracked_objects::Location& from_here,
    281     const Closure& task) {
    282   task_runner_->PostTask(from_here, task);
    283 }
    284 
    285 void MessageLoop::PostDelayedTask(
    286     const tracked_objects::Location& from_here,
    287     const Closure& task,
    288     TimeDelta delay) {
    289   task_runner_->PostDelayedTask(from_here, task, delay);
    290 }
    291 
    292 void MessageLoop::Run() {
    293   DCHECK(pump_);
    294   RunLoop run_loop;
    295   run_loop.Run();
    296 }
    297 
    298 void MessageLoop::RunUntilIdle() {
    299   DCHECK(pump_);
    300   RunLoop run_loop;
    301   run_loop.RunUntilIdle();
    302 }
    303 
    304 void MessageLoop::QuitWhenIdle() {
    305   DCHECK_EQ(this, current());
    306   if (run_loop_) {
    307     run_loop_->QuitWhenIdle();
    308   } else {
    309     NOTREACHED() << "Must be inside Run to call QuitWhenIdle";
    310   }
    311 }
    312 
    313 void MessageLoop::QuitNow() {
    314   DCHECK_EQ(this, current());
    315   if (run_loop_) {
    316     pump_->Quit();
    317   } else {
    318     NOTREACHED() << "Must be inside Run to call Quit";
    319   }
    320 }
    321 
    322 bool MessageLoop::IsType(Type type) const {
    323   return type_ == type;
    324 }
    325 
    326 static void QuitCurrentWhenIdle() {
    327   MessageLoop::current()->QuitWhenIdle();
    328 }
    329 
    330 // static
    331 Closure MessageLoop::QuitWhenIdleClosure() {
    332   return Bind(&QuitCurrentWhenIdle);
    333 }
    334 
    335 void MessageLoop::SetNestableTasksAllowed(bool allowed) {
    336   if (allowed) {
    337     // Kick the native pump just in case we enter a OS-driven nested message
    338     // loop.
    339     pump_->ScheduleWork();
    340   }
    341   nestable_tasks_allowed_ = allowed;
    342 }
    343 
    344 bool MessageLoop::NestableTasksAllowed() const {
    345   return nestable_tasks_allowed_;
    346 }
    347 
    348 bool MessageLoop::IsNested() {
    349   return run_loop_->run_depth_ > 1;
    350 }
    351 
    352 void MessageLoop::AddTaskObserver(TaskObserver* task_observer) {
    353   DCHECK_EQ(this, current());
    354   task_observers_.AddObserver(task_observer);
    355 }
    356 
    357 void MessageLoop::RemoveTaskObserver(TaskObserver* task_observer) {
    358   DCHECK_EQ(this, current());
    359   task_observers_.RemoveObserver(task_observer);
    360 }
    361 
    362 bool MessageLoop::is_running() const {
    363   DCHECK_EQ(this, current());
    364   return run_loop_ != NULL;
    365 }
    366 
    367 bool MessageLoop::HasHighResolutionTasks() {
    368   return incoming_task_queue_->HasHighResolutionTasks();
    369 }
    370 
    371 bool MessageLoop::IsIdleForTesting() {
    372   // We only check the incoming queue, since we don't want to lock the work
    373   // queue.
    374   return incoming_task_queue_->IsIdleForTesting();
    375 }
    376 
    377 //------------------------------------------------------------------------------
    378 
    379 // static
    380 std::unique_ptr<MessageLoop> MessageLoop::CreateUnbound(
    381     Type type,
    382     MessagePumpFactoryCallback pump_factory) {
    383   return WrapUnique(new MessageLoop(type, pump_factory));
    384 }
    385 
    386 MessageLoop::MessageLoop(Type type, MessagePumpFactoryCallback pump_factory)
    387     : type_(type),
    388 #if defined(OS_WIN)
    389       pending_high_res_tasks_(0),
    390       in_high_res_mode_(false),
    391 #endif
    392       nestable_tasks_allowed_(true),
    393       pump_factory_(pump_factory),
    394       message_histogram_(NULL),
    395       run_loop_(NULL),
    396       incoming_task_queue_(new internal::IncomingTaskQueue(this)),
    397       unbound_task_runner_(
    398           new internal::MessageLoopTaskRunner(incoming_task_queue_)),
    399       task_runner_(unbound_task_runner_),
    400       thread_id_(kInvalidThreadId) {
    401   // If type is TYPE_CUSTOM non-null pump_factory must be given.
