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) {
149 std::lock_guard<std::mutex> lock(libevent_mutex_);
151 // The value 'current_base' (libevent 1) or
152 // 'event_global_current_base_' (libevent 2) is filled in by event_set(),
153 // allowing examination of its value without an explicit reference here.
154 // If ev.ev_base is NULL, then event_init() must be called, otherwise
155 // call event_base_new().
157 event_set(&ev, 0, 0, nullptr, nullptr);
158 evb_ = (ev.ev_base) ? event_base_new() : event_init();
160 if (UNLIKELY(evb_ == nullptr)) {
161 LOG(ERROR) << "EventBase(): Failed to init event base.";
162 folly::throwSystemError("error in EventBase::EventBase()");
164 VLOG(5) << "EventBase(): Created.";
165 initNotificationQueue();
166 RequestContext::saveContext();
169 // takes ownership of the event_base
170 EventBase::EventBase(event_base* evb, bool enableTimeMeasurement)
171 : runOnceCallbacks_(nullptr)
178 , avgLoopTime_(2000000)
179 , maxLatencyLoopTime_(avgLoopTime_)
180 , enableTimeMeasurement_(enableTimeMeasurement)
181 , nextLoopCnt_(-40) // Early wrap-around so bugs will manifest soon
182 , latestLoopCnt_(nextLoopCnt_)
185 , observerSampleCount_(0)
186 , executionObserver_(nullptr) {
187 if (UNLIKELY(evb_ == nullptr)) {
188 LOG(ERROR) << "EventBase(): Pass nullptr as event base.";
189 throw std::invalid_argument("EventBase(): event base cannot be nullptr");
191 initNotificationQueue();
192 RequestContext::saveContext();
195 EventBase::~EventBase() {
196 // Call all destruction callbacks, before we start cleaning up our state.
197 while (!onDestructionCallbacks_.empty()) {
198 LoopCallback* callback = &onDestructionCallbacks_.front();
199 onDestructionCallbacks_.pop_front();
200 callback->runLoopCallback();
203 // Delete any unfired callback objects, so that we don't leak memory
204 // (Note that we don't fire them. The caller is responsible for cleaning up
205 // its own data structures if it destroys the EventBase with unfired events
207 while (!pendingCobTimeouts_.empty()) {
208 CobTimeout* timeout = &pendingCobTimeouts_.front();
212 while (!runBeforeLoopCallbacks_.empty()) {
213 delete &runBeforeLoopCallbacks_.front();
216 (void) runLoopCallbacks(false);
218 if (!fnRunner_->consumeUntilDrained()) {
219 LOG(ERROR) << "~EventBase(): Unable to drain notification queue";
222 // Stop consumer before deleting NotificationQueue
223 fnRunner_->stopConsuming();
225 std::lock_guard<std::mutex> lock(libevent_mutex_);
226 event_base_free(evb_);
229 while (!runAfterDrainCallbacks_.empty()) {
230 LoopCallback* callback = &runAfterDrainCallbacks_.front();
231 runAfterDrainCallbacks_.pop_front();
232 callback->runLoopCallback();
236 std::lock_guard<std::mutex> lock(localStorageMutex_);
237 for (auto storage : localStorageToDtor_) {
238 storage->onEventBaseDestruction(*this);
241 VLOG(5) << "EventBase(): Destroyed.";
244 int EventBase::getNotificationQueueSize() const {
245 return queue_->size();
248 void EventBase::setMaxReadAtOnce(uint32_t maxAtOnce) {
249 fnRunner_->setMaxReadAtOnce(maxAtOnce);
252 // Set smoothing coefficient for loop load average; input is # of milliseconds
253 // for exp(-1) decay.
