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.
30 #include <unordered_map>
31 #include <unordered_set>
34 #include <boost/intrusive/list.hpp>
35 #include <boost/utility.hpp>
37 #include <folly/Executor.h>
38 #include <folly/Function.h>
39 #include <folly/Portability.h>
40 #include <folly/experimental/ExecutionObserver.h>
41 #include <folly/futures/DrivableExecutor.h>
42 #include <folly/io/async/AsyncTimeout.h>
43 #include <folly/io/async/HHWheelTimer.h>
44 #include <folly/io/async/Request.h>
45 #include <folly/io/async/TimeoutManager.h>
46 #include <folly/portability/PThread.h>
47 #include <glog/logging.h>
49 #include <event.h> // libevent
53 typedef std::function<void()> Cob;
54 template <typename MessageT>
55 class NotificationQueue;
58 class EventBaseLocalBase;
60 class EventBaseLocalBaseBase {
62 virtual void onEventBaseDestruction(EventBase& evb) = 0;
63 virtual ~EventBaseLocalBaseBase() = default;
69 class EventBaseObserver {
71 virtual ~EventBaseObserver() = default;
73 virtual uint32_t getSampleRate() const = 0;
75 virtual void loopSample(
76 int64_t busyTime, int64_t idleTime) = 0;
79 // Helper class that sets and retrieves the EventBase associated with a given
80 // request via RequestContext. See Request.h for that mechanism.
81 class RequestEventBase : public RequestData {
83 static EventBase* get() {
84 auto data = dynamic_cast<RequestEventBase*>(
85 RequestContext::get()->getContextData(kContextDataName));
92 static void set(EventBase* eb) {
93 RequestContext::get()->setContextData(
95 std::unique_ptr<RequestEventBase>(new RequestEventBase(eb)));
99 explicit RequestEventBase(EventBase* eb) : eb_(eb) {}
101 static constexpr const char* kContextDataName{"EventBase"};
105 * This class is a wrapper for all asynchronous I/O processing functionality
107 * EventBase provides a main loop that notifies EventHandler callback objects
108 * when I/O is ready on a file descriptor, and notifies AsyncTimeout objects
109 * when a specified timeout has expired. More complex, higher-level callback
110 * mechanisms can then be built on top of EventHandler and AsyncTimeout.
112 * A EventBase object can only drive an event loop for a single thread. To
113 * take advantage of multiple CPU cores, most asynchronous I/O servers have one
114 * thread per CPU, and use a separate EventBase for each thread.
116 * In general, most EventBase methods may only be called from the thread
117 * running the EventBase's loop. There are a few exceptions to this rule, for
118 * methods that are explicitly intended to allow communication with a
119 * EventBase from other threads. When it is safe to call a method from
120 * another thread it is explicitly listed in the method comments.
122 class EventBase : private boost::noncopyable,
123 public TimeoutManager,
124 public DrivableExecutor {
126 using Func = folly::Function<void()>;
129 * A callback interface to use with runInLoop()
131 * Derive from this class if you need to delay some code execution until the
132 * next iteration of the event loop. This allows you to schedule code to be
133 * invoked from the top-level of the loop, after your immediate callers have
136 * If a LoopCallback object is destroyed while it is scheduled to be run in
137 * the next loop iteration, it will automatically be cancelled.
141 virtual ~LoopCallback() = default;
143 virtual void runLoopCallback() noexcept = 0;
144 void cancelLoopCallback() {
148 bool isLoopCallbackScheduled() const {
149 return hook_.is_linked();
153 typedef boost::intrusive::list_member_hook<
154 boost::intrusive::link_mode<boost::intrusive::auto_unlink> > ListHook;
158 typedef boost::intrusive::list<
160 boost::intrusive::member_hook<LoopCallback, ListHook,
161 &LoopCallback::hook_>,
162 boost::intrusive::constant_time_size<false> > List;
164 // EventBase needs access to LoopCallbackList (and therefore to hook_)
165 friend class EventBase;
166 std::shared_ptr<RequestContext> context_;
170 * Create a new EventBase object.
