2 * Copyright 2015 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)
45 : function_(function) {}
47 virtual void runLoopCallback() noexcept {
63 * EventBase::FunctionRunner
66 class EventBase::FunctionRunner
67 : public NotificationQueue<std::pair<void (*)(void*), void*>>::Consumer {
69 void messageAvailable(std::pair<void (*)(void*), void*>&& msg) {
71 // In libevent2, internal events do not break the loop.
72 // Most users would expect loop(), followed by runInEventBaseThread(),
73 // to break the loop and check if it should exit or not.
74 // To have similar bejaviour to libevent1.4, tell the loop to break here.
75 // Note that loop() may still continue to loop, but it will also check the
76 // stop_ flag as well as runInLoop callbacks, etc.
77 event_base_loopbreak(getEventBase()->evb_);
79 if (msg.first == nullptr && msg.second == nullptr) {
80 // terminateLoopSoon() sends a null message just to
81 // wake up the loop. We can ignore these messages.
85 // If function is nullptr, just log and move on
87 LOG(ERROR) << "nullptr callback registered to be run in "
88 << "event base thread";
92 // The function should never throw an exception, because we have no
93 // way of knowing what sort of error handling to perform.
95 // If it does throw, log a message and abort the program.
97 msg.first(msg.second);
98 } catch (const std::exception& ex) {
99 LOG(ERROR) << "runInEventBaseThread() function threw a "
100 << typeid(ex).name() << " exception: " << ex.what();
103 LOG(ERROR) << "runInEventBaseThread() function threw an exception";
110 * EventBase::CobTimeout methods
113 void EventBase::CobTimeout::timeoutExpired() noexcept {
114 // For now, we just swallow any exceptions that the callback threw.
117 } catch (const std::exception& ex) {
118 LOG(ERROR) << "EventBase::runAfterDelay() callback threw "
119 << typeid(ex).name() << " exception: " << ex.what();
121 LOG(ERROR) << "EventBase::runAfterDelay() callback threw non-exception "
125 // The CobTimeout object was allocated on the heap by runAfterDelay(),
126 // so delete it now that the it has fired.
131 // The interface used to libevent is not thread-safe. Calls to
132 // event_init() and event_base_free() directly modify an internal
133 // global 'current_base', so a mutex is required to protect this.
135 // event_init() should only ever be called once. Subsequent calls
136 // should be made to event_base_new(). We can recognise that
137 // event_init() has already been called by simply inspecting current_base.
138 static std::mutex libevent_mutex_;
144 EventBase::EventBase(bool enableTimeMeasurement)
145 : runOnceCallbacks_(nullptr)
151 , avgLoopTime_(2000000)
152 , maxLatencyLoopTime_(avgLoopTime_)
153 , enableTimeMeasurement_(enableTimeMeasurement)
154 , nextLoopCnt_(-40) // Early wrap-around so bugs will manifest soon
155 , latestLoopCnt_(nextLoopCnt_)
158 , observerSampleCount_(0) {
160 std::lock_guard<std::mutex> lock(libevent_mutex_);
162 // The value 'current_base' (libevent 1) or
163 // 'event_global_current_base_' (libevent 2) is filled in by event_set(),
164 // allowing examination of its value without an explicit reference here.
165 // If ev.ev_base is NULL, then event_init() must be called, otherwise
166 // call event_base_new().
