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>
26 #include <boost/static_assert.hpp>
27 #include <condition_variable>
36 using folly::EventBase;
38 template <typename Callback>
39 class FunctionLoopCallback : public EventBase::LoopCallback {
41 explicit FunctionLoopCallback(Cob&& function)
42 : function_(std::move(function)) {}
44 explicit FunctionLoopCallback(const Cob& function) : function_(function) {}
46 void runLoopCallback() noexcept override {
59 * EventBase::FunctionRunner
62 class EventBase::FunctionRunner : public NotificationQueue<Cob>::Consumer {
64 void messageAvailable(Cob&& msg) override {
66 // In libevent2, internal events do not break the loop.
67 // Most users would expect loop(), followed by runInEventBaseThread(),
68 // to break the loop and check if it should exit or not.
69 // To have similar bejaviour to libevent1.4, tell the loop to break here.
70 // Note that loop() may still continue to loop, but it will also check the
71 // stop_ flag as well as runInLoop callbacks, etc.
72 event_base_loopbreak(getEventBase()->evb_);
75 // terminateLoopSoon() sends a null message just to
76 // wake up the loop. We can ignore these messages.
80 // The function should never throw an exception, because we have no
81 // way of knowing what sort of error handling to perform.
83 // If it does throw, log a message and abort the program.
86 } catch (const std::exception& ex) {
87 LOG(ERROR) << "runInEventBaseThread() function threw a "
88 << typeid(ex).name() << " exception: " << ex.what();
91 LOG(ERROR) << "runInEventBaseThread() function threw an exception";
98 * EventBase::CobTimeout methods
101 void EventBase::CobTimeout::timeoutExpired() noexcept {
102 // For now, we just swallow any exceptions that the callback threw.
105 } catch (const std::exception& ex) {
106 LOG(ERROR) << "EventBase::runAfterDelay() callback threw "
107 << typeid(ex).name() << " exception: " << ex.what();
109 LOG(ERROR) << "EventBase::runAfterDelay() callback threw non-exception "
113 // The CobTimeout object was allocated on the heap by runAfterDelay(),
114 // so delete it now that the it has fired.
119 // The interface used to libevent is not thread-safe. Calls to
120 // event_init() and event_base_free() directly modify an internal
121 // global 'current_base', so a mutex is required to protect this.
123 // event_init() should only ever be called once. Subsequent calls
124 // should be made to event_base_new(). We can recognise that
125 // event_init() has already been called by simply inspecting current_base.
126 static std::mutex libevent_mutex_;
132 EventBase::EventBase(bool enableTimeMeasurement)
133 : runOnceCallbacks_(nullptr)
139 , avgLoopTime_(2000000)
140 , maxLatencyLoopTime_(avgLoopTime_)
141 , enableTimeMeasurement_(enableTimeMeasurement)
142 , nextLoopCnt_(-40) // Early wrap-around so bugs will manifest soon
143 , latestLoopCnt_(nextLoopCnt_)
146 , observerSampleCount_(0)
147 , executionObserver_(nullptr) {
150 std::lock_guard<std::mutex> lock(libevent_mutex_);
152 // The value 'current_base' (libevent 1) or
153 // 'event_global_current_base_' (libevent 2) is filled in by event_set(),
154 // allowing examination of its value without an explicit reference here.
155 // If ev.ev_base is NULL, then event_init() must be called, otherwise
156 // call event_base_new().
