2 * Copyright 2016 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
17 #ifndef __STDC_FORMAT_MACROS
18 #define __STDC_FORMAT_MACROS
21 #include <folly/io/async/EventBase.h>
23 #include <folly/ThreadName.h>
24 #include <folly/io/async/NotificationQueue.h>
25 #include <folly/portability/Unistd.h>
27 #include <condition_variable>
34 using folly::EventBase;
36 class FunctionLoopCallback : public EventBase::LoopCallback {
38 explicit FunctionLoopCallback(EventBase::Func&& function)
39 : function_(std::move(function)) {}
41 void runLoopCallback() noexcept override {
47 EventBase::Func function_;
54 * EventBase::FunctionRunner
57 class EventBase::FunctionRunner
58 : public NotificationQueue<EventBase::Func>::Consumer {
60 void messageAvailable(Func&& msg) override {
61 // In libevent2, internal events do not break the loop.
62 // Most users would expect loop(), followed by runInEventBaseThread(),
63 // to break the loop and check if it should exit or not.
64 // To have similar bejaviour to libevent1.4, tell the loop to break here.
65 // Note that loop() may still continue to loop, but it will also check the
66 // stop_ flag as well as runInLoop callbacks, etc.
67 event_base_loopbreak(getEventBase()->evb_);
70 // terminateLoopSoon() sends a null message just to
71 // wake up the loop. We can ignore these messages.
75 // The function should never throw an exception, because we have no
76 // way of knowing what sort of error handling to perform.
78 // If it does throw, log a message and abort the program.
81 } catch (const std::exception& ex) {
82 LOG(ERROR) << "runInEventBaseThread() function threw a "
83 << typeid(ex).name() << " exception: " << ex.what();
86 LOG(ERROR) << "runInEventBaseThread() function threw an exception";
93 * EventBase::CobTimeout methods
96 void EventBase::CobTimeout::timeoutExpired() noexcept {
97 // For now, we just swallow any exceptions that the callback threw.
100 } catch (const std::exception& ex) {
101 LOG(ERROR) << "EventBase::runAfterDelay() callback threw "
102 << typeid(ex).name() << " exception: " << ex.what();
104 LOG(ERROR) << "EventBase::runAfterDelay() callback threw non-exception "
108 // The CobTimeout object was allocated on the heap by runAfterDelay(),
109 // so delete it now that the it has fired.
114 // The interface used to libevent is not thread-safe. Calls to
115 // event_init() and event_base_free() directly modify an internal
116 // global 'current_base', so a mutex is required to protect this.
118 // event_init() should only ever be called once. Subsequent calls
119 // should be made to event_base_new(). We can recognise that
120 // event_init() has already been called by simply inspecting current_base.
121 static std::mutex libevent_mutex_;
127 EventBase::EventBase(bool enableTimeMeasurement)
128 : runOnceCallbacks_(nullptr)
134 , avgLoopTime_(2000000)
135 , maxLatencyLoopTime_(avgLoopTime_)
136 , enableTimeMeasurement_(enableTimeMeasurement)
137 , nextLoopCnt_(-40) // Early wrap-around so bugs will manifest soon
138 , latestLoopCnt_(nextLoopCnt_)
141 , observerSampleCount_(0)
142 , executionObserver_(nullptr) {
145 std::lock_guard<std::mutex> lock(libevent_mutex_);
147 // The value 'current_base' (libevent 1) or
148 // 'event_global_current_base_' (libevent 2) is filled in by event_set(),
149 // allowing examination of its value without an explicit reference here.
150 // If ev.ev_base is NULL, then event_init() must be called, otherwise
151 // call event_base_new().
