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/ScopeGuard.h>
41 #include <folly/experimental/ExecutionObserver.h>
42 #include <folly/futures/DrivableExecutor.h>
43 #include <folly/io/async/AsyncTimeout.h>
44 #include <folly/io/async/HHWheelTimer.h>
45 #include <folly/io/async/Request.h>
46 #include <folly/io/async/TimeoutManager.h>
47 #include <folly/portability/PThread.h>
48 #include <glog/logging.h>
50 #include <event.h> // libevent
54 using Cob = Func; // defined in folly/Executor.h
55 template <typename MessageT>
56 class NotificationQueue;
59 class EventBaseLocalBase;
61 class EventBaseLocalBaseBase {
63 virtual void onEventBaseDestruction(EventBase& evb) = 0;
64 virtual ~EventBaseLocalBaseBase() = default;
70 class EventBaseObserver {
72 virtual ~EventBaseObserver() = default;
74 virtual uint32_t getSampleRate() const = 0;
76 virtual void loopSample(
77 int64_t busyTime, int64_t idleTime) = 0;
80 // Helper class that sets and retrieves the EventBase associated with a given
81 // request via RequestContext. See Request.h for that mechanism.
82 class RequestEventBase : public RequestData {
84 static EventBase* get() {
85 auto data = dynamic_cast<RequestEventBase*>(
86 RequestContext::get()->getContextData(kContextDataName));
93 static void set(EventBase* eb) {
94 RequestContext::get()->setContextData(
96 std::unique_ptr<RequestEventBase>(new RequestEventBase(eb)));
100 explicit RequestEventBase(EventBase* eb) : eb_(eb) {}
102 static constexpr const char* kContextDataName{"EventBase"};
105 class VirtualEventBase;
108 * This class is a wrapper for all asynchronous I/O processing functionality
110 * EventBase provides a main loop that notifies EventHandler callback objects
111 * when I/O is ready on a file descriptor, and notifies AsyncTimeout objects
112 * when a specified timeout has expired. More complex, higher-level callback
113 * mechanisms can then be built on top of EventHandler and AsyncTimeout.
115 * A EventBase object can only drive an event loop for a single thread. To
116 * take advantage of multiple CPU cores, most asynchronous I/O servers have one
117 * thread per CPU, and use a separate EventBase for each thread.
119 * In general, most EventBase methods may only be called from the thread
120 * running the EventBase's loop. There are a few exceptions to this rule, for
121 * methods that are explicitly intended to allow communication with a
122 * EventBase from other threads. When it is safe to call a method from
123 * another thread it is explicitly listed in the method comments.
125 class EventBase : private boost::noncopyable,
126 public TimeoutManager,
127 public DrivableExecutor {
129 using Func = folly::Function<void()>;
132 * A callback interface to use with runInLoop()
134 * Derive from this class if you need to delay some code execution until the
135 * next iteration of the event loop. This allows you to schedule code to be
136 * invoked from the top-level of the loop, after your immediate callers have
139 * If a LoopCallback object is destroyed while it is scheduled to be run in
140 * the next loop iteration, it will automatically be cancelled.
143 : public boost::intrusive::list_base_hook<
144 boost::intrusive::link_mode<boost::intrusive::auto_unlink>> {
146 virtual ~LoopCallback() = default;
148 virtual void runLoopCallback() noexcept = 0;
149 void cancelLoopCallback() {
153 bool isLoopCallbackScheduled() const {
158 typedef boost::intrusive::list<
160 boost::intrusive::constant_time_size<false> > List;
162 // EventBase needs access to LoopCallbackList (and therefore to hook_)
163 friend class EventBase;
164 friend class VirtualEventBase;
165 std::shared_ptr<RequestContext> context_;
168 class FunctionLoopCallback : public LoopCallback {
170 explicit FunctionLoopCallback(Func&& function)
171 : function_(std::move(function)) {}
173 void runLoopCallback() noexcept override {
183 * Create a new EventBase object.
185 * @param enableTimeMeasurement Informs whether this event base should measure
186 * time. Disabling it would likely improve
187 * performance, but will disable some features
188 * that relies on time-measurement, including:
189 * observer, max latency and avg loop time.
191 explicit EventBase(bool enableTimeMeasurement = true);
194 * Create a new EventBase object that will use the specified libevent
195 * event_base object to drive the event loop.
197 * The EventBase will take ownership of this event_base, and will call
198 * event_base_free(evb) when the EventBase is destroyed.
200 * @param enableTimeMeasurement Informs whether this event base should measure
201 * time. Disabling it would likely improve
202 * performance, but will disable some features
203 * that relies on time-measurement, including:
204 * observer, max latency and avg loop time.
206 explicit EventBase(event_base* evb, bool enableTimeMeasurement = true);
210 * Runs the event loop.
212 * loop() will loop waiting for I/O or timeouts and invoking EventHandler
213 * and AsyncTimeout callbacks as their events become ready. loop() will
214 * only return when there are no more events remaining to process, or after
215 * terminateLoopSoon() has been called.
217 * loop() may be called again to restart event processing after a previous
218 * call to loop() or loopForever() has returned.
220 * Returns true if the loop completed normally (if it processed all
221 * outstanding requests, or if terminateLoopSoon() was called). If an error
222 * occurs waiting for events, false will be returned.
227 * Wait for some events to become active, run them, then return.
229 * When EVLOOP_NONBLOCK is set in flags, the loop won't block if there
230 * are not any events to process.
232 * This is useful for callers that want to run the loop manually.
234 * Returns the same result as loop().
236 bool loopOnce(int flags = 0);
239 * Runs the event loop.
241 * loopForever() behaves like loop(), except that it keeps running even if
242 * when there are no more user-supplied EventHandlers or AsyncTimeouts
243 * registered. It will only return after terminateLoopSoon() has been
246 * This is useful for callers that want to wait for other threads to call
247 * runInEventBaseThread(), even when there are no other scheduled events.
249 * loopForever() may be called again to restart event processing after a
250 * previous call to loop() or loopForever() has returned.
252 * Throws a std::system_error if an error occurs.
257 * Causes the event loop to exit soon.
259 * This will cause an existing call to loop() or loopForever() to stop event
260 * processing and return, even if there are still events remaining to be
263 * It is safe to call terminateLoopSoon() from another thread to cause loop()
264 * to wake up and return in the EventBase loop thread. terminateLoopSoon()
265 * may also be called from the loop thread itself (for example, a
266 * EventHandler or AsyncTimeout callback may call terminateLoopSoon() to
267 * cause the loop to exit after the callback returns.) If the loop is not
268 * running, this will cause the next call to loop to terminate soon after
269 * starting. If a loop runs out of work (and so terminates on its own)
270 * concurrently with a call to terminateLoopSoon(), this may cause a race
273 * Note that the caller is responsible for ensuring that cleanup of all event
274 * callbacks occurs properly. Since terminateLoopSoon() causes the loop to
275 * exit even when there are pending events present, there may be remaining
276 * callbacks present waiting to be invoked. If the loop is later restarted
277 * pending events will continue to be processed normally, however if the
278 * EventBase is destroyed after calling terminateLoopSoon() it is the
279 * caller's responsibility to ensure that cleanup happens properly even if
280 * some outstanding events are never processed.
282 void terminateLoopSoon();
285 * Adds the given callback to a queue of things run after the current pass
286 * through the event loop completes. Note that if this callback calls
287 * runInLoop() the new callback won't be called until the main event loop
288 * has gone through a cycle.
290 * This method may only be called from the EventBase's thread. This
291 * essentially allows an event handler to schedule an additional callback to
292 * be invoked after it returns.
294 * Use runInEventBaseThread() to schedule functions from another thread.
296 * The thisIteration parameter makes this callback run in this loop
297 * iteration, instead of the next one, even if called from a
298 * runInLoop callback (normal io callbacks that call runInLoop will
299 * always run in this iteration). This was originally added to
300 * support detachEventBase, as a user callback may have called
301 * terminateLoopSoon(), but we want to make sure we detach. Also,
302 * detachEventBase almost always must be called from the base event
303 * loop to ensure the stack is unwound, since most users of
304 * EventBase are not thread safe.
306 * Ideally we would not need thisIteration, and instead just use
307 * runInLoop with loop() (instead of terminateLoopSoon).
309 void runInLoop(LoopCallback* callback, bool thisIteration = false);
312 * Convenience function to call runInLoop() with a folly::Function.
314 * This creates a LoopCallback object to wrap the folly::Function, and invoke
315 * the folly::Function when the loop callback fires. This is slightly more
316 * expensive than defining your own LoopCallback, but more convenient in
317 * areas that aren't too performance sensitive.
319 * This method may only be called from the EventBase's thread. This
320 * essentially allows an event handler to schedule an additional callback to
321 * be invoked after it returns.
323 * Use runInEventBaseThread() to schedule functions from another thread.
325 void runInLoop(Func c, bool thisIteration = false);
328 * Adds the given callback to a queue of things run before destruction
329 * of current EventBase.
331 * This allows users of EventBase that run in it, but don't control it,
332 * to be notified before EventBase gets destructed.
334 * Note: will be called from the thread that invoked EventBase destructor,
335 * before the final run of loop callbacks.
337 void runOnDestruction(LoopCallback* callback);
340 * Adds a callback that will run immediately *before* the event loop.
341 * This is very similar to runInLoop(), but will not cause the loop to break:
342 * For example, this callback could be used to get loop times.
344 void runBeforeLoop(LoopCallback* callback);
347 * Run the specified function in the EventBase's thread.
349 * This method is thread-safe, and may be called from another thread.
351 * If runInEventBaseThread() is called when the EventBase loop is not
352 * running, the function call will be delayed until the next time the loop is
355 * If runInEventBaseThread() returns true the function has successfully been
356 * scheduled to run in the loop thread. However, if the loop is terminated
357 * (and never later restarted) before it has a chance to run the requested
358 * function, the function will be run upon the EventBase's destruction.
360 * If two calls to runInEventBaseThread() are made from the same thread, the
361 * functions will always be run in the order that they were scheduled.
362 * Ordering between functions scheduled from separate threads is not
365 * @param fn The function to run. The function must not throw any
367 * @param arg An argument to pass to the function.
369 * @return Returns true if the function was successfully scheduled, or false
370 * if there was an error scheduling the function.
372 template <typename T>
373 bool runInEventBaseThread(void (*fn)(T*), T* arg);
376 * Run the specified function in the EventBase's thread
378 * This version of runInEventBaseThread() takes a folly::Function object.
379 * Note that this may be less efficient than the version that takes a plain
380 * function pointer and void* argument, if moving the function is expensive
381 * (e.g., if it wraps a lambda which captures some values with expensive move
384 * If the loop is terminated (and never later restarted) before it has a
385 * chance to run the requested function, the function will be run upon the
386 * EventBase's destruction.
388 * The function must not throw any exceptions.
390 bool runInEventBaseThread(Func fn);
393 * Like runInEventBaseThread, but the caller waits for the callback to be
396 template <typename T>
397 bool runInEventBaseThreadAndWait(void (*fn)(T*), T* arg);
400 * Like runInEventBaseThread, but the caller waits for the callback to be
403 bool runInEventBaseThreadAndWait(Func fn);
406 * Like runInEventBaseThreadAndWait, except if the caller is already in the
407 * event base thread, the functor is simply run inline.
409 template <typename T>
410 bool runImmediatelyOrRunInEventBaseThreadAndWait(void (*fn)(T*), T* arg);
413 * Like runInEventBaseThreadAndWait, except if the caller is already in the
414 * event base thread, the functor is simply run inline.
416 bool runImmediatelyOrRunInEventBaseThreadAndWait(Func fn);
419 * Set the maximum desired latency in us and provide a callback which will be
420 * called when that latency is exceeded.
421 * OBS: This functionality depends on time-measurement.
423 void setMaxLatency(int64_t maxLatency, Func maxLatencyCob) {
424 assert(enableTimeMeasurement_);
425 maxLatency_ = maxLatency;
426 maxLatencyCob_ = std::move(maxLatencyCob);
430 * Set smoothing coefficient for loop load average; # of milliseconds
431 * for exp(-1) (1/2.71828...) decay.
433 void setLoadAvgMsec(uint32_t ms);
436 * reset the load average to a desired value
438 void resetLoadAvg(double value = 0.0);
441 * Get the average loop time in microseconds (an exponentially-smoothed ave)
443 double getAvgLoopTime() const {
444 assert(enableTimeMeasurement_);
445 return avgLoopTime_.get();
449 * check if the event base loop is running.
451 bool isRunning() const {
452 return loopThread_.load(std::memory_order_relaxed) != 0;
456 * wait until the event loop starts (after starting the event loop thread).
458 void waitUntilRunning();
460 size_t getNotificationQueueSize() const;
462 void setMaxReadAtOnce(uint32_t maxAtOnce);
465 * Verify that current thread is the EventBase thread, if the EventBase is
468 bool isInEventBaseThread() const {
469 auto tid = loopThread_.load(std::memory_order_relaxed);
470 return tid == 0 || pthread_equal(tid, pthread_self());
473 bool inRunningEventBaseThread() const {
474 return pthread_equal(
475 loopThread_.load(std::memory_order_relaxed), pthread_self());
478 HHWheelTimer& timer() {
480 wheelTimer_ = HHWheelTimer::newTimer(this);
482 return *wheelTimer_.get();
485 // --------- interface to underlying libevent base ------------
486 // Avoid using these functions if possible. These functions are not
487 // guaranteed to always be present if we ever provide alternative EventBase
488 // implementations that do not use libevent internally.
489 event_base* getLibeventBase() const { return evb_; }
490 static const char* getLibeventVersion();
491 static const char* getLibeventMethod();
494 * only EventHandler/AsyncTimeout subclasses and ourselves should
497 * This is used to mark the beginning of a new loop cycle by the
498 * first handler fired within that cycle.
501 void bumpHandlingTime() override final;
503 class SmoothLoopTime {
505 explicit SmoothLoopTime(uint64_t timeInterval)
506 : expCoeff_(-1.0/timeInterval)
508 , oldBusyLeftover_(0) {
509 VLOG(11) << "expCoeff_ " << expCoeff_ << " " << __PRETTY_FUNCTION__;
512 void setTimeInterval(uint64_t timeInterval);
513 void reset(double value = 0.0);
515 void addSample(int64_t idle, int64_t busy);
521 void dampen(double factor) {
528 int64_t oldBusyLeftover_;
531 void setObserver(const std::shared_ptr<EventBaseObserver>& observer) {
532 assert(enableTimeMeasurement_);
533 observer_ = observer;
536 const std::shared_ptr<EventBaseObserver>& getObserver() {
541 * Setup execution observation/instrumentation for every EventHandler
542 * executed in this EventBase.
544 * @param executionObserver EventHandle's execution observer.
546 void setExecutionObserver(ExecutionObserver* observer) {
547 executionObserver_ = observer;
551 * Gets the execution observer associated with this EventBase.
553 ExecutionObserver* getExecutionObserver() {
554 return executionObserver_;
558 * Set the name of the thread that runs this event base.
560 void setName(const std::string& name);
563 * Returns the name of the thread that runs this event base.
565 const std::string& getName();
567 /// Implements the Executor interface
568 void add(Cob fn) override {
569 // runInEventBaseThread() takes a const&,
570 // so no point in doing std::move here.
571 runInEventBaseThread(std::move(fn));
574 /// Implements the DrivableExecutor interface
575 void drive() override {
576 // We can't use loopKeepAlive() here since LoopKeepAlive token can only be
577 // released inside a loop.
578 ++loopKeepAliveCount_;
580 --loopKeepAliveCount_;
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);
605 // Thread-safe version of loopKeepAlive()
606 LoopKeepAlive loopKeepAliveAtomic() {
607 if (inRunningEventBaseThread()) {
608 return loopKeepAlive();
610 loopKeepAliveCountAtomic_.fetch_add(1, std::memory_order_relaxed);
611 return LoopKeepAlive(this);
615 void attachTimeoutManager(
617 TimeoutManager::InternalEnum internal) override final;
619 void detachTimeoutManager(AsyncTimeout* obj) override final;
621 bool scheduleTimeout(AsyncTimeout* obj, TimeoutManager::timeout_type timeout)
624 void cancelTimeout(AsyncTimeout* obj) override final;
626 bool isInTimeoutManagerThread() override final {
627 return isInEventBaseThread();
631 void applyLoopKeepAlive();
633 ssize_t loopKeepAliveCount();
636 * Helper function that tells us whether we have already handled
637 * some event/timeout/callback in this loop iteration.
639 bool nothingHandledYet() const noexcept;
641 typedef LoopCallback::List LoopCallbackList;
642 class FunctionRunner;
644 bool loopBody(int flags = 0);
646 // executes any callbacks queued by runInLoop(); returns false if none found
647 bool runLoopCallbacks();
649 void initNotificationQueue();
651 // should only be accessed through public getter
652 HHWheelTimer::UniquePtr wheelTimer_;
654 LoopCallbackList loopCallbacks_;
655 LoopCallbackList runBeforeLoopCallbacks_;
656 LoopCallbackList onDestructionCallbacks_;
658 // This will be null most of the time, but point to currentCallbacks
659 // if we are in the middle of running loop callbacks, such that
660 // runInLoop(..., true) will always run in the current loop
662 LoopCallbackList* runOnceCallbacks_;
664 // stop_ is set by terminateLoopSoon() and is used by the main loop
665 // to determine if it should exit
666 std::atomic<bool> stop_;
668 // The ID of the thread running the main loop.
669 // 0 if loop is not running.
670 // Note: POSIX doesn't guarantee that 0 is an invalid pthread_t (or
671 // even that atomic<pthread_t> is valid), but that's how it is
672 // everywhere (at least on Linux, FreeBSD, and OSX).
673 std::atomic<pthread_t> loopThread_;
675 // pointer to underlying event_base class doing the heavy lifting
678 // A notification queue for runInEventBaseThread() to use
679 // to send function requests to the EventBase thread.
680 std::unique_ptr<NotificationQueue<Func>> queue_;
681 std::unique_ptr<FunctionRunner> fnRunner_;
682 ssize_t loopKeepAliveCount_{0};
683 std::atomic<ssize_t> loopKeepAliveCountAtomic_{0};
684 bool loopKeepAliveActive_{false};
686 // limit for latency in microseconds (0 disables)
689 // exponentially-smoothed average loop time for latency-limiting
690 SmoothLoopTime avgLoopTime_;
692 // smoothed loop time used to invoke latency callbacks; differs from
693 // avgLoopTime_ in that it's scaled down after triggering a callback
694 // to reduce spamminess
695 SmoothLoopTime maxLatencyLoopTime_;
697 // callback called when latency limit is exceeded
700 // Enables/disables time measurements in loopBody(). if disabled, the
701 // following functionality that relies on time-measurement, will not
702 // be supported: avg loop time, observer and max latency.
703 const bool enableTimeMeasurement_;
705 // we'll wait this long before running deferred callbacks if the event
707 static const int kDEFAULT_IDLE_WAIT_USEC = 20000; // 20ms
709 // Wrap-around loop counter to detect beginning of each loop
710 uint64_t nextLoopCnt_;
711 uint64_t latestLoopCnt_;
713 // Prevent undefined behavior from invoking event_base_loop() reentrantly.
714 // This is needed since many projects use libevent-1.4, which lacks commit
715 // b557b175c00dc462c1fce25f6e7dd67121d2c001 from
716 // https://github.com/libevent/libevent/.
717 bool invokingLoop_{false};
719 // Observer to export counters
720 std::shared_ptr<EventBaseObserver> observer_;
721 uint32_t observerSampleCount_;
723 // EventHandler's execution observer.
724 ExecutionObserver* executionObserver_;
726 // Name of the thread running this EventBase
729 // allow runOnDestruction() to be called from any threads
730 std::mutex onDestructionCallbacksMutex_;
732 // see EventBaseLocal
733 friend class detail::EventBaseLocalBase;
734 template <typename T> friend class EventBaseLocal;
735 std::mutex localStorageMutex_;
736 std::unordered_map<uint64_t, std::shared_ptr<void>> localStorage_;
737 std::unordered_set<detail::EventBaseLocalBaseBase*> localStorageToDtor_;
740 template <typename T>
741 bool EventBase::runInEventBaseThread(void (*fn)(T*), T* arg) {
742 return runInEventBaseThread([=] { fn(arg); });
745 template <typename T>
746 bool EventBase::runInEventBaseThreadAndWait(void (*fn)(T*), T* arg) {
747 return runInEventBaseThreadAndWait([=] { fn(arg); });
750 template <typename T>
751 bool EventBase::runImmediatelyOrRunInEventBaseThreadAndWait(
754 return runImmediatelyOrRunInEventBaseThreadAndWait([=] { fn(arg); });