172 * @param enableTimeMeasurement Informs whether this event base should measure
173 * time. Disabling it would likely improve
174 * performance, but will disable some features
175 * that relies on time-measurement, including:
176 * observer, max latency and avg loop time.
178 explicit EventBase(bool enableTimeMeasurement = true);
181 * Create a new EventBase object that will use the specified libevent
182 * event_base object to drive the event loop.
184 * The EventBase will take ownership of this event_base, and will call
185 * event_base_free(evb) when the EventBase is destroyed.
187 * @param enableTimeMeasurement Informs whether this event base should measure
188 * time. Disabling it would likely improve
189 * performance, but will disable some features
190 * that relies on time-measurement, including:
191 * observer, max latency and avg loop time.
193 explicit EventBase(event_base* evb, bool enableTimeMeasurement = true);
197 * Runs the event loop.
199 * loop() will loop waiting for I/O or timeouts and invoking EventHandler
200 * and AsyncTimeout callbacks as their events become ready. loop() will
201 * only return when there are no more events remaining to process, or after
202 * terminateLoopSoon() has been called.
204 * loop() may be called again to restart event processing after a previous
205 * call to loop() or loopForever() has returned.
207 * Returns true if the loop completed normally (if it processed all
208 * outstanding requests, or if terminateLoopSoon() was called). If an error
209 * occurs waiting for events, false will be returned.
214 * Wait for some events to become active, run them, then return.
216 * When EVLOOP_NONBLOCK is set in flags, the loop won't block if there
217 * are not any events to process.
219 * This is useful for callers that want to run the loop manually.
221 * Returns the same result as loop().
223 bool loopOnce(int flags = 0);
226 * Runs the event loop.
228 * loopForever() behaves like loop(), except that it keeps running even if
229 * when there are no more user-supplied EventHandlers or AsyncTimeouts
230 * registered. It will only return after terminateLoopSoon() has been
233 * This is useful for callers that want to wait for other threads to call
234 * runInEventBaseThread(), even when there are no other scheduled events.
236 * loopForever() may be called again to restart event processing after a
237 * previous call to loop() or loopForever() has returned.
239 * Throws a std::system_error if an error occurs.
244 * Causes the event loop to exit soon.
246 * This will cause an existing call to loop() or loopForever() to stop event
247 * processing and return, even if there are still events remaining to be
250 * It is safe to call terminateLoopSoon() from another thread to cause loop()
251 * to wake up and return in the EventBase loop thread. terminateLoopSoon()
252 * may also be called from the loop thread itself (for example, a
253 * EventHandler or AsyncTimeout callback may call terminateLoopSoon() to
254 * cause the loop to exit after the callback returns.) If the loop is not
255 * running, this will cause the next call to loop to terminate soon after
256 * starting. If a loop runs out of work (and so terminates on its own)
257 * concurrently with a call to terminateLoopSoon(), this may cause a race
260 * Note that the caller is responsible for ensuring that cleanup of all event
261 * callbacks occurs properly. Since terminateLoopSoon() causes the loop to
262 * exit even when there are pending events present, there may be remaining
263 * callbacks present waiting to be invoked. If the loop is later restarted
264 * pending events will continue to be processed normally, however if the
265 * EventBase is destroyed after calling terminateLoopSoon() it is the
266 * caller's responsibility to ensure that cleanup happens properly even if
267 * some outstanding events are never processed.
269 void terminateLoopSoon();
272 * Adds the given callback to a queue of things run after the current pass
273 * through the event loop completes. Note that if this callback calls
274 * runInLoop() the new callback won't be called until the main event loop
275 * has gone through a cycle.
277 * This method may only be called from the EventBase's thread. This
278 * essentially allows an event handler to schedule an additional callback to
279 * be invoked after it returns.
