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>
36 #include <folly/Executor.h>
37 #include <folly/Portability.h>
38 #include <folly/experimental/ExecutionObserver.h>
39 #include <folly/futures/DrivableExecutor.h>
40 #include <folly/io/async/AsyncTimeout.h>
41 #include <folly/io/async/Request.h>
42 #include <folly/io/async/TimeoutManager.h>
43 #include <glog/logging.h>
45 #include <event.h> // libevent
49 typedef std::function<void()> Cob;
50 template <typename MessageT>
51 class NotificationQueue;
54 class EventBaseLocalBase;
56 class EventBaseLocalBaseBase {
58 virtual void onEventBaseDestruction(EventBase& evb) = 0;
59 virtual ~EventBaseLocalBaseBase() = default;
65 class EventBaseObserver {
67 virtual ~EventBaseObserver() = default;
69 virtual uint32_t getSampleRate() const = 0;
71 virtual void loopSample(
72 int64_t busyTime, int64_t idleTime) = 0;
75 // Helper class that sets and retrieves the EventBase associated with a given
76 // request via RequestContext. See Request.h for that mechanism.
77 class RequestEventBase : public RequestData {
79 static EventBase* get() {
80 auto data = dynamic_cast<RequestEventBase*>(
81 RequestContext::get()->getContextData(kContextDataName));
88 static void set(EventBase* eb) {
89 RequestContext::get()->setContextData(
91 std::unique_ptr<RequestEventBase>(new RequestEventBase(eb)));
95 explicit RequestEventBase(EventBase* eb) : eb_(eb) {}
97 static constexpr const char* kContextDataName{"EventBase"};
101 * This class is a wrapper for all asynchronous I/O processing functionality
103 * EventBase provides a main loop that notifies EventHandler callback objects
104 * when I/O is ready on a file descriptor, and notifies AsyncTimeout objects
105 * when a specified timeout has expired. More complex, higher-level callback
106 * mechanisms can then be built on top of EventHandler and AsyncTimeout.
108 * A EventBase object can only drive an event loop for a single thread. To
109 * take advantage of multiple CPU cores, most asynchronous I/O servers have one
110 * thread per CPU, and use a separate EventBase for each thread.
112 * In general, most EventBase methods may only be called from the thread
113 * running the EventBase's loop. There are a few exceptions to this rule, for
114 * methods that are explicitly intended to allow communication with a
115 * EventBase from other threads. When it is safe to call a method from
116 * another thread it is explicitly listed in the method comments.
118 class EventBase : private boost::noncopyable,
119 public TimeoutManager,
120 public DrivableExecutor {
123 * A callback interface to use with runInLoop()
125 * Derive from this class if you need to delay some code execution until the
126 * next iteration of the event loop. This allows you to schedule code to be
127 * invoked from the top-level of the loop, after your immediate callers have
130 * If a LoopCallback object is destroyed while it is scheduled to be run in
131 * the next loop iteration, it will automatically be cancelled.
135 virtual ~LoopCallback() = default;
137 virtual void runLoopCallback() noexcept = 0;
138 void cancelLoopCallback() {
142 bool isLoopCallbackScheduled() const {
143 return hook_.is_linked();
147 typedef boost::intrusive::list_member_hook<
148 boost::intrusive::link_mode<boost::intrusive::auto_unlink> > ListHook;
152 typedef boost::intrusive::list<
154 boost::intrusive::member_hook<LoopCallback, ListHook,
155 &LoopCallback::hook_>,
156 boost::intrusive::constant_time_size<false> > List;
158 // EventBase needs access to LoopCallbackList (and therefore to hook_)
159 friend class EventBase;
160 std::shared_ptr<RequestContext> context_;
164 * Create a new EventBase object.
166 * @param enableTimeMeasurement Informs whether this event base should measure
167 * time. Disabling it would likely improve
168 * performance, but will disable some features
169 * that relies on time-measurement, including:
170 * observer, max latency and avg loop time.
