blob: 909698611e988fbeed8084f5b9a9da78d75dbec6 [file] [log] [blame]
* 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.
#include "rtc_base/task_queue_libevent.h"
#include <errno.h>
#include <fcntl.h>
#include <pthread.h>
#include <signal.h>
#include <stdint.h>
#include <time.h>
#include <unistd.h>
#include <list>
#include <memory>
#include <type_traits>
#include <utility>
#include "absl/container/inlined_vector.h"
#include "absl/strings/string_view.h"
#include "api/task_queue/queued_task.h"
#include "api/task_queue/task_queue_base.h"
#include "base/third_party/libevent/event.h"
#include "rtc_base/checks.h"
#include "rtc_base/logging.h"
#include "rtc_base/numerics/safe_conversions.h"
#include "rtc_base/platform_thread.h"
#include "rtc_base/platform_thread_types.h"
#include "rtc_base/synchronization/mutex.h"
#include "rtc_base/thread_annotations.h"
#include "rtc_base/time_utils.h"
namespace webrtc {
namespace {
constexpr char kQuit = 1;
constexpr char kRunTasks = 2;
using Priority = TaskQueueFactory::Priority;
// This ignores the SIGPIPE signal on the calling thread.
// This signal can be fired when trying to write() to a pipe that's being
// closed or while closing a pipe that's being written to.
// We can run into that situation so we ignore this signal and continue as
// normal.
// As a side note for this implementation, it would be great if we could safely
// restore the sigmask, but unfortunately the operation of restoring it, can
// itself actually cause SIGPIPE to be signaled :-| (e.g. on MacOS)
// The SIGPIPE signal by default causes the process to be terminated, so we
// don't want to risk that.
// An alternative to this approach is to ignore the signal for the whole
// process:
// signal(SIGPIPE, SIG_IGN);
void IgnoreSigPipeSignalOnCurrentThread() {
sigset_t sigpipe_mask;
sigaddset(&sigpipe_mask, SIGPIPE);
pthread_sigmask(SIG_BLOCK, &sigpipe_mask, nullptr);
bool SetNonBlocking(int fd) {
const int flags = fcntl(fd, F_GETFL);
RTC_CHECK(flags != -1);
return (flags & O_NONBLOCK) || fcntl(fd, F_SETFL, flags | O_NONBLOCK) != -1;
// TODO(tommi): This is a hack to support two versions of libevent that we're
// compatible with. The method we really want to call is event_assign(),
// since event_set() has been marked as deprecated (and doesn't accept
// passing event_base__ as a parameter). However, the version of libevent
// that we have in Chromium, doesn't have event_assign(), so we need to call
// event_set() there.
void EventAssign(struct event* ev,
struct event_base* base,
int fd,
short events,
void (*callback)(int, short, void*),
void* arg) {
#if defined(_EVENT2_EVENT_H_)
RTC_CHECK_EQ(0, event_assign(ev, base, fd, events, callback, arg));
event_set(ev, fd, events, callback, arg);
RTC_CHECK_EQ(0, event_base_set(base, ev));
rtc::ThreadPriority TaskQueuePriorityToThreadPriority(Priority priority) {
switch (priority) {
case Priority::HIGH:
return rtc::ThreadPriority::kRealtime;
case Priority::LOW:
return rtc::ThreadPriority::kLow;
case Priority::NORMAL:
return rtc::ThreadPriority::kNormal;
class TaskQueueLibevent final : public TaskQueueBase {
TaskQueueLibevent(absl::string_view queue_name, rtc::ThreadPriority priority);
void Delete() override;
void PostTask(std::unique_ptr<QueuedTask> task) override;
void PostDelayedTask(std::unique_ptr<QueuedTask> task,
uint32_t milliseconds) override;
class SetTimerTask;
struct TimerEvent;
~TaskQueueLibevent() override = default;
static void OnWakeup(int socket, short flags, void* context); // NOLINT
static void RunTimer(int fd, short flags, void* context); // NOLINT
bool is_active_ = true;
int wakeup_pipe_in_ = -1;
int wakeup_pipe_out_ = -1;
event_base* event_base_;
event wakeup_event_;
rtc::PlatformThread thread_;
Mutex pending_lock_;
absl::InlinedVector<std::unique_ptr<QueuedTask>, 4> pending_
// Holds a list of events pending timers for cleanup when the loop exits.
std::list<TimerEvent*> pending_timers_;
struct TaskQueueLibevent::TimerEvent {
TimerEvent(TaskQueueLibevent* task_queue, std::unique_ptr<QueuedTask> task)
: task_queue(task_queue), task(std::move(task)) {}
~TimerEvent() { event_del(&ev); }
event ev;
TaskQueueLibevent* task_queue;
std::unique_ptr<QueuedTask> task;
class TaskQueueLibevent::SetTimerTask : public QueuedTask {
SetTimerTask(std::unique_ptr<QueuedTask> task, uint32_t milliseconds)
: task_(std::move(task)),
posted_(rtc::Time32()) {}
bool Run() override {
// Compensate for the time that has passed since construction
// and until we got here.