254 void EventBase::setLoadAvgMsec(uint32_t ms) {
255 assert(enableTimeMeasurement_);
256 uint64_t us = 1000 * ms;
258 maxLatencyLoopTime_.setTimeInterval(us);
259 avgLoopTime_.setTimeInterval(us);
261 LOG(ERROR) << "non-positive arg to setLoadAvgMsec()";
265 void EventBase::resetLoadAvg(double value) {
266 assert(enableTimeMeasurement_);
267 avgLoopTime_.reset(value);
268 maxLatencyLoopTime_.reset(value);
271 static std::chrono::milliseconds
272 getTimeDelta(std::chrono::steady_clock::time_point* prev) {
273 auto result = std::chrono::steady_clock::now() - *prev;
274 *prev = std::chrono::steady_clock::now();
276 return std::chrono::duration_cast<std::chrono::milliseconds>(result);
279 void EventBase::waitUntilRunning() {
280 while (!isRunning()) {
285 // enters the event_base loop -- will only exit when forced to
286 bool EventBase::loop() {
290 bool EventBase::loopOnce(int flags) {
291 return loopBody(flags | EVLOOP_ONCE);
294 bool EventBase::loopBody(int flags) {
295 VLOG(5) << "EventBase(): Starting loop.";
297 bool ranLoopCallbacks;
298 bool blocking = !(flags & EVLOOP_NONBLOCK);
299 bool once = (flags & EVLOOP_ONCE);
301 // time-measurement variables.
302 std::chrono::steady_clock::time_point prev;
303 int64_t idleStart = 0;
307 loopThread_.store(pthread_self(), std::memory_order_release);
309 if (!name_.empty()) {
310 setThreadName(name_);
313 if (enableTimeMeasurement_) {
314 prev = std::chrono::steady_clock::now();
315 idleStart = std::chrono::duration_cast<std::chrono::microseconds>(
316 std::chrono::steady_clock::now().time_since_epoch()).count();
319 while (!stop_.load(std::memory_order_acquire)) {
322 // Run the before loop callbacks
323 LoopCallbackList callbacks;
324 callbacks.swap(runBeforeLoopCallbacks_);
326 while(!callbacks.empty()) {
327 auto* item = &callbacks.front();
328 callbacks.pop_front();
329 item->runLoopCallback();
332 // nobody can add loop callbacks from within this thread if
333 // we don't have to handle anything to start with...
334 if (blocking && loopCallbacks_.empty()) {
335 res = event_base_loop(evb_, EVLOOP_ONCE);
337 res = event_base_loop(evb_, EVLOOP_ONCE | EVLOOP_NONBLOCK);
340 ranLoopCallbacks = runLoopCallbacks();
342 if (enableTimeMeasurement_) {
343 busy = std::chrono::duration_cast<std::chrono::microseconds>(
344 std::chrono::steady_clock::now().time_since_epoch()).count() -
346 idle = startWork_ - idleStart;
348 avgLoopTime_.addSample(idle, busy);
349 maxLatencyLoopTime_.addSample(idle, busy);
352 if (observerSampleCount_++ == observer_->getSampleRate()) {
353 observerSampleCount_ = 0;
354 observer_->loopSample(busy, idle);
358 VLOG(11) << "EventBase " << this << " did not timeout "
359 " loop time guess: " << busy + idle <<
360 " idle time: " << idle <<
361 " busy time: " << busy <<
362 " avgLoopTime: " << avgLoopTime_.get() <<
363 " maxLatencyLoopTime: " << maxLatencyLoopTime_.get() <<
364 " maxLatency_: " << maxLatency_ <<
365 " notificationQueueSize: " << getNotificationQueueSize() <<
366 " nothingHandledYet(): "<< nothingHandledYet();
368 // see if our average loop time has exceeded our limit
369 if ((maxLatency_ > 0) &&
370 (maxLatencyLoopTime_.get() > double(maxLatency_))) {
372 // back off temporarily -- don't keep spamming maxLatencyCob_
373 // if we're only a bit over the limit
374 maxLatencyLoopTime_.dampen(0.9);
377 // Our loop run did real work; reset the idle timer
378 idleStart = std::chrono::duration_cast<std::chrono::microseconds>(
379 std::chrono::steady_clock::now().time_since_epoch()).count();
381 VLOG(11) << "EventBase " << this << " did not timeout "
382 " time measurement is disabled "
383 " nothingHandledYet(): "<< nothingHandledYet();
386 // If the event loop indicate that there were no more events, and
387 // we also didn't have any loop callbacks to run, there is nothing left to
389 if (res != 0 && !ranLoopCallbacks) {
390 // Since Notification Queue is marked 'internal' some events may not have
391 // run. Run them manually if so, and continue looping.