152 event_set(&ev, 0, 0, nullptr, nullptr);
159 evb_ = event_base_new();
162 if (UNLIKELY(evb_ == nullptr)) {
163 LOG(ERROR) << "EventBase(): Failed to init event base.";
164 folly::throwSystemError("error in EventBase::EventBase()");
166 VLOG(5) << "EventBase(): Created.";
167 initNotificationQueue();
168 RequestContext::saveContext();
171 // takes ownership of the event_base
172 EventBase::EventBase(event_base* evb, bool enableTimeMeasurement)
173 : runOnceCallbacks_(nullptr)
180 , avgLoopTime_(2000000)
181 , maxLatencyLoopTime_(avgLoopTime_)
182 , enableTimeMeasurement_(enableTimeMeasurement)
183 , nextLoopCnt_(-40) // Early wrap-around so bugs will manifest soon
184 , latestLoopCnt_(nextLoopCnt_)
187 , observerSampleCount_(0)
188 , executionObserver_(nullptr) {
189 if (UNLIKELY(evb_ == nullptr)) {
190 LOG(ERROR) << "EventBase(): Pass nullptr as event base.";
191 throw std::invalid_argument("EventBase(): event base cannot be nullptr");
193 initNotificationQueue();
194 RequestContext::saveContext();
197 EventBase::~EventBase() {
198 // Keep looping until all keep-alive handles are released. Each keep-alive
199 // handle signals that some external code will still schedule some work on
200 // this EventBase (so it's not safe to destroy it).
201 while (loopKeepAliveCount_ > 0) {
202 applyLoopKeepAlive();
206 // Call all destruction callbacks, before we start cleaning up our state.
207 while (!onDestructionCallbacks_.empty()) {
208 LoopCallback* callback = &onDestructionCallbacks_.front();
209 onDestructionCallbacks_.pop_front();
210 callback->runLoopCallback();
213 // Delete any unfired callback objects, so that we don't leak memory
214 // (Note that we don't fire them. The caller is responsible for cleaning up
215 // its own data structures if it destroys the EventBase with unfired events
217 while (!pendingCobTimeouts_.empty()) {
218 CobTimeout* timeout = &pendingCobTimeouts_.front();
222 while (!runBeforeLoopCallbacks_.empty()) {
223 delete &runBeforeLoopCallbacks_.front();
226 (void)runLoopCallbacks();
228 if (!fnRunner_->consumeUntilDrained()) {
229 LOG(ERROR) << "~EventBase(): Unable to drain notification queue";
232 // Stop consumer before deleting NotificationQueue
233 fnRunner_->stopConsuming();
235 std::lock_guard<std::mutex> lock(libevent_mutex_);
236 event_base_free(evb_);
240 std::lock_guard<std::mutex> lock(localStorageMutex_);
241 for (auto storage : localStorageToDtor_) {
242 storage->onEventBaseDestruction(*this);
245 VLOG(5) << "EventBase(): Destroyed.";
248 int EventBase::getNotificationQueueSize() const {
249 return queue_->size();
252 void EventBase::setMaxReadAtOnce(uint32_t maxAtOnce) {
253 fnRunner_->setMaxReadAtOnce(maxAtOnce);
256 // Set smoothing coefficient for loop load average; input is # of milliseconds
257 // for exp(-1) decay.
258 void EventBase::setLoadAvgMsec(uint32_t ms) {
259 assert(enableTimeMeasurement_);
260 uint64_t us = 1000 * ms;
262 maxLatencyLoopTime_.setTimeInterval(us);
263 avgLoopTime_.setTimeInterval(us);
265 LOG(ERROR) << "non-positive arg to setLoadAvgMsec()";
269 void EventBase::resetLoadAvg(double value) {
270 assert(enableTimeMeasurement_);
271 avgLoopTime_.reset(value);
272 maxLatencyLoopTime_.reset(value);
275 static std::chrono::milliseconds
276 getTimeDelta(std::chrono::steady_clock::time_point* prev) {
277 auto result = std::chrono::steady_clock::now() - *prev;
278 *prev = std::chrono::steady_clock::now();
280 return std::chrono::duration_cast<std::chrono::milliseconds>(result);
283 void EventBase::waitUntilRunning() {
284 while (!isRunning()) {
289 // enters the event_base loop -- will only exit when forced to
290 bool EventBase::loop() {
294 bool EventBase::loopOnce(int flags) {
295 return loopBody(flags | EVLOOP_ONCE);
298 bool EventBase::loopBody(int flags) {
299 VLOG(5) << "EventBase(): Starting loop.";
301 DCHECK(!invokingLoop_)
302 << "Your code just tried to loop over an event base from inside another "
303 << "event base loop. Since libevent is not reentrant, this leads to "
304 << "undefined behavior in opt builds. Please fix immediately. For the "
305 << "common case of an inner function that needs to do some synchronous "
306 << "computation on an event-base, replace getEventBase() by a new, "
307 << "stack-allocated EvenBase.";
308 invokingLoop_ = true;
310 invokingLoop_ = false;
314 bool ranLoopCallbacks;
315 bool blocking = !(flags & EVLOOP_NONBLOCK);
316 bool once = (flags & EVLOOP_ONCE);
318 // time-measurement variables.