172 explicit EventBase(bool enableTimeMeasurement = true);
175 * Create a new EventBase object that will use the specified libevent
176 * event_base object to drive the event loop.
178 * The EventBase will take ownership of this event_base, and will call
179 * event_base_free(evb) when the EventBase is destroyed.
181 * @param enableTimeMeasurement Informs whether this event base should measure
182 * time. Disabling it would likely improve
183 * performance, but will disable some features
184 * that relies on time-measurement, including:
185 * observer, max latency and avg loop time.
187 explicit EventBase(event_base* evb, bool enableTimeMeasurement = true);
191 * Runs the event loop.
193 * loop() will loop waiting for I/O or timeouts and invoking EventHandler
194 * and AsyncTimeout callbacks as their events become ready. loop() will
195 * only return when there are no more events remaining to process, or after
196 * terminateLoopSoon() has been called.
198 * loop() may be called again to restart event processing after a previous
199 * call to loop() or loopForever() has returned.
201 * Returns true if the loop completed normally (if it processed all
202 * outstanding requests, or if terminateLoopSoon() was called). If an error
203 * occurs waiting for events, false will be returned.
208 * Wait for some events to become active, run them, then return.
210 * When EVLOOP_NONBLOCK is set in flags, the loop won't block if there
211 * are not any events to process.
213 * This is useful for callers that want to run the loop manually.
215 * Returns the same result as loop().
217 bool loopOnce(int flags = 0);
220 * Runs the event loop.
222 * loopForever() behaves like loop(), except that it keeps running even if
223 * when there are no more user-supplied EventHandlers or AsyncTimeouts
224 * registered. It will only return after terminateLoopSoon() has been
227 * This is useful for callers that want to wait for other threads to call
228 * runInEventBaseThread(), even when there are no other scheduled events.
230 * loopForever() may be called again to restart event processing after a
231 * previous call to loop() or loopForever() has returned.
233 * Throws a std::system_error if an error occurs.
238 * Causes the event loop to exit soon.
240 * This will cause an existing call to loop() or loopForever() to stop event
241 * processing and return, even if there are still events remaining to be
244 * It is safe to call terminateLoopSoon() from another thread to cause loop()
245 * to wake up and return in the EventBase loop thread. terminateLoopSoon()
246 * may also be called from the loop thread itself (for example, a
247 * EventHandler or AsyncTimeout callback may call terminateLoopSoon() to
248 * cause the loop to exit after the callback returns.) If the loop is not
249 * running, this will cause the next call to loop to terminate soon after
250 * starting. If a loop runs out of work (and so terminates on its own)
251 * concurrently with a call to terminateLoopSoon(), this may cause a race
254 * Note that the caller is responsible for ensuring that cleanup of all event
255 * callbacks occurs properly. Since terminateLoopSoon() causes the loop to
256 * exit even when there are pending events present, there may be remaining
257 * callbacks present waiting to be invoked. If the loop is later restarted
258 * pending events will continue to be processed normally, however if the
259 * EventBase is destroyed after calling terminateLoopSoon() it is the
260 * caller's responsibility to ensure that cleanup happens properly even if
261 * some outstanding events are never processed.
263 void terminateLoopSoon();
266 * Adds the given callback to a queue of things run after the current pass
267 * through the event loop completes. Note that if this callback calls
268 * runInLoop() the new callback won't be called until the main event loop
269 * has gone through a cycle.
271 * This method may only be called from the EventBase's thread. This
272 * essentially allows an event handler to schedule an additional callback to
273 * be invoked after it returns.
275 * Use runInEventBaseThread() to schedule functions from another thread.
277 * The thisIteration parameter makes this callback run in this loop
278 * iteration, instead of the next one, even if called from a
279 * runInLoop callback (normal io callbacks that call runInLoop will
280 * always run in this iteration). This was originally added to
281 * support detachEventBase, as a user callback may have called
282 * terminateLoopSoon(), but we want to make sure we detach. Also,
283 * detachEventBase almost always must be called from the base event
284 * loop to ensure the stack is unwound, since most users of
285 * EventBase are not thread safe.