393 if (getNotificationQueueSize() > 0) {
394 fnRunner_->handlerReady(0);
400 if (enableTimeMeasurement_) {
401 VLOG(5) << "EventBase " << this << " loop time: " <<
402 getTimeDelta(&prev).count();
409 // Reset stop_ so loop() can be called again
413 LOG(ERROR) << "EventBase: -- error in event loop, res = " << res;
415 } else if (res == 1) {
416 VLOG(5) << "EventBase: ran out of events (exiting loop)!";
417 } else if (res > 1) {
418 LOG(ERROR) << "EventBase: unknown event loop result = " << res;
422 loopThread_.store(0, std::memory_order_release);
424 VLOG(5) << "EventBase(): Done with loop.";
428 void EventBase::loopForever() {
429 // Update the notification queue event to treat it as a normal (non-internal)
430 // event. The notification queue event always remains installed, and the main
431 // loop won't exit with it installed.
432 fnRunner_->stopConsuming();
433 fnRunner_->startConsuming(this, queue_.get());
437 // Restore the notification queue internal flag
438 fnRunner_->stopConsuming();
439 fnRunner_->startConsumingInternal(this, queue_.get());
442 folly::throwSystemError("error in EventBase::loopForever()");
446 bool EventBase::bumpHandlingTime() {
447 VLOG(11) << "EventBase " << this << " " << __PRETTY_FUNCTION__ <<
448 " (loop) latest " << latestLoopCnt_ << " next " << nextLoopCnt_;
449 if(nothingHandledYet()) {
450 latestLoopCnt_ = nextLoopCnt_;
451 if (enableTimeMeasurement_) {
453 startWork_ = std::chrono::duration_cast<std::chrono::microseconds>(
454 std::chrono::steady_clock::now().time_since_epoch()).count();
456 VLOG(11) << "EventBase " << this << " " << __PRETTY_FUNCTION__ <<
457 " (loop) startWork_ " << startWork_;
464 void EventBase::terminateLoopSoon() {
465 VLOG(5) << "EventBase(): Received terminateLoopSoon() command.";
467 // Set stop to true, so the event loop will know to exit.
468 // TODO: We should really use an atomic operation here with a release
472 // Call event_base_loopbreak() so that libevent will exit the next time
474 event_base_loopbreak(evb_);
476 // If terminateLoopSoon() is called from another thread,
477 // the EventBase thread might be stuck waiting for events.
478 // In this case, it won't wake up and notice that stop_ is set until it
479 // receives another event. Send an empty frame to the notification queue
480 // so that the event loop will wake up even if there are no other events.
482 // We don't care about the return value of trySendFrame(). If it fails
483 // this likely means the EventBase already has lots of events waiting
486 queue_->putMessage(nullptr);
488 // We don't care if putMessage() fails. This likely means
489 // the EventBase already has lots of events waiting anyway.
493 void EventBase::runInLoop(LoopCallback* callback, bool thisIteration) {
494 DCHECK(isInEventBaseThread());
495 callback->cancelLoopCallback();
496 callback->context_ = RequestContext::saveContext();
497 if (runOnceCallbacks_ != nullptr && thisIteration) {
498 runOnceCallbacks_->push_back(*callback);
500 loopCallbacks_.push_back(*callback);
504 void EventBase::runInLoop(const Cob& cob, bool thisIteration) {
505 DCHECK(isInEventBaseThread());
506 auto wrapper = new FunctionLoopCallback<Cob>(cob);
507 wrapper->context_ = RequestContext::saveContext();
508 if (runOnceCallbacks_ != nullptr && thisIteration) {
509 runOnceCallbacks_->push_back(*wrapper);
511 loopCallbacks_.push_back(*wrapper);
515 void EventBase::runInLoop(Cob&& cob, bool thisIteration) {
516 DCHECK(isInEventBaseThread());
517 auto wrapper = new FunctionLoopCallback<Cob>(std::move(cob));
518 wrapper->context_ = RequestContext::saveContext();
519 if (runOnceCallbacks_ != nullptr && thisIteration) {
520 runOnceCallbacks_->push_back(*wrapper);
522 loopCallbacks_.push_back(*wrapper);
526 void EventBase::runAfterDrain(Cob&& cob) {
527 auto callback = new FunctionLoopCallback<Cob>(std::move(cob));
528 std::lock_guard<std::mutex> lg(runAfterDrainCallbacksMutex_);
529 callback->cancelLoopCallback();
530 runAfterDrainCallbacks_.push_back(*callback);
533 void EventBase::runOnDestruction(LoopCallback* callback) {
534 std::lock_guard<std::mutex> lg(onDestructionCallbacksMutex_);
535 callback->cancelLoopCallback();
536 onDestructionCallbacks_.push_back(*callback);
539 void EventBase::runBeforeLoop(LoopCallback* callback) {
540 DCHECK(isInEventBaseThread());
541 callback->cancelLoopCallback();
542 runBeforeLoopCallbacks_.push_back(*callback);
545 bool EventBase::runInEventBaseThread(const Cob& fn) {
547 // It will be received by the FunctionRunner in the EventBase's thread.