319 std::chrono::steady_clock::time_point prev;
320 int64_t idleStart = 0;
324 loopThread_.store(pthread_self(), std::memory_order_release);
326 if (!name_.empty()) {
327 setThreadName(name_);
330 if (enableTimeMeasurement_) {
331 prev = std::chrono::steady_clock::now();
332 idleStart = std::chrono::duration_cast<std::chrono::microseconds>(
333 std::chrono::steady_clock::now().time_since_epoch()).count();
336 while (!stop_.load(std::memory_order_acquire)) {
337 applyLoopKeepAlive();
340 // Run the before loop callbacks
341 LoopCallbackList callbacks;
342 callbacks.swap(runBeforeLoopCallbacks_);
344 while(!callbacks.empty()) {
345 auto* item = &callbacks.front();
346 callbacks.pop_front();
347 item->runLoopCallback();
350 // nobody can add loop callbacks from within this thread if
351 // we don't have to handle anything to start with...
352 if (blocking && loopCallbacks_.empty()) {
353 res = event_base_loop(evb_, EVLOOP_ONCE);
355 res = event_base_loop(evb_, EVLOOP_ONCE | EVLOOP_NONBLOCK);
358 ranLoopCallbacks = runLoopCallbacks();
360 if (enableTimeMeasurement_) {
361 busy = std::chrono::duration_cast<std::chrono::microseconds>(
362 std::chrono::steady_clock::now().time_since_epoch()).count() -
364 idle = startWork_ - idleStart;
366 avgLoopTime_.addSample(idle, busy);
367 maxLatencyLoopTime_.addSample(idle, busy);
370 if (observerSampleCount_++ == observer_->getSampleRate()) {
371 observerSampleCount_ = 0;
372 observer_->loopSample(busy, idle);
376 VLOG(11) << "EventBase " << this << " did not timeout "
377 " loop time guess: " << busy + idle <<
378 " idle time: " << idle <<
379 " busy time: " << busy <<
380 " avgLoopTime: " << avgLoopTime_.get() <<
381 " maxLatencyLoopTime: " << maxLatencyLoopTime_.get() <<
382 " maxLatency_: " << maxLatency_ <<
383 " notificationQueueSize: " << getNotificationQueueSize() <<
384 " nothingHandledYet(): "<< nothingHandledYet();
386 // see if our average loop time has exceeded our limit
387 if ((maxLatency_ > 0) &&
388 (maxLatencyLoopTime_.get() > double(maxLatency_))) {
390 // back off temporarily -- don't keep spamming maxLatencyCob_
391 // if we're only a bit over the limit
392 maxLatencyLoopTime_.dampen(0.9);
395 // Our loop run did real work; reset the idle timer
396 idleStart = std::chrono::duration_cast<std::chrono::microseconds>(
397 std::chrono::steady_clock::now().time_since_epoch()).count();
399 VLOG(11) << "EventBase " << this << " did not timeout";
402 // If the event loop indicate that there were no more events, and
403 // we also didn't have any loop callbacks to run, there is nothing left to
405 if (res != 0 && !ranLoopCallbacks) {
406 // Since Notification Queue is marked 'internal' some events may not have
407 // run. Run them manually if so, and continue looping.