287 * Ideally we would not need thisIteration, and instead just use
288 * runInLoop with loop() (instead of terminateLoopSoon).
290 void runInLoop(LoopCallback* callback, bool thisIteration = false);
293 * Convenience function to call runInLoop() with a std::function.
295 * This creates a LoopCallback object to wrap the std::function, and invoke
296 * the std::function when the loop callback fires. This is slightly more
297 * expensive than defining your own LoopCallback, but more convenient in
298 * areas that aren't performance sensitive where you just want to use
299 * std::bind. (std::bind is fairly slow on even by itself.)
301 * This method may only be called from the EventBase's thread. This
302 * essentially allows an event handler to schedule an additional callback to
303 * be invoked after it returns.
305 * Use runInEventBaseThread() to schedule functions from another thread.
307 void runInLoop(const Cob& c, bool thisIteration = false);
309 void runInLoop(Cob&& c, bool thisIteration = false);
312 * Adds the given callback to a queue of things run before destruction
313 * of current EventBase.
315 * This allows users of EventBase that run in it, but don't control it,
316 * to be notified before EventBase gets destructed.
318 * Note: will be called from the thread that invoked EventBase destructor,
319 * before the final run of loop callbacks.
321 void runOnDestruction(LoopCallback* callback);
324 * Adds the given callback to a queue of things run after the notification
325 * queue is drained before the destruction of current EventBase.
327 * Note: will be called from the thread that invoked EventBase destructor,
328 * after the final run of loop callbacks.
330 void runAfterDrain(Cob&& cob);
333 * Adds a callback that will run immediately *before* the event loop.
334 * This is very similar to runInLoop(), but will not cause the loop to break:
335 * For example, this callback could be used to get loop times.
337 void runBeforeLoop(LoopCallback* callback);
340 * Run the specified function in the EventBase's thread.
342 * This method is thread-safe, and may be called from another thread.
344 * If runInEventBaseThread() is called when the EventBase loop is not
345 * running, the function call will be delayed until the next time the loop is
348 * If runInEventBaseThread() returns true the function has successfully been
349 * scheduled to run in the loop thread. However, if the loop is terminated
350 * (and never later restarted) before it has a chance to run the requested
351 * function, the function will be run upon the EventBase's destruction.
353 * If two calls to runInEventBaseThread() are made from the same thread, the
354 * functions will always be run in the order that they were scheduled.
355 * Ordering between functions scheduled from separate threads is not
358 * @param fn The function to run. The function must not throw any
360 * @param arg An argument to pass to the function.
362 * @return Returns true if the function was successfully scheduled, or false
363 * if there was an error scheduling the function.
365 template <typename T>
366 bool runInEventBaseThread(void (*fn)(T*), T* arg);
369 * Run the specified function in the EventBase's thread
371 * This version of runInEventBaseThread() takes a std::function object.
372 * Note that this is less efficient than the version that takes a plain
373 * function pointer and void* argument, as it has to allocate memory to copy
374 * the std::function object.
376 * If the loop is terminated (and never later restarted) before it has a
377 * chance to run the requested function, the function will be run upon the
378 * EventBase's destruction.
380 * The function must not throw any exceptions.
382 bool runInEventBaseThread(const Cob& fn);
385 * Like runInEventBaseThread, but the caller waits for the callback to be
388 template <typename T>
389 bool runInEventBaseThreadAndWait(void (*fn)(T*), T* arg);
392 * Like runInEventBaseThread, but the caller waits for the callback to be
395 bool runInEventBaseThreadAndWait(const Cob& fn);
398 * Like runInEventBaseThreadAndWait, except if the caller is already in the
399 * event base thread, the functor is simply run inline.
