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.
19 #include <glog/logging.h>
20 #include <folly/io/async/AsyncTimeout.h>
21 #include <folly/io/async/TimeoutManager.h>
22 #include <folly/io/async/Request.h>
23 #include <folly/Executor.h>
24 #include <folly/experimental/ExecutionObserver.h>
25 #include <folly/futures/DrivableExecutor.h>
32 #include <unordered_set>
33 #include <unordered_map>
36 #include <boost/intrusive/list.hpp>
37 #include <boost/utility.hpp>
39 #include <event.h> // libevent
46 typedef std::function<void()> Cob;
47 template <typename MessageT>
48 class NotificationQueue;
51 class EventBaseLocalBase;
53 class EventBaseLocalBaseBase {
55 virtual void onEventBaseDestruction(EventBase& evb) = 0;
56 virtual ~EventBaseLocalBaseBase() = default;
62 class EventBaseObserver {
64 virtual ~EventBaseObserver() = default;
66 virtual uint32_t getSampleRate() const = 0;
68 virtual void loopSample(
69 int64_t busyTime, int64_t idleTime) = 0;
72 // Helper class that sets and retrieves the EventBase associated with a given
73 // request via RequestContext. See Request.h for that mechanism.
74 class RequestEventBase : public RequestData {
76 static EventBase* get() {
77 auto data = dynamic_cast<RequestEventBase*>(
78 RequestContext::get()->getContextData(kContextDataName));
85 static void set(EventBase* eb) {
86 RequestContext::get()->setContextData(
88 std::unique_ptr<RequestEventBase>(new RequestEventBase(eb)));
92 explicit RequestEventBase(EventBase* eb) : eb_(eb) {}
94 static constexpr const char* kContextDataName{"EventBase"};
98 * This class is a wrapper for all asynchronous I/O processing functionality
100 * EventBase provides a main loop that notifies EventHandler callback objects
101 * when I/O is ready on a file descriptor, and notifies AsyncTimeout objects
102 * when a specified timeout has expired. More complex, higher-level callback
103 * mechanisms can then be built on top of EventHandler and AsyncTimeout.
105 * A EventBase object can only drive an event loop for a single thread. To
106 * take advantage of multiple CPU cores, most asynchronous I/O servers have one
107 * thread per CPU, and use a separate EventBase for each thread.
109 * In general, most EventBase methods may only be called from the thread
110 * running the EventBase's loop. There are a few exceptions to this rule, for
111 * methods that are explicitly intended to allow communication with a
112 * EventBase from other threads. When it is safe to call a method from
113 * another thread it is explicitly listed in the method comments.
115 class EventBase : private boost::noncopyable,
116 public TimeoutManager,
117 public DrivableExecutor {
120 * A callback interface to use with runInLoop()
122 * Derive from this class if you need to delay some code execution until the
123 * next iteration of the event loop. This allows you to schedule code to be
124 * invoked from the top-level of the loop, after your immediate callers have
127 * If a LoopCallback object is destroyed while it is scheduled to be run in
128 * the next loop iteration, it will automatically be cancelled.
132 virtual ~LoopCallback() = default;
134 virtual void runLoopCallback() noexcept = 0;
135 void cancelLoopCallback() {
139 bool isLoopCallbackScheduled() const {
140 return hook_.is_linked();
144 typedef boost::intrusive::list_member_hook<
145 boost::intrusive::link_mode<boost::intrusive::auto_unlink> > ListHook;
149 typedef boost::intrusive::list<
151 boost::intrusive::member_hook<LoopCallback, ListHook,
152 &LoopCallback::hook_>,
153 boost::intrusive::constant_time_size<false> > List;
155 // EventBase needs access to LoopCallbackList (and therefore to hook_)
156 friend class EventBase;
157 std::shared_ptr<RequestContext> context_;
161 * Create a new EventBase object.
163 * @param enableTimeMeasurement Informs whether this event base should measure
164 * time. Disabling it would likely improve
165 * performance, but will disable some features
166 * that relies on time-measurement, including:
167 * observer, max latency and avg loop time.
169 explicit EventBase(bool enableTimeMeasurement = true);
172 * Create a new EventBase object that will use the specified libevent
173 * event_base object to drive the event loop.
175 * The EventBase will take ownership of this event_base, and will call
176 * event_base_free(evb) when the EventBase is destroyed.
178 * @param enableTimeMeasurement Informs whether this event base should measure
179 * time. Disabling it would likely improve
180 * performance, but will disable some features
181 * that relies on time-measurement, including:
182 * observer, max latency and avg loop time.
184 explicit EventBase(event_base* evb, bool enableTimeMeasurement = true);
188 * Runs the event loop.
190 * loop() will loop waiting for I/O or timeouts and invoking EventHandler
191 * and AsyncTimeout callbacks as their events become ready. loop() will
192 * only return when there are no more events remaining to process, or after
193 * terminateLoopSoon() has been called.
195 * loop() may be called again to restart event processing after a previous
196 * call to loop() or loopForever() has returned.
198 * Returns true if the loop completed normally (if it processed all
199 * outstanding requests, or if terminateLoopSoon() was called). If an error
200 * occurs waiting for events, false will be returned.
205 * Wait for some events to become active, run them, then return.
207 * When EVLOOP_NONBLOCK is set in flags, the loop won't block if there
208 * are not any events to process.
210 * This is useful for callers that want to run the loop manually.
212 * Returns the same result as loop().
214 bool loopOnce(int flags = 0);
217 * Runs the event loop.
219 * loopForever() behaves like loop(), except that it keeps running even if
220 * when there are no more user-supplied EventHandlers or AsyncTimeouts
221 * registered. It will only return after terminateLoopSoon() has been
224 * This is useful for callers that want to wait for other threads to call
225 * runInEventBaseThread(), even when there are no other scheduled events.
227 * loopForever() may be called again to restart event processing after a
228 * previous call to loop() or loopForever() has returned.
230 * Throws a std::system_error if an error occurs.
235 * Causes the event loop to exit soon.
237 * This will cause an existing call to loop() or loopForever() to stop event
238 * processing and return, even if there are still events remaining to be
241 * It is safe to call terminateLoopSoon() from another thread to cause loop()
242 * to wake up and return in the EventBase loop thread. terminateLoopSoon()
243 * may also be called from the loop thread itself (for example, a
244 * EventHandler or AsyncTimeout callback may call terminateLoopSoon() to
245 * cause the loop to exit after the callback returns.) If the loop is not
246 * running, this will cause the next call to loop to terminate soon after
247 * starting. If a loop runs out of work (and so terminates on its own)
248 * concurrently with a call to terminateLoopSoon(), this may cause a race
251 * Note that the caller is responsible for ensuring that cleanup of all event
252 * callbacks occurs properly. Since terminateLoopSoon() causes the loop to
253 * exit even when there are pending events present, there may be remaining
254 * callbacks present waiting to be invoked. If the loop is later restarted
255 * pending events will continue to be processed normally, however if the
256 * EventBase is destroyed after calling terminateLoopSoon() it is the
257 * caller's responsibility to ensure that cleanup happens properly even if
258 * some outstanding events are never processed.
260 void terminateLoopSoon();
263 * Adds the given callback to a queue of things run after the current pass
264 * through the event loop completes. Note that if this callback calls
265 * runInLoop() the new callback won't be called until the main event loop
266 * has gone through a cycle.
268 * This method may only be called from the EventBase's thread. This
269 * essentially allows an event handler to schedule an additional callback to
270 * be invoked after it returns.
272 * Use runInEventBaseThread() to schedule functions from another thread.
274 * The thisIteration parameter makes this callback run in this loop
275 * iteration, instead of the next one, even if called from a
276 * runInLoop callback (normal io callbacks that call runInLoop will
277 * always run in this iteration). This was originally added to
278 * support detachEventBase, as a user callback may have called
279 * terminateLoopSoon(), but we want to make sure we detach. Also,
280 * detachEventBase almost always must be called from the base event
281 * loop to ensure the stack is unwound, since most users of
282 * EventBase are not thread safe.
284 * Ideally we would not need thisIteration, and instead just use
285 * runInLoop with loop() (instead of terminateLoopSoon).
287 void runInLoop(LoopCallback* callback, bool thisIteration = false);
290 * Convenience function to call runInLoop() with a std::function.
292 * This creates a LoopCallback object to wrap the std::function, and invoke
293 * the std::function when the loop callback fires. This is slightly more
294 * expensive than defining your own LoopCallback, but more convenient in
295 * areas that aren't performance sensitive where you just want to use
296 * std::bind. (std::bind is fairly slow on even by itself.)
298 * This method may only be called from the EventBase's thread. This
299 * essentially allows an event handler to schedule an additional callback to
300 * be invoked after it returns.
302 * Use runInEventBaseThread() to schedule functions from another thread.
304 void runInLoop(const Cob& c, bool thisIteration = false);
306 void runInLoop(Cob&& c, bool thisIteration = false);
309 * Adds the given callback to a queue of things run before destruction
310 * of current EventBase.
312 * This allows users of EventBase that run in it, but don't control it,
313 * to be notified before EventBase gets destructed.
315 * Note: will be called from the thread that invoked EventBase destructor,
316 * before the final run of loop callbacks.
318 void runOnDestruction(LoopCallback* callback);
321 * Adds the given callback to a queue of things run after the notification
322 * queue is drained before the destruction of current EventBase.
324 * Note: will be called from the thread that invoked EventBase destructor,
325 * after the final run of loop callbacks.
327 void runAfterDrain(Cob&& cob);
330 * Adds a callback that will run immediately *before* the event loop.
331 * This is very similar to runInLoop(), but will not cause the loop to break:
332 * For example, this callback could be used to get loop times.
334 void runBeforeLoop(LoopCallback* callback);
337 * Run the specified function in the EventBase's thread.
339 * This method is thread-safe, and may be called from another thread.
341 * If runInEventBaseThread() is called when the EventBase loop is not
342 * running, the function call will be delayed until the next time the loop is
345 * If runInEventBaseThread() returns true the function has successfully been
346 * scheduled to run in the loop thread. However, if the loop is terminated
347 * (and never later restarted) before it has a chance to run the requested
348 * function, the function will be run upon the EventBase's destruction.
350 * If two calls to runInEventBaseThread() are made from the same thread, the
351 * functions will always be run in the order that they were scheduled.
352 * Ordering between functions scheduled from separate threads is not
355 * @param fn The function to run. The function must not throw any
357 * @param arg An argument to pass to the function.
359 * @return Returns true if the function was successfully scheduled, or false
360 * if there was an error scheduling the function.
363 bool runInEventBaseThread(void (*fn)(T*), T* arg) {
364 return runInEventBaseThread(reinterpret_cast<void (*)(void*)>(fn),
365 reinterpret_cast<void*>(arg));
368 bool runInEventBaseThread(void (*fn)(void*), void* arg);
371 * Run the specified function in the EventBase's thread
373 * This version of runInEventBaseThread() takes a std::function object.
374 * Note that this is less efficient than the version that takes a plain
375 * function pointer and void* argument, as it has to allocate memory to copy
376 * the std::function object.
378 * If the loop is terminated (and never later restarted) before it has a
379 * chance to run the requested function, the function will be run upon the
380 * EventBase's destruction.
382 * The function must not throw any exceptions.
384 bool runInEventBaseThread(const Cob& fn);
387 * Like runInEventBaseThread, but the caller waits for the callback to be
391 bool runInEventBaseThreadAndWait(void (*fn)(T*), T* arg) {
392 return runInEventBaseThreadAndWait(reinterpret_cast<void (*)(void*)>(fn),
393 reinterpret_cast<void*>(arg));
397 * Like runInEventBaseThread, but the caller waits for the callback to be
400 bool runInEventBaseThreadAndWait(void (*fn)(void*), void* arg) {
401 return runInEventBaseThreadAndWait(std::bind(fn, arg));
405 * Like runInEventBaseThread, but the caller waits for the callback to be
408 bool runInEventBaseThreadAndWait(const Cob& fn);
411 * Like runInEventBaseThreadAndWait, except if the caller is already in the
412 * event base thread, the functor is simply run inline.
415 bool runImmediatelyOrRunInEventBaseThreadAndWait(void (*fn)(T*), T* arg) {
416 return runImmediatelyOrRunInEventBaseThreadAndWait(
417 reinterpret_cast<void (*)(void*)>(fn), reinterpret_cast<void*>(arg));
421 * Like runInEventBaseThreadAndWait, except if the caller is already in the
422 * event base thread, the functor is simply run inline.
424 bool runImmediatelyOrRunInEventBaseThreadAndWait(
425 void (*fn)(void*), void* arg) {
426 return runImmediatelyOrRunInEventBaseThreadAndWait(std::bind(fn, arg));
430 * Like runInEventBaseThreadAndWait, except if the caller is already in the
431 * event base thread, the functor is simply run inline.
433 bool runImmediatelyOrRunInEventBaseThreadAndWait(const Cob& fn);
436 * Runs the given Cob at some time after the specified number of
437 * milliseconds. (No guarantees exactly when.)
439 * Throws a std::system_error if an error occurs.
443 uint32_t milliseconds,
444 TimeoutManager::InternalEnum in = TimeoutManager::InternalEnum::NORMAL);
447 * @see tryRunAfterDelay for more details
449 * @return true iff the cob was successfully registered.
452 bool tryRunAfterDelay(
454 uint32_t milliseconds,
455 TimeoutManager::InternalEnum in = TimeoutManager::InternalEnum::NORMAL);
458 * Set the maximum desired latency in us and provide a callback which will be
459 * called when that latency is exceeded.
460 * OBS: This functionality depends on time-measurement.
462 void setMaxLatency(int64_t maxLatency, const Cob& maxLatencyCob) {
463 assert(enableTimeMeasurement_);
464 maxLatency_ = maxLatency;
465 maxLatencyCob_ = maxLatencyCob;
470 * Set smoothing coefficient for loop load average; # of milliseconds
471 * for exp(-1) (1/2.71828...) decay.
473 void setLoadAvgMsec(uint32_t ms);
476 * reset the load average to a desired value
478 void resetLoadAvg(double value = 0.0);
481 * Get the average loop time in microseconds (an exponentially-smoothed ave)
483 double getAvgLoopTime() const {
484 assert(enableTimeMeasurement_);
485 return avgLoopTime_.get();
489 * check if the event base loop is running.
491 bool isRunning() const {
492 return loopThread_.load(std::memory_order_relaxed) != 0;
496 * wait until the event loop starts (after starting the event loop thread).
498 void waitUntilRunning();
500 int getNotificationQueueSize() const;
502 void setMaxReadAtOnce(uint32_t maxAtOnce);
505 * Verify that current thread is the EventBase thread, if the EventBase is
508 bool isInEventBaseThread() const {
509 auto tid = loopThread_.load(std::memory_order_relaxed);
510 return tid == 0 || pthread_equal(tid, pthread_self());
513 bool inRunningEventBaseThread() const {
514 return pthread_equal(
515 loopThread_.load(std::memory_order_relaxed), pthread_self());
518 // --------- interface to underlying libevent base ------------
519 // Avoid using these functions if possible. These functions are not
520 // guaranteed to always be present if we ever provide alternative EventBase
521 // implementations that do not use libevent internally.
522 event_base* getLibeventBase() const { return evb_; }
523 static const char* getLibeventVersion();
524 static const char* getLibeventMethod();
527 * only EventHandler/AsyncTimeout subclasses and ourselves should
530 * This is used to mark the beginning of a new loop cycle by the
531 * first handler fired within that cycle.
534 bool bumpHandlingTime() override;
536 class SmoothLoopTime {
538 explicit SmoothLoopTime(uint64_t timeInterval)
539 : expCoeff_(-1.0/timeInterval)
541 , oldBusyLeftover_(0) {
542 VLOG(11) << "expCoeff_ " << expCoeff_ << " " << __PRETTY_FUNCTION__;
545 void setTimeInterval(uint64_t timeInterval);
546 void reset(double value = 0.0);
548 void addSample(int64_t idle, int64_t busy);
554 void dampen(double factor) {
561 int64_t oldBusyLeftover_;
564 void setObserver(const std::shared_ptr<EventBaseObserver>& observer) {
565 assert(enableTimeMeasurement_);
566 observer_ = observer;
569 const std::shared_ptr<EventBaseObserver>& getObserver() {
574 * Setup execution observation/instrumentation for every EventHandler
575 * executed in this EventBase.
577 * @param executionObserver EventHandle's execution observer.
579 void setExecutionObserver(ExecutionObserver* observer) {
580 executionObserver_ = observer;
584 * Gets the execution observer associated with this EventBase.
586 ExecutionObserver* getExecutionObserver() {
587 return executionObserver_;
591 * Set the name of the thread that runs this event base.
593 void setName(const std::string& name);
596 * Returns the name of the thread that runs this event base.
598 const std::string& getName();
600 /// Implements the Executor interface
601 void add(Cob fn) override {
602 // runInEventBaseThread() takes a const&,
603 // so no point in doing std::move here.
604 runInEventBaseThread(fn);
607 /// Implements the DrivableExecutor interface
608 void drive() override {
615 void attachTimeoutManager(AsyncTimeout* obj,
616 TimeoutManager::InternalEnum internal) override;
618 void detachTimeoutManager(AsyncTimeout* obj) override;
620 bool scheduleTimeout(AsyncTimeout* obj, TimeoutManager::timeout_type timeout)
623 void cancelTimeout(AsyncTimeout* obj) override;
625 bool isInTimeoutManagerThread() override {
626 return isInEventBaseThread();
629 // Helper class used to short circuit runInEventBaseThread
630 class RunInLoopCallback : public LoopCallback {
632 RunInLoopCallback(void (*fn)(void*), void* arg);
633 void runLoopCallback() noexcept;
641 * Helper function that tells us whether we have already handled
642 * some event/timeout/callback in this loop iteration.
644 bool nothingHandledYet();
646 // --------- libevent callbacks (not for client use) ------------
648 static void runFunctionPtr(std::function<void()>* fn);
650 // small object used as a callback arg with enough info to execute the
651 // appropriate client-provided Cob
652 class CobTimeout : public AsyncTimeout {
654 CobTimeout(EventBase* b, const Cob& c, TimeoutManager::InternalEnum in)
655 : AsyncTimeout(b, in), cob_(c) {}
657 virtual void timeoutExpired() noexcept;
663 typedef boost::intrusive::list_member_hook<
664 boost::intrusive::link_mode<boost::intrusive::auto_unlink> > ListHook;
668 typedef boost::intrusive::list<
670 boost::intrusive::member_hook<CobTimeout, ListHook, &CobTimeout::hook>,
671 boost::intrusive::constant_time_size<false> > List;
674 typedef LoopCallback::List LoopCallbackList;
675 class FunctionRunner;
677 bool loopBody(int flags = 0);
679 // executes any callbacks queued by runInLoop(); returns false if none found
680 bool runLoopCallbacks(bool setContext = true);
682 void initNotificationQueue();
684 CobTimeout::List pendingCobTimeouts_;
686 LoopCallbackList loopCallbacks_;
687 LoopCallbackList runBeforeLoopCallbacks_;
688 LoopCallbackList onDestructionCallbacks_;
689 LoopCallbackList runAfterDrainCallbacks_;
691 // This will be null most of the time, but point to currentCallbacks
692 // if we are in the middle of running loop callbacks, such that
693 // runInLoop(..., true) will always run in the current loop
695 LoopCallbackList* runOnceCallbacks_;
697 // stop_ is set by terminateLoopSoon() and is used by the main loop
698 // to determine if it should exit
699 std::atomic<bool> stop_;
701 // The ID of the thread running the main loop.
702 // 0 if loop is not running.
703 // Note: POSIX doesn't guarantee that 0 is an invalid pthread_t (or
704 // even that atomic<pthread_t> is valid), but that's how it is
705 // everywhere (at least on Linux, FreeBSD, and OSX).
706 std::atomic<pthread_t> loopThread_;
708 // pointer to underlying event_base class doing the heavy lifting
711 // A notification queue for runInEventBaseThread() to use
712 // to send function requests to the EventBase thread.
713 std::unique_ptr<NotificationQueue<std::pair<void (*)(void*), void*>>> queue_;
714 std::unique_ptr<FunctionRunner> fnRunner_;
716 // limit for latency in microseconds (0 disables)
719 // exponentially-smoothed average loop time for latency-limiting
720 SmoothLoopTime avgLoopTime_;
722 // smoothed loop time used to invoke latency callbacks; differs from
723 // avgLoopTime_ in that it's scaled down after triggering a callback
724 // to reduce spamminess
725 SmoothLoopTime maxLatencyLoopTime_;
727 // callback called when latency limit is exceeded
730 // Enables/disables time measurements in loopBody(). if disabled, the
731 // following functionality that relies on time-measurement, will not
732 // be supported: avg loop time, observer and max latency.
733 const bool enableTimeMeasurement_;
735 // we'll wait this long before running deferred callbacks if the event
737 static const int kDEFAULT_IDLE_WAIT_USEC = 20000; // 20ms
739 // Wrap-around loop counter to detect beginning of each loop
740 uint64_t nextLoopCnt_;
741 uint64_t latestLoopCnt_;
744 // Observer to export counters
745 std::shared_ptr<EventBaseObserver> observer_;
746 uint32_t observerSampleCount_;
748 // EventHandler's execution observer.
749 ExecutionObserver* executionObserver_;
751 // Name of the thread running this EventBase
754 // allow runOnDestruction() to be called from any threads
755 std::mutex onDestructionCallbacksMutex_;
757 // allow runAfterDrain() to be called from any threads
758 std::mutex runAfterDrainCallbacksMutex_;
760 // see EventBaseLocal
761 friend class detail::EventBaseLocalBase;
762 template <typename T> friend class EventBaseLocal;
763 std::mutex localStorageMutex_;
764 std::unordered_map<uint64_t, std::shared_ptr<void>> localStorage_;
765 std::unordered_set<detail::EventBaseLocalBaseBase*> localStorageToDtor_;