168 event_set(&ev, 0, 0, nullptr, nullptr);
169 evb_ = (ev.ev_base) ? event_base_new() : event_init();
171 if (UNLIKELY(evb_ == nullptr)) {
172 LOG(ERROR) << "EventBase(): Failed to init event base.";
173 folly::throwSystemError("error in EventBase::EventBase()");
175 VLOG(5) << "EventBase(): Created.";
176 initNotificationQueue();
177 RequestContext::getStaticContext();
180 // takes ownership of the event_base
181 EventBase::EventBase(event_base* evb, bool enableTimeMeasurement)
182 : runOnceCallbacks_(nullptr)
189 , avgLoopTime_(2000000)
190 , maxLatencyLoopTime_(avgLoopTime_)
191 , enableTimeMeasurement_(enableTimeMeasurement)
192 , nextLoopCnt_(-40) // Early wrap-around so bugs will manifest soon
193 , latestLoopCnt_(nextLoopCnt_)
196 , observerSampleCount_(0) {
197 if (UNLIKELY(evb_ == nullptr)) {
198 LOG(ERROR) << "EventBase(): Pass nullptr as event base.";
199 throw std::invalid_argument("EventBase(): event base cannot be nullptr");
201 initNotificationQueue();
202 RequestContext::getStaticContext();
205 EventBase::~EventBase() {
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(false);
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_);
238 VLOG(5) << "EventBase(): Destroyed.";
241 int EventBase::getNotificationQueueSize() const {
242 return queue_->size();
245 void EventBase::setMaxReadAtOnce(uint32_t maxAtOnce) {
246 fnRunner_->setMaxReadAtOnce(maxAtOnce);
249 // Set smoothing coefficient for loop load average; input is # of milliseconds
250 // for exp(-1) decay.
251 void EventBase::setLoadAvgMsec(uint32_t ms) {
252 assert(enableTimeMeasurement_);
253 uint64_t us = 1000 * ms;
255 maxLatencyLoopTime_.setTimeInterval(us);
256 avgLoopTime_.setTimeInterval(us);
258 LOG(ERROR) << "non-positive arg to setLoadAvgMsec()";
262 void EventBase::resetLoadAvg(double value) {
263 assert(enableTimeMeasurement_);
264 avgLoopTime_.reset(value);
265 maxLatencyLoopTime_.reset(value);
268 static std::chrono::milliseconds
269 getTimeDelta(std::chrono::steady_clock::time_point* prev) {
270 auto result = std::chrono::steady_clock::now() - *prev;
271 *prev = std::chrono::steady_clock::now();
273 return std::chrono::duration_cast<std::chrono::milliseconds>(result);
276 void EventBase::waitUntilRunning() {
277 while (!isRunning()) {
282 // enters the event_base loop -- will only exit when forced to
283 bool EventBase::loop() {
287 bool EventBase::loopOnce(int flags) {
288 return loopBody(flags | EVLOOP_ONCE);
291 bool EventBase::loopBody(int flags) {
292 VLOG(5) << "EventBase(): Starting loop.";
294 bool ranLoopCallbacks;
295 bool blocking = !(flags & EVLOOP_NONBLOCK);
296 bool once = (flags & EVLOOP_ONCE);
298 // time-measurement variables.
299 std::chrono::steady_clock::time_point prev;
304 loopThread_.store(pthread_self(), std::memory_order_release);
306 if (!name_.empty()) {
307 setThreadName(name_);
310 if (enableTimeMeasurement_) {
311 prev = std::chrono::steady_clock::now();
312 idleStart = std::chrono::duration_cast<std::chrono::microseconds>(
313 std::chrono::steady_clock::now().time_since_epoch()).count();
316 // TODO: Read stop_ atomically with an acquire barrier.
320 // Run the before loop callbacks
321 LoopCallbackList callbacks;
322 callbacks.swap(runBeforeLoopCallbacks_);
324 while(!callbacks.empty()) {
325 auto* item = &callbacks.front();
326 callbacks.pop_front();
327 item->runLoopCallback();
330 // nobody can add loop callbacks from within this thread if
331 // we don't have to handle anything to start with...