401 template <typename T>
402 bool runImmediatelyOrRunInEventBaseThreadAndWait(void (*fn)(T*), T* arg);
405 * Like runInEventBaseThreadAndWait, except if the caller is already in the
406 * event base thread, the functor is simply run inline.
408 bool runImmediatelyOrRunInEventBaseThreadAndWait(const Cob& fn);
411 * Runs the given Cob at some time after the specified number of
412 * milliseconds. (No guarantees exactly when.)
414 * Throws a std::system_error if an error occurs.
418 uint32_t milliseconds,
419 TimeoutManager::InternalEnum in = TimeoutManager::InternalEnum::NORMAL);
422 * @see tryRunAfterDelay for more details
424 * @return true iff the cob was successfully registered.
427 bool tryRunAfterDelay(
429 uint32_t milliseconds,
430 TimeoutManager::InternalEnum in = TimeoutManager::InternalEnum::NORMAL);
433 * Set the maximum desired latency in us and provide a callback which will be
434 * called when that latency is exceeded.
435 * OBS: This functionality depends on time-measurement.
437 void setMaxLatency(int64_t maxLatency, const Cob& maxLatencyCob) {
438 assert(enableTimeMeasurement_);
439 maxLatency_ = maxLatency;
440 maxLatencyCob_ = maxLatencyCob;
445 * Set smoothing coefficient for loop load average; # of milliseconds
446 * for exp(-1) (1/2.71828...) decay.
448 void setLoadAvgMsec(uint32_t ms);
451 * reset the load average to a desired value
453 void resetLoadAvg(double value = 0.0);
456 * Get the average loop time in microseconds (an exponentially-smoothed ave)
458 double getAvgLoopTime() const {
459 assert(enableTimeMeasurement_);
460 return avgLoopTime_.get();
464 * check if the event base loop is running.
466 bool isRunning() const {
467 return loopThread_.load(std::memory_order_relaxed) != 0;
471 * wait until the event loop starts (after starting the event loop thread).
473 void waitUntilRunning();
475 int getNotificationQueueSize() const;
477 void setMaxReadAtOnce(uint32_t maxAtOnce);
480 * Verify that current thread is the EventBase thread, if the EventBase is
483 bool isInEventBaseThread() const {
484 auto tid = loopThread_.load(std::memory_order_relaxed);
485 return tid == 0 || pthread_equal(tid, pthread_self());
488 bool inRunningEventBaseThread() const {
489 return pthread_equal(
490 loopThread_.load(std::memory_order_relaxed), pthread_self());
493 // --------- interface to underlying libevent base ------------
494 // Avoid using these functions if possible. These functions are not
495 // guaranteed to always be present if we ever provide alternative EventBase
496 // implementations that do not use libevent internally.
497 event_base* getLibeventBase() const { return evb_; }
498 static const char* getLibeventVersion();
499 static const char* getLibeventMethod();
502 * only EventHandler/AsyncTimeout subclasses and ourselves should
505 * This is used to mark the beginning of a new loop cycle by the
506 * first handler fired within that cycle.
509 bool bumpHandlingTime() override;
511 class SmoothLoopTime {
513 explicit SmoothLoopTime(uint64_t timeInterval)
514 : expCoeff_(-1.0/timeInterval)
516 , oldBusyLeftover_(0) {
517 VLOG(11) << "expCoeff_ " << expCoeff_ << " " << __PRETTY_FUNCTION__;
520 void setTimeInterval(uint64_t timeInterval);
521 void reset(double value = 0.0);
523 void addSample(int64_t idle, int64_t busy);
529 void dampen(double factor) {
536 int64_t oldBusyLeftover_;
539 void setObserver(const std::shared_ptr<EventBaseObserver>& observer) {
540 assert(enableTimeMeasurement_);
541 observer_ = observer;
544 const std::shared_ptr<EventBaseObserver>& getObserver() {
549 * Setup execution observation/instrumentation for every EventHandler
550 * executed in this EventBase.
