2 * Copyright 2014 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>
34 using folly::EventBase;
36 template <typename Callback>
37 class FunctionLoopCallback : public EventBase::LoopCallback {
39 explicit FunctionLoopCallback(Cob&& function)
40 : function_(std::move(function)) {}
42 explicit FunctionLoopCallback(const Cob& function)
43 : function_(function) {}
45 virtual void runLoopCallback() noexcept {
61 * EventBase::FunctionRunner
64 class EventBase::FunctionRunner
65 : public NotificationQueue<std::pair<void (*)(void*), void*>>::Consumer {
67 void messageAvailable(std::pair<void (*)(void*), void*>&& msg) {
69 // In libevent2, internal events do not break the loop.
70 // Most users would expect loop(), followed by runInEventBaseThread(),
71 // to break the loop and check if it should exit or not.
72 // To have similar bejaviour to libevent1.4, tell the loop to break here.
73 // Note that loop() may still continue to loop, but it will also check the
74 // stop_ flag as well as runInLoop callbacks, etc.
75 event_base_loopbreak(getEventBase()->evb_);
77 if (msg.first == nullptr && msg.second == nullptr) {
78 // terminateLoopSoon() sends a null message just to
79 // wake up the loop. We can ignore these messages.
83 // If function is nullptr, just log and move on
85 LOG(ERROR) << "nullptr callback registered to be run in "
86 << "event base thread";
90 // The function should never throw an exception, because we have no
91 // way of knowing what sort of error handling to perform.
93 // If it does throw, log a message and abort the program.
95 msg.first(msg.second);
96 } catch (const std::exception& ex) {
97 LOG(ERROR) << "runInEventBaseThread() function threw a "
98 << typeid(ex).name() << " exception: " << ex.what();
101 LOG(ERROR) << "runInEventBaseThread() function threw an exception";
108 * EventBase::CobTimeout methods
111 void EventBase::CobTimeout::timeoutExpired() noexcept {
112 // For now, we just swallow any exceptions that the callback threw.
115 } catch (const std::exception& ex) {
116 LOG(ERROR) << "EventBase::runAfterDelay() callback threw "
117 << typeid(ex).name() << " exception: " << ex.what();
119 LOG(ERROR) << "EventBase::runAfterDelay() callback threw non-exception "
123 // The CobTimeout object was allocated on the heap by runAfterDelay(),
124 // so delete it now that the it has fired.
129 // The interface used to libevent is not thread-safe. Calls to
130 // event_init() and event_base_free() directly modify an internal
131 // global 'current_base', so a mutex is required to protect this.
133 // event_init() should only ever be called once. Subsequent calls
134 // should be made to event_base_new(). We can recognise that
135 // event_init() has already been called by simply inspecting current_base.
136 static std::mutex libevent_mutex_;
142 EventBase::EventBase()
143 : runOnceCallbacks_(nullptr)
149 , avgLoopTime_(2000000)
150 , maxLatencyLoopTime_(avgLoopTime_)
151 , nextLoopCnt_(-40) // Early wrap-around so bugs will manifest soon
152 , latestLoopCnt_(nextLoopCnt_)
155 , observerSampleCount_(0) {
157 std::lock_guard<std::mutex> lock(libevent_mutex_);
159 // The value 'current_base' (libevent 1) or
160 // 'event_global_current_base_' (libevent 2) is filled in by event_set(),
161 // allowing examination of its value without an explicit reference here.
162 // If ev.ev_base is NULL, then event_init() must be called, otherwise
163 // call event_base_new().
165 event_set(&ev, 0, 0, nullptr, nullptr);
166 evb_ = (ev.ev_base) ? event_base_new() : event_init();
168 if (UNLIKELY(evb_ == nullptr)) {
169 LOG(ERROR) << "EventBase(): Failed to init event base.";
170 folly::throwSystemError("error in EventBase::EventBase()");
172 VLOG(5) << "EventBase(): Created.";
173 initNotificationQueue();
174 RequestContext::getStaticContext();
177 // takes ownership of the event_base
178 EventBase::EventBase(event_base* evb)
179 : runOnceCallbacks_(nullptr)
186 , avgLoopTime_(2000000)
187 , maxLatencyLoopTime_(avgLoopTime_)
188 , nextLoopCnt_(-40) // Early wrap-around so bugs will manifest soon
189 , latestLoopCnt_(nextLoopCnt_)
192 , observerSampleCount_(0) {
193 if (UNLIKELY(evb_ == nullptr)) {
194 LOG(ERROR) << "EventBase(): Pass nullptr as event base.";
195 throw std::invalid_argument("EventBase(): event base cannot be nullptr");
197 initNotificationQueue();
198 RequestContext::getStaticContext();
201 EventBase::~EventBase() {
202 // Call all destruction callbacks, before we start cleaning up our state.