549 // We try not to schedule nullptr callbacks
551 LOG(ERROR) << "EventBase " << this
552 << ": Scheduling nullptr callbacks is not allowed";
556 // Short-circuit if we are already in our event base
557 if (inRunningEventBaseThread()) {
564 queue_->putMessage(fn);
565 } catch (const std::exception& ex) {
566 LOG(ERROR) << "EventBase " << this << ": failed to schedule function "
567 << "for EventBase thread: " << ex.what();
574 bool EventBase::runInEventBaseThreadAndWait(const Cob& fn) {
575 if (inRunningEventBaseThread()) {
576 LOG(ERROR) << "EventBase " << this << ": Waiting in the event loop is not "
583 std::condition_variable cv;
584 runInEventBaseThread([&] {
586 std::unique_lock<std::mutex> l(m);
589 // We cannot release the lock before notify_one, because a spurious
590 // wakeup in the waiting thread may lead to cv and m going out of scope
595 std::unique_lock<std::mutex> l(m);
596 cv.wait(l, [&] { return ready; });
601 bool EventBase::runImmediatelyOrRunInEventBaseThreadAndWait(const Cob& fn) {
602 if (isInEventBaseThread()) {
606 return runInEventBaseThreadAndWait(fn);
610 void EventBase::runAfterDelay(const Cob& cob,
611 uint32_t milliseconds,
612 TimeoutManager::InternalEnum in) {
613 if (!tryRunAfterDelay(cob, milliseconds, in)) {
614 folly::throwSystemError(
615 "error in EventBase::runAfterDelay(), failed to schedule timeout");
619 bool EventBase::tryRunAfterDelay(const Cob& cob,
620 uint32_t milliseconds,
621 TimeoutManager::InternalEnum in) {
622 CobTimeout* timeout = new CobTimeout(this, cob, in);
623 if (!timeout->scheduleTimeout(milliseconds)) {
627 pendingCobTimeouts_.push_back(*timeout);
631 bool EventBase::runLoopCallbacks(bool setContext) {
632 if (!loopCallbacks_.empty()) {
634 // Swap the loopCallbacks_ list with a temporary list on our stack.
635 // This way we will only run callbacks scheduled at the time
636 // runLoopCallbacks() was invoked.
638 // If any of these callbacks in turn call runInLoop() to schedule more
639 // callbacks, those new callbacks won't be run until the next iteration
640 // around the event loop. This prevents runInLoop() callbacks from being
641 // able to start file descriptor and timeout based events.
642 LoopCallbackList currentCallbacks;
643 currentCallbacks.swap(loopCallbacks_);
644 runOnceCallbacks_ = ¤tCallbacks;
646 while (!currentCallbacks.empty()) {
647 LoopCallback* callback = ¤tCallbacks.front();
648 currentCallbacks.pop_front();
650 RequestContext::setContext(callback->context_);
652 callback->runLoopCallback();
655 runOnceCallbacks_ = nullptr;
661 void EventBase::initNotificationQueue() {
662 // Infinite size queue
663 queue_.reset(new NotificationQueue<Cob>());
665 // We allocate fnRunner_ separately, rather than declaring it directly
666 // as a member of EventBase solely so that we don't need to include
667 // NotificationQueue.h from EventBase.h
668 fnRunner_.reset(new FunctionRunner());
670 // Mark this as an internal event, so event_base_loop() will return if
671 // there are no other events besides this one installed.
673 // Most callers don't care about the internal notification queue used by
674 // EventBase. The queue is always installed, so if we did count the queue as
675 // an active event, loop() would never exit with no more events to process.
676 // Users can use loopForever() if they do care about the notification queue.
677 // (This is useful for EventBase threads that do nothing but process
678 // runInEventBaseThread() notifications.)
679 fnRunner_->startConsumingInternal(this, queue_.get());
682 void EventBase::SmoothLoopTime::setTimeInterval(uint64_t timeInterval) {
683 expCoeff_ = -1.0/timeInterval;
684 VLOG(11) << "expCoeff_ " << expCoeff_ << " " << __PRETTY_FUNCTION__;
687 void EventBase::SmoothLoopTime::reset(double value) {
691 void EventBase::SmoothLoopTime::addSample(int64_t idle, int64_t busy) {
693 * Position at which the busy sample is considered to be taken.
694 * (Allows to quickly skew our average without editing much code)
696 enum BusySamplePosition {
697 RIGHT = 0, // busy sample placed at the end of the iteration
698 CENTER = 1, // busy sample placed at the middle point of the iteration
699 LEFT = 2, // busy sample placed at the beginning of the iteration
702 // See http://en.wikipedia.org/wiki/Moving_average#Exponential_moving_average
703 // and D676020 for more info on this calculation.
704 VLOG(11) << "idle " << idle << " oldBusyLeftover_ " << oldBusyLeftover_ <<
705 " idle + oldBusyLeftover_ " << idle + oldBusyLeftover_ <<
706 " busy " << busy << " " << __PRETTY_FUNCTION__;
707 idle += oldBusyLeftover_ + busy;
708 oldBusyLeftover_ = (busy * BusySamplePosition::CENTER) / 2;
709 idle -= oldBusyLeftover_;
711 double coeff = exp(idle * expCoeff_);
713 value_ += (1.0 - coeff) * busy;
716 bool EventBase::nothingHandledYet() {
717 VLOG(11) << "latest " << latestLoopCnt_ << " next " << nextLoopCnt_;
718 return (nextLoopCnt_ != latestLoopCnt_);
722 void EventBase::runFunctionPtr(Cob* fn) {
723 // The function should never throw an exception, because we have no
724 // way of knowing what sort of error handling to perform.
726 // If it does throw, log a message and abort the program.
729 } catch (const std::exception &ex) {
730 LOG(ERROR) << "runInEventBaseThread() std::function threw a "
731 << typeid(ex).name() << " exception: " << ex.what();
734 LOG(ERROR) << "runInEventBaseThread() std::function threw an exception";
738 // The function object was allocated by runInEventBaseThread().
739 // Delete it once it has been run.
743 void EventBase::attachTimeoutManager(AsyncTimeout* obj,
744 InternalEnum internal) {
746 struct event* ev = obj->getEvent();
747 assert(ev->ev_base == nullptr);
749 event_base_set(getLibeventBase(), ev);
750 if (internal == AsyncTimeout::InternalEnum::INTERNAL) {
751 // Set the EVLIST_INTERNAL flag
752 event_ref_flags(ev) |= EVLIST_INTERNAL;
756 void EventBase::detachTimeoutManager(AsyncTimeout* obj) {
758 struct event* ev = obj->getEvent();
759 ev->ev_base = nullptr;
762 bool EventBase::scheduleTimeout(AsyncTimeout* obj,
763 TimeoutManager::timeout_type timeout) {
764 assert(isInEventBaseThread());
765 // Set up the timeval and add the event
767 tv.tv_sec = timeout.count() / 1000LL;
768 tv.tv_usec = (timeout.count() % 1000LL) * 1000LL;
770 struct event* ev = obj->getEvent();
771 if (event_add(ev, &tv) < 0) {
772 LOG(ERROR) << "EventBase: failed to schedule timeout: " << strerror(errno);
779 void EventBase::cancelTimeout(AsyncTimeout* obj) {
780 assert(isInEventBaseThread());
781 struct event* ev = obj->getEvent();
782 if (EventUtil::isEventRegistered(ev)) {
787 void EventBase::setName(const std::string& name) {
788 assert(isInEventBaseThread());
792 setThreadName(loopThread_.load(std::memory_order_relaxed),
797 const std::string& EventBase::getName() {
798 assert(isInEventBaseThread());
802 const char* EventBase::getLibeventVersion() { return event_get_version(); }
803 const char* EventBase::getLibeventMethod() { return event_get_method(); }