157 event_set(&ev, 0, 0, nullptr, nullptr);
164 evb_ = event_base_new();
167 if (UNLIKELY(evb_ == nullptr)) {
168 LOG(ERROR) << "EventBase(): Failed to init event base.";
169 folly::throwSystemError("error in EventBase::EventBase()");
171 VLOG(5) << "EventBase(): Created.";
172 initNotificationQueue();
173 RequestContext::saveContext();
176 // takes ownership of the event_base
177 EventBase::EventBase(event_base* evb, bool enableTimeMeasurement)
178 : runOnceCallbacks_(nullptr)
185 , avgLoopTime_(2000000)
186 , maxLatencyLoopTime_(avgLoopTime_)
187 , enableTimeMeasurement_(enableTimeMeasurement)
188 , nextLoopCnt_(-40) // Early wrap-around so bugs will manifest soon
189 , latestLoopCnt_(nextLoopCnt_)
192 , observerSampleCount_(0)
193 , executionObserver_(nullptr) {
194 if (UNLIKELY(evb_ == nullptr)) {
195 LOG(ERROR) << "EventBase(): Pass nullptr as event base.";
196 throw std::invalid_argument("EventBase(): event base cannot be nullptr");
198 initNotificationQueue();
199 RequestContext::saveContext();
202 EventBase::~EventBase() {
203 // Call all destruction callbacks, before we start cleaning up our state.
204 while (!onDestructionCallbacks_.empty()) {
205 LoopCallback* callback = &onDestructionCallbacks_.front();
206 onDestructionCallbacks_.pop_front();
207 callback->runLoopCallback();
210 // Delete any unfired callback objects, so that we don't leak memory
211 // (Note that we don't fire them. The caller is responsible for cleaning up
212 // its own data structures if it destroys the EventBase with unfired events
214 while (!pendingCobTimeouts_.empty()) {
215 CobTimeout* timeout = &pendingCobTimeouts_.front();
219 while (!runBeforeLoopCallbacks_.empty()) {
220 delete &runBeforeLoopCallbacks_.front();
223 (void) runLoopCallbacks(false);
225 if (!fnRunner_->consumeUntilDrained()) {
226 LOG(ERROR) << "~EventBase(): Unable to drain notification queue";
229 // Stop consumer before deleting NotificationQueue
230 fnRunner_->stopConsuming();
232 std::lock_guard<std::mutex> lock(libevent_mutex_);
233 event_base_free(evb_);
236 while (!runAfterDrainCallbacks_.empty()) {
237 LoopCallback* callback = &runAfterDrainCallbacks_.front();
238 runAfterDrainCallbacks_.pop_front();
239 callback->runLoopCallback();
243 std::lock_guard<std::mutex> lock(localStorageMutex_);
244 for (auto storage : localStorageToDtor_) {
245 storage->onEventBaseDestruction(*this);
248 VLOG(5) << "EventBase(): Destroyed.";
251 int EventBase::getNotificationQueueSize() const {
252 return queue_->size();
255 void EventBase::setMaxReadAtOnce(uint32_t maxAtOnce) {
256 fnRunner_->setMaxReadAtOnce(maxAtOnce);
259 // Set smoothing coefficient for loop load average; input is # of milliseconds
260 // for exp(-1) decay.
261 void EventBase::setLoadAvgMsec(uint32_t ms) {
262 assert(enableTimeMeasurement_);
263 uint64_t us = 1000 * ms;
265 maxLatencyLoopTime_.setTimeInterval(us);
266 avgLoopTime_.setTimeInterval(us);
268 LOG(ERROR) << "non-positive arg to setLoadAvgMsec()";
272 void EventBase::resetLoadAvg(double value) {
273 assert(enableTimeMeasurement_);
274 avgLoopTime_.reset(value);
275 maxLatencyLoopTime_.reset(value);
278 static std::chrono::milliseconds
279 getTimeDelta(std::chrono::steady_clock::time_point* prev) {
280 auto result = std::chrono::steady_clock::now() - *prev;
281 *prev = std::chrono::steady_clock::now();
283 return std::chrono::duration_cast<std::chrono::milliseconds>(result);
286 void EventBase::waitUntilRunning() {
287 while (!isRunning()) {
292 // enters the event_base loop -- will only exit when forced to
293 bool EventBase::loop() {
297 bool EventBase::loopOnce(int flags) {
298 return loopBody(flags | EVLOOP_ONCE);
301 bool EventBase::loopBody(int flags) {
302 VLOG(5) << "EventBase(): Starting loop.";
304 bool ranLoopCallbacks;
305 bool blocking = !(flags & EVLOOP_NONBLOCK);
306 bool once = (flags & EVLOOP_ONCE);
308 // time-measurement variables.
