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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/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 #include "build/build_config.h"
     15 
     16 namespace base {
     17 namespace internal {
     18 
     19 namespace {
     20 
     21 #ifndef NDEBUG
     22 // Delays larger than this are often bogus, and a warning should be emitted in
     23 // debug builds to warn developers.  http://crbug.com/450045
     24 const int kTaskDelayWarningThresholdInSeconds =
     25     14 * 24 * 60 * 60;  // 14 days.
     26 #endif
     27 
     28 // Returns true if MessagePump::ScheduleWork() must be called one
     29 // time for every task that is added to the MessageLoop incoming queue.
     30 #if defined(OS_ANDROID)
     31 bool AlwaysNotifyPump(MessageLoop::Type type) {
     32   // The Android UI message loop needs to get notified each time a task is
     33   // added to the incoming queue.
     34   return type == MessageLoop::TYPE_UI || type == MessageLoop::TYPE_JAVA;
     35 }
     36 #else
     37 bool AlwaysNotifyPump(MessageLoop::Type /* type */) {
     38   return false;
     39 }
     40 #endif
     41 
     42 }  // namespace
     43 
     44 IncomingTaskQueue::IncomingTaskQueue(MessageLoop* message_loop)
     45     : high_res_task_count_(0),
     46       message_loop_(message_loop),
     47       next_sequence_num_(0),
     48       message_loop_scheduled_(false),
     49       always_schedule_work_(AlwaysNotifyPump(message_loop_->type())),
     50       is_ready_for_scheduling_(false) {
     51 }
     52 
     53 bool IncomingTaskQueue::AddToIncomingQueue(
     54     const tracked_objects::Location& from_here,
     55     const Closure& task,
     56     TimeDelta delay,
     57     bool nestable) {
     58   DLOG_IF(WARNING,
     59           delay.InSeconds() > kTaskDelayWarningThresholdInSeconds)
     60       << "Requesting super-long task delay period of " << delay.InSeconds()
     61       << " seconds from here: " << from_here.ToString();
     62 
     63   AutoLock locked(incoming_queue_lock_);
     64   PendingTask pending_task(
     65       from_here, task, CalculateDelayedRuntime(delay), nestable);
     66 #if defined(OS_WIN)
     67   // We consider the task needs a high resolution timer if the delay is
     68   // more than 0 and less than 32ms. This caps the relative error to
     69   // less than 50% : a 33ms wait can wake at 48ms since the default
     70   // resolution on Windows is between 10 and 15ms.
     71   if (delay > TimeDelta() &&
     72       delay.InMilliseconds() < (2 * Time::kMinLowResolutionThresholdMs)) {
     73     ++high_res_task_count_;
     74     pending_task.is_high_res = true;
     75   }
     76 #endif
     77   return PostPendingTask(&pending_task);
     78 }
     79 
     80 bool IncomingTaskQueue::HasHighResolutionTasks() {
     81   AutoLock lock(incoming_queue_lock_);
     82   return high_res_task_count_ > 0;
     83 }
     84 
     85 bool IncomingTaskQueue::IsIdleForTesting() {
     86   AutoLock lock(incoming_queue_lock_);
     87   return incoming_queue_.empty();
     88 }
     89 
     90 int IncomingTaskQueue::ReloadWorkQueue(TaskQueue* work_queue) {
     91   // Make sure no tasks are lost.
     92   DCHECK(work_queue->empty());
     93 
     94   // Acquire all we can from the inter-thread queue with one lock acquisition.
     95   AutoLock lock(incoming_queue_lock_);
     96   if (incoming_queue_.empty()) {
     97     // If the loop attempts to reload but there are no tasks in the incoming
     98     // queue, that means it will go to sleep waiting for more work. If the
     99     // incoming queue becomes nonempty we need to schedule it again.
    100     message_loop_scheduled_ = false;
    101   } else {
    102     incoming_queue_.Swap(work_queue);
    103   }
    104   // Reset the count of high resolution tasks since our queue is now empty.
    105   int high_res_tasks = high_res_task_count_;
    106   high_res_task_count_ = 0;
    107   return high_res_tasks;
    108 }
    109 
    110 void IncomingTaskQueue::WillDestroyCurrentMessageLoop() {
    111   AutoLock lock(incoming_queue_lock_);
    112   message_loop_ = NULL;
    113 }
    114 
    115 void IncomingTaskQueue::StartScheduling() {
    116   AutoLock lock(incoming_queue_lock_);
    117   DCHECK(!is_ready_for_scheduling_);
    118   DCHECK(!message_loop_scheduled_);
    119   is_ready_for_scheduling_ = true;
    120   if (!incoming_queue_.empty())
    121     ScheduleWork();
    122 }
    123 
    124 IncomingTaskQueue::~IncomingTaskQueue() {
    125   // Verify that WillDestroyCurrentMessageLoop() has been called.
    126   DCHECK(!message_loop_);
    127 }
    128 
    129 TimeTicks IncomingTaskQueue::CalculateDelayedRuntime(TimeDelta delay) {
    130   TimeTicks delayed_run_time;
    131   if (delay > TimeDelta())
    132     delayed_run_time = TimeTicks::Now() + delay;
    133   else
    134     DCHECK_EQ(delay.InMilliseconds(), 0) << "delay should not be negative";
    135   return delayed_run_time;
    136 }
    137 
    138 bool IncomingTaskQueue::PostPendingTask(PendingTask* pending_task) {
    139   // Warning: Don't try to short-circuit, and handle this thread's tasks more
    140   // directly, as it could starve handling of foreign threads.  Put every task
    141   // into this queue.
    142 
    143   // This should only be called while the lock is taken.
    144   incoming_queue_lock_.AssertAcquired();
    145 
    146   if (!message_loop_) {
    147     pending_task->task.Reset();
    148     return false;
    149   }
    150 
    151   // Initialize the sequence number. The sequence number is used for delayed
    152   // tasks (to facilitate FIFO sorting when two tasks have the same
    153   // delayed_run_time value) and for identifying the task in about:tracing.
    154   pending_task->sequence_num = next_sequence_num_++;
    155 
    156   message_loop_->task_annotator()->DidQueueTask("MessageLoop::PostTask",
    157                                                 *pending_task);
    158 
    159   bool was_empty = incoming_queue_.empty();
    160   incoming_queue_.push(*pending_task);
    161   pending_task->task.Reset();
    162 
    163   if (is_ready_for_scheduling_ &&
    164       (always_schedule_work_ || (!message_loop_scheduled_ && was_empty))) {
    165     ScheduleWork();
    166   }
    167 
    168   return true;
    169 }
    170 
    171 void IncomingTaskQueue::ScheduleWork() {
    172   DCHECK(is_ready_for_scheduling_);
    173   // Wake up the message loop.
    174   message_loop_->ScheduleWork();
    175   // After we've scheduled the message loop, we do not need to do so again
    176   // until we know it has processed all of the work in our queue and is
    177   // waiting for more work again. The message loop will always attempt to
    178   // reload from the incoming queue before waiting again so we clear this flag
    179   // in ReloadWorkQueue().
    180   message_loop_scheduled_ = true;
    181 }
    182 
    183 }  // namespace internal
    184 }  // namespace base
    185