2 * Copyright 2017 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>
22 #include <folly/io/async/VirtualEventBase.h>
24 #include <folly/Memory.h>
25 #include <folly/ThreadName.h>
26 #include <folly/io/async/NotificationQueue.h>
27 #include <folly/portability/Unistd.h>
29 #include <condition_variable>
37 * EventBase::FunctionRunner
40 class EventBase::FunctionRunner
41 : public NotificationQueue<EventBase::Func>::Consumer {
43 void messageAvailable(Func&& msg) noexcept override {
44 // In libevent2, internal events do not break the loop.
45 // Most users would expect loop(), followed by runInEventBaseThread(),
46 // to break the loop and check if it should exit or not.
47 // To have similar bejaviour to libevent1.4, tell the loop to break here.
48 // Note that loop() may still continue to loop, but it will also check the
49 // stop_ flag as well as runInLoop callbacks, etc.
50 event_base_loopbreak(getEventBase()->evb_);
53 // terminateLoopSoon() sends a null message just to
54 // wake up the loop. We can ignore these messages.
61 // The interface used to libevent is not thread-safe. Calls to
62 // event_init() and event_base_free() directly modify an internal
63 // global 'current_base', so a mutex is required to protect this.
65 // event_init() should only ever be called once. Subsequent calls
66 // should be made to event_base_new(). We can recognise that
67 // event_init() has already been called by simply inspecting current_base.
68 static std::mutex libevent_mutex_;
74 EventBase::EventBase(bool enableTimeMeasurement)
75 : runOnceCallbacks_(nullptr)
81 , avgLoopTime_(std::chrono::seconds(2))
82 , maxLatencyLoopTime_(avgLoopTime_)
83 , enableTimeMeasurement_(enableTimeMeasurement)
84 , nextLoopCnt_(uint64_t(-40)) // Early wrap-around so bugs will manifest soon
85 , latestLoopCnt_(nextLoopCnt_)
88 , observerSampleCount_(0)
89 , executionObserver_(nullptr) {
92 std::lock_guard<std::mutex> lock(libevent_mutex_);
94 // The value 'current_base' (libevent 1) or
95 // 'event_global_current_base_' (libevent 2) is filled in by event_set(),
96 // allowing examination of its value without an explicit reference here.
97 // If ev.ev_base is NULL, then event_init() must be called, otherwise
98 // call event_base_new().
99 event_set(&ev, 0, 0, nullptr, nullptr);
106 evb_ = event_base_new();
109 if (UNLIKELY(evb_ == nullptr)) {
110 LOG(ERROR) << "EventBase(): Failed to init event base.";
111 folly::throwSystemError("error in EventBase::EventBase()");
113 VLOG(5) << "EventBase(): Created.";
114 initNotificationQueue();
115 RequestContext::saveContext();
118 // takes ownership of the event_base
119 EventBase::EventBase(event_base* evb, bool enableTimeMeasurement)
120 : runOnceCallbacks_(nullptr)
127 , avgLoopTime_(std::chrono::seconds(2))
128 , maxLatencyLoopTime_(avgLoopTime_)
129 , enableTimeMeasurement_(enableTimeMeasurement)
130 , nextLoopCnt_(uint64_t(-40)) // Early wrap-around so bugs will manifest soon
131 , latestLoopCnt_(nextLoopCnt_)
134 , observerSampleCount_(0)
135 , executionObserver_(nullptr) {
136 if (UNLIKELY(evb_ == nullptr)) {
137 LOG(ERROR) << "EventBase(): Pass nullptr as event base.";
138 throw std::invalid_argument("EventBase(): event base cannot be nullptr");
140 initNotificationQueue();
141 RequestContext::saveContext();
144 EventBase::~EventBase() {
145 std::future<void> virtualEventBaseDestroyFuture;
146 if (virtualEventBase_) {
147 virtualEventBaseDestroyFuture = virtualEventBase_->destroy();
150 // Keep looping until all keep-alive handles are released. Each keep-alive
151 // handle signals that some external code will still schedule some work on
152 // this EventBase (so it's not safe to destroy it).