552 * @param executionObserver EventHandle's execution observer.
554 void setExecutionObserver(ExecutionObserver* observer) {
555 executionObserver_ = observer;
559 * Gets the execution observer associated with this EventBase.
561 ExecutionObserver* getExecutionObserver() {
562 return executionObserver_;
566 * Set the name of the thread that runs this event base.
568 void setName(const std::string& name);
571 * Returns the name of the thread that runs this event base.
573 const std::string& getName();
575 /// Implements the Executor interface
576 void add(Cob fn) override {
577 // runInEventBaseThread() takes a const&,
578 // so no point in doing std::move here.
579 runInEventBaseThread(fn);
582 /// Implements the DrivableExecutor interface
583 void drive() override {
589 void attachTimeoutManager(AsyncTimeout* obj,
590 TimeoutManager::InternalEnum internal) override;
592 void detachTimeoutManager(AsyncTimeout* obj) override;
594 bool scheduleTimeout(AsyncTimeout* obj, TimeoutManager::timeout_type timeout)
597 void cancelTimeout(AsyncTimeout* obj) override;
599 bool isInTimeoutManagerThread() override {
600 return isInEventBaseThread();
604 * Helper function that tells us whether we have already handled
605 * some event/timeout/callback in this loop iteration.
607 bool nothingHandledYet();
609 // --------- libevent callbacks (not for client use) ------------
611 static void runFunctionPtr(Cob* fn);
613 // small object used as a callback arg with enough info to execute the
614 // appropriate client-provided Cob
615 class CobTimeout : public AsyncTimeout {
617 CobTimeout(EventBase* b, const Cob& c, TimeoutManager::InternalEnum in)
618 : AsyncTimeout(b, in), cob_(c) {}
620 virtual void timeoutExpired() noexcept;
626 typedef boost::intrusive::list_member_hook<
627 boost::intrusive::link_mode<boost::intrusive::auto_unlink> > ListHook;
631 typedef boost::intrusive::list<
633 boost::intrusive::member_hook<CobTimeout, ListHook, &CobTimeout::hook>,
634 boost::intrusive::constant_time_size<false> > List;
637 typedef LoopCallback::List LoopCallbackList;
638 class FunctionRunner;
640 bool loopBody(int flags = 0);
642 // executes any callbacks queued by runInLoop(); returns false if none found
643 bool runLoopCallbacks(bool setContext = true);
645 void initNotificationQueue();
647 CobTimeout::List pendingCobTimeouts_;
649 LoopCallbackList loopCallbacks_;
650 LoopCallbackList runBeforeLoopCallbacks_;
651 LoopCallbackList onDestructionCallbacks_;
652 LoopCallbackList runAfterDrainCallbacks_;
654 // This will be null most of the time, but point to currentCallbacks
655 // if we are in the middle of running loop callbacks, such that
656 // runInLoop(..., true) will always run in the current loop
658 LoopCallbackList* runOnceCallbacks_;
660 // stop_ is set by terminateLoopSoon() and is used by the main loop
661 // to determine if it should exit
662 std::atomic<bool> stop_;
664 // The ID of the thread running the main loop.
665 // 0 if loop is not running.
666 // Note: POSIX doesn't guarantee that 0 is an invalid pthread_t (or
667 // even that atomic<pthread_t> is valid), but that's how it is
668 // everywhere (at least on Linux, FreeBSD, and OSX).
669 std::atomic<pthread_t> loopThread_;
671 // pointer to underlying event_base class doing the heavy lifting
674 // A notification queue for runInEventBaseThread() to use
675 // to send function requests to the EventBase thread.
