base/message_loop/incoming_task_queue.cc

   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/incoming_task_queue.h"
   6
   7 #include <limits>
   8
   9 #include "base/location.h"
  10 #include "base/message_loop/message_loop.h"
  11 #include "base/metrics/histogram.h"
  12 #include "base/synchronization/waitable_event.h"
  13 #include "base/time/time.h"
  14
  15 namespace base {
  16 namespace internal {
  17
  18 namespace {
  19
  20 #ifndef NDEBUG
  21 // Delays larger than this are often bogus, and a warning should be emitted in
  22 // debug builds to warn developers.  http://crbug.com/450045
  23 const int kTaskDelayWarningThresholdInSeconds =
  24     14 * 24 * 60 * 60;  // 14 days.
  25 #endif
  26
  27 // Returns true if MessagePump::ScheduleWork() must be called one
  28 // time for every task that is added to the MessageLoop incoming queue.
  29 bool AlwaysNotifyPump(MessageLoop::Type type) {
  30 #if defined(OS_ANDROID)
  31   // The Android UI message loop needs to get notified each time a task is
  32   // added
  33   // to the incoming queue.
  34   return type == MessageLoop::TYPE_UI || type == MessageLoop::TYPE_JAVA;
  35 #else
  36   return false;
  37 #endif
  38 }
  39
  40 }  // namespace
  41
  42 IncomingTaskQueue::IncomingTaskQueue(MessageLoop* message_loop)
  43     : high_res_task_count_(0),
  44       message_loop_(message_loop),
  45       next_sequence_num_(0),
  46       message_loop_scheduled_(false),
  47       always_schedule_work_(AlwaysNotifyPump(message_loop_->type())),
  48       is_ready_for_scheduling_(false) {
  49 }
  50
  51 bool IncomingTaskQueue::AddToIncomingQueue(
  52     const tracked_objects::Location& from_here,
  53     const Closure& task,
  54     TimeDelta delay,
  55     bool nestable) {
  56   DLOG_IF(WARNING,
  57           delay.InSeconds() > kTaskDelayWarningThresholdInSeconds)
  58       << "Requesting super-long task delay period of " << delay.InSeconds()
  59       << " seconds from here: " << from_here.ToString();
  60
  61   AutoLock locked(incoming_queue_lock_);
  62   PendingTask pending_task(
  63       from_here, task, CalculateDelayedRuntime(delay), nestable);
  64 #if defined(OS_WIN)
  65   // We consider the task needs a high resolution timer if the delay is
  66   // more than 0 and less than 32ms. This caps the relative error to
  67   // less than 50% : a 33ms wait can wake at 48ms since the default
  68   // resolution on Windows is between 10 and 15ms.
  69   if (delay > TimeDelta() &&
  70       delay.InMilliseconds() < (2 * Time::kMinLowResolutionThresholdMs)) {
  71     ++high_res_task_count_;
  72     pending_task.is_high_res = true;
  73   }
  74 #endif
  75   return PostPendingTask(&pending_task);
  76 }
  77
  78 bool IncomingTaskQueue::HasHighResolutionTasks() {
  79   AutoLock lock(incoming_queue_lock_);
  80   return high_res_task_count_ > 0;
  81 }
  82
  83 bool IncomingTaskQueue::IsIdleForTesting() {
  84   AutoLock lock(incoming_queue_lock_);
  85   return incoming_queue_.empty();
  86 }
  87
  88 int IncomingTaskQueue::ReloadWorkQueue(TaskQueue* work_queue) {
  89   // Make sure no tasks are lost.
  90   DCHECK(work_queue->empty());
  91
  92   // Acquire all we can from the inter-thread queue with one lock acquisition.
  93   AutoLock lock(incoming_queue_lock_);
  94   if (incoming_queue_.empty()) {
  95     // If the loop attempts to reload but there are no tasks in the incoming
  96     // queue, that means it will go to sleep waiting for more work. If the
  97     // incoming queue becomes nonempty we need to schedule it again.
  98     message_loop_scheduled_ = false;
  99   } else {
 100     incoming_queue_.Swap(work_queue);
 101   }
 102   // Reset the count of high resolution tasks since our queue is now empty.
 103   int high_res_tasks = high_res_task_count_;
 104   high_res_task_count_ = 0;
 105   return high_res_tasks;
 106 }
 107
 108 void IncomingTaskQueue::WillDestroyCurrentMessageLoop() {
 109   AutoLock lock(incoming_queue_lock_);
 110   message_loop_ = NULL;
 111 }
 112
 113 void IncomingTaskQueue::StartScheduling() {
 114   AutoLock lock(incoming_queue_lock_);
 115   DCHECK(!is_ready_for_scheduling_);
 116   DCHECK(!message_loop_scheduled_);
 117   is_ready_for_scheduling_ = true;
 118   if (!incoming_queue_.empty())
 119     ScheduleWork();
 120 }
 121
 122 IncomingTaskQueue::~IncomingTaskQueue() {
 123   // Verify that WillDestroyCurrentMessageLoop() has been called.
 124   DCHECK(!message_loop_);
 125 }
 126
 127 TimeTicks IncomingTaskQueue::CalculateDelayedRuntime(TimeDelta delay) {
 128   TimeTicks delayed_run_time;
 129   if (delay > TimeDelta())
 130     delayed_run_time = TimeTicks::Now() + delay;
 131   else
 132     DCHECK_EQ(delay.InMilliseconds(), 0) << "delay should not be negative";
 133   return delayed_run_time;
 134 }
 135
 136 bool IncomingTaskQueue::PostPendingTask(PendingTask* pending_task) {
 137   // Warning: Don't try to short-circuit, and handle this thread's tasks more
 138   // directly, as it could starve handling of foreign threads.  Put every task
 139   // into this queue.
 140
 141   // This should only be called while the lock is taken.
 142   incoming_queue_lock_.AssertAcquired();
 143
 144   if (!message_loop_) {
 145     pending_task->task.Reset();
 146     return false;
 147   }
 148
 149   // Initialize the sequence number. The sequence number is used for delayed
 150   // tasks (to facilitate FIFO sorting when two tasks have the same
 151   // delayed_run_time value) and for identifying the task in about:tracing.
 152   pending_task->sequence_num = next_sequence_num_++;
 153
 154   message_loop_->task_annotator()->DidQueueTask("MessageLoop::PostTask",
 155                                                 *pending_task);
 156
 157   bool was_empty = incoming_queue_.empty();
 158   incoming_queue_.push(*pending_task);
 159   pending_task->task.Reset();
 160
 161   if (is_ready_for_scheduling_ &&
 162       (always_schedule_work_ || (!message_loop_scheduled_ && was_empty))) {
 163     ScheduleWork();
 164   }
 165
 166   return true;
 167 }
 168
 169 void IncomingTaskQueue::ScheduleWork() {
 170   DCHECK(is_ready_for_scheduling_);
 171   // Wake up the message loop.
 172   message_loop_->ScheduleWork();
 173   // After we've scheduled the message loop, we do not need to do so again
 174   // until we know it has processed all of the work in our queue and is
 175   // waiting for more work again. The message loop will always attempt to
 176   // reload from the incoming queue before waiting again so we clear this flag
 177   // in ReloadWorkQueue().
 178   message_loop_scheduled_ = true;
 179 }
 180
 181 }  // namespace internal
 182 }  // namespace base