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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.
*/
#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/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/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"
#include "third_party/libevent/event.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;
sigemptyset(&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));
#else
event_set(ev, fd, events, callback, arg);
RTC_CHECK_EQ(0, event_base_set(base, ev));
#endif
}
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 {
public:
TaskQueueLibevent(absl::string_view queue_name, rtc::ThreadPriority priority);
void Delete() override;
protected:
void PostTaskImpl(absl::AnyInvocable<void() &&> task,
const PostTaskTraits& traits,
const Location& location) override;
void PostDelayedTaskImpl(absl::AnyInvocable<void() &&> task,
TimeDelta delay,
const PostDelayedTaskTraits& traits,
const Location& location) override;
private:
struct TimerEvent;
void PostDelayedTaskOnTaskQueue(absl::AnyInvocable<void() &&> task,
TimeDelta delay);
~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<absl::AnyInvocable<void() &&>, 4> pending_
RTC_GUARDED_BY(pending_lock_);
// 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, absl::AnyInvocable<void() &&> task)
: task_queue(task_queue), task(std::move(task)) {}
~TimerEvent() { event_del(&ev); }
event ev;
TaskQueueLibevent* task_queue;
absl::AnyInvocable<void() &&> task;
};
TaskQueueLibevent::TaskQueueLibevent(absl::string_view queue_name,
rtc::ThreadPriority priority)
: event_base_(event_base_new()) {
int fds[2];
RTC_CHECK(pipe(fds) == 0);
SetNonBlocking(fds[0]);
SetNonBlocking(fds[1]);
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);
// Ensure remaining deleted tasks are destroyed with Current() set up
// to this task queue.
absl::InlinedVector<absl::AnyInvocable<void() &&>, 4> pending;
MutexLock lock(&pending_lock_);
pending_.swap(pending);
}
for (TimerEvent* timer : pending_timers_)
delete timer;
#if RTC_DCHECK_IS_ON
MutexLock lock(&pending_lock_);
RTC_DCHECK(pending_.empty());
#endif
},
queue_name, rtc::ThreadAttributes().SetPriority(priority));
}
void TaskQueueLibevent::Delete() {
RTC_DCHECK(!IsCurrent());
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.
RTC_CHECK_EQ(EAGAIN, errno);
ts.tv_sec = 0;
ts.tv_nsec = 1000000;
nanosleep(&ts, nullptr);
}
thread_.Finalize();
event_del(&wakeup_event_);
IgnoreSigPipeSignalOnCurrentThread();
close(wakeup_pipe_in_);
close(wakeup_pipe_out_);
wakeup_pipe_in_ = -1;
wakeup_pipe_out_ = -1;
event_base_free(event_base_);
delete this;
}
void TaskQueueLibevent::PostTaskImpl(absl::AnyInvocable<void() &&> task,
const PostTaskTraits& traits,
const Location& location) {
{
MutexLock lock(&pending_lock_);
bool had_pending_tasks = !pending_.empty();
pending_.push_back(std::move(task));
// 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) {
return;
}
}
// 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)),
sizeof(message));
}
void TaskQueueLibevent::PostDelayedTaskOnTaskQueue(
absl::AnyInvocable<void() &&> task,
TimeDelta delay) {
// libevent api is not thread safe by default, thus event_add need to be
// called on the `thread_`.
RTC_DCHECK(IsCurrent());
TimerEvent* timer = new TimerEvent(this, std::move(task));
EventAssign(&timer->ev, event_base_, -1, 0, &TaskQueueLibevent::RunTimer,
timer);
pending_timers_.push_back(timer);
timeval tv = {.tv_sec = rtc::dchecked_cast<int>(delay.us() / 1'000'000),
.tv_usec = rtc::dchecked_cast<int>(delay.us() % 1'000'000)};
event_add(&timer->ev, &tv);
}
void TaskQueueLibevent::PostDelayedTaskImpl(absl::AnyInvocable<void() &&> task,
TimeDelta delay,
const PostDelayedTaskTraits& traits,
const Location& location) {
if (IsCurrent()) {
PostDelayedTaskOnTaskQueue(std::move(task), delay);
} else {
int64_t posted_us = rtc::TimeMicros();
PostTask([posted_us, delay, task = std::move(task), this]() mutable {
// Compensate for the time that has passed since the posting.
TimeDelta post_time = TimeDelta::Micros(rtc::TimeMicros() - posted_us);
PostDelayedTaskOnTaskQueue(
std::move(task), std::max(delay - post_time, TimeDelta::Zero()));
});
}
}
// 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;
event_base_loopbreak(me->event_base_);
break;
case kRunTasks: {
absl::InlinedVector<absl::AnyInvocable<void() &&>, 4> tasks;
{
MutexLock lock(&me->pending_lock_);
tasks.swap(me->pending_);
}
RTC_DCHECK(!tasks.empty());
for (auto& task : tasks) {
std::move(task)();
// Prefer to delete the `task` before running the next one.
task = nullptr;
}
break;
}
default:
RTC_DCHECK_NOTREACHED();
break;
}
}
// static
void TaskQueueLibevent::RunTimer(int fd,
short flags, // NOLINT
void* context) {
TimerEvent* timer = static_cast<TimerEvent*>(context);
std::move(timer->task)();
timer->task_queue->pending_timers_.remove(timer);
delete timer;
}
class TaskQueueLibeventFactory 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 TaskQueueLibevent(name,
TaskQueuePriorityToThreadPriority(priority)));
}
};
} // namespace
std::unique_ptr<TaskQueueFactory> CreateTaskQueueLibeventFactory() {
return std::make_unique<TaskQueueLibeventFactory>();
}
} // namespace webrtc