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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/synchronization/waitable_event.h"
     12 #include "base/time/time.h"
     13 #include "build/build_config.h"
     14 
     15 namespace base {
     16 namespace internal {
     17 
     18 namespace {
     19 
     20 #if !defined(NDEBUG) || defined(DCHECK_ALWAYS_ON)
     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   (void)type;  // Avoid an unused warning.
     37   return false;
     38 #endif
     39 }
     40 
     41 TimeTicks CalculateDelayedRuntime(TimeDelta delay) {
     42   TimeTicks delayed_run_time;
     43   if (delay > TimeDelta())
     44     delayed_run_time = TimeTicks::Now() + delay;
     45   else
     46     DCHECK_EQ(delay.InMilliseconds(), 0) << "delay should not be negative";
     47   return delayed_run_time;
     48 }
     49 
     50 }  // namespace
     51 
     52 IncomingTaskQueue::IncomingTaskQueue(MessageLoop* message_loop)
     53     : high_res_task_count_(0),
     54       message_loop_(message_loop),
     55       next_sequence_num_(0),
     56       message_loop_scheduled_(false),
     57       always_schedule_work_(AlwaysNotifyPump(message_loop_->type())),
     58       is_ready_for_scheduling_(false) {
     59 }
     60 
     61 bool IncomingTaskQueue::AddToIncomingQueue(
     62     const tracked_objects::Location& from_here,
     63     const Closure& task,
     64     TimeDelta delay,
     65     bool nestable) {
     66   DLOG_IF(WARNING,
     67           delay.InSeconds() > kTaskDelayWarningThresholdInSeconds)
     68       << "Requesting super-long task delay period of " << delay.InSeconds()
     69       << " seconds from here: " << from_here.ToString();
     70 
     71   PendingTask pending_task(
     72       from_here, task, CalculateDelayedRuntime(delay), nestable);
     73 #if defined(OS_WIN)
     74   // We consider the task needs a high resolution timer if the delay is
     75   // more than 0 and less than 32ms. This caps the relative error to
     76   // less than 50% : a 33ms wait can wake at 48ms since the default
     77   // resolution on Windows is between 10 and 15ms.
     78   if (delay > TimeDelta() &&
     79       delay.InMilliseconds() < (2 * Time::kMinLowResolutionThresholdMs)) {
     80     pending_task.is_high_res = true;
     81   }
     82 #endif
     83   return PostPendingTask(&pending_task);
     84 }
     85 
     86 bool IncomingTaskQueue::HasHighResolutionTasks() {
     87   AutoLock lock(incoming_queue_lock_);
     88   return high_res_task_count_ > 0;
     89 }
     90 
     91 bool IncomingTaskQueue::IsIdleForTesting() {
     92   AutoLock lock(incoming_queue_lock_);
     93   return incoming_queue_.empty();
     94 }
     95 
     96 int IncomingTaskQueue::ReloadWorkQueue(TaskQueue* work_queue) {
     97   // Make sure no tasks are lost.
     98   DCHECK(work_queue->empty());
     99 
    100   // Acquire all we can from the inter-thread queue with one lock acquisition.
    101   AutoLock lock(incoming_queue_lock_);
    102   if (incoming_queue_.empty()) {
    103     // If the loop attempts to reload but there are no tasks in the incoming
    104     // queue, that means it will go to sleep waiting for more work. If the
    105     // incoming queue becomes nonempty we need to schedule it again.
    106     message_loop_scheduled_ = false;
    107   } else {
    108     incoming_queue_.swap(*work_queue);
    109   }
    110   // Reset the count of high resolution tasks since our queue is now empty.
    111   int high_res_tasks = high_res_task_count_;
    112   high_res_task_count_ = 0;
    113   return high_res_tasks;
    114 }
    115 
    116 void IncomingTaskQueue::WillDestroyCurrentMessageLoop() {
    117   base::subtle::AutoWriteLock lock(message_loop_lock_);
    118   message_loop_ = NULL;
    119 }
    120 
    121 void IncomingTaskQueue::StartScheduling() {
    122   bool schedule_work;
    123   {
    124     AutoLock lock(incoming_queue_lock_);
    125     DCHECK(!is_ready_for_scheduling_);
    126     DCHECK(!message_loop_scheduled_);
    127     is_ready_for_scheduling_ = true;
    128     schedule_work = !incoming_queue_.empty();
    129   }
    130   if (schedule_work) {
    131     DCHECK(message_loop_);
    132     // Don't need to lock |message_loop_lock_| here because this function is
    133     // called by MessageLoop on its thread.
    134     message_loop_->ScheduleWork();
    135   }
    136 }
    137 
    138 IncomingTaskQueue::~IncomingTaskQueue() {
    139   // Verify that WillDestroyCurrentMessageLoop() has been called.
    140   DCHECK(!message_loop_);
    141 }
    142 
    143 bool IncomingTaskQueue::PostPendingTask(PendingTask* pending_task) {
    144   // Warning: Don't try to short-circuit, and handle this thread's tasks more
    145   // directly, as it could starve handling of foreign threads.  Put every task
    146   // into this queue.
    147 
    148   // Ensures |message_loop_| isn't destroyed while running.
    149   base::subtle::AutoReadLock hold_message_loop(message_loop_lock_);
    150 
    151   if (!message_loop_) {
    152     pending_task->task.Reset();
    153     return false;
    154   }
    155 
    156   bool schedule_work = false;
    157   {
    158     AutoLock hold(incoming_queue_lock_);
    159 
    160 #if defined(OS_WIN)
    161     if (pending_task->is_high_res)
    162       ++high_res_task_count_;
    163 #endif
    164 
    165     // Initialize the sequence number. The sequence number is used for delayed
    166     // tasks (to facilitate FIFO sorting when two tasks have the same
    167     // delayed_run_time value) and for identifying the task in about:tracing.
    168     pending_task->sequence_num = next_sequence_num_++;
    169 
    170     message_loop_->task_annotator()->DidQueueTask("MessageLoop::PostTask",
    171                                                   *pending_task);
    172 
    173     bool was_empty = incoming_queue_.empty();
    174     incoming_queue_.push(std::move(*pending_task));
    175 
    176     if (is_ready_for_scheduling_ &&
    177         (always_schedule_work_ || (!message_loop_scheduled_ && was_empty))) {
    178       schedule_work = true;
    179       // After we've scheduled the message loop, we do not need to do so again
    180       // until we know it has processed all of the work in our queue and is
    181       // waiting for more work again. The message loop will always attempt to
    182       // reload from the incoming queue before waiting again so we clear this
    183       // flag in ReloadWorkQueue().
    184       message_loop_scheduled_ = true;
    185     }
    186   }
    187 
    188   // Wake up the message loop and schedule work. This is done outside
    189   // |incoming_queue_lock_| because signaling the message loop may cause this
    190   // thread to be switched. If |incoming_queue_lock_| is held, any other thread
    191   // that wants to post a task will be blocked until this thread switches back
    192   // in and releases |incoming_queue_lock_|.
    193   if (schedule_work)
    194     message_loop_->ScheduleWork();
    195 
    196   return true;
    197 }
    198 
    199 }  // namespace internal
    200 }  // namespace base
    201