309 std::chrono::steady_clock::time_point prev;
310 int64_t idleStart = 0;
314 loopThread_.store(pthread_self(), std::memory_order_release);
316 if (!name_.empty()) {
317 setThreadName(name_);
320 if (enableTimeMeasurement_) {
321 prev = std::chrono::steady_clock::now();
322 idleStart = std::chrono::duration_cast<std::chrono::microseconds>(
323 std::chrono::steady_clock::now().time_since_epoch()).count();
326 while (!stop_.load(std::memory_order_acquire)) {
329 // Run the before loop callbacks
330 LoopCallbackList callbacks;
331 callbacks.swap(runBeforeLoopCallbacks_);
333 while(!callbacks.empty()) {
334 auto* item = &callbacks.front();
335 callbacks.pop_front();
336 item->runLoopCallback();
339 // nobody can add loop callbacks from within this thread if
340 // we don't have to handle anything to start with...
341 if (blocking && loopCallbacks_.empty()) {
342 res = event_base_loop(evb_, EVLOOP_ONCE);
344 res = event_base_loop(evb_, EVLOOP_ONCE | EVLOOP_NONBLOCK);
347 ranLoopCallbacks = runLoopCallbacks();
349 if (enableTimeMeasurement_) {
350 busy = std::chrono::duration_cast<std::chrono::microseconds>(
351 std::chrono::steady_clock::now().time_since_epoch()).count() -
353 idle = startWork_ - idleStart;
355 avgLoopTime_.addSample(idle, busy);
356 maxLatencyLoopTime_.addSample(idle, busy);
359 if (observerSampleCount_++ == observer_->getSampleRate()) {
360 observerSampleCount_ = 0;
361 observer_->loopSample(busy, idle);
365 VLOG(11) << "EventBase " << this << " did not timeout "
366 " loop time guess: " << busy + idle <<
367 " idle time: " << idle <<
368 " busy time: " << busy <<
369 " avgLoopTime: " << avgLoopTime_.get() <<
370 " maxLatencyLoopTime: " << maxLatencyLoopTime_.get() <<
371 " maxLatency_: " << maxLatency_ <<
372 " notificationQueueSize: " << getNotificationQueueSize() <<
373 " nothingHandledYet(): "<< nothingHandledYet();
375 // see if our average loop time has exceeded our limit
376 if ((maxLatency_ > 0) &&
377 (maxLatencyLoopTime_.get() > double(maxLatency_))) {
379 // back off temporarily -- don't keep spamming maxLatencyCob_
380 // if we're only a bit over the limit
381 maxLatencyLoopTime_.dampen(0.9);
384 // Our loop run did real work; reset the idle timer
385 idleStart = std::chrono::duration_cast<std::chrono::microseconds>(
386 std::chrono::steady_clock::now().time_since_epoch()).count();
388 VLOG(11) << "EventBase " << this << " did not timeout "
389 " time measurement is disabled "
390 " nothingHandledYet(): "<< nothingHandledYet();
393 // If the event loop indicate that there were no more events, and
394 // we also didn't have any loop callbacks to run, there is nothing left to
396 if (res != 0 && !ranLoopCallbacks) {
397 // Since Notification Queue is marked 'internal' some events may not have
398 // run. Run them manually if so, and continue looping.
400 if (getNotificationQueueSize() > 0) {
401 fnRunner_->handlerReady(0);
407 if (enableTimeMeasurement_) {
408 VLOG(5) << "EventBase " << this << " loop time: " <<
409 getTimeDelta(&prev).count();
416 // Reset stop_ so loop() can be called again
420 LOG(ERROR) << "EventBase: -- error in event loop, res = " << res;
422 } else if (res == 1) {
423 VLOG(5) << "EventBase: ran out of events (exiting loop)!";
424 } else if (res > 1) {
425 LOG(ERROR) << "EventBase: unknown event loop result = " << res;
429 loopThread_.store(0, std::memory_order_release);
431 VLOG(5) << "EventBase(): Done with loop.";
435 void EventBase::loopForever() {
436 // Update the notification queue event to treat it as a normal (non-internal)
437 // event. The notification queue event always remains installed, and the main
438 // loop won't exit with it installed.