409 if (getNotificationQueueSize() > 0) {
410 fnRunner_->handlerReady(0);
416 if (enableTimeMeasurement_) {
417 VLOG(5) << "EventBase " << this << " loop time: " <<
418 getTimeDelta(&prev).count();
425 // Reset stop_ so loop() can be called again
429 LOG(ERROR) << "EventBase: -- error in event loop, res = " << res;
431 } else if (res == 1) {
432 VLOG(5) << "EventBase: ran out of events (exiting loop)!";
433 } else if (res > 1) {
434 LOG(ERROR) << "EventBase: unknown event loop result = " << res;
438 loopThread_.store({}, std::memory_order_release);
440 VLOG(5) << "EventBase(): Done with loop.";
444 void EventBase::applyLoopKeepAlive() {
445 if (loopKeepAliveActive_ && loopKeepAliveCount_ == 0) {
446 // Restore the notification queue internal flag
447 fnRunner_->stopConsuming();
448 fnRunner_->startConsumingInternal(this, queue_.get());
449 loopKeepAliveActive_ = false;
450 } else if (!loopKeepAliveActive_ && loopKeepAliveCount_ > 0) {
451 // Update the notification queue event to treat it as a normal
452 // (non-internal) event. The notification queue event always remains
453 // installed, and the main loop won't exit with it installed.
454 fnRunner_->stopConsuming();
455 fnRunner_->startConsuming(this, queue_.get());
456 loopKeepAliveActive_ = true;
460 void EventBase::loopForever() {
464 applyLoopKeepAlive();
466 // Make sure notification queue events are treated as normal events.
467 auto keepAlive = loopKeepAlive();
472 folly::throwSystemError("error in EventBase::loopForever()");
476 void EventBase::bumpHandlingTime() {
477 if (!enableTimeMeasurement_) {
481 VLOG(11) << "EventBase " << this << " " << __PRETTY_FUNCTION__ <<
482 " (loop) latest " << latestLoopCnt_ << " next " << nextLoopCnt_;
483 if (nothingHandledYet()) {
484 latestLoopCnt_ = nextLoopCnt_;
486 startWork_ = std::chrono::duration_cast<std::chrono::microseconds>(
487 std::chrono::steady_clock::now().time_since_epoch())
490 VLOG(11) << "EventBase " << this << " " << __PRETTY_FUNCTION__
491 << " (loop) startWork_ " << startWork_;
495 void EventBase::terminateLoopSoon() {
496 VLOG(5) << "EventBase(): Received terminateLoopSoon() command.";
498 // Set stop to true, so the event loop will know to exit.
499 // TODO: We should really use an atomic operation here with a release
503 // Call event_base_loopbreak() so that libevent will exit the next time
505 event_base_loopbreak(evb_);
507 // If terminateLoopSoon() is called from another thread,
508 // the EventBase thread might be stuck waiting for events.
509 // In this case, it won't wake up and notice that stop_ is set until it
510 // receives another event. Send an empty frame to the notification queue
511 // so that the event loop will wake up even if there are no other events.
513 // We don't care about the return value of trySendFrame(). If it fails
514 // this likely means the EventBase already has lots of events waiting
517 queue_->putMessage(nullptr);
519 // We don't care if putMessage() fails. This likely means
520 // the EventBase already has lots of events waiting anyway.
524 void EventBase::runInLoop(LoopCallback* callback, bool thisIteration) {
525 DCHECK(isInEventBaseThread());
526 callback->cancelLoopCallback();
527 callback->context_ = RequestContext::saveContext();
528 if (runOnceCallbacks_ != nullptr && thisIteration) {
529 runOnceCallbacks_->push_back(*callback);
531 loopCallbacks_.push_back(*callback);
535 void EventBase::runInLoop(Func cob, bool thisIteration) {
536 DCHECK(isInEventBaseThread());
537 auto wrapper = new FunctionLoopCallback(std::move(cob));
538 wrapper->context_ = RequestContext::saveContext();
539 if (runOnceCallbacks_ != nullptr && thisIteration) {
540 runOnceCallbacks_->push_back(*wrapper);
542 loopCallbacks_.push_back(*wrapper);
546 void EventBase::runOnDestruction(LoopCallback* callback) {
547 std::lock_guard<std::mutex> lg(onDestructionCallbacksMutex_);
548 callback->cancelLoopCallback();
549 onDestructionCallbacks_.push_back(*callback);
552 void EventBase::runBeforeLoop(LoopCallback* callback) {
553 DCHECK(isInEventBaseThread());
554 callback->cancelLoopCallback();
555 runBeforeLoopCallbacks_.push_back(*callback);
558 bool EventBase::runInEventBaseThread(Func fn) {
560 // It will be received by the FunctionRunner in the EventBase's thread.
