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 using Cob = Func; // defined in folly/Executor.h
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.
140 : public boost::intrusive::list_base_hook<
141 boost::intrusive::link_mode<boost::intrusive::auto_unlink>> {
143 virtual ~LoopCallback() = default;
145 virtual void runLoopCallback() noexcept = 0;
146 void cancelLoopCallback() {
150 bool isLoopCallbackScheduled() const {
155 typedef boost::intrusive::list<
157 boost::intrusive::constant_time_size<false> > List;
159 // EventBase needs access to LoopCallbackList (and therefore to hook_)
160 friend class EventBase;
161 std::shared_ptr<RequestContext> context_;
165 * Create a new EventBase object.
167 * @param enableTimeMeasurement Informs whether this event base should measure
168 * time. Disabling it would likely improve
169 * performance, but will disable some features
170 * that relies on time-measurement, including:
171 * observer, max latency and avg loop time.
173 explicit EventBase(bool enableTimeMeasurement = true);
176 * Create a new EventBase object that will use the specified libevent
177 * event_base object to drive the event loop.
179 * The EventBase will take ownership of this event_base, and will call
180 * event_base_free(evb) when the EventBase is destroyed.
182 * @param enableTimeMeasurement Informs whether this event base should measure
183 * time. Disabling it would likely improve
184 * performance, but will disable some features
185 * that relies on time-measurement, including:
186 * observer, max latency and avg loop time.
188 explicit EventBase(event_base* evb, bool enableTimeMeasurement = true);
192 * Runs the event loop.
194 * loop() will loop waiting for I/O or timeouts and invoking EventHandler
195 * and AsyncTimeout callbacks as their events become ready. loop() will
196 * only return when there are no more events remaining to process, or after
197 * terminateLoopSoon() has been called.
199 * loop() may be called again to restart event processing after a previous
200 * call to loop() or loopForever() has returned.
202 * Returns true if the loop completed normally (if it processed all
203 * outstanding requests, or if terminateLoopSoon() was called). If an error
204 * occurs waiting for events, false will be returned.
209 * Wait for some events to become active, run them, then return.
211 * When EVLOOP_NONBLOCK is set in flags, the loop won't block if there
212 * are not any events to process.
214 * This is useful for callers that want to run the loop manually.
216 * Returns the same result as loop().
218 bool loopOnce(int flags = 0);
221 * Runs the event loop.
223 * loopForever() behaves like loop(), except that it keeps running even if
224 * when there are no more user-supplied EventHandlers or AsyncTimeouts
225 * registered. It will only return after terminateLoopSoon() has been
228 * This is useful for callers that want to wait for other threads to call
229 * runInEventBaseThread(), even when there are no other scheduled events.
231 * loopForever() may be called again to restart event processing after a
232 * previous call to loop() or loopForever() has returned.
234 * Throws a std::system_error if an error occurs.
239 * Causes the event loop to exit soon.
241 * This will cause an existing call to loop() or loopForever() to stop event
242 * processing and return, even if there are still events remaining to be
245 * It is safe to call terminateLoopSoon() from another thread to cause loop()
246 * to wake up and return in the EventBase loop thread. terminateLoopSoon()
247 * may also be called from the loop thread itself (for example, a
248 * EventHandler or AsyncTimeout callback may call terminateLoopSoon() to
249 * cause the loop to exit after the callback returns.) If the loop is not
250 * running, this will cause the next call to loop to terminate soon after
251 * starting. If a loop runs out of work (and so terminates on its own)
252 * concurrently with a call to terminateLoopSoon(), this may cause a race
255 * Note that the caller is responsible for ensuring that cleanup of all event
256 * callbacks occurs properly. Since terminateLoopSoon() causes the loop to
257 * exit even when there are pending events present, there may be remaining
258 * callbacks present waiting to be invoked. If the loop is later restarted
259 * pending events will continue to be processed normally, however if the
260 * EventBase is destroyed after calling terminateLoopSoon() it is the
261 * caller's responsibility to ensure that cleanup happens properly even if
262 * some outstanding events are never processed.
264 void terminateLoopSoon();
267 * Adds the given callback to a queue of things run after the current pass
268 * through the event loop completes. Note that if this callback calls
269 * runInLoop() the new callback won't be called until the main event loop
270 * has gone through a cycle.
272 * This method may only be called from the EventBase's thread. This
273 * essentially allows an event handler to schedule an additional callback to
274 * be invoked after it returns.
276 * Use runInEventBaseThread() to schedule functions from another thread.
278 * The thisIteration parameter makes this callback run in this loop
279 * iteration, instead of the next one, even if called from a
280 * runInLoop callback (normal io callbacks that call runInLoop will
281 * always run in this iteration). This was originally added to
282 * support detachEventBase, as a user callback may have called
283 * terminateLoopSoon(), but we want to make sure we detach. Also,
284 * detachEventBase almost always must be called from the base event
285 * loop to ensure the stack is unwound, since most users of
286 * EventBase are not thread safe.
288 * Ideally we would not need thisIteration, and instead just use
289 * runInLoop with loop() (instead of terminateLoopSoon).
291 void runInLoop(LoopCallback* callback, bool thisIteration = false);
294 * Convenience function to call runInLoop() with a folly::Function.
296 * This creates a LoopCallback object to wrap the folly::Function, and invoke
297 * the folly::Function when the loop callback fires. This is slightly more
298 * expensive than defining your own LoopCallback, but more convenient in
299 * areas that aren't too performance sensitive.
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(Func c, bool thisIteration = false);
310 * Adds the given callback to a queue of things run before destruction
311 * of current EventBase.
313 * This allows users of EventBase that run in it, but don't control it,
314 * to be notified before EventBase gets destructed.
316 * Note: will be called from the thread that invoked EventBase destructor,
317 * before the final run of loop callbacks.
319 void runOnDestruction(LoopCallback* callback);
322 * Adds a callback that will run immediately *before* the event loop.
323 * This is very similar to runInLoop(), but will not cause the loop to break:
324 * For example, this callback could be used to get loop times.
326 void runBeforeLoop(LoopCallback* callback);
329 * Run the specified function in the EventBase's thread.
331 * This method is thread-safe, and may be called from another thread.
333 * If runInEventBaseThread() is called when the EventBase loop is not
334 * running, the function call will be delayed until the next time the loop is
337 * If runInEventBaseThread() returns true the function has successfully been
338 * scheduled to run in the loop thread. However, if the loop is terminated
339 * (and never later restarted) before it has a chance to run the requested
340 * function, the function will be run upon the EventBase's destruction.
342 * If two calls to runInEventBaseThread() are made from the same thread, the
343 * functions will always be run in the order that they were scheduled.
344 * Ordering between functions scheduled from separate threads is not
347 * @param fn The function to run. The function must not throw any
349 * @param arg An argument to pass to the function.
351 * @return Returns true if the function was successfully scheduled, or false
352 * if there was an error scheduling the function.
354 template <typename T>
355 bool runInEventBaseThread(void (*fn)(T*), T* arg);
358 * Run the specified function in the EventBase's thread
360 * This version of runInEventBaseThread() takes a folly::Function object.
361 * Note that this may be less efficient than the version that takes a plain
362 * function pointer and void* argument, if moving the function is expensive
363 * (e.g., if it wraps a lambda which captures some values with expensive move
366 * If the loop is terminated (and never later restarted) before it has a
367 * chance to run the requested function, the function will be run upon the
368 * EventBase's destruction.
370 * The function must not throw any exceptions.
372 bool runInEventBaseThread(Func fn);
375 * Like runInEventBaseThread, but the caller waits for the callback to be
378 template <typename T>
379 bool runInEventBaseThreadAndWait(void (*fn)(T*), T* arg);
382 * Like runInEventBaseThread, but the caller waits for the callback to be
385 bool runInEventBaseThreadAndWait(Func fn);
388 * Like runInEventBaseThreadAndWait, except if the caller is already in the
389 * event base thread, the functor is simply run inline.
391 template <typename T>
392 bool runImmediatelyOrRunInEventBaseThreadAndWait(void (*fn)(T*), T* arg);
395 * Like runInEventBaseThreadAndWait, except if the caller is already in the
396 * event base thread, the functor is simply run inline.
398 bool runImmediatelyOrRunInEventBaseThreadAndWait(Func fn);
401 * Runs the given Cob at some time after the specified number of
402 * milliseconds. (No guarantees exactly when.)
404 * Throws a std::system_error if an error occurs.
408 uint32_t milliseconds,
409 TimeoutManager::InternalEnum in = TimeoutManager::InternalEnum::NORMAL);
412 * @see tryRunAfterDelay for more details
414 * @return true iff the cob was successfully registered.
417 bool tryRunAfterDelay(
419 uint32_t milliseconds,
420 TimeoutManager::InternalEnum in = TimeoutManager::InternalEnum::NORMAL);
423 * Set the maximum desired latency in us and provide a callback which will be
424 * called when that latency is exceeded.
425 * OBS: This functionality depends on time-measurement.
427 void setMaxLatency(int64_t maxLatency, Func maxLatencyCob) {
428 assert(enableTimeMeasurement_);
429 maxLatency_ = maxLatency;
430 maxLatencyCob_ = std::move(maxLatencyCob);
435 * Set smoothing coefficient for loop load average; # of milliseconds
436 * for exp(-1) (1/2.71828...) decay.
438 void setLoadAvgMsec(uint32_t ms);
441 * reset the load average to a desired value
443 void resetLoadAvg(double value = 0.0);
446 * Get the average loop time in microseconds (an exponentially-smoothed ave)
448 double getAvgLoopTime() const {
449 assert(enableTimeMeasurement_);
450 return avgLoopTime_.get();
454 * check if the event base loop is running.
456 bool isRunning() const {
457 return loopThread_.load(std::memory_order_relaxed) != 0;
461 * wait until the event loop starts (after starting the event loop thread).
463 void waitUntilRunning();
465 int getNotificationQueueSize() const;
467 void setMaxReadAtOnce(uint32_t maxAtOnce);
470 * Verify that current thread is the EventBase thread, if the EventBase is
473 bool isInEventBaseThread() const {
474 auto tid = loopThread_.load(std::memory_order_relaxed);
475 return tid == 0 || pthread_equal(tid, pthread_self());
478 bool inRunningEventBaseThread() const {
479 return pthread_equal(
480 loopThread_.load(std::memory_order_relaxed), pthread_self());
483 HHWheelTimer& timer() {
485 wheelTimer_ = HHWheelTimer::newTimer(this);
487 return *wheelTimer_.get();
490 // --------- interface to underlying libevent base ------------
491 // Avoid using these functions if possible. These functions are not
492 // guaranteed to always be present if we ever provide alternative EventBase
493 // implementations that do not use libevent internally.
494 event_base* getLibeventBase() const { return evb_; }
495 static const char* getLibeventVersion();
496 static const char* getLibeventMethod();
499 * only EventHandler/AsyncTimeout subclasses and ourselves should
502 * This is used to mark the beginning of a new loop cycle by the
503 * first handler fired within that cycle.
506 void bumpHandlingTime() override final;
508 class SmoothLoopTime {
510 explicit SmoothLoopTime(uint64_t timeInterval)
511 : expCoeff_(-1.0/timeInterval)
513 , oldBusyLeftover_(0) {
514 VLOG(11) << "expCoeff_ " << expCoeff_ << " " << __PRETTY_FUNCTION__;
517 void setTimeInterval(uint64_t timeInterval);
518 void reset(double value = 0.0);
520 void addSample(int64_t idle, int64_t busy);
526 void dampen(double factor) {
533 int64_t oldBusyLeftover_;
536 void setObserver(const std::shared_ptr<EventBaseObserver>& observer) {
537 assert(enableTimeMeasurement_);
538 observer_ = observer;
541 const std::shared_ptr<EventBaseObserver>& getObserver() {
546 * Setup execution observation/instrumentation for every EventHandler
547 * executed in this EventBase.
549 * @param executionObserver EventHandle's execution observer.
551 void setExecutionObserver(ExecutionObserver* observer) {
552 executionObserver_ = observer;
556 * Gets the execution observer associated with this EventBase.
558 ExecutionObserver* getExecutionObserver() {
559 return executionObserver_;
563 * Set the name of the thread that runs this event base.
565 void setName(const std::string& name);
568 * Returns the name of the thread that runs this event base.
570 const std::string& getName();
572 /// Implements the Executor interface
573 void add(Cob fn) override {
574 // runInEventBaseThread() takes a const&,
575 // so no point in doing std::move here.
576 runInEventBaseThread(std::move(fn));
579 /// Implements the DrivableExecutor interface
580 void drive() override {
581 auto keepAlive = loopKeepAlive();
585 struct LoopKeepAliveDeleter {
586 void operator()(EventBase* evb) {
587 DCHECK(evb->isInEventBaseThread());
588 evb->loopKeepAliveCount_--;
591 using LoopKeepAlive = std::unique_ptr<EventBase, LoopKeepAliveDeleter>;
593 /// Returns you a handle which make loop() behave like loopForever() until
594 /// destroyed. loop() will return to its original behavior only when all
595 /// loop keep-alives are released. Loop holder is safe to release only from
596 /// EventBase thread.
598 /// May return no op LoopKeepAlive if loopForever() is already running.
599 LoopKeepAlive loopKeepAlive() {
600 DCHECK(isInEventBaseThread());
601 loopKeepAliveCount_++;
602 return LoopKeepAlive(this);
607 void attachTimeoutManager(AsyncTimeout* obj,
608 TimeoutManager::InternalEnum internal) override;
610 void detachTimeoutManager(AsyncTimeout* obj) override;
612 bool scheduleTimeout(AsyncTimeout* obj, TimeoutManager::timeout_type timeout)
615 void cancelTimeout(AsyncTimeout* obj) override;
617 bool isInTimeoutManagerThread() override final {
618 return isInEventBaseThread();
621 void applyLoopKeepAlive();
624 * Helper function that tells us whether we have already handled
625 * some event/timeout/callback in this loop iteration.
627 bool nothingHandledYet() const noexcept;
629 // small object used as a callback arg with enough info to execute the
630 // appropriate client-provided Cob
631 class CobTimeout : public AsyncTimeout {
633 CobTimeout(EventBase* b, Func c, TimeoutManager::InternalEnum in)
634 : AsyncTimeout(b, in), cob_(std::move(c)) {}
636 virtual void timeoutExpired() noexcept;
642 typedef boost::intrusive::list_member_hook<
643 boost::intrusive::link_mode<boost::intrusive::auto_unlink> > ListHook;
647 typedef boost::intrusive::list<
649 boost::intrusive::member_hook<CobTimeout, ListHook, &CobTimeout::hook>,
650 boost::intrusive::constant_time_size<false> > List;
653 typedef LoopCallback::List LoopCallbackList;
654 class FunctionRunner;
656 bool loopBody(int flags = 0);
658 // executes any callbacks queued by runInLoop(); returns false if none found
659 bool runLoopCallbacks();
661 void initNotificationQueue();
663 // should only be accessed through public getter
664 HHWheelTimer::UniquePtr wheelTimer_;
666 CobTimeout::List pendingCobTimeouts_;
668 LoopCallbackList loopCallbacks_;
669 LoopCallbackList runBeforeLoopCallbacks_;
670 LoopCallbackList onDestructionCallbacks_;
672 // This will be null most of the time, but point to currentCallbacks
673 // if we are in the middle of running loop callbacks, such that
674 // runInLoop(..., true) will always run in the current loop
676 LoopCallbackList* runOnceCallbacks_;
678 // stop_ is set by terminateLoopSoon() and is used by the main loop
679 // to determine if it should exit
680 std::atomic<bool> stop_;
682 // The ID of the thread running the main loop.
683 // 0 if loop is not running.
684 // Note: POSIX doesn't guarantee that 0 is an invalid pthread_t (or
685 // even that atomic<pthread_t> is valid), but that's how it is
686 // everywhere (at least on Linux, FreeBSD, and OSX).
687 std::atomic<pthread_t> loopThread_;
689 // pointer to underlying event_base class doing the heavy lifting
692 // A notification queue for runInEventBaseThread() to use
693 // to send function requests to the EventBase thread.
694 std::unique_ptr<NotificationQueue<Func>> queue_;
695 std::unique_ptr<FunctionRunner> fnRunner_;
696 size_t loopKeepAliveCount_{0};
697 bool loopKeepAliveActive_{false};
699 // limit for latency in microseconds (0 disables)
702 // exponentially-smoothed average loop time for latency-limiting
703 SmoothLoopTime avgLoopTime_;
705 // smoothed loop time used to invoke latency callbacks; differs from
706 // avgLoopTime_ in that it's scaled down after triggering a callback
707 // to reduce spamminess
708 SmoothLoopTime maxLatencyLoopTime_;
710 // callback called when latency limit is exceeded
713 // Enables/disables time measurements in loopBody(). if disabled, the
714 // following functionality that relies on time-measurement, will not
715 // be supported: avg loop time, observer and max latency.
716 const bool enableTimeMeasurement_;
718 // we'll wait this long before running deferred callbacks if the event
720 static const int kDEFAULT_IDLE_WAIT_USEC = 20000; // 20ms
722 // Wrap-around loop counter to detect beginning of each loop
723 uint64_t nextLoopCnt_;
724 uint64_t latestLoopCnt_;
726 // Prevent undefined behavior from invoking event_base_loop() reentrantly.
727 // This is needed since many projects use libevent-1.4, which lacks commit
728 // b557b175c00dc462c1fce25f6e7dd67121d2c001 from
729 // https://github.com/libevent/libevent/.
730 bool invokingLoop_{false};
732 // Observer to export counters
733 std::shared_ptr<EventBaseObserver> observer_;
734 uint32_t observerSampleCount_;
736 // EventHandler's execution observer.
737 ExecutionObserver* executionObserver_;
739 // Name of the thread running this EventBase
742 // allow runOnDestruction() to be called from any threads
743 std::mutex onDestructionCallbacksMutex_;
745 // see EventBaseLocal
746 friend class detail::EventBaseLocalBase;
747 template <typename T> friend class EventBaseLocal;
748 std::mutex localStorageMutex_;
749 std::unordered_map<uint64_t, std::shared_ptr<void>> localStorage_;
750 std::unordered_set<detail::EventBaseLocalBaseBase*> localStorageToDtor_;
753 template <typename T>
754 bool EventBase::runInEventBaseThread(void (*fn)(T*), T* arg) {
755 return runInEventBaseThread([=] { fn(arg); });
758 template <typename T>
759 bool EventBase::runInEventBaseThreadAndWait(void (*fn)(T*), T* arg) {
760 return runInEventBaseThreadAndWait([=] { fn(arg); });
763 template <typename T>
764 bool EventBase::runImmediatelyOrRunInEventBaseThreadAndWait(
767 return runImmediatelyOrRunInEventBaseThreadAndWait([=] { fn(arg); });