uint32_t post_time = rtc::Time32() - posted_;
post_time > milliseconds_ ? 0 : milliseconds_ - post_time);
return true;
std::unique_ptr<QueuedTask> task_;
const uint32_t milliseconds_;
const uint32_t posted_;
TaskQueueLibevent::TaskQueueLibevent(absl::string_view queue_name,
rtc::ThreadPriority priority)
: event_base_(event_base_new()) {
int fds[2];
RTC_CHECK(pipe(fds) == 0);
wakeup_pipe_out_ = fds[0];
wakeup_pipe_in_ = fds[1];
EventAssign(&wakeup_event_, event_base_, wakeup_pipe_out_,
EV_READ | EV_PERSIST, OnWakeup, this);
event_add(&wakeup_event_, 0);
thread_ = rtc::PlatformThread::SpawnJoinable(
[this] {
CurrentTaskQueueSetter set_current(this);
while (is_active_)
event_base_loop(event_base_, 0);
for (TimerEvent* timer : pending_timers_)
delete timer;
queue_name, rtc::ThreadAttributes().SetPriority(priority));
void TaskQueueLibevent::Delete() {
struct timespec ts;
char message = kQuit;
while (write(wakeup_pipe_in_, &message, sizeof(message)) != sizeof(message)) {
// The queue is full, so we have no choice but to wait and retry.
ts.tv_sec = 0;
ts.tv_nsec = 1000000;
nanosleep(&ts, nullptr);
wakeup_pipe_in_ = -1;
wakeup_pipe_out_ = -1;
delete this;
void TaskQueueLibevent::PostTask(std::unique_ptr<QueuedTask> task) {
MutexLock lock(&pending_lock_);
bool had_pending_tasks = !pending_.empty();
// Only write to the pipe if there were no pending tasks before this one
// since the thread could be sleeping. If there were already pending tasks
// then we know there's either a pending write in the pipe or the thread has
// not yet processed the pending tasks. In either case, the thread will
// eventually wake up and process all pending tasks including this one.
if (had_pending_tasks) {
// Note: This behvior outlined above ensures we never fill up the pipe write
// buffer since there will only ever be 1 byte pending.
char message = kRunTasks;
RTC_CHECK_EQ(write(wakeup_pipe_in_, &message, sizeof(message)),
void TaskQueueLibevent::PostDelayedTask(std::unique_ptr<QueuedTask> task,
uint32_t milliseconds) {
if (IsCurrent()) {
TimerEvent* timer = new TimerEvent(this, std::move(task));
EventAssign(&timer->ev, event_base_, -1, 0, &TaskQueueLibevent::RunTimer,
timeval tv = {rtc::dchecked_cast<int>(milliseconds / 1000),
rtc::dchecked_cast<int>(milliseconds % 1000) * 1000};
event_add(&timer->ev, &tv);
} else {
PostTask(std::make_unique<SetTimerTask>(std::move(task), milliseconds));
// static
void TaskQueueLibevent::OnWakeup(int socket,
short flags, // NOLINT
void* context) {
TaskQueueLibevent* me = static_cast<TaskQueueLibevent*>(context);
RTC_DCHECK(me->wakeup_pipe_out_ == socket);
char buf;
RTC_CHECK(sizeof(buf) == read(socket, &buf, sizeof(buf)));
switch (buf) {
case kQuit:
me->is_active_ = false;
case kRunTasks: {
absl::InlinedVector<std::unique_ptr<QueuedTask>, 4> tasks;
MutexLock lock(&me->pending_lock_);
for (auto& task : tasks) {
if (task->Run()) {
} else {
// |false| means the task should *not* be deleted.
// static
void TaskQueueLibevent::RunTimer(int fd,
short flags, // NOLINT
void* context) {
TimerEvent* timer = static_cast<TimerEvent*>(context);
if (!timer->task->Run())
delete timer;
class TaskQueueLibeventFactory final : public TaskQueueFactory {
std::unique_ptr<TaskQueueBase, TaskQueueDeleter> CreateTaskQueue(
absl::string_view name,
Priority priority) const override {
return std::unique_ptr<TaskQueueBase, TaskQueueDeleter>(
new TaskQueueLibevent(name,
} // namespace
std::unique_ptr<TaskQueueFactory> CreateTaskQueueLibeventFactory() {
return std::make_unique<TaskQueueLibeventFactory>();
} // namespace webrtc