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/*
* Copyright 2016 The WebRTC Project Authors. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
// This file contains the implementation of TaskQueue for Mac and iOS.
// The implementation uses Grand Central Dispatch queues (GCD) to
// do the actual task queuing.
#include "rtc_base/task_queue_gcd.h"
#include <dispatch/dispatch.h>
#include <string.h>
#include <memory>
#include "absl/functional/any_invocable.h"
#include "absl/strings/string_view.h"
#include "api/task_queue/task_queue_base.h"
#include "api/units/time_delta.h"
#include "rtc_base/checks.h"
#include "rtc_base/logging.h"
#include "rtc_base/system/gcd_helpers.h"
namespace webrtc {
namespace {
int TaskQueuePriorityToGCD(TaskQueueFactory::Priority priority) {
switch (priority) {
case TaskQueueFactory::Priority::NORMAL:
return DISPATCH_QUEUE_PRIORITY_DEFAULT;
case TaskQueueFactory::Priority::HIGH:
return DISPATCH_QUEUE_PRIORITY_HIGH;
case TaskQueueFactory::Priority::LOW:
return DISPATCH_QUEUE_PRIORITY_LOW;
}
}
class TaskQueueGcd final : public TaskQueueBase {
public:
TaskQueueGcd(absl::string_view queue_name, int gcd_priority);
void Delete() override;
void PostTask(absl::AnyInvocable<void() &&> task) override;
void PostDelayedTask(absl::AnyInvocable<void() &&> task,
TimeDelta delay) override;
void PostDelayedHighPrecisionTask(absl::AnyInvocable<void() &&> task,
TimeDelta delay) override;
private:
struct TaskContext {
TaskContext(TaskQueueGcd* queue, absl::AnyInvocable<void() &&> task)
: queue(queue), task(std::move(task)) {}
TaskQueueGcd* const queue;
absl::AnyInvocable<void() &&> task;
};
~TaskQueueGcd() override;
static void RunTask(void* task_context);
static void SetNotActive(void* task_queue);
static void DeleteQueue(void* task_queue);
dispatch_queue_t queue_;
bool is_active_;
};
TaskQueueGcd::TaskQueueGcd(absl::string_view queue_name, int gcd_priority)
: queue_(RTCDispatchQueueCreateWithTarget(
std::string(queue_name).c_str(),
DISPATCH_QUEUE_SERIAL,
dispatch_get_global_queue(gcd_priority, 0))),
is_active_(true) {
RTC_CHECK(queue_);
dispatch_set_context(queue_, this);
// Assign a finalizer that will delete the queue when the last reference
// is released. This may run after the TaskQueue::Delete.
dispatch_set_finalizer_f(queue_, &DeleteQueue);
}
TaskQueueGcd::~TaskQueueGcd() = default;
void TaskQueueGcd::Delete() {
RTC_DCHECK(!IsCurrent());
// Implementation/behavioral note:
// Dispatch queues are reference counted via calls to dispatch_retain and
// dispatch_release. Pending blocks submitted to a queue also hold a
// reference to the queue until they have finished. Once all references to a
// queue have been released, the queue will be deallocated by the system.
// This is why we check the is_active_ before running tasks.
// Use dispatch_sync to set the is_active_ to guarantee that there's not a
// race with checking it from a task.
dispatch_sync_f(queue_, this, &SetNotActive);
dispatch_release(queue_);
}
void TaskQueueGcd::PostTask(absl::AnyInvocable<void() &&> task) {
auto* context = new TaskContext(this, std::move(task));
dispatch_async_f(queue_, context, &RunTask);
}
void TaskQueueGcd::PostDelayedTask(absl::AnyInvocable<void() &&> task,
TimeDelta delay) {
auto* context = new TaskContext(this, std::move(task));
dispatch_after_f(dispatch_time(DISPATCH_TIME_NOW, delay.us() * NSEC_PER_USEC),
queue_, context, &RunTask);
}
void TaskQueueGcd::PostDelayedHighPrecisionTask(
absl::AnyInvocable<void() &&> task,
TimeDelta delay) {
PostDelayedTask(std::move(task), delay);
}
// static
void TaskQueueGcd::RunTask(void* task_context) {
std::unique_ptr<TaskContext> tc(static_cast<TaskContext*>(task_context));
if (!tc->queue->is_active_)
return;
CurrentTaskQueueSetter set_current(tc->queue);
std::move(tc->task)();
// Delete the task before CurrentTaskQueueSetter clears state that this code
// is running on the task queue.
tc = nullptr;
}
// static
void TaskQueueGcd::SetNotActive(void* task_queue) {
static_cast<TaskQueueGcd*>(task_queue)->is_active_ = false;
}
// static
void TaskQueueGcd::DeleteQueue(void* task_queue) {
delete static_cast<TaskQueueGcd*>(task_queue);
}
class TaskQueueGcdFactory final : public TaskQueueFactory {
public:
std::unique_ptr<TaskQueueBase, TaskQueueDeleter> CreateTaskQueue(
absl::string_view name,
Priority priority) const override {
return std::unique_ptr<TaskQueueBase, TaskQueueDeleter>(
new TaskQueueGcd(name, TaskQueuePriorityToGCD(priority)));
}
};
} // namespace
std::unique_ptr<TaskQueueFactory> CreateTaskQueueGcdFactory() {
return std::make_unique<TaskQueueGcdFactory>();
}
} // namespace webrtc
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