332 if (blocking && loopCallbacks_.empty()) {
333 res = event_base_loop(evb_, EVLOOP_ONCE);
335 res = event_base_loop(evb_, EVLOOP_ONCE | EVLOOP_NONBLOCK);
338 ranLoopCallbacks = runLoopCallbacks();
340 if (enableTimeMeasurement_) {
341 busy = std::chrono::duration_cast<std::chrono::microseconds>(
342 std::chrono::steady_clock::now().time_since_epoch()).count() -
344 idle = startWork_ - idleStart;
346 avgLoopTime_.addSample(idle, busy);
347 maxLatencyLoopTime_.addSample(idle, busy);
350 if (observerSampleCount_++ == observer_->getSampleRate()) {
351 observerSampleCount_ = 0;
352 observer_->loopSample(busy, idle);
356 VLOG(11) << "EventBase " << this << " did not timeout "
357 " loop time guess: " << busy + idle <<
358 " idle time: " << idle <<
359 " busy time: " << busy <<
360 " avgLoopTime: " << avgLoopTime_.get() <<
361 " maxLatencyLoopTime: " << maxLatencyLoopTime_.get() <<
362 " maxLatency_: " << maxLatency_ <<
363 " nothingHandledYet(): "<< nothingHandledYet();
365 // see if our average loop time has exceeded our limit
366 if ((maxLatency_ > 0) &&
367 (maxLatencyLoopTime_.get() > double(maxLatency_))) {
369 // back off temporarily -- don't keep spamming maxLatencyCob_
370 // if we're only a bit over the limit
371 maxLatencyLoopTime_.dampen(0.9);
374 // Our loop run did real work; reset the idle timer
375 idleStart = std::chrono::duration_cast<std::chrono::microseconds>(
376 std::chrono::steady_clock::now().time_since_epoch()).count();
378 VLOG(11) << "EventBase " << this << " did not timeout "
379 " time measurement is disabled "
380 " nothingHandledYet(): "<< nothingHandledYet();
383 // If the event loop indicate that there were no more events, and
384 // we also didn't have any loop callbacks to run, there is nothing left to
386 if (res != 0 && !ranLoopCallbacks) {
387 // Since Notification Queue is marked 'internal' some events may not have
388 // run. Run them manually if so, and continue looping.
390 if (getNotificationQueueSize() > 0) {
391 fnRunner_->handlerReady(0);
397 if (enableTimeMeasurement_) {
398 VLOG(5) << "EventBase " << this << " loop time: " <<
399 getTimeDelta(&prev).count();
406 // Reset stop_ so loop() can be called again
410 LOG(ERROR) << "EventBase: -- error in event loop, res = " << res;
412 } else if (res == 1) {
413 VLOG(5) << "EventBase: ran out of events (exiting loop)!";
414 } else if (res > 1) {
415 LOG(ERROR) << "EventBase: unknown event loop result = " << res;
419 loopThread_.store(0, std::memory_order_release);
421 VLOG(5) << "EventBase(): Done with loop.";
425 void EventBase::loopForever() {
426 // Update the notification queue event to treat it as a normal (non-internal)
427 // event. The notification queue event always remains installed, and the main
428 // loop won't exit with it installed.
429 fnRunner_->stopConsuming();
430 fnRunner_->startConsuming(this, queue_.get());
434 // Restore the notification queue internal flag
435 fnRunner_->stopConsuming();
436 fnRunner_->startConsumingInternal(this, queue_.get());
439 folly::throwSystemError("error in EventBase::loopForever()");
443 bool EventBase::bumpHandlingTime() {
444 VLOG(11) << "EventBase " << this << " " << __PRETTY_FUNCTION__ <<
445 " (loop) latest " << latestLoopCnt_ << " next " << nextLoopCnt_;
446 if(nothingHandledYet()) {
447 latestLoopCnt_ = nextLoopCnt_;
449 startWork_ = std::chrono::duration_cast<std::chrono::microseconds>(
450 std::chrono::steady_clock::now().time_since_epoch()).count();
452 VLOG(11) << "EventBase " << this << " " << __PRETTY_FUNCTION__ <<
453 " (loop) startWork_ " << startWork_;
459 void EventBase::terminateLoopSoon() {
460 VLOG(5) << "EventBase(): Received terminateLoopSoon() command.";
462 // Set stop to true, so the event loop will know to exit.