153 while (loopKeepAliveCount() > 0) {
154 applyLoopKeepAlive();
158 if (virtualEventBaseDestroyFuture.valid()) {
159 virtualEventBaseDestroyFuture.get();
162 // Call all destruction callbacks, before we start cleaning up our state.
163 while (!onDestructionCallbacks_.empty()) {
164 LoopCallback* callback = &onDestructionCallbacks_.front();
165 onDestructionCallbacks_.pop_front();
166 callback->runLoopCallback();
171 DCHECK_EQ(0u, runBeforeLoopCallbacks_.size());
173 (void)runLoopCallbacks();
175 if (!fnRunner_->consumeUntilDrained()) {
176 LOG(ERROR) << "~EventBase(): Unable to drain notification queue";
179 // Stop consumer before deleting NotificationQueue
180 fnRunner_->stopConsuming();
182 std::lock_guard<std::mutex> lock(libevent_mutex_);
183 event_base_free(evb_);
187 std::lock_guard<std::mutex> lock(localStorageMutex_);
188 for (auto storage : localStorageToDtor_) {
189 storage->onEventBaseDestruction(*this);
192 VLOG(5) << "EventBase(): Destroyed.";
195 size_t EventBase::getNotificationQueueSize() const {
196 return queue_->size();
199 void EventBase::setMaxReadAtOnce(uint32_t maxAtOnce) {
200 fnRunner_->setMaxReadAtOnce(maxAtOnce);
203 // Set smoothing coefficient for loop load average; input is # of milliseconds
204 // for exp(-1) decay.
205 void EventBase::setLoadAvgMsec(std::chrono::milliseconds ms) {
206 assert(enableTimeMeasurement_);
207 std::chrono::microseconds us = std::chrono::milliseconds(ms);
208 if (ms > std::chrono::milliseconds::zero()) {
209 maxLatencyLoopTime_.setTimeInterval(us);
210 avgLoopTime_.setTimeInterval(us);
212 LOG(ERROR) << "non-positive arg to setLoadAvgMsec()";
216 void EventBase::resetLoadAvg(double value) {
217 assert(enableTimeMeasurement_);
218 avgLoopTime_.reset(value);
219 maxLatencyLoopTime_.reset(value);
222 static std::chrono::milliseconds
223 getTimeDelta(std::chrono::steady_clock::time_point* prev) {
224 auto result = std::chrono::steady_clock::now() - *prev;
225 *prev = std::chrono::steady_clock::now();
227 return std::chrono::duration_cast<std::chrono::milliseconds>(result);
230 void EventBase::waitUntilRunning() {
231 while (!isRunning()) {
232 std::this_thread::yield();
236 // enters the event_base loop -- will only exit when forced to
237 bool EventBase::loop() {
241 bool EventBase::loopOnce(int flags) {
242 return loopBody(flags | EVLOOP_ONCE);
245 bool EventBase::loopBody(int flags) {
246 VLOG(5) << "EventBase(): Starting loop.";
248 DCHECK(!invokingLoop_)
249 << "Your code just tried to loop over an event base from inside another "
250 << "event base loop. Since libevent is not reentrant, this leads to "
251 << "undefined behavior in opt builds. Please fix immediately. For the "
252 << "common case of an inner function that needs to do some synchronous "
253 << "computation on an event-base, replace getEventBase() by a new, "
254 << "stack-allocated EvenBase.";
255 invokingLoop_ = true;
257 invokingLoop_ = false;
261 bool ranLoopCallbacks;
262 bool blocking = !(flags & EVLOOP_NONBLOCK);
263 bool once = (flags & EVLOOP_ONCE);
265 // time-measurement variables.
