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 a callback that will run immediately *before* the event loop.
322 * This is very similar to runInLoop(), but will not cause the loop to break:
323 * For example, this callback could be used to get loop times.
325 void runBeforeLoop(LoopCallback* callback);
328 * Run the specified function in the EventBase's thread.
330 * This method is thread-safe, and may be called from another thread.
332 * If runInEventBaseThread() is called when the EventBase loop is not
333 * running, the function call will be delayed until the next time the loop is
336 * If runInEventBaseThread() returns true the function has successfully been
337 * scheduled to run in the loop thread. However, if the loop is terminated
338 * (and never later restarted) before it has a chance to run the requested
339 * function, the function will be run upon the EventBase's destruction.
341 * If two calls to runInEventBaseThread() are made from the same thread, the
342 * functions will always be run in the order that they were scheduled.
343 * Ordering between functions scheduled from separate threads is not
346 * @param fn The function to run. The function must not throw any
348 * @param arg An argument to pass to the function.
350 * @return Returns true if the function was successfully scheduled, or false
351 * if there was an error scheduling the function.
354 bool runInEventBaseThread(void (*fn)(T*), T* arg) {
355 return runInEventBaseThread(reinterpret_cast<void (*)(void*)>(fn),
356 reinterpret_cast<void*>(arg));
359 bool runInEventBaseThread(void (*fn)(void*), void* arg);
362 * Run the specified function in the EventBase's thread
364 * This version of runInEventBaseThread() takes a std::function object.
365 * Note that this is less efficient than the version that takes a plain
366 * function pointer and void* argument, as it has to allocate memory to copy
367 * the std::function object.
369 * If the loop is terminated (and never later restarted) before it has a
370 * chance to run the requested function, the function will be run upon the
371 * EventBase's destruction.
373 * The function must not throw any exceptions.
375 bool runInEventBaseThread(const Cob& fn);
378 * Like runInEventBaseThread, but the caller waits for the callback to be
382 bool runInEventBaseThreadAndWait(void (*fn)(T*), T* arg) {
383 return runInEventBaseThreadAndWait(reinterpret_cast<void (*)(void*)>(fn),
384 reinterpret_cast<void*>(arg));
388 * Like runInEventBaseThread, but the caller waits for the callback to be
391 bool runInEventBaseThreadAndWait(void (*fn)(void*), void* arg) {
392 return runInEventBaseThreadAndWait(std::bind(fn, arg));
396 * Like runInEventBaseThread, but the caller waits for the callback to be
399 bool runInEventBaseThreadAndWait(const Cob& fn);
402 * Like runInEventBaseThreadAndWait, except if the caller is already in the
403 * event base thread, the functor is simply run inline.
406 bool runImmediatelyOrRunInEventBaseThreadAndWait(void (*fn)(T*), T* arg) {
407 return runImmediatelyOrRunInEventBaseThreadAndWait(
408 reinterpret_cast<void (*)(void*)>(fn), reinterpret_cast<void*>(arg));
412 * Like runInEventBaseThreadAndWait, except if the caller is already in the
413 * event base thread, the functor is simply run inline.
415 bool runImmediatelyOrRunInEventBaseThreadAndWait(
416 void (*fn)(void*), void* arg) {
417 return runImmediatelyOrRunInEventBaseThreadAndWait(std::bind(fn, 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(const Cob& fn);
427 * Runs the given Cob at some time after the specified number of
428 * milliseconds. (No guarantees exactly when.)
430 * Throws a std::system_error if an error occurs.
435 TimeoutManager::InternalEnum in = TimeoutManager::InternalEnum::NORMAL);
438 * @see tryRunAfterDelay for more details
440 * @return true iff the cob was successfully registered.
443 bool tryRunAfterDelay(
446 TimeoutManager::InternalEnum in = TimeoutManager::InternalEnum::NORMAL);
449 * Set the maximum desired latency in us and provide a callback which will be
450 * called when that latency is exceeded.
451 * OBS: This functionality depends on time-measurement.
453 void setMaxLatency(int64_t maxLatency, const Cob& maxLatencyCob) {
454 assert(enableTimeMeasurement_);
455 maxLatency_ = maxLatency;
456 maxLatencyCob_ = maxLatencyCob;
461 * Set smoothing coefficient for loop load average; # of milliseconds
462 * for exp(-1) (1/2.71828...) decay.
464 void setLoadAvgMsec(uint32_t ms);
467 * reset the load average to a desired value
469 void resetLoadAvg(double value = 0.0);
472 * Get the average loop time in microseconds (an exponentially-smoothed ave)
474 double getAvgLoopTime() const {
475 assert(enableTimeMeasurement_);
476 return avgLoopTime_.get();
480 * check if the event base loop is running.
482 bool isRunning() const {
483 return loopThread_.load(std::memory_order_relaxed) != 0;
487 * wait until the event loop starts (after starting the event loop thread).