281 * Use runInEventBaseThread() to schedule functions from another thread.
283 * The thisIteration parameter makes this callback run in this loop
284 * iteration, instead of the next one, even if called from a
285 * runInLoop callback (normal io callbacks that call runInLoop will
286 * always run in this iteration). This was originally added to
287 * support detachEventBase, as a user callback may have called
288 * terminateLoopSoon(), but we want to make sure we detach. Also,
289 * detachEventBase almost always must be called from the base event
290 * loop to ensure the stack is unwound, since most users of
291 * EventBase are not thread safe.
293 * Ideally we would not need thisIteration, and instead just use
294 * runInLoop with loop() (instead of terminateLoopSoon).
296 void runInLoop(LoopCallback* callback, bool thisIteration = false);
299 * Convenience function to call runInLoop() with a folly::Function.
301 * This creates a LoopCallback object to wrap the folly::Function, and invoke
302 * the folly::Function when the loop callback fires. This is slightly more
303 * expensive than defining your own LoopCallback, but more convenient in
304 * areas that aren't too performance sensitive.
306 * This method may only be called from the EventBase's thread. This
307 * essentially allows an event handler to schedule an additional callback to
308 * be invoked after it returns.
310 * Use runInEventBaseThread() to schedule functions from another thread.
312 void runInLoop(Func c, bool thisIteration = false);
315 * Adds the given callback to a queue of things run before destruction
316 * of current EventBase.
318 * This allows users of EventBase that run in it, but don't control it,
319 * to be notified before EventBase gets destructed.
321 * Note: will be called from the thread that invoked EventBase destructor,
322 * before the final run of loop callbacks.
324 void runOnDestruction(LoopCallback* callback);
327 * Adds the given callback to a queue of things run after the notification
328 * queue is drained before the destruction of current EventBase.
330 * Note: will be called from the thread that invoked EventBase destructor,
331 * after the final run of loop callbacks.
333 void runAfterDrain(Func cob);
336 * Adds a callback that will run immediately *before* the event loop.
337 * This is very similar to runInLoop(), but will not cause the loop to break:
338 * For example, this callback could be used to get loop times.
340 void runBeforeLoop(LoopCallback* callback);
343 * Run the specified function in the EventBase's thread.
345 * This method is thread-safe, and may be called from another thread.
347 * If runInEventBaseThread() is called when the EventBase loop is not
348 * running, the function call will be delayed until the next time the loop is
351 * If runInEventBaseThread() returns true the function has successfully been
352 * scheduled to run in the loop thread. However, if the loop is terminated
353 * (and never later restarted) before it has a chance to run the requested
354 * function, the function will be run upon the EventBase's destruction.
356 * If two calls to runInEventBaseThread() are made from the same thread, the
357 * functions will always be run in the order that they were scheduled.
358 * Ordering between functions scheduled from separate threads is not
361 * @param fn The function to run. The function must not throw any
363 * @param arg An argument to pass to the function.
365 * @return Returns true if the function was successfully scheduled, or false
366 * if there was an error scheduling the function.
368 template <typename T>
369 bool runInEventBaseThread(void (*fn)(T*), T* arg);
372 * Run the specified function in the EventBase's thread
374 * This version of runInEventBaseThread() takes a folly::Function object.
375 * Note that this may be less efficient than the version that takes a plain
376 * function pointer and void* argument, if moving the function is expensive
377 * (e.g., if it wraps a lambda which captures some values with expensive move
380 * If the loop is terminated (and never later restarted) before it has a
381 * chance to run the requested function, the function will be run upon the
382 * EventBase's destruction.
384 * The function must not throw any exceptions.
386 bool runInEventBaseThread(Func fn);
389 * Like runInEventBaseThread, but the caller waits for the callback to be
392 template <typename T>
393 bool runInEventBaseThreadAndWait(void (*fn)(T*), T* arg);
396 * Like runInEventBaseThread, but the caller waits for the callback to be
399 bool runInEventBaseThreadAndWait(Func fn);
402 * Like runInEventBaseThreadAndWait, except if the caller is already in the
403 * event base thread, the functor is simply run inline.