266 std::chrono::steady_clock::time_point prev;
267 std::chrono::steady_clock::time_point idleStart = {};
268 std::chrono::microseconds busy;
269 std::chrono::microseconds idle;
271 loopThread_.store(std::this_thread::get_id(), std::memory_order_release);
273 if (!name_.empty()) {
274 setThreadName(name_);
277 if (enableTimeMeasurement_) {
278 prev = std::chrono::steady_clock::now();
279 idleStart = std::chrono::steady_clock::now();
282 while (!stop_.load(std::memory_order_acquire)) {
283 applyLoopKeepAlive();
286 // Run the before loop callbacks
287 LoopCallbackList callbacks;
288 callbacks.swap(runBeforeLoopCallbacks_);
290 while(!callbacks.empty()) {
291 auto* item = &callbacks.front();
292 callbacks.pop_front();
293 item->runLoopCallback();
296 // nobody can add loop callbacks from within this thread if
297 // we don't have to handle anything to start with...
298 if (blocking && loopCallbacks_.empty()) {
299 res = event_base_loop(evb_, EVLOOP_ONCE);
301 res = event_base_loop(evb_, EVLOOP_ONCE | EVLOOP_NONBLOCK);
304 ranLoopCallbacks = runLoopCallbacks();
306 if (enableTimeMeasurement_) {
307 busy = std::chrono::duration_cast<std::chrono::microseconds>(
308 std::chrono::steady_clock::now() - startWork_);
309 idle = std::chrono::duration_cast<std::chrono::microseconds>(
310 startWork_ - idleStart);
312 avgLoopTime_.addSample(std::chrono::microseconds(idle),
313 std::chrono::microseconds(busy));
314 maxLatencyLoopTime_.addSample(std::chrono::microseconds(idle),
315 std::chrono::microseconds(busy));
318 if (observerSampleCount_++ == observer_->getSampleRate()) {
319 observerSampleCount_ = 0;
320 observer_->loopSample(busy.count(), idle.count());
324 VLOG(11) << "EventBase " << this << " did not timeout " <<
325 " loop time guess: " << (busy + idle).count() <<
326 " idle time: " << idle.count() <<
327 " busy time: " << busy.count() <<
328 " avgLoopTime: " << avgLoopTime_.get() <<
329 " maxLatencyLoopTime: " << maxLatencyLoopTime_.get() <<
330 " maxLatency_: " << maxLatency_.count() << "us" <<
331 " notificationQueueSize: " << getNotificationQueueSize() <<
332 " nothingHandledYet(): " << nothingHandledYet();
334 // see if our average loop time has exceeded our limit
335 if ((maxLatency_ > std::chrono::microseconds::zero()) &&
336 (maxLatencyLoopTime_.get() > double(maxLatency_.count()))) {
338 // back off temporarily -- don't keep spamming maxLatencyCob_
339 // if we're only a bit over the limit
340 maxLatencyLoopTime_.dampen(0.9);
343 // Our loop run did real work; reset the idle timer
344 idleStart = std::chrono::steady_clock::now();
346 VLOG(11) << "EventBase " << this << " did not timeout";
349 // If the event loop indicate that there were no more events, and
350 // we also didn't have any loop callbacks to run, there is nothing left to
352 if (res != 0 && !ranLoopCallbacks) {
353 // Since Notification Queue is marked 'internal' some events may not have
354 // run. Run them manually if so, and continue looping.
356 if (getNotificationQueueSize() > 0) {
357 fnRunner_->handlerReady(0);
363 if (enableTimeMeasurement_) {
364 VLOG(11) << "EventBase " << this << " loop time: " <<
365 getTimeDelta(&prev).count();
372 // Reset stop_ so loop() can be called again
376 LOG(ERROR) << "EventBase: -- error in event loop, res = " << res;
378 } else if (res == 1) {
379 VLOG(5) << "EventBase: ran out of events (exiting loop)!";
380 } else if (res > 1) {
381 LOG(ERROR) << "EventBase: unknown event loop result = " << res;
385 loopThread_.store({}, std::memory_order_release);
387 VLOG(5) << "EventBase(): Done with loop.";
391 ssize_t EventBase::loopKeepAliveCount() {
392 if (loopKeepAliveCountAtomic_.load(std::memory_order_relaxed)) {
393 loopKeepAliveCount_ +=
394 loopKeepAliveCountAtomic_.exchange(0, std::memory_order_relaxed);
396 DCHECK_GE(loopKeepAliveCount_, 0);
398 return loopKeepAliveCount_;
401 void EventBase::applyLoopKeepAlive() {
402 auto keepAliveCount = loopKeepAliveCount();
403 // Make sure default VirtualEventBase won't hold EventBase::loop() forever.