    402   DCHECK(type_ != TYPE_CUSTOM || !pump_factory_.is_null());
    403 }
    404 
    405 void MessageLoop::BindToCurrentThread() {
    406   DCHECK(!pump_);
    407   if (!pump_factory_.is_null())
    408     pump_ = pump_factory_.Run();
    409   else
    410     pump_ = CreateMessagePumpForType(type_);
    411 
    412   DCHECK(!current()) << "should only have one message loop per thread";
    413   lazy_tls_ptr.Pointer()->Set(this);
    414 
    415   incoming_task_queue_->StartScheduling();
    416   unbound_task_runner_->BindToCurrentThread();
    417   unbound_task_runner_ = nullptr;
    418   SetThreadTaskRunnerHandle();
    419   {
    420     // Save the current thread's ID for potential use by other threads
    421     // later from GetThreadName().
    422     thread_id_ = PlatformThread::CurrentId();
    423     subtle::MemoryBarrier();
    424   }
    425 }
    426 
    427 std::string MessageLoop::GetThreadName() const {
    428   if (thread_id_ == kInvalidThreadId) {
    429     // |thread_id_| may already have been initialized but this thread might not
    430     // have received the update yet.
    431     subtle::MemoryBarrier();
    432     DCHECK_NE(kInvalidThreadId, thread_id_);
    433   }
    434   return ThreadIdNameManager::GetInstance()->GetName(thread_id_);
    435 }
    436 
    437 void MessageLoop::SetTaskRunner(
    438     scoped_refptr<SingleThreadTaskRunner> task_runner) {
    439   DCHECK_EQ(this, current());
    440   DCHECK(task_runner->BelongsToCurrentThread());
    441   DCHECK(!unbound_task_runner_);
    442   task_runner_ = std::move(task_runner);
    443   SetThreadTaskRunnerHandle();
    444 }
    445 
    446 void MessageLoop::SetThreadTaskRunnerHandle() {
    447   DCHECK_EQ(this, current());
    448   // Clear the previous thread task runner first, because only one can exist at
    449   // a time.
    450   thread_task_runner_handle_.reset();
    451   thread_task_runner_handle_.reset(new ThreadTaskRunnerHandle(task_runner_));
    452 }
    453 
    454 void MessageLoop::RunHandler() {
    455   DCHECK_EQ(this, current());
    456   StartHistogrammer();
    457   pump_->Run(this);
    458 }
    459 
    460 bool MessageLoop::ProcessNextDelayedNonNestableTask() {
    461   if (run_loop_->run_depth_ != 1)
    462     return false;
    463 
    464   if (deferred_non_nestable_work_queue_.empty())
    465     return false;
    466 
    467   PendingTask pending_task =
    468       std::move(deferred_non_nestable_work_queue_.front());
    469   deferred_non_nestable_work_queue_.pop();
    470 
    471   RunTask(pending_task);
    472   return true;
    473 }
    474 
    475 void MessageLoop::RunTask(const PendingTask& pending_task) {
    476   DCHECK(nestable_tasks_allowed_);
    477 
    478 #if defined(OS_WIN)
    479   if (pending_task.is_high_res) {
    480     pending_high_res_tasks_--;
    481     CHECK_GE(pending_high_res_tasks_, 0);
    482   }
    483 #endif
    484 
    485   // Execute the task and assume the worst: It is probably not reentrant.