439 fnRunner_->stopConsuming();
440 fnRunner_->startConsuming(this, queue_.get());
444 // Restore the notification queue internal flag
445 fnRunner_->stopConsuming();
446 fnRunner_->startConsumingInternal(this, queue_.get());
449 folly::throwSystemError("error in EventBase::loopForever()");
453 bool EventBase::bumpHandlingTime() {
454 VLOG(11) << "EventBase " << this << " " << __PRETTY_FUNCTION__ <<
455 " (loop) latest " << latestLoopCnt_ << " next " << nextLoopCnt_;
456 if(nothingHandledYet()) {
457 latestLoopCnt_ = nextLoopCnt_;
458 if (enableTimeMeasurement_) {
460 startWork_ = std::chrono::duration_cast<std::chrono::microseconds>(
461 std::chrono::steady_clock::now().time_since_epoch()).count();
463 VLOG(11) << "EventBase " << this << " " << __PRETTY_FUNCTION__ <<
464 " (loop) startWork_ " << startWork_;
471 void EventBase::terminateLoopSoon() {
472 VLOG(5) << "EventBase(): Received terminateLoopSoon() command.";
474 // Set stop to true, so the event loop will know to exit.
475 // TODO: We should really use an atomic operation here with a release
479 // Call event_base_loopbreak() so that libevent will exit the next time
481 event_base_loopbreak(evb_);
483 // If terminateLoopSoon() is called from another thread,
484 // the EventBase thread might be stuck waiting for events.
485 // In this case, it won't wake up and notice that stop_ is set until it
486 // receives another event. Send an empty frame to the notification queue
487 // so that the event loop will wake up even if there are no other events.
489 // We don't care about the return value of trySendFrame(). If it fails
490 // this likely means the EventBase already has lots of events waiting
493 queue_->putMessage(nullptr);
495 // We don't care if putMessage() fails. This likely means
496 // the EventBase already has lots of events waiting anyway.
500 void EventBase::runInLoop(LoopCallback* callback, bool thisIteration) {
501 DCHECK(isInEventBaseThread());
502 callback->cancelLoopCallback();
503 callback->context_ = RequestContext::saveContext();
504 if (runOnceCallbacks_ != nullptr && thisIteration) {
505 runOnceCallbacks_->push_back(*callback);
507 loopCallbacks_.push_back(*callback);
511 void EventBase::runInLoop(const Cob& cob, bool thisIteration) {
512 DCHECK(isInEventBaseThread());
513 auto wrapper = new FunctionLoopCallback<Cob>(cob);
514 wrapper->context_ = RequestContext::saveContext();
515 if (runOnceCallbacks_ != nullptr && thisIteration) {
516 runOnceCallbacks_->push_back(*wrapper);
518 loopCallbacks_.push_back(*wrapper);
522 void EventBase::runInLoop(Cob&& cob, bool thisIteration) {
523 DCHECK(isInEventBaseThread());
524 auto wrapper = new FunctionLoopCallback<Cob>(std::move(cob));
525 wrapper->context_ = RequestContext::saveContext();
526 if (runOnceCallbacks_ != nullptr && thisIteration) {
527 runOnceCallbacks_->push_back(*wrapper);
529 loopCallbacks_.push_back(*wrapper);
533 void EventBase::runAfterDrain(Cob&& cob) {
534 auto callback = new FunctionLoopCallback<Cob>(std::move(cob));
535 std::lock_guard<std::mutex> lg(runAfterDrainCallbacksMutex_);
536 callback->cancelLoopCallback();
537 runAfterDrainCallbacks_.push_back(*callback);
540 void EventBase::runOnDestruction(LoopCallback* callback) {
541 std::lock_guard<std::mutex> lg(onDestructionCallbacksMutex_);
542 callback->cancelLoopCallback();
543 onDestructionCallbacks_.push_back(*callback);
546 void EventBase::runBeforeLoop(LoopCallback* callback) {
547 DCHECK(isInEventBaseThread());
548 callback->cancelLoopCallback();
549 runBeforeLoopCallbacks_.push_back(*callback);
552 bool EventBase::runInEventBaseThread(const Cob& fn) {
554 // It will be received by the FunctionRunner in the EventBase's thread.