562 // We try not to schedule nullptr callbacks
564 LOG(ERROR) << "EventBase " << this
565 << ": Scheduling nullptr callbacks is not allowed";
569 // Short-circuit if we are already in our event base
570 if (inRunningEventBaseThread()) {
571 runInLoop(std::move(fn));
577 queue_->putMessage(std::move(fn));
578 } catch (const std::exception& ex) {
579 LOG(ERROR) << "EventBase " << this << ": failed to schedule function "
580 << "for EventBase thread: " << ex.what();
587 bool EventBase::runInEventBaseThreadAndWait(Func fn) {
588 if (inRunningEventBaseThread()) {
589 LOG(ERROR) << "EventBase " << this << ": Waiting in the event loop is not "
596 std::condition_variable cv;
597 runInEventBaseThread([&] {
599 std::unique_lock<std::mutex> l(m);
602 // We cannot release the lock before notify_one, because a spurious
603 // wakeup in the waiting thread may lead to cv and m going out of scope
608 std::unique_lock<std::mutex> l(m);
609 cv.wait(l, [&] { return ready; });
614 bool EventBase::runImmediatelyOrRunInEventBaseThreadAndWait(Func fn) {
615 if (isInEventBaseThread()) {
619 return runInEventBaseThreadAndWait(std::move(fn));
623 void EventBase::runAfterDelay(
625 uint32_t milliseconds,
626 TimeoutManager::InternalEnum in) {
627 if (!tryRunAfterDelay(std::move(cob), milliseconds, in)) {
628 folly::throwSystemError(
629 "error in EventBase::runAfterDelay(), failed to schedule timeout");
633 bool EventBase::tryRunAfterDelay(
635 uint32_t milliseconds,
636 TimeoutManager::InternalEnum in) {
637 CobTimeout* timeout = new CobTimeout(this, std::move(cob), in);
638 if (!timeout->scheduleTimeout(milliseconds)) {
642 pendingCobTimeouts_.push_back(*timeout);
646 bool EventBase::runLoopCallbacks() {
647 if (!loopCallbacks_.empty()) {
649 // Swap the loopCallbacks_ list with a temporary list on our stack.
650 // This way we will only run callbacks scheduled at the time
651 // runLoopCallbacks() was invoked.
653 // If any of these callbacks in turn call runInLoop() to schedule more
654 // callbacks, those new callbacks won't be run until the next iteration
655 // around the event loop. This prevents runInLoop() callbacks from being
656 // able to start file descriptor and timeout based events.
657 LoopCallbackList currentCallbacks;
658 currentCallbacks.swap(loopCallbacks_);
659 runOnceCallbacks_ = ¤tCallbacks;
661 while (!currentCallbacks.empty()) {
662 LoopCallback* callback = ¤tCallbacks.front();
663 currentCallbacks.pop_front();
664 folly::RequestContextScopeGuard rctx(callback->context_);
665 callback->runLoopCallback();
668 runOnceCallbacks_ = nullptr;
674 void EventBase::initNotificationQueue() {
675 // Infinite size queue
676 queue_.reset(new NotificationQueue<Func>());
678 // We allocate fnRunner_ separately, rather than declaring it directly
679 // as a member of EventBase solely so that we don't need to include
680 // NotificationQueue.h from EventBase.h
681 fnRunner_.reset(new FunctionRunner());
683 // Mark this as an internal event, so event_base_loop() will return if
684 // there are no other events besides this one installed.