676 std::unique_ptr<NotificationQueue<Cob>> queue_;
677 std::unique_ptr<FunctionRunner> fnRunner_;
679 // limit for latency in microseconds (0 disables)
682 // exponentially-smoothed average loop time for latency-limiting
683 SmoothLoopTime avgLoopTime_;
685 // smoothed loop time used to invoke latency callbacks; differs from
686 // avgLoopTime_ in that it's scaled down after triggering a callback
687 // to reduce spamminess
688 SmoothLoopTime maxLatencyLoopTime_;
690 // callback called when latency limit is exceeded
693 // Enables/disables time measurements in loopBody(). if disabled, the
694 // following functionality that relies on time-measurement, will not
695 // be supported: avg loop time, observer and max latency.
696 const bool enableTimeMeasurement_;
698 // we'll wait this long before running deferred callbacks if the event
700 static const int kDEFAULT_IDLE_WAIT_USEC = 20000; // 20ms
702 // Wrap-around loop counter to detect beginning of each loop
703 uint64_t nextLoopCnt_;
704 uint64_t latestLoopCnt_;
707 // Observer to export counters
708 std::shared_ptr<EventBaseObserver> observer_;
709 uint32_t observerSampleCount_;
711 // EventHandler's execution observer.
712 ExecutionObserver* executionObserver_;
714 // Name of the thread running this EventBase
717 // allow runOnDestruction() to be called from any threads
718 std::mutex onDestructionCallbacksMutex_;
720 // allow runAfterDrain() to be called from any threads
721 std::mutex runAfterDrainCallbacksMutex_;
723 // see EventBaseLocal
724 friend class detail::EventBaseLocalBase;
725 template <typename T> friend class EventBaseLocal;
726 std::mutex localStorageMutex_;
727 std::unordered_map<uint64_t, std::shared_ptr<void>> localStorage_;
728 std::unordered_set<detail::EventBaseLocalBaseBase*> localStorageToDtor_;
734 * Define a small functor (2 pointers) and specialize
735 * std::__is_location_invariant so that std::function does not require
738 * std::function<void()> func = SmallFunctor{f, p};
740 * TODO(lucian): remove this hack once GCC <= 4.9 are deprecated.
741 * In GCC >= 5.0 just use a lambda like:
743 * std::function<void()> func = [=] { f(p); };
745 * See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61909
748 struct SmallFunctor {
751 void operator()() { fn(p); }
756 template <typename T>
757 bool EventBase::runInEventBaseThread(void (*fn)(T*), T* arg) {
758 return runInEventBaseThread(detail::SmallFunctor<T>{fn, arg});
761 template <typename T>
762 bool EventBase::runInEventBaseThreadAndWait(void (*fn)(T*), T* arg) {
763 return runInEventBaseThreadAndWait(detail::SmallFunctor<T>{fn, arg});
766 template <typename T>
767 bool EventBase::runImmediatelyOrRunInEventBaseThreadAndWait(void (*fn)(T*),
769 return runImmediatelyOrRunInEventBaseThreadAndWait(
770 detail::SmallFunctor<T>{fn, arg});
775 FOLLY_NAMESPACE_STD_BEGIN
778 * GCC's libstdc++ uses __is_location_invariant to decide wether to
779 * use small object optimization and embed the functor's contents in
780 * the std::function object.
782 * (gcc 4.9) $ libstdc++-v3/include/std/functional
783 * template<typename _Tp>
784 * struct __is_location_invariant
785 * : integral_constant<bool, (is_pointer<_Tp>::value
786 * || is_member_pointer<_Tp>::value)>
789 * (gcc 5.0) $ libstdc++-v3/include/std/functional
791 * template<typename _Tp>
792 * struct __is_location_invariant
793 * : is_trivially_copyable<_Tp>::type
797 * NOTE: Forward declare so this doesn't break when using other
798 * standard libraries: it just wont have any effect.
800 template <typename T>
801 struct __is_location_invariant;
803 template <typename T>
804 struct __is_location_invariant<folly::detail::SmallFunctor<T>>
805 : public std::true_type {};
807 FOLLY_NAMESPACE_STD_END