556 // We try not to schedule nullptr callbacks
558 LOG(ERROR) << "EventBase " << this
559 << ": Scheduling nullptr callbacks is not allowed";
563 // Short-circuit if we are already in our event base
564 if (inRunningEventBaseThread()) {
571 queue_->putMessage(fn);
572 } catch (const std::exception& ex) {
573 LOG(ERROR) << "EventBase " << this << ": failed to schedule function "
574 << "for EventBase thread: " << ex.what();
581 bool EventBase::runInEventBaseThreadAndWait(const Cob& fn) {
582 if (inRunningEventBaseThread()) {
583 LOG(ERROR) << "EventBase " << this << ": Waiting in the event loop is not "
590 std::condition_variable cv;
591 runInEventBaseThread([&] {
593 std::unique_lock<std::mutex> l(m);
596 // We cannot release the lock before notify_one, because a spurious
597 // wakeup in the waiting thread may lead to cv and m going out of scope
602 std::unique_lock<std::mutex> l(m);
603 cv.wait(l, [&] { return ready; });
608 bool EventBase::runImmediatelyOrRunInEventBaseThreadAndWait(const Cob& fn) {
609 if (isInEventBaseThread()) {
613 return runInEventBaseThreadAndWait(fn);
617 void EventBase::runAfterDelay(const Cob& cob,
618 uint32_t milliseconds,
619 TimeoutManager::InternalEnum in) {
620 if (!tryRunAfterDelay(cob, milliseconds, in)) {
621 folly::throwSystemError(
622 "error in EventBase::runAfterDelay(), failed to schedule timeout");
626 bool EventBase::tryRunAfterDelay(const Cob& cob,
627 uint32_t milliseconds,
628 TimeoutManager::InternalEnum in) {
629 CobTimeout* timeout = new CobTimeout(this, cob, in);
630 if (!timeout->scheduleTimeout(milliseconds)) {
634 pendingCobTimeouts_.push_back(*timeout);
638 bool EventBase::runLoopCallbacks(bool setContext) {
639 if (!loopCallbacks_.empty()) {
641 // Swap the loopCallbacks_ list with a temporary list on our stack.
642 // This way we will only run callbacks scheduled at the time
643 // runLoopCallbacks() was invoked.
645 // If any of these callbacks in turn call runInLoop() to schedule more
646 // callbacks, those new callbacks won't be run until the next iteration
647 // around the event loop. This prevents runInLoop() callbacks from being
648 // able to start file descriptor and timeout based events.
649 LoopCallbackList currentCallbacks;
650 currentCallbacks.swap(loopCallbacks_);
651 runOnceCallbacks_ = ¤tCallbacks;
653 while (!currentCallbacks.empty()) {
654 LoopCallback* callback = ¤tCallbacks.front();
655 currentCallbacks.pop_front();
657 RequestContext::setContext(callback->context_);
659 callback->runLoopCallback();
662 runOnceCallbacks_ = nullptr;
668 void EventBase::initNotificationQueue() {
669 // Infinite size queue
670 queue_.reset(new NotificationQueue<Cob>());
672 // We allocate fnRunner_ separately, rather than declaring it directly
673 // as a member of EventBase solely so that we don't need to include
674 // NotificationQueue.h from EventBase.h
675 fnRunner_.reset(new FunctionRunner());
677 // Mark this as an internal event, so event_base_loop() will return if
678 // there are no other events besides this one installed.
680 // Most callers don't care about the internal notification queue used by
681 // EventBase. The queue is always installed, so if we did count the queue as
682 // an active event, loop() would never exit with no more events to process.
683 // Users can use loopForever() if they do care about the notification queue.
684 // (This is useful for EventBase threads that do nothing but process
685 // runInEventBaseThread() notifications.)