405 template <typename T>
406 bool runImmediatelyOrRunInEventBaseThreadAndWait(void (*fn)(T*), T* arg);
409 * Like runInEventBaseThreadAndWait, except if the caller is already in the
410 * event base thread, the functor is simply run inline.
412 bool runImmediatelyOrRunInEventBaseThreadAndWait(Func fn);
415 * Runs the given Cob at some time after the specified number of
416 * milliseconds. (No guarantees exactly when.)
418 * Throws a std::system_error if an error occurs.
422 uint32_t milliseconds,
423 TimeoutManager::InternalEnum in = TimeoutManager::InternalEnum::NORMAL);
426 * @see tryRunAfterDelay for more details
428 * @return true iff the cob was successfully registered.
431 bool tryRunAfterDelay(
433 uint32_t milliseconds,
434 TimeoutManager::InternalEnum in = TimeoutManager::InternalEnum::NORMAL);
437 * Set the maximum desired latency in us and provide a callback which will be
438 * called when that latency is exceeded.
439 * OBS: This functionality depends on time-measurement.
441 void setMaxLatency(int64_t maxLatency, Func maxLatencyCob) {
442 assert(enableTimeMeasurement_);
443 maxLatency_ = maxLatency;
444 maxLatencyCob_ = std::move(maxLatencyCob);
449 * Set smoothing coefficient for loop load average; # of milliseconds
450 * for exp(-1) (1/2.71828...) decay.
452 void setLoadAvgMsec(uint32_t ms);
455 * reset the load average to a desired value
457 void resetLoadAvg(double value = 0.0);
460 * Get the average loop time in microseconds (an exponentially-smoothed ave)
462 double getAvgLoopTime() const {
463 assert(enableTimeMeasurement_);
464 return avgLoopTime_.get();
468 * check if the event base loop is running.
470 bool isRunning() const {
471 return loopThread_.load(std::memory_order_relaxed) != 0;
475 * wait until the event loop starts (after starting the event loop thread).
477 void waitUntilRunning();
479 int getNotificationQueueSize() const;
481 void setMaxReadAtOnce(uint32_t maxAtOnce);
484 * Verify that current thread is the EventBase thread, if the EventBase is
487 bool isInEventBaseThread() const {
488 auto tid = loopThread_.load(std::memory_order_relaxed);
489 return tid == 0 || pthread_equal(tid, pthread_self());
492 bool inRunningEventBaseThread() const {
493 return pthread_equal(
494 loopThread_.load(std::memory_order_relaxed), pthread_self());
497 HHWheelTimer& timer() {
499 wheelTimer_ = HHWheelTimer::newTimer(this, std::chrono::milliseconds(1));
501 return *wheelTimer_.get();
504 // --------- interface to underlying libevent base ------------
505 // Avoid using these functions if possible. These functions are not
506 // guaranteed to always be present if we ever provide alternative EventBase
507 // implementations that do not use libevent internally.
508 event_base* getLibeventBase() const { return evb_; }
509 static const char* getLibeventVersion();
510 static const char* getLibeventMethod();
513 * only EventHandler/AsyncTimeout subclasses and ourselves should
516 * This is used to mark the beginning of a new loop cycle by the
517 * first handler fired within that cycle.
520 void bumpHandlingTime() override final;
522 class SmoothLoopTime {
524 explicit SmoothLoopTime(uint64_t timeInterval)
525 : expCoeff_(-1.0/timeInterval)
527 , oldBusyLeftover_(0) {
528 VLOG(11) << "expCoeff_ " << expCoeff_ << " " << __PRETTY_FUNCTION__;
531 void setTimeInterval(uint64_t timeInterval);
532 void reset(double value = 0.0);
534 void addSample(int64_t idle, int64_t busy);
540 void dampen(double factor) {
547 int64_t oldBusyLeftover_;
550 void setObserver(const std::shared_ptr<EventBaseObserver>& observer) {
551 assert(enableTimeMeasurement_);
552 observer_ = observer;
555 const std::shared_ptr<EventBaseObserver>& getObserver() {
560 * Setup execution observation/instrumentation for every EventHandler
561 * executed in this EventBase.