404 if (virtualEventBase_ && virtualEventBase_->keepAliveCount() == 1) {
408 if (loopKeepAliveActive_ && keepAliveCount == 0) {
409 // Restore the notification queue internal flag
410 fnRunner_->stopConsuming();
411 fnRunner_->startConsumingInternal(this, queue_.get());
412 loopKeepAliveActive_ = false;
413 } else if (!loopKeepAliveActive_ && keepAliveCount > 0) {
414 // Update the notification queue event to treat it as a normal
415 // (non-internal) event. The notification queue event always remains
416 // installed, and the main loop won't exit with it installed.
417 fnRunner_->stopConsuming();
418 fnRunner_->startConsuming(this, queue_.get());
419 loopKeepAliveActive_ = true;
423 void EventBase::loopForever() {
427 applyLoopKeepAlive();
429 // Make sure notification queue events are treated as normal events.
430 // We can't use loopKeepAlive() here since LoopKeepAlive token can only be
431 // released inside a loop.
432 ++loopKeepAliveCount_;
434 --loopKeepAliveCount_;
440 folly::throwSystemError("error in EventBase::loopForever()");
444 void EventBase::bumpHandlingTime() {
445 if (!enableTimeMeasurement_) {
449 VLOG(11) << "EventBase " << this << " " << __PRETTY_FUNCTION__ <<
450 " (loop) latest " << latestLoopCnt_ << " next " << nextLoopCnt_;
451 if (nothingHandledYet()) {
452 latestLoopCnt_ = nextLoopCnt_;
454 startWork_ = std::chrono::steady_clock::now();
456 VLOG(11) << "EventBase " << this << " " << __PRETTY_FUNCTION__
457 << " (loop) startWork_ " << startWork_.time_since_epoch().count();
461 void EventBase::terminateLoopSoon() {
462 VLOG(5) << "EventBase(): Received terminateLoopSoon() command.";
464 // Set stop to true, so the event loop will know to exit.
465 // TODO: We should really use an atomic operation here with a release
469 // Call event_base_loopbreak() so that libevent will exit the next time
471 event_base_loopbreak(evb_);
473 // If terminateLoopSoon() is called from another thread,
474 // the EventBase thread might be stuck waiting for events.
475 // In this case, it won't wake up and notice that stop_ is set until it
476 // receives another event. Send an empty frame to the notification queue
477 // so that the event loop will wake up even if there are no other events.
479 // We don't care about the return value of trySendFrame(). If it fails
480 // this likely means the EventBase already has lots of events waiting
483 queue_->putMessage(nullptr);
485 // We don't care if putMessage() fails. This likely means
486 // the EventBase already has lots of events waiting anyway.