686 fnRunner_->startConsumingInternal(this, queue_.get());
689 void EventBase::SmoothLoopTime::setTimeInterval(uint64_t timeInterval) {
690 expCoeff_ = -1.0/timeInterval;
691 VLOG(11) << "expCoeff_ " << expCoeff_ << " " << __PRETTY_FUNCTION__;
694 void EventBase::SmoothLoopTime::reset(double value) {
698 void EventBase::SmoothLoopTime::addSample(int64_t idle, int64_t busy) {
700 * Position at which the busy sample is considered to be taken.
701 * (Allows to quickly skew our average without editing much code)
703 enum BusySamplePosition {
704 RIGHT = 0, // busy sample placed at the end of the iteration
705 CENTER = 1, // busy sample placed at the middle point of the iteration
706 LEFT = 2, // busy sample placed at the beginning of the iteration
709 // See http://en.wikipedia.org/wiki/Moving_average#Exponential_moving_average
710 // and D676020 for more info on this calculation.
711 VLOG(11) << "idle " << idle << " oldBusyLeftover_ " << oldBusyLeftover_ <<
712 " idle + oldBusyLeftover_ " << idle + oldBusyLeftover_ <<
713 " busy " << busy << " " << __PRETTY_FUNCTION__;
714 idle += oldBusyLeftover_ + busy;
715 oldBusyLeftover_ = (busy * BusySamplePosition::CENTER) / 2;
716 idle -= oldBusyLeftover_;
718 double coeff = exp(idle * expCoeff_);
720 value_ += (1.0 - coeff) * busy;
723 bool EventBase::nothingHandledYet() {
724 VLOG(11) << "latest " << latestLoopCnt_ << " next " << nextLoopCnt_;
725 return (nextLoopCnt_ != latestLoopCnt_);
729 void EventBase::runFunctionPtr(Cob* fn) {
730 // The function should never throw an exception, because we have no
731 // way of knowing what sort of error handling to perform.
733 // If it does throw, log a message and abort the program.
736 } catch (const std::exception &ex) {
737 LOG(ERROR) << "runInEventBaseThread() std::function threw a "
738 << typeid(ex).name() << " exception: " << ex.what();
741 LOG(ERROR) << "runInEventBaseThread() std::function threw an exception";
745 // The function object was allocated by runInEventBaseThread().
746 // Delete it once it has been run.
750 void EventBase::attachTimeoutManager(AsyncTimeout* obj,
751 InternalEnum internal) {
753 struct event* ev = obj->getEvent();
754 assert(ev->ev_base == nullptr);
756 event_base_set(getLibeventBase(), ev);
757 if (internal == AsyncTimeout::InternalEnum::INTERNAL) {
758 // Set the EVLIST_INTERNAL flag
759 event_ref_flags(ev) |= EVLIST_INTERNAL;
763 void EventBase::detachTimeoutManager(AsyncTimeout* obj) {
765 struct event* ev = obj->getEvent();
766 ev->ev_base = nullptr;
769 bool EventBase::scheduleTimeout(AsyncTimeout* obj,
770 TimeoutManager::timeout_type timeout) {
771 assert(isInEventBaseThread());
772 // Set up the timeval and add the event
774 tv.tv_sec = timeout.count() / 1000LL;
775 tv.tv_usec = (timeout.count() % 1000LL) * 1000LL;
777 struct event* ev = obj->getEvent();
778 if (event_add(ev, &tv) < 0) {
779 LOG(ERROR) << "EventBase: failed to schedule timeout: " << strerror(errno);
786 void EventBase::cancelTimeout(AsyncTimeout* obj) {
787 assert(isInEventBaseThread());
788 struct event* ev = obj->getEvent();
789 if (EventUtil::isEventRegistered(ev)) {
794 void EventBase::setName(const std::string& name) {
795 assert(isInEventBaseThread());
799 setThreadName(loopThread_.load(std::memory_order_relaxed),
804 const std::string& EventBase::getName() {
805 assert(isInEventBaseThread());
809 const char* EventBase::getLibeventVersion() { return event_get_version(); }
810 const char* EventBase::getLibeventMethod() { return event_get_method(); }