563 * @param executionObserver EventHandle's execution observer.
565 void setExecutionObserver(ExecutionObserver* observer) {
566 executionObserver_ = observer;
570 * Gets the execution observer associated with this EventBase.
572 ExecutionObserver* getExecutionObserver() {
573 return executionObserver_;
577 * Set the name of the thread that runs this event base.
579 void setName(const std::string& name);
582 * Returns the name of the thread that runs this event base.
584 const std::string& getName();
586 /// Implements the Executor interface
587 void add(Cob fn) override {
588 // runInEventBaseThread() takes a const&,
589 // so no point in doing std::move here.
590 runInEventBaseThread(std::move(fn));
593 /// Implements the DrivableExecutor interface
594 void drive() override {
598 struct LoopKeepAliveDeleter {
599 void operator()(EventBase* evb) {
600 DCHECK(evb->isInEventBaseThread());
601 evb->loopKeepAliveCount_--;
604 using LoopKeepAlive = std::unique_ptr<EventBase, LoopKeepAliveDeleter>;
606 /// Returns you a handle which make loop() behave like loopForever() until
607 /// destroyed. loop() will return to its original behavior only when all
608 /// loop keep-alives are released. Loop holder is safe to release only from
609 /// EventBase thread.
611 /// May return no op LoopKeepAlive if loopForever() is already running.
612 LoopKeepAlive loopKeepAlive() {
613 DCHECK(isInEventBaseThread());
614 loopKeepAliveCount_++;
615 return LoopKeepAlive(this);
620 void attachTimeoutManager(AsyncTimeout* obj,
621 TimeoutManager::InternalEnum internal) override;
623 void detachTimeoutManager(AsyncTimeout* obj) override;
625 bool scheduleTimeout(AsyncTimeout* obj, TimeoutManager::timeout_type timeout)
628 void cancelTimeout(AsyncTimeout* obj) override;
630 bool isInTimeoutManagerThread() override final {
631 return isInEventBaseThread();
634 void applyLoopKeepAlive();
637 * Helper function that tells us whether we have already handled
638 * some event/timeout/callback in this loop iteration.
640 bool nothingHandledYet() const noexcept;
642 // small object used as a callback arg with enough info to execute the
643 // appropriate client-provided Cob
644 class CobTimeout : public AsyncTimeout {
646 CobTimeout(EventBase* b, Func c, TimeoutManager::InternalEnum in)
647 : AsyncTimeout(b, in), cob_(std::move(c)) {}
649 virtual void timeoutExpired() noexcept;
655 typedef boost::intrusive::list_member_hook<
656 boost::intrusive::link_mode<boost::intrusive::auto_unlink> > ListHook;
660 typedef boost::intrusive::list<
662 boost::intrusive::member_hook<CobTimeout, ListHook, &CobTimeout::hook>,
663 boost::intrusive::constant_time_size<false> > List;
666 typedef LoopCallback::List LoopCallbackList;
667 class FunctionRunner;
669 bool loopBody(int flags = 0);
671 // executes any callbacks queued by runInLoop(); returns false if none found
672 bool runLoopCallbacks(bool setContext = true);
674 void initNotificationQueue();
676 // should only be accessed through public getter
677 HHWheelTimer::UniquePtr wheelTimer_;
679 CobTimeout::List pendingCobTimeouts_;
681 LoopCallbackList loopCallbacks_;
682 LoopCallbackList runBeforeLoopCallbacks_;
683 LoopCallbackList onDestructionCallbacks_;
684 LoopCallbackList runAfterDrainCallbacks_;
686 // This will be null most of the time, but point to currentCallbacks
687 // if we are in the middle of running loop callbacks, such that
688 // runInLoop(..., true) will always run in the current loop
690 LoopCallbackList* runOnceCallbacks_;
692 // stop_ is set by terminateLoopSoon() and is used by the main loop
693 // to determine if it should exit
694 std::atomic<bool> stop_;
696 // The ID of the thread running the main loop.