490 void EventBase::runInLoop(LoopCallback* callback, bool thisIteration) {
491 DCHECK(isInEventBaseThread());
492 callback->cancelLoopCallback();
493 callback->context_ = RequestContext::saveContext();
494 if (runOnceCallbacks_ != nullptr && thisIteration) {
495 runOnceCallbacks_->push_back(*callback);
497 loopCallbacks_.push_back(*callback);
501 void EventBase::runInLoop(Func cob, bool thisIteration) {
502 DCHECK(isInEventBaseThread());
503 auto wrapper = new FunctionLoopCallback(std::move(cob));
504 wrapper->context_ = RequestContext::saveContext();
505 if (runOnceCallbacks_ != nullptr && thisIteration) {
506 runOnceCallbacks_->push_back(*wrapper);
508 loopCallbacks_.push_back(*wrapper);
512 void EventBase::runOnDestruction(LoopCallback* callback) {
513 std::lock_guard<std::mutex> lg(onDestructionCallbacksMutex_);
514 callback->cancelLoopCallback();
515 onDestructionCallbacks_.push_back(*callback);
518 void EventBase::runBeforeLoop(LoopCallback* callback) {
519 DCHECK(isInEventBaseThread());
520 callback->cancelLoopCallback();
521 runBeforeLoopCallbacks_.push_back(*callback);
524 bool EventBase::runInEventBaseThread(Func fn) {
526 // It will be received by the FunctionRunner in the EventBase's thread.
528 // We try not to schedule nullptr callbacks
530 LOG(ERROR) << "EventBase " << this
531 << ": Scheduling nullptr callbacks is not allowed";
535 // Short-circuit if we are already in our event base
536 if (inRunningEventBaseThread()) {
537 runInLoop(std::move(fn));
543 queue_->putMessage(std::move(fn));
544 } catch (const std::exception& ex) {
545 LOG(ERROR) << "EventBase " << this << ": failed to schedule function "
546 << "for EventBase thread: " << ex.what();
553 bool EventBase::runInEventBaseThreadAndWait(FuncRef fn) {
554 if (inRunningEventBaseThread()) {
555 LOG(ERROR) << "EventBase " << this << ": Waiting in the event loop is not "
562 std::condition_variable cv;
563 runInEventBaseThread([&] {
565 std::unique_lock<std::mutex> l(m);
568 // We cannot release the lock before notify_one, because a spurious
569 // wakeup in the waiting thread may lead to cv and m going out of scope
574 std::unique_lock<std::mutex> l(m);
575 cv.wait(l, [&] { return ready; });
580 bool EventBase::runImmediatelyOrRunInEventBaseThreadAndWait(FuncRef fn) {
581 if (isInEventBaseThread()) {
585 return runInEventBaseThreadAndWait(std::move(fn));
589 bool EventBase::runLoopCallbacks() {
590 if (!loopCallbacks_.empty()) {
592 // Swap the loopCallbacks_ list with a temporary list on our stack.
593 // This way we will only run callbacks scheduled at the time
594 // runLoopCallbacks() was invoked.
596 // If any of these callbacks in turn call runInLoop() to schedule more
597 // callbacks, those new callbacks won't be run until the next iteration
598 // around the event loop. This prevents runInLoop() callbacks from being
599 // able to start file descriptor and timeout based events.
600 LoopCallbackList currentCallbacks;
601 currentCallbacks.swap(loopCallbacks_);
602 runOnceCallbacks_ = ¤tCallbacks;
604 while (!currentCallbacks.empty()) {
605 LoopCallback* callback = ¤tCallbacks.front();
606 currentCallbacks.pop_front();
607 folly::RequestContextScopeGuard rctx(callback->context_);
608 callback->runLoopCallback();
611 runOnceCallbacks_ = nullptr;
617 void EventBase::initNotificationQueue() {
618 // Infinite size queue
619 queue_.reset(new NotificationQueue<Func>());
621 // We allocate fnRunner_ separately, rather than declaring it directly
622 // as a member of EventBase solely so that we don't need to include
623 // NotificationQueue.h from EventBase.h
624 fnRunner_.reset(new FunctionRunner());
626 // Mark this as an internal event, so event_base_loop() will return if
627 // there are no other events besides this one installed.
629 // Most callers don't care about the internal notification queue used by
630 // EventBase. The queue is always installed, so if we did count the queue as
631 // an active event, loop() would never exit with no more events to process.
632 // Users can use loopForever() if they do care about the notification queue.
633 // (This is useful for EventBase threads that do nothing but process
634 // runInEventBaseThread() notifications.)