    486   nestable_tasks_allowed_ = false;
    487 
    488   HistogramEvent(kTaskRunEvent);
    489 
    490   TRACE_TASK_EXECUTION("MessageLoop::RunTask", pending_task);
    491 
    492   FOR_EACH_OBSERVER(TaskObserver, task_observers_,
    493                     WillProcessTask(pending_task));
    494   task_annotator_.RunTask("MessageLoop::PostTask", pending_task);
    495   FOR_EACH_OBSERVER(TaskObserver, task_observers_,
    496                     DidProcessTask(pending_task));
    497 
    498   nestable_tasks_allowed_ = true;
    499 }
    500 
    501 bool MessageLoop::DeferOrRunPendingTask(PendingTask pending_task) {
    502   if (pending_task.nestable || run_loop_->run_depth_ == 1) {
    503     RunTask(pending_task);
    504     // Show that we ran a task (Note: a new one might arrive as a
    505     // consequence!).
    506     return true;
    507   }
    508 
    509   // We couldn't run the task now because we're in a nested message loop
    510   // and the task isn't nestable.
    511   deferred_non_nestable_work_queue_.push(std::move(pending_task));
    512   return false;
    513 }
    514 
    515 void MessageLoop::AddToDelayedWorkQueue(PendingTask pending_task) {
    516   // Move to the delayed work queue.
    517   delayed_work_queue_.push(std::move(pending_task));
    518 }
    519 
    520 bool MessageLoop::DeletePendingTasks() {
    521   bool did_work = !work_queue_.empty();
    522   while (!work_queue_.empty()) {
    523     PendingTask pending_task = std::move(work_queue_.front());
    524     work_queue_.pop();
    525     if (!pending_task.delayed_run_time.is_null()) {
    526       // We want to delete delayed tasks in the same order in which they would
    527       // normally be deleted in case of any funny dependencies between delayed
    528       // tasks.
    529       AddToDelayedWorkQueue(std::move(pending_task));
    530     }
    531   }
    532   did_work |= !deferred_non_nestable_work_queue_.empty();
    533   while (!deferred_non_nestable_work_queue_.empty()) {
    534     deferred_non_nestable_work_queue_.pop();
    535   }
    536   did_work |= !delayed_work_queue_.empty();
    537 
    538   // Historically, we always delete the task regardless of valgrind status. It's
    539   // not completely clear why we want to leak them in the loops above.  This
    540   // code is replicating legacy behavior, and should not be considered
    541   // absolutely "correct" behavior.  See TODO above about deleting all tasks
    542   // when it's safe.
    543   while (!delayed_work_queue_.empty()) {
    544     delayed_work_queue_.pop();
    545   }
    546   return did_work;
    547 }
    548 
    549 void MessageLoop::ReloadWorkQueue() {
    550   // We can improve performance of our loading tasks from the incoming queue to
    551   // |*work_queue| by waiting until the last minute (|*work_queue| is empty) to
    552   // load. That reduces the number of locks-per-task significantly when our
    553   // queues get large.
    554   if (work_queue_.empty()) {
    555 #if defined(OS_WIN)
    556     pending_high_res_tasks_ +=
    557         incoming_task_queue_->ReloadWorkQueue(&work_queue_);
    558 #else
    559     incoming_task_queue_->ReloadWorkQueue(&work_queue_);
    560 #endif
    561   }
    562 }
    563 
    564 void MessageLoop::ScheduleWork() {
    565   pump_->ScheduleWork();
    566 }
    567 
    568 #if defined(OS_WIN)
    569 bool MessageLoop::MessagePumpWasSignaled() {
    570   return pump_->WasSignaled();
    571 }
    572 #endif
    573 
    574 //------------------------------------------------------------------------------
    575 // Method and data for histogramming events and actions taken by each instance
    576 // on each thread.
    577 
    578 void MessageLoop::StartHistogrammer() {
    579 #if !defined(OS_NACL)  // NaCl build has no metrics code.