697 // 0 if loop is not running.
698 // Note: POSIX doesn't guarantee that 0 is an invalid pthread_t (or
699 // even that atomic<pthread_t> is valid), but that's how it is
700 // everywhere (at least on Linux, FreeBSD, and OSX).
701 std::atomic<pthread_t> loopThread_;
703 // pointer to underlying event_base class doing the heavy lifting
706 // A notification queue for runInEventBaseThread() to use
707 // to send function requests to the EventBase thread.
708 std::unique_ptr<NotificationQueue<Func>> queue_;
709 std::unique_ptr<FunctionRunner> fnRunner_;
710 size_t loopKeepAliveCount_{0};
711 bool loopKeepAliveActive_{false};
713 // limit for latency in microseconds (0 disables)
716 // exponentially-smoothed average loop time for latency-limiting
717 SmoothLoopTime avgLoopTime_;
719 // smoothed loop time used to invoke latency callbacks; differs from
720 // avgLoopTime_ in that it's scaled down after triggering a callback
721 // to reduce spamminess
722 SmoothLoopTime maxLatencyLoopTime_;
724 // callback called when latency limit is exceeded
727 // Enables/disables time measurements in loopBody(). if disabled, the
728 // following functionality that relies on time-measurement, will not
729 // be supported: avg loop time, observer and max latency.
730 const bool enableTimeMeasurement_;
732 // we'll wait this long before running deferred callbacks if the event
734 static const int kDEFAULT_IDLE_WAIT_USEC = 20000; // 20ms
736 // Wrap-around loop counter to detect beginning of each loop
737 uint64_t nextLoopCnt_;
738 uint64_t latestLoopCnt_;
740 // Prevent undefined behavior from invoking event_base_loop() reentrantly.
741 // This is needed since many projects use libevent-1.4, which lacks commit
742 // b557b175c00dc462c1fce25f6e7dd67121d2c001 from
743 // https://github.com/libevent/libevent/.
744 bool invokingLoop_{false};
746 // Observer to export counters
747 std::shared_ptr<EventBaseObserver> observer_;
748 uint32_t observerSampleCount_;
750 // EventHandler's execution observer.
751 ExecutionObserver* executionObserver_;
753 // Name of the thread running this EventBase
756 // allow runOnDestruction() to be called from any threads
757 std::mutex onDestructionCallbacksMutex_;
759 // allow runAfterDrain() to be called from any threads
760 std::mutex runAfterDrainCallbacksMutex_;
762 // see EventBaseLocal
763 friend class detail::EventBaseLocalBase;
764 template <typename T> friend class EventBaseLocal;
765 std::mutex localStorageMutex_;
766 std::unordered_map<uint64_t, std::shared_ptr<void>> localStorage_;
767 std::unordered_set<detail::EventBaseLocalBaseBase*> localStorageToDtor_;
770 template <typename T>
771 bool EventBase::runInEventBaseThread(void (*fn)(T*), T* arg) {
772 return runInEventBaseThread([=] { fn(arg); });
775 template <typename T>
776 bool EventBase::runInEventBaseThreadAndWait(void (*fn)(T*), T* arg) {
777 return runInEventBaseThreadAndWait([=] { fn(arg); });
780 template <typename T>
781 bool EventBase::runImmediatelyOrRunInEventBaseThreadAndWait(
784 return runImmediatelyOrRunInEventBaseThreadAndWait([=] { fn(arg); });