635 fnRunner_->startConsumingInternal(this, queue_.get());
638 void EventBase::SmoothLoopTime::setTimeInterval(
639 std::chrono::microseconds timeInterval) {
640 expCoeff_ = -1.0 / timeInterval.count();
641 VLOG(11) << "expCoeff_ " << expCoeff_ << " " << __PRETTY_FUNCTION__;
644 void EventBase::SmoothLoopTime::reset(double value) {
648 void EventBase::SmoothLoopTime::addSample(
649 std::chrono::microseconds idle,
650 std::chrono::microseconds busy) {
652 * Position at which the busy sample is considered to be taken.
653 * (Allows to quickly skew our average without editing much code)
655 enum BusySamplePosition {
656 RIGHT = 0, // busy sample placed at the end of the iteration
657 CENTER = 1, // busy sample placed at the middle point of the iteration
658 LEFT = 2, // busy sample placed at the beginning of the iteration
661 // See http://en.wikipedia.org/wiki/Moving_average#Exponential_moving_average
662 // and D676020 for more info on this calculation.
663 VLOG(11) << "idle " << idle.count() << " oldBusyLeftover_ "
664 << oldBusyLeftover_.count() << " idle + oldBusyLeftover_ "
665 << (idle + oldBusyLeftover_).count() << " busy " << busy.count()
666 << " " << __PRETTY_FUNCTION__;
667 idle += oldBusyLeftover_ + busy;
668 oldBusyLeftover_ = (busy * BusySamplePosition::CENTER) / 2;
669 idle -= oldBusyLeftover_;
671 double coeff = exp(idle.count() * expCoeff_);
673 value_ += (1.0 - coeff) * busy.count();
676 bool EventBase::nothingHandledYet() const noexcept {
677 VLOG(11) << "latest " << latestLoopCnt_ << " next " << nextLoopCnt_;
678 return (nextLoopCnt_ != latestLoopCnt_);
681 void EventBase::attachTimeoutManager(AsyncTimeout* obj,
682 InternalEnum internal) {
684 struct event* ev = obj->getEvent();
685 assert(ev->ev_base == nullptr);
687 event_base_set(getLibeventBase(), ev);
688 if (internal == AsyncTimeout::InternalEnum::INTERNAL) {
689 // Set the EVLIST_INTERNAL flag
690 event_ref_flags(ev) |= EVLIST_INTERNAL;
694 void EventBase::detachTimeoutManager(AsyncTimeout* obj) {
696 struct event* ev = obj->getEvent();
697 ev->ev_base = nullptr;
700 bool EventBase::scheduleTimeout(AsyncTimeout* obj,
701 TimeoutManager::timeout_type timeout) {
702 assert(isInEventBaseThread());
703 // Set up the timeval and add the event
705 tv.tv_sec = long(timeout.count() / 1000LL);
706 tv.tv_usec = long((timeout.count() % 1000LL) * 1000LL);
708 struct event* ev = obj->getEvent();
709 if (event_add(ev, &tv) < 0) {
710 LOG(ERROR) << "EventBase: failed to schedule timeout: " << strerror(errno);
717 void EventBase::cancelTimeout(AsyncTimeout* obj) {
718 assert(isInEventBaseThread());
719 struct event* ev = obj->getEvent();
720 if (EventUtil::isEventRegistered(ev)) {
725 void EventBase::setName(const std::string& name) {
726 assert(isInEventBaseThread());
730 setThreadName(loopThread_.load(std::memory_order_relaxed),
735 const std::string& EventBase::getName() {
736 assert(isInEventBaseThread());
740 const char* EventBase::getLibeventVersion() { return event_get_version(); }
741 const char* EventBase::getLibeventMethod() { return event_get_method(); }
743 VirtualEventBase& EventBase::getVirtualEventBase() {
744 folly::call_once(virtualEventBaseInitFlag_, [&] {
745 virtualEventBase_ = folly::make_unique<VirtualEventBase>(*this);
748 return *virtualEventBase_;