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// Copyright 2016 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "base/task_scheduler/task_tracker.h"
#include "base/callback.h"
#include "base/debug/task_annotator.h"
#include "base/metrics/histogram_macros.h"
namespace base {
namespace internal {
namespace {
const char kQueueFunctionName[] = "base::PostTask";
// Upper bound for the
// TaskScheduler.BlockShutdownTasksPostedDuringShutdown histogram.
const HistogramBase::Sample kMaxBlockShutdownTasksPostedDuringShutdown = 1000;
void RecordNumBlockShutdownTasksPostedDuringShutdown(
HistogramBase::Sample value) {
UMA_HISTOGRAM_CUSTOM_COUNTS(
"TaskScheduler.BlockShutdownTasksPostedDuringShutdown", value, 1,
kMaxBlockShutdownTasksPostedDuringShutdown, 50);
}
} // namespace
TaskTracker::TaskTracker() = default;
TaskTracker::~TaskTracker() = default;
void TaskTracker::Shutdown() {
AutoSchedulerLock auto_lock(lock_);
// This method should only be called once.
DCHECK(!shutdown_completed_);
DCHECK(!shutdown_cv_);
shutdown_cv_ = lock_.CreateConditionVariable();
// Wait until the number of tasks blocking shutdown is zero.
while (num_tasks_blocking_shutdown_ != 0)
shutdown_cv_->Wait();
shutdown_cv_.reset();
shutdown_completed_ = true;
// Record the TaskScheduler.BlockShutdownTasksPostedDuringShutdown if less
// than |kMaxBlockShutdownTasksPostedDuringShutdown| BLOCK_SHUTDOWN tasks were
// posted during shutdown. Otherwise, the histogram has already been recorded
// in BeforePostTask().
if (num_block_shutdown_tasks_posted_during_shutdown_ <
kMaxBlockShutdownTasksPostedDuringShutdown) {
RecordNumBlockShutdownTasksPostedDuringShutdown(
num_block_shutdown_tasks_posted_during_shutdown_);
}
}
bool TaskTracker::WillPostTask(const Task* task) {
DCHECK(task);
if (!BeforePostTask(task->traits.shutdown_behavior()))
return false;
debug::TaskAnnotator task_annotator;
task_annotator.DidQueueTask(kQueueFunctionName, *task);
return true;
}
void TaskTracker::RunTask(const Task* task) {
DCHECK(task);
const TaskShutdownBehavior shutdown_behavior =
task->traits.shutdown_behavior();
if (!BeforeRunTask(shutdown_behavior))
return;
debug::TaskAnnotator task_annotator;
task_annotator.RunTask(kQueueFunctionName, *task);
AfterRunTask(shutdown_behavior);
}
bool TaskTracker::IsShuttingDownForTesting() const {
AutoSchedulerLock auto_lock(lock_);
return !!shutdown_cv_;
}
bool TaskTracker::BeforePostTask(TaskShutdownBehavior shutdown_behavior) {
AutoSchedulerLock auto_lock(lock_);
if (shutdown_completed_) {
// A BLOCK_SHUTDOWN task posted after shutdown has completed is an ordering
// bug. This DCHECK aims to catch those early.
DCHECK_NE(shutdown_behavior, TaskShutdownBehavior::BLOCK_SHUTDOWN);
// No task is allowed to be posted after shutdown.
return false;
}
if (shutdown_behavior == TaskShutdownBehavior::BLOCK_SHUTDOWN) {
// BLOCK_SHUTDOWN tasks block shutdown between the moment they are posted
// and the moment they complete their execution.
++num_tasks_blocking_shutdown_;
if (shutdown_cv_) {
++num_block_shutdown_tasks_posted_during_shutdown_;
if (num_block_shutdown_tasks_posted_during_shutdown_ ==
kMaxBlockShutdownTasksPostedDuringShutdown) {
// Record the TaskScheduler.BlockShutdownTasksPostedDuringShutdown
// histogram as soon as its upper bound is hit. That way, a value will
// be recorded even if an infinite number of BLOCK_SHUTDOWN tasks are
// posted, preventing shutdown to complete.
RecordNumBlockShutdownTasksPostedDuringShutdown(
num_block_shutdown_tasks_posted_during_shutdown_);
}
}
// A BLOCK_SHUTDOWN task is allowed to be posted iff shutdown hasn't
// completed.
return true;
}
// A non BLOCK_SHUTDOWN task is allowed to be posted iff shutdown hasn't
// started.
return !shutdown_cv_;
}
bool TaskTracker::BeforeRunTask(TaskShutdownBehavior shutdown_behavior) {
AutoSchedulerLock auto_lock(lock_);
if (shutdown_completed_) {
// Trying to run a BLOCK_SHUTDOWN task after shutdown has completed is
// unexpected as it either shouldn't have been posted if shutdown completed
// or should be blocking shutdown if it was posted before it did.
DCHECK_NE(shutdown_behavior, TaskShutdownBehavior::BLOCK_SHUTDOWN);
// A WorkerThread might extract a non BLOCK_SHUTDOWN task from a
// PriorityQueue after shutdown. It shouldn't be allowed to run it.
return false;
}
switch (shutdown_behavior) {
case TaskShutdownBehavior::BLOCK_SHUTDOWN:
DCHECK_GT(num_tasks_blocking_shutdown_, 0U);
return true;
case TaskShutdownBehavior::SKIP_ON_SHUTDOWN:
if (shutdown_cv_)
return false;
// SKIP_ON_SHUTDOWN tasks block shutdown while they are running.
++num_tasks_blocking_shutdown_;
return true;
case TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN:
return !shutdown_cv_;
}
NOTREACHED();
return false;
}
void TaskTracker::AfterRunTask(TaskShutdownBehavior shutdown_behavior) {
if (shutdown_behavior == TaskShutdownBehavior::BLOCK_SHUTDOWN ||
shutdown_behavior == TaskShutdownBehavior::SKIP_ON_SHUTDOWN) {
AutoSchedulerLock auto_lock(lock_);
DCHECK_GT(num_tasks_blocking_shutdown_, 0U);
--num_tasks_blocking_shutdown_;
if (num_tasks_blocking_shutdown_ == 0 && shutdown_cv_)
shutdown_cv_->Signal();
}
}
} // namespace internal
} // namespace base
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