    580   if (enable_histogrammer_ && !message_histogram_
    581       && StatisticsRecorder::IsActive()) {
    582     std::string thread_name = GetThreadName();
    583     DCHECK(!thread_name.empty());
    584     message_histogram_ = LinearHistogram::FactoryGetWithRangeDescription(
    585         "MsgLoop:" + thread_name, kLeastNonZeroMessageId, kMaxMessageId,
    586         kNumberOfDistinctMessagesDisplayed,
    587         HistogramBase::kHexRangePrintingFlag, event_descriptions_);
    588   }
    589 #endif
    590 }
    591 
    592 void MessageLoop::HistogramEvent(int event) {
    593 #if !defined(OS_NACL)
    594   if (message_histogram_)
    595     message_histogram_->Add(event);
    596 #endif
    597 }
    598 
    599 void MessageLoop::NotifyBeginNestedLoop() {
    600   FOR_EACH_OBSERVER(NestingObserver, nesting_observers_,
    601                     OnBeginNestedMessageLoop());
    602 }
    603 
    604 bool MessageLoop::DoWork() {
    605   if (!nestable_tasks_allowed_) {
    606     // Task can't be executed right now.
    607     return false;
    608   }
    609 
    610   for (;;) {
    611     ReloadWorkQueue();
    612     if (work_queue_.empty())
    613       break;
    614 
    615     // Execute oldest task.
    616     do {
    617       PendingTask pending_task = std::move(work_queue_.front());
    618       work_queue_.pop();
    619       if (!pending_task.delayed_run_time.is_null()) {
    620         int sequence_num = pending_task.sequence_num;
    621         TimeTicks delayed_run_time = pending_task.delayed_run_time;
    622         AddToDelayedWorkQueue(std::move(pending_task));
    623         // If we changed the topmost task, then it is time to reschedule.
    624         if (delayed_work_queue_.top().sequence_num == sequence_num)
    625           pump_->ScheduleDelayedWork(delayed_run_time);
    626       } else {
    627         if (DeferOrRunPendingTask(std::move(pending_task)))
    628           return true;
    629       }
    630     } while (!work_queue_.empty());
    631   }
    632 
    633   // Nothing happened.
    634   return false;
    635 }
    636 
    637 bool MessageLoop::DoDelayedWork(TimeTicks* next_delayed_work_time) {
    638   if (!nestable_tasks_allowed_ || delayed_work_queue_.empty()) {
    639     recent_time_ = *next_delayed_work_time = TimeTicks();
    640     return false;
    641   }
    642 
    643   // When we "fall behind", there will be a lot of tasks in the delayed work
    644   // queue that are ready to run.  To increase efficiency when we fall behind,
    645   // we will only call Time::Now() intermittently, and then process all tasks
    646   // that are ready to run before calling it again.  As a result, the more we
    647   // fall behind (and have a lot of ready-to-run delayed tasks), the more
    648   // efficient we'll be at handling the tasks.
    649 
    650   TimeTicks next_run_time = delayed_work_queue_.top().delayed_run_time;
    651   if (next_run_time > recent_time_) {
    652     recent_time_ = TimeTicks::Now();  // Get a better view of Now();
    653     if (next_run_time > recent_time_) {
    654       *next_delayed_work_time = next_run_time;
    655       return false;
    656     }
    657   }
    658 
    659   PendingTask pending_task =
    660       std::move(const_cast<PendingTask&>(delayed_work_queue_.top()));
    661   delayed_work_queue_.pop();
    662 
    663   if (!delayed_work_queue_.empty())
    664     *next_delayed_work_time = delayed_work_queue_.top().delayed_run_time;
    665 
    666   return DeferOrRunPendingTask(std::move(pending_task));
    667 }
    668 
    669 bool MessageLoop::DoIdleWork() {
    670   if (ProcessNextDelayedNonNestableTask())
    671     return true;
    672 
    673   if (run_loop_->quit_when_idle_received_)
    674     pump_->Quit();
    675 
    676   // When we return we will do a kernel wait for more tasks.
    677 #if defined(OS_WIN)
    678   // On Windows we activate the high resolution timer so that the wait
    679   // _if_ triggered by the timer happens with good resolution. If we don't
    680   // do this the default resolution is 15ms which might not be acceptable
    681   // for some tasks.