203 while (!onDestructionCallbacks_.empty()) {
204 LoopCallback* callback = &onDestructionCallbacks_.front();
205 onDestructionCallbacks_.pop_front();
206 callback->runLoopCallback();
209 // Delete any unfired callback objects, so that we don't leak memory
210 // (Note that we don't fire them. The caller is responsible for cleaning up
211 // its own data structures if it destroys the EventBase with unfired events
213 while (!pendingCobTimeouts_.empty()) {
214 CobTimeout* timeout = &pendingCobTimeouts_.front();
218 while (!runBeforeLoopCallbacks_.empty()) {
219 delete &runBeforeLoopCallbacks_.front();
222 (void) runLoopCallbacks(false);
224 // Stop consumer before deleting NotificationQueue
225 fnRunner_->stopConsuming();
227 std::lock_guard<std::mutex> lock(libevent_mutex_);
228 event_base_free(evb_);
230 VLOG(5) << "EventBase(): Destroyed.";
233 int EventBase::getNotificationQueueSize() const {
234 return queue_->size();
237 void EventBase::setMaxReadAtOnce(uint32_t maxAtOnce) {
238 fnRunner_->setMaxReadAtOnce(maxAtOnce);
241 // Set smoothing coefficient for loop load average; input is # of milliseconds
242 // for exp(-1) decay.
243 void EventBase::setLoadAvgMsec(uint32_t ms) {
244 uint64_t us = 1000 * ms;
246 maxLatencyLoopTime_.setTimeInterval(us);
247 avgLoopTime_.setTimeInterval(us);
249 LOG(ERROR) << "non-positive arg to setLoadAvgMsec()";
253 void EventBase::resetLoadAvg(double value) {
254 avgLoopTime_.reset(value);
255 maxLatencyLoopTime_.reset(value);
258 static std::chrono::milliseconds
259 getTimeDelta(std::chrono::steady_clock::time_point* prev) {
260 auto result = std::chrono::steady_clock::now() - *prev;
261 *prev = std::chrono::steady_clock::now();
263 return std::chrono::duration_cast<std::chrono::milliseconds>(result);
266 void EventBase::waitUntilRunning() {
267 while (!isRunning()) {
272 // enters the event_base loop -- will only exit when forced to
273 bool EventBase::loop() {
277 bool EventBase::loopOnce(int flags) {
278 return loopBody(flags | EVLOOP_ONCE);
281 bool EventBase::loopBody(int flags) {
282 VLOG(5) << "EventBase(): Starting loop.";
284 bool ranLoopCallbacks;
285 bool blocking = !(flags & EVLOOP_NONBLOCK);
286 bool once = (flags & EVLOOP_ONCE);
288 loopThread_.store(pthread_self(), std::memory_order_release);
290 if (!name_.empty()) {
291 setThreadName(name_);
294 auto prev = std::chrono::steady_clock::now();
295 int64_t idleStart = std::chrono::duration_cast<std::chrono::microseconds>(
296 std::chrono::steady_clock::now().time_since_epoch()).count();
298 // TODO: Read stop_ atomically with an acquire barrier.
302 // Run the before loop callbacks
303 LoopCallbackList callbacks;
304 callbacks.swap(runBeforeLoopCallbacks_);
306 while(!callbacks.empty()) {
307 auto* item = &callbacks.front();
308 callbacks.pop_front();
309 item->runLoopCallback();
312 // nobody can add loop callbacks from within this thread if
313 // we don't have to handle anything to start with...
