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.
AlwaysNotifyPump(MessageLoop::Type type)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
CalculateDelayedRuntime(TimeDelta delay)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
IncomingTaskQueue(MessageLoop * message_loop)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
AddToIncomingQueue(const tracked_objects::Location & from_here,const Closure & task,TimeDelta delay,bool nestable)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
HasHighResolutionTasks()86 bool IncomingTaskQueue::HasHighResolutionTasks() {
87 AutoLock lock(incoming_queue_lock_);
88 return high_res_task_count_ > 0;
89 }
90
IsIdleForTesting()91 bool IncomingTaskQueue::IsIdleForTesting() {
92 AutoLock lock(incoming_queue_lock_);
93 return incoming_queue_.empty();
94 }
95
ReloadWorkQueue(TaskQueue * work_queue)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
WillDestroyCurrentMessageLoop()116 void IncomingTaskQueue::WillDestroyCurrentMessageLoop() {
117 base::subtle::AutoWriteLock lock(message_loop_lock_);
118 message_loop_ = NULL;
119 }
120
StartScheduling()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
~IncomingTaskQueue()138 IncomingTaskQueue::~IncomingTaskQueue() {
139 // Verify that WillDestroyCurrentMessageLoop() has been called.
140 DCHECK(!message_loop_);
141 }
142
PostPendingTask(PendingTask * pending_task)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