    682   bool high_res = pending_high_res_tasks_ > 0;
    683   if (high_res != in_high_res_mode_) {
    684     in_high_res_mode_ = high_res;
    685     Time::ActivateHighResolutionTimer(in_high_res_mode_);
    686   }
    687 #endif
    688   return false;
    689 }
    690 
    691 void MessageLoop::DeleteSoonInternal(const tracked_objects::Location& from_here,
    692                                      void(*deleter)(const void*),
    693                                      const void* object) {
    694   task_runner()->PostNonNestableTask(from_here, Bind(deleter, object));
    695 }
    696 
    697 void MessageLoop::ReleaseSoonInternal(
    698     const tracked_objects::Location& from_here,
    699     void(*releaser)(const void*),
    700     const void* object) {
    701   task_runner()->PostNonNestableTask(from_here, Bind(releaser, object));
    702 }
    703 
    704 #if !defined(OS_NACL)
    705 //------------------------------------------------------------------------------
    706 // MessageLoopForUI
    707 
    708 MessageLoopForUI::MessageLoopForUI(std::unique_ptr<MessagePump> pump)
    709     : MessageLoop(TYPE_UI, Bind(&ReturnPump, Passed(&pump))) {}
    710 
    711 #if defined(OS_ANDROID)
    712 void MessageLoopForUI::Start() {
    713   // No Histogram support for UI message loop as it is managed by Java side
    714   static_cast<MessagePumpForUI*>(pump_.get())->Start(this);
    715 }
    716 #endif
    717 
    718 #if defined(OS_IOS)
    719 void MessageLoopForUI::Attach() {
    720   static_cast<MessagePumpUIApplication*>(pump_.get())->Attach(this);
    721 }
    722 #endif
    723 
    724 #if defined(USE_OZONE) || (defined(USE_X11) && !defined(USE_GLIB))
    725 bool MessageLoopForUI::WatchFileDescriptor(
    726     int fd,
    727     bool persistent,
    728     MessagePumpLibevent::Mode mode,
    729     MessagePumpLibevent::FileDescriptorWatcher *controller,
    730     MessagePumpLibevent::Watcher *delegate) {
    731   return static_cast<MessagePumpLibevent*>(pump_.get())->WatchFileDescriptor(
    732       fd,
    733       persistent,
    734       mode,
    735       controller,
    736       delegate);
    737 }
    738 #endif
    739 
    740 #endif  // !defined(OS_NACL)
    741 
    742 //------------------------------------------------------------------------------
    743 // MessageLoopForIO
    744 
    745 MessageLoopForIO::MessageLoopForIO() : MessageLoop(TYPE_IO) {}
    746 
    747 #if !defined(OS_NACL_SFI)
    748 
    749 #if defined(OS_WIN)
    750 void MessageLoopForIO::RegisterIOHandler(HANDLE file, IOHandler* handler) {
    751   ToPumpIO(pump_.get())->RegisterIOHandler(file, handler);
    752 }
    753 
    754 bool MessageLoopForIO::RegisterJobObject(HANDLE job, IOHandler* handler) {
    755   return ToPumpIO(pump_.get())->RegisterJobObject(job, handler);
    756 }
    757 
    758 bool MessageLoopForIO::WaitForIOCompletion(DWORD timeout, IOHandler* filter) {
    759   return ToPumpIO(pump_.get())->WaitForIOCompletion(timeout, filter);
    760 }
    761 #elif defined(OS_POSIX)
    762 bool MessageLoopForIO::WatchFileDescriptor(int fd,
    763                                            bool persistent,
    764                                            Mode mode,
    765                                            FileDescriptorWatcher* controller,
    766                                            Watcher* delegate) {
    767   return ToPumpIO(pump_.get())->WatchFileDescriptor(
    768       fd,
    769       persistent,
    770       mode,
    771       controller,
    772       delegate);
    773 }
    774 #endif
    775 
    776 #endif  // !defined(OS_NACL_SFI)
    777 
    778 }  // namespace base
    779