314 if (blocking && loopCallbacks_.empty()) {
315 res = event_base_loop(evb_, EVLOOP_ONCE);
317 res = event_base_loop(evb_, EVLOOP_ONCE | EVLOOP_NONBLOCK);
320 ranLoopCallbacks = runLoopCallbacks();
322 int64_t busy = std::chrono::duration_cast<std::chrono::microseconds>(
323 std::chrono::steady_clock::now().time_since_epoch()).count() - startWork_;
324 int64_t idle = startWork_ - idleStart;
326 avgLoopTime_.addSample(idle, busy);
327 maxLatencyLoopTime_.addSample(idle, busy);
330 if (observerSampleCount_++ == observer_->getSampleRate()) {
331 observerSampleCount_ = 0;
332 observer_->loopSample(busy, idle);
336 VLOG(11) << "EventBase " << this << " did not timeout "
337 " loop time guess: " << busy + idle <<
338 " idle time: " << idle <<
339 " busy time: " << busy <<
340 " avgLoopTime: " << avgLoopTime_.get() <<
341 " maxLatencyLoopTime: " << maxLatencyLoopTime_.get() <<
342 " maxLatency_: " << maxLatency_ <<
343 " nothingHandledYet(): "<< nothingHandledYet();
345 // see if our average loop time has exceeded our limit
346 if ((maxLatency_ > 0) &&
347 (maxLatencyLoopTime_.get() > double(maxLatency_))) {
349 // back off temporarily -- don't keep spamming maxLatencyCob_
350 // if we're only a bit over the limit
351 maxLatencyLoopTime_.dampen(0.9);
354 // Our loop run did real work; reset the idle timer
355 idleStart = std::chrono::duration_cast<std::chrono::microseconds>(
356 std::chrono::steady_clock::now().time_since_epoch()).count();
358 // If the event loop indicate that there were no more events, and
359 // we also didn't have any loop callbacks to run, there is nothing left to
361 if (res != 0 && !ranLoopCallbacks) {
362 // Since Notification Queue is marked 'internal' some events may not have
363 // run. Run them manually if so, and continue looping.
365 if (getNotificationQueueSize() > 0) {
366 fnRunner_->handlerReady(0);
372 VLOG(5) << "EventBase " << this << " loop time: " <<
373 getTimeDelta(&prev).count();
379 // Reset stop_ so loop() can be called again
383 LOG(ERROR) << "EventBase: -- error in event loop, res = " << res;
385 } else if (res == 1) {
386 VLOG(5) << "EventBase: ran out of events (exiting loop)!";
387 } else if (res > 1) {
388 LOG(ERROR) << "EventBase: unknown event loop result = " << res;
392 loopThread_.store(0, std::memory_order_release);
394 VLOG(5) << "EventBase(): Done with loop.";
398 void EventBase::loopForever() {
399 // Update the notification queue event to treat it as a normal (non-internal)
400 // event. The notification queue event always remains installed, and the main
401 // loop won't exit with it installed.
402 fnRunner_->stopConsuming();
403 fnRunner_->startConsuming(this, queue_.get());
407 // Restore the notification queue internal flag
408 fnRunner_->stopConsuming();
409 fnRunner_->startConsumingInternal(this, queue_.get());
412 folly::throwSystemError("error in EventBase::loopForever()");
416 bool EventBase::bumpHandlingTime() {
417 VLOG(11) << "EventBase " << this << " " << __PRETTY_FUNCTION__ <<
418 " (loop) latest " << latestLoopCnt_ << " next " << nextLoopCnt_;
419 if(nothingHandledYet()) {
420 latestLoopCnt_ = nextLoopCnt_;
422 startWork_ = std::chrono::duration_cast<std::chrono::microseconds>(
423 std::chrono::steady_clock::now().time_since_epoch()).count();
425 VLOG(11) << "EventBase " << this << " " << __PRETTY_FUNCTION__ <<
426 " (loop) startWork_ " << startWork_;
432 void EventBase::terminateLoopSoon() {
433 VLOG(5) << "EventBase(): Received terminateLoopSoon() command.";
435 // Set stop to true, so the event loop will know to exit.
436 // TODO: We should really use an atomic operation here with a release
440 // Call event_base_loopbreak() so that libevent will exit the next time
442 event_base_loopbreak(evb_);
444 // If terminateLoopSoon() is called from another thread,
445 // the EventBase thread might be stuck waiting for events.
446 // In this case, it won't wake up and notice that stop_ is set until it
447 // receives another event. Send an empty frame to the notification queue
448 // so that the event loop will wake up even if there are no other events.
450 // We don't care about the return value of trySendFrame(). If it fails
451 // this likely means the EventBase already has lots of events waiting
454 queue_->putMessage(std::make_pair(nullptr, nullptr));
456 // We don't care if putMessage() fails. This likely means
457 // the EventBase already has lots of events waiting anyway.