686 // Most callers don't care about the internal notification queue used by
687 // EventBase. The queue is always installed, so if we did count the queue as
688 // an active event, loop() would never exit with no more events to process.
689 // Users can use loopForever() if they do care about the notification queue.
690 // (This is useful for EventBase threads that do nothing but process
691 // runInEventBaseThread() notifications.)
692 fnRunner_->startConsumingInternal(this, queue_.get());
695 void EventBase::SmoothLoopTime::setTimeInterval(uint64_t timeInterval) {
696 expCoeff_ = -1.0/timeInterval;
697 VLOG(11) << "expCoeff_ " << expCoeff_ << " " << __PRETTY_FUNCTION__;
700 void EventBase::SmoothLoopTime::reset(double value) {
704 void EventBase::SmoothLoopTime::addSample(int64_t idle, int64_t busy) {
706 * Position at which the busy sample is considered to be taken.
707 * (Allows to quickly skew our average without editing much code)
709 enum BusySamplePosition {
710 RIGHT = 0, // busy sample placed at the end of the iteration
711 CENTER = 1, // busy sample placed at the middle point of the iteration
712 LEFT = 2, // busy sample placed at the beginning of the iteration
715 // See http://en.wikipedia.org/wiki/Moving_average#Exponential_moving_average
716 // and D676020 for more info on this calculation.
717 VLOG(11) << "idle " << idle << " oldBusyLeftover_ " << oldBusyLeftover_ <<
718 " idle + oldBusyLeftover_ " << idle + oldBusyLeftover_ <<
719 " busy " << busy << " " << __PRETTY_FUNCTION__;
720 idle += oldBusyLeftover_ + busy;
721 oldBusyLeftover_ = (busy * BusySamplePosition::CENTER) / 2;
722 idle -= oldBusyLeftover_;
724 double coeff = exp(idle * expCoeff_);
726 value_ += (1.0 - coeff) * busy;
729 bool EventBase::nothingHandledYet() const noexcept {
730 VLOG(11) << "latest " << latestLoopCnt_ << " next " << nextLoopCnt_;
731 return (nextLoopCnt_ != latestLoopCnt_);
734 void EventBase::attachTimeoutManager(AsyncTimeout* obj,
735 InternalEnum internal) {
737 struct event* ev = obj->getEvent();
738 assert(ev->ev_base == nullptr);
740 event_base_set(getLibeventBase(), ev);
741 if (internal == AsyncTimeout::InternalEnum::INTERNAL) {
742 // Set the EVLIST_INTERNAL flag
743 event_ref_flags(ev) |= EVLIST_INTERNAL;
747 void EventBase::detachTimeoutManager(AsyncTimeout* obj) {
749 struct event* ev = obj->getEvent();
750 ev->ev_base = nullptr;
753 bool EventBase::scheduleTimeout(AsyncTimeout* obj,
754 TimeoutManager::timeout_type timeout) {
755 assert(isInEventBaseThread());
756 // Set up the timeval and add the event
758 tv.tv_sec = timeout.count() / 1000LL;
759 tv.tv_usec = (timeout.count() % 1000LL) * 1000LL;
761 struct event* ev = obj->getEvent();
762 if (event_add(ev, &tv) < 0) {
763 LOG(ERROR) << "EventBase: failed to schedule timeout: " << strerror(errno);
770 void EventBase::cancelTimeout(AsyncTimeout* obj) {
771 assert(isInEventBaseThread());
772 struct event* ev = obj->getEvent();
773 if (EventUtil::isEventRegistered(ev)) {
778 void EventBase::setName(const std::string& name) {
779 assert(isInEventBaseThread());
783 setThreadName(loopThread_.load(std::memory_order_relaxed),
788 const std::string& EventBase::getName() {
789 assert(isInEventBaseThread());
793 const char* EventBase::getLibeventVersion() { return event_get_version(); }
794 const char* EventBase::getLibeventMethod() { return event_get_method(); }