463 // TODO: We should really use an atomic operation here with a release
467 // Call event_base_loopbreak() so that libevent will exit the next time
469 event_base_loopbreak(evb_);
471 // If terminateLoopSoon() is called from another thread,
472 // the EventBase thread might be stuck waiting for events.
473 // In this case, it won't wake up and notice that stop_ is set until it
474 // receives another event. Send an empty frame to the notification queue
475 // so that the event loop will wake up even if there are no other events.
477 // We don't care about the return value of trySendFrame(). If it fails
478 // this likely means the EventBase already has lots of events waiting
481 queue_->putMessage(std::make_pair(nullptr, nullptr));
483 // We don't care if putMessage() fails. This likely means
484 // the EventBase already has lots of events waiting anyway.
488 void EventBase::runInLoop(LoopCallback* callback, bool thisIteration) {
489 DCHECK(isInEventBaseThread());
490 callback->cancelLoopCallback();
491 callback->context_ = RequestContext::saveContext();
492 if (runOnceCallbacks_ != nullptr && thisIteration) {
493 runOnceCallbacks_->push_back(*callback);
495 loopCallbacks_.push_back(*callback);
499 void EventBase::runInLoop(const Cob& cob, bool thisIteration) {
500 DCHECK(isInEventBaseThread());
501 auto wrapper = new FunctionLoopCallback<Cob>(cob);
502 wrapper->context_ = RequestContext::saveContext();
503 if (runOnceCallbacks_ != nullptr && thisIteration) {
504 runOnceCallbacks_->push_back(*wrapper);
506 loopCallbacks_.push_back(*wrapper);
510 void EventBase::runInLoop(Cob&& cob, bool thisIteration) {
511 DCHECK(isInEventBaseThread());
512 auto wrapper = new FunctionLoopCallback<Cob>(std::move(cob));
513 wrapper->context_ = RequestContext::saveContext();
514 if (runOnceCallbacks_ != nullptr && thisIteration) {
515 runOnceCallbacks_->push_back(*wrapper);
517 loopCallbacks_.push_back(*wrapper);
521 void EventBase::runOnDestruction(LoopCallback* callback) {
522 DCHECK(isInEventBaseThread());
523 callback->cancelLoopCallback();
524 onDestructionCallbacks_.push_back(*callback);
527 void EventBase::runBeforeLoop(LoopCallback* callback) {
528 DCHECK(isInEventBaseThread());
529 callback->cancelLoopCallback();
530 runBeforeLoopCallbacks_.push_back(*callback);
533 bool EventBase::runInEventBaseThread(void (*fn)(void*), void* arg) {
535 // It will be received by the FunctionRunner in the EventBase's thread.
537 // We try not to schedule nullptr callbacks
539 LOG(ERROR) << "EventBase " << this
540 << ": Scheduling nullptr callbacks is not allowed";
544 // Short-circuit if we are already in our event base
545 if (inRunningEventBaseThread()) {
546 runInLoop(new RunInLoopCallback(fn, arg));
552 queue_->putMessage(std::make_pair(fn, arg));
553 } catch (const std::exception& ex) {
554 LOG(ERROR) << "EventBase " << this << ": failed to schedule function "
555 << fn << "for EventBase thread: " << ex.what();
562 bool EventBase::runInEventBaseThread(const Cob& fn) {
563 // Short-circuit if we are already in our event base
564 if (inRunningEventBaseThread()) {
570 // Allocate a copy of the function so we can pass it to the other thread
571 // The other thread will delete this copy once the function has been run
573 fnCopy = new Cob(fn);
574 } catch (const std::bad_alloc& ex) {
575 LOG(ERROR) << "failed to allocate tr::function copy "
576 << "for runInEventBaseThread()";
580 if (!runInEventBaseThread(&EventBase::runFunctionPtr, fnCopy)) {
588 bool EventBase::runInEventBaseThreadAndWait(const Cob& fn) {
589 if (inRunningEventBaseThread()) {
590 LOG(ERROR) << "EventBase " << this << ": Waiting in the event loop is not "
597 std::condition_variable cv;
598 runInEventBaseThread([&] {
600 std::unique_lock<std::mutex> l(m);
603 // We cannot release the lock before notify_one, because a spurious
604 // wakeup in the waiting thread may lead to cv and m going out of scope
609 std::unique_lock<std::mutex> l(m);
610 cv.wait(l, [&] { return ready; });
615 bool EventBase::runImmediatelyOrRunInEventBaseThreadAndWait(const Cob& fn) {
616 if (isInEventBaseThread()) {
620 return runInEventBaseThreadAndWait(fn);
624 void EventBase::runAfterDelay(const Cob& cob,
626 TimeoutManager::InternalEnum in) {
627 if (!tryRunAfterDelay(cob, milliseconds, in)) {
628 folly::throwSystemError(
629 "error in EventBase::runAfterDelay(), failed to schedule timeout");
633 bool EventBase::tryRunAfterDelay(const Cob& cob,
635 TimeoutManager::InternalEnum in) {
636 CobTimeout* timeout = new CobTimeout(this, cob, in);
637 if (!timeout->scheduleTimeout(milliseconds)) {
641 pendingCobTimeouts_.push_back(*timeout);
645 bool EventBase::runLoopCallbacks(bool setContext) {
646 if (!loopCallbacks_.empty()) {
648 // Swap the loopCallbacks_ list with a temporary list on our stack.
649 // This way we will only run callbacks scheduled at the time
650 // runLoopCallbacks() was invoked.
652 // If any of these callbacks in turn call runInLoop() to schedule more
653 // callbacks, those new callbacks won't be run until the next iteration
654 // around the event loop. This prevents runInLoop() callbacks from being
655 // able to start file descriptor and timeout based events.
656 LoopCallbackList currentCallbacks;
657 currentCallbacks.swap(loopCallbacks_);
658 runOnceCallbacks_ = ¤tCallbacks;
660 while (!currentCallbacks.empty()) {
661 LoopCallback* callback = ¤tCallbacks.front();
662 currentCallbacks.pop_front();
664 RequestContext::setContext(callback->context_);
666 callback->runLoopCallback();
669 runOnceCallbacks_ = nullptr;
675 void EventBase::initNotificationQueue() {
676 // Infinite size queue
677 queue_.reset(new NotificationQueue<std::pair<void (*)(void*), void*>>());
679 // We allocate fnRunner_ separately, rather than declaring it directly
680 // as a member of EventBase solely so that we don't need to include
681 // NotificationQueue.h from EventBase.h
682 fnRunner_.reset(new FunctionRunner());
684 // Mark this as an internal event, so event_base_loop() will return if
685 // there are no other events besides this one installed.
687 // Most callers don't care about the internal notification queue used by
688 // EventBase. The queue is always installed, so if we did count the queue as
689 // an active event, loop() would never exit with no more events to process.
690 // Users can use loopForever() if they do care about the notification queue.
691 // (This is useful for EventBase threads that do nothing but process
692 // runInEventBaseThread() notifications.)
693 fnRunner_->startConsumingInternal(this, queue_.get());
696 void EventBase::SmoothLoopTime::setTimeInterval(uint64_t timeInterval) {
697 expCoeff_ = -1.0/timeInterval;
698 VLOG(11) << "expCoeff_ " << expCoeff_ << " " << __PRETTY_FUNCTION__;
701 void EventBase::SmoothLoopTime::reset(double value) {
705 void EventBase::SmoothLoopTime::addSample(int64_t idle, int64_t busy) {
707 * Position at which the busy sample is considered to be taken.
708 * (Allows to quickly skew our average without editing much code)
710 enum BusySamplePosition {
711 RIGHT = 0, // busy sample placed at the end of the iteration
712 CENTER = 1, // busy sample placed at the middle point of the iteration
713 LEFT = 2, // busy sample placed at the beginning of the iteration
716 // See http://en.wikipedia.org/wiki/Moving_average#Exponential_moving_average
717 // and D676020 for more info on this calculation.
718 VLOG(11) << "idle " << idle << " oldBusyLeftover_ " << oldBusyLeftover_ <<
719 " idle + oldBusyLeftover_ " << idle + oldBusyLeftover_ <<
720 " busy " << busy << " " << __PRETTY_FUNCTION__;
721 idle += oldBusyLeftover_ + busy;
722 oldBusyLeftover_ = (busy * BusySamplePosition::CENTER) / 2;
723 idle -= oldBusyLeftover_;
725 double coeff = exp(idle * expCoeff_);
727 value_ += (1.0 - coeff) * busy;
730 bool EventBase::nothingHandledYet() {
731 VLOG(11) << "latest " << latestLoopCnt_ << " next " << nextLoopCnt_;
732 return (nextLoopCnt_ != latestLoopCnt_);
736 void EventBase::runFunctionPtr(Cob* fn) {
737 // The function should never throw an exception, because we have no
738 // way of knowing what sort of error handling to perform.
740 // If it does throw, log a message and abort the program.
743 } catch (const std::exception &ex) {
744 LOG(ERROR) << "runInEventBaseThread() std::function threw a "
745 << typeid(ex).name() << " exception: " << ex.what();
748 LOG(ERROR) << "runInEventBaseThread() std::function threw an exception";
752 // The function object was allocated by runInEventBaseThread().
753 // Delete it once it has been run.
757 EventBase::RunInLoopCallback::RunInLoopCallback(void (*fn)(void*), void* arg)
761 void EventBase::RunInLoopCallback::runLoopCallback() noexcept {
766 void EventBase::attachTimeoutManager(AsyncTimeout* obj,
767 InternalEnum internal) {
769 struct event* ev = obj->getEvent();
770 assert(ev->ev_base == nullptr);
772 event_base_set(getLibeventBase(), ev);
773 if (internal == AsyncTimeout::InternalEnum::INTERNAL) {
774 // Set the EVLIST_INTERNAL flag
775 ev->ev_flags |= EVLIST_INTERNAL;
779 void EventBase::detachTimeoutManager(AsyncTimeout* obj) {
781 struct event* ev = obj->getEvent();
782 ev->ev_base = nullptr;
785 bool EventBase::scheduleTimeout(AsyncTimeout* obj,
786 TimeoutManager::timeout_type timeout) {
787 assert(isInEventBaseThread());
788 // Set up the timeval and add the event
790 tv.tv_sec = timeout.count() / 1000LL;
791 tv.tv_usec = (timeout.count() % 1000LL) * 1000LL;
793 struct event* ev = obj->getEvent();
794 if (event_add(ev, &tv) < 0) {
795 LOG(ERROR) << "EventBase: failed to schedule timeout: " << strerror(errno);
802 void EventBase::cancelTimeout(AsyncTimeout* obj) {
803 assert(isInEventBaseThread());
804 struct event* ev = obj->getEvent();
805 if (EventUtil::isEventRegistered(ev)) {
810 void EventBase::setName(const std::string& name) {
811 assert(isInEventBaseThread());
815 setThreadName(loopThread_.load(std::memory_order_relaxed),
820 const std::string& EventBase::getName() {
821 assert(isInEventBaseThread());
825 const char* EventBase::getLibeventVersion() { return event_get_version(); }
826 const char* EventBase::getLibeventMethod() { return event_get_method(); }