461 void EventBase::runInLoop(LoopCallback* callback, bool thisIteration) {
462 DCHECK(isInEventBaseThread());
463 callback->cancelLoopCallback();
464 callback->context_ = RequestContext::saveContext();
465 if (runOnceCallbacks_ != nullptr && thisIteration) {
466 runOnceCallbacks_->push_back(*callback);
468 loopCallbacks_.push_back(*callback);
472 void EventBase::runInLoop(const Cob& cob, bool thisIteration) {
473 DCHECK(isInEventBaseThread());
474 auto wrapper = new FunctionLoopCallback<Cob>(cob);
475 wrapper->context_ = RequestContext::saveContext();
476 if (runOnceCallbacks_ != nullptr && thisIteration) {
477 runOnceCallbacks_->push_back(*wrapper);
479 loopCallbacks_.push_back(*wrapper);
483 void EventBase::runInLoop(Cob&& cob, bool thisIteration) {
484 DCHECK(isInEventBaseThread());
485 auto wrapper = new FunctionLoopCallback<Cob>(std::move(cob));
486 wrapper->context_ = RequestContext::saveContext();
487 if (runOnceCallbacks_ != nullptr && thisIteration) {
488 runOnceCallbacks_->push_back(*wrapper);
490 loopCallbacks_.push_back(*wrapper);
494 void EventBase::runOnDestruction(LoopCallback* callback) {
495 DCHECK(isInEventBaseThread());
496 callback->cancelLoopCallback();
497 onDestructionCallbacks_.push_back(*callback);
500 void EventBase::runBeforeLoop(LoopCallback* callback) {
501 DCHECK(isInEventBaseThread());
502 callback->cancelLoopCallback();
503 runBeforeLoopCallbacks_.push_back(*callback);
506 bool EventBase::runInEventBaseThread(void (*fn)(void*), void* arg) {
508 // It will be received by the FunctionRunner in the EventBase's thread.
510 // We try not to schedule nullptr callbacks
512 LOG(ERROR) << "EventBase " << this
513 << ": Scheduling nullptr callbacks is not allowed";
517 // Short-circuit if we are already in our event base
518 if (inRunningEventBaseThread()) {
519 runInLoop(new RunInLoopCallback(fn, arg));
525 queue_->putMessage(std::make_pair(fn, arg));
526 } catch (const std::exception& ex) {
527 LOG(ERROR) << "EventBase " << this << ": failed to schedule function "
528 << fn << "for EventBase thread: " << ex.what();
535 bool EventBase::runInEventBaseThread(const Cob& fn) {
536 // Short-circuit if we are already in our event base
537 if (inRunningEventBaseThread()) {
543 // Allocate a copy of the function so we can pass it to the other thread
544 // The other thread will delete this copy once the function has been run
546 fnCopy = new Cob(fn);
547 } catch (const std::bad_alloc& ex) {
548 LOG(ERROR) << "failed to allocate tr::function copy "
549 << "for runInEventBaseThread()";
553 if (!runInEventBaseThread(&EventBase::runFunctionPtr, fnCopy)) {
561 bool EventBase::runAfterDelay(const Cob& cob,
563 TimeoutManager::InternalEnum in) {
564 CobTimeout* timeout = new CobTimeout(this, cob, in);
565 if (!timeout->scheduleTimeout(milliseconds)) {
570 pendingCobTimeouts_.push_back(*timeout);
574 bool EventBase::runLoopCallbacks(bool setContext) {
575 if (!loopCallbacks_.empty()) {
577 // Swap the loopCallbacks_ list with a temporary list on our stack.
578 // This way we will only run callbacks scheduled at the time
579 // runLoopCallbacks() was invoked.
581 // If any of these callbacks in turn call runInLoop() to schedule more
582 // callbacks, those new callbacks won't be run until the next iteration
583 // around the event loop. This prevents runInLoop() callbacks from being
584 // able to start file descriptor and timeout based events.
585 LoopCallbackList currentCallbacks;
586 currentCallbacks.swap(loopCallbacks_);
587 runOnceCallbacks_ = ¤tCallbacks;
589 while (!currentCallbacks.empty()) {
590 LoopCallback* callback = ¤tCallbacks.front();
591 currentCallbacks.pop_front();
593 RequestContext::setContext(callback->context_);
595 callback->runLoopCallback();
598 runOnceCallbacks_ = nullptr;
604 void EventBase::initNotificationQueue() {
605 // Infinite size queue
606 queue_.reset(new NotificationQueue<std::pair<void (*)(void*), void*>>());
608 // We allocate fnRunner_ separately, rather than declaring it directly
609 // as a member of EventBase solely so that we don't need to include
610 // NotificationQueue.h from EventBase.h
611 fnRunner_.reset(new FunctionRunner());
613 // Mark this as an internal event, so event_base_loop() will return if
614 // there are no other events besides this one installed.
616 // Most callers don't care about the internal notification queue used by
617 // EventBase. The queue is always installed, so if we did count the queue as
618 // an active event, loop() would never exit with no more events to process.
619 // Users can use loopForever() if they do care about the notification queue.
620 // (This is useful for EventBase threads that do nothing but process
621 // runInEventBaseThread() notifications.)
622 fnRunner_->startConsumingInternal(this, queue_.get());
625 void EventBase::SmoothLoopTime::setTimeInterval(uint64_t timeInterval) {
626 expCoeff_ = -1.0/timeInterval;
627 VLOG(11) << "expCoeff_ " << expCoeff_ << " " << __PRETTY_FUNCTION__;
630 void EventBase::SmoothLoopTime::reset(double value) {
634 void EventBase::SmoothLoopTime::addSample(int64_t idle, int64_t busy) {
636 * Position at which the busy sample is considered to be taken.
637 * (Allows to quickly skew our average without editing much code)
639 enum BusySamplePosition {
640 RIGHT = 0, // busy sample placed at the end of the iteration
641 CENTER = 1, // busy sample placed at the middle point of the iteration
642 LEFT = 2, // busy sample placed at the beginning of the iteration
645 VLOG(11) << "idle " << idle << " oldBusyLeftover_ " << oldBusyLeftover_ <<
646 " idle + oldBusyLeftover_ " << idle + oldBusyLeftover_ <<
647 " busy " << busy << " " << __PRETTY_FUNCTION__;
648 idle += oldBusyLeftover_ + busy;
649 oldBusyLeftover_ = (busy * BusySamplePosition::CENTER) / 2;
650 idle -= oldBusyLeftover_;
652 double coeff = exp(idle * expCoeff_);
654 value_ += (1.0 - coeff) * busy;
657 bool EventBase::nothingHandledYet() {
658 VLOG(11) << "latest " << latestLoopCnt_ << " next " << nextLoopCnt_;
659 return (nextLoopCnt_ != latestLoopCnt_);
663 void EventBase::runFunctionPtr(Cob* fn) {
664 // The function should never throw an exception, because we have no
665 // way of knowing what sort of error handling to perform.
667 // If it does throw, log a message and abort the program.
670 } catch (const std::exception &ex) {
671 LOG(ERROR) << "runInEventBaseThread() std::function threw a "
672 << typeid(ex).name() << " exception: " << ex.what();
675 LOG(ERROR) << "runInEventBaseThread() std::function threw an exception";
679 // The function object was allocated by runInEventBaseThread().
680 // Delete it once it has been run.
684 EventBase::RunInLoopCallback::RunInLoopCallback(void (*fn)(void*), void* arg)
688 void EventBase::RunInLoopCallback::runLoopCallback() noexcept {
693 void EventBase::attachTimeoutManager(AsyncTimeout* obj,
694 InternalEnum internal) {
696 struct event* ev = obj->getEvent();
697 assert(ev->ev_base == nullptr);
699 event_base_set(getLibeventBase(), ev);
700 if (internal == AsyncTimeout::InternalEnum::INTERNAL) {
701 // Set the EVLIST_INTERNAL flag
702 ev->ev_flags |= EVLIST_INTERNAL;
706 void EventBase::detachTimeoutManager(AsyncTimeout* obj) {
708 struct event* ev = obj->getEvent();
709 ev->ev_base = nullptr;
712 bool EventBase::scheduleTimeout(AsyncTimeout* obj,
713 std::chrono::milliseconds timeout) {
714 assert(isInEventBaseThread());
715 // Set up the timeval and add the event
717 tv.tv_sec = timeout.count() / 1000LL;
718 tv.tv_usec = (timeout.count() % 1000LL) * 1000LL;
720 struct event* ev = obj->getEvent();
721 if (event_add(ev, &tv) < 0) {
722 LOG(ERROR) << "EventBase: failed to schedule timeout: " << strerror(errno);
729 void EventBase::cancelTimeout(AsyncTimeout* obj) {
730 assert(isInEventBaseThread());
731 struct event* ev = obj->getEvent();
732 if (EventUtil::isEventRegistered(ev)) {
737 void EventBase::setName(const std::string& name) {
738 assert(isInEventBaseThread());
742 setThreadName(loopThread_.load(std::memory_order_relaxed),
747 const std::string& EventBase::getName() {
748 assert(isInEventBaseThread());
752 const char* EventBase::getLibeventVersion() { return event_get_version(); }
753 const char* EventBase::getLibeventMethod() { return event_get_method(); }