489 void waitUntilRunning();
491 int getNotificationQueueSize() const;
493 void setMaxReadAtOnce(uint32_t maxAtOnce);
496 * Verify that current thread is the EventBase thread, if the EventBase is
499 bool isInEventBaseThread() const {
500 auto tid = loopThread_.load(std::memory_order_relaxed);
501 return tid == 0 || pthread_equal(tid, pthread_self());
504 bool inRunningEventBaseThread() const {
505 return pthread_equal(
506 loopThread_.load(std::memory_order_relaxed), pthread_self());
509 // --------- interface to underlying libevent base ------------
510 // Avoid using these functions if possible. These functions are not
511 // guaranteed to always be present if we ever provide alternative EventBase
512 // implementations that do not use libevent internally.
513 event_base* getLibeventBase() const { return evb_; }
514 static const char* getLibeventVersion();
515 static const char* getLibeventMethod();
518 * only EventHandler/AsyncTimeout subclasses and ourselves should
521 * This is used to mark the beginning of a new loop cycle by the
522 * first handler fired within that cycle.
525 bool bumpHandlingTime() override;
527 class SmoothLoopTime {
529 explicit SmoothLoopTime(uint64_t timeInterval)
530 : expCoeff_(-1.0/timeInterval)
532 , oldBusyLeftover_(0) {
533 VLOG(11) << "expCoeff_ " << expCoeff_ << " " << __PRETTY_FUNCTION__;
536 void setTimeInterval(uint64_t timeInterval);
537 void reset(double value = 0.0);
539 void addSample(int64_t idle, int64_t busy);
545 void dampen(double factor) {
552 int64_t oldBusyLeftover_;
555 void setObserver(const std::shared_ptr<EventBaseObserver>& observer) {
556 assert(enableTimeMeasurement_);
557 observer_ = observer;
560 const std::shared_ptr<EventBaseObserver>& getObserver() {
565 * Setup execution observation/instrumentation for every EventHandler
566 * executed in this EventBase.
568 * @param executionObserver EventHandle's execution observer.
570 void setExecutionObserver(ExecutionObserver* observer) {
571 executionObserver_ = observer;
575 * Gets the execution observer associated with this EventBase.
577 ExecutionObserver* getExecutionObserver() {
578 return executionObserver_;
582 * Set the name of the thread that runs this event base.
584 void setName(const std::string& name);
587 * Returns the name of the thread that runs this event base.
589 const std::string& getName();
591 /// Implements the Executor interface
592 void add(Cob fn) override {
593 // runInEventBaseThread() takes a const&,
594 // so no point in doing std::move here.
595 runInEventBaseThread(fn);
598 /// Implements the DrivableExecutor interface
599 void drive() override {
606 void attachTimeoutManager(AsyncTimeout* obj,
607 TimeoutManager::InternalEnum internal) override;
609 void detachTimeoutManager(AsyncTimeout* obj) override;
611 bool scheduleTimeout(AsyncTimeout* obj, TimeoutManager::timeout_type timeout)
614 void cancelTimeout(AsyncTimeout* obj) override;
616 bool isInTimeoutManagerThread() override {
617 return isInEventBaseThread();
620 // Helper class used to short circuit runInEventBaseThread
621 class RunInLoopCallback : public LoopCallback {
623 RunInLoopCallback(void (*fn)(void*), void* arg);
624 void runLoopCallback() noexcept;
632 * Helper function that tells us whether we have already handled
633 * some event/timeout/callback in this loop iteration.
635 bool nothingHandledYet();
637 // --------- libevent callbacks (not for client use) ------------
639 static void runFunctionPtr(std::function<void()>* fn);
641 // small object used as a callback arg with enough info to execute the
642 // appropriate client-provided Cob
643 class CobTimeout : public AsyncTimeout {
645 CobTimeout(EventBase* b, const Cob& c, TimeoutManager::InternalEnum in)
646 : AsyncTimeout(b, in), cob_(c) {}
648 virtual void timeoutExpired() noexcept;
654 typedef boost::intrusive::list_member_hook<
655 boost::intrusive::link_mode<boost::intrusive::auto_unlink> > ListHook;
659 typedef boost::intrusive::list<
661 boost::intrusive::member_hook<CobTimeout, ListHook, &CobTimeout::hook>,
662 boost::intrusive::constant_time_size<false> > List;
665 typedef LoopCallback::List LoopCallbackList;
666 class FunctionRunner;
668 bool loopBody(int flags = 0);
670 // executes any callbacks queued by runInLoop(); returns false if none found
671 bool runLoopCallbacks(bool setContext = true);
673 void initNotificationQueue();
675 CobTimeout::List pendingCobTimeouts_;
677 LoopCallbackList loopCallbacks_;
678 LoopCallbackList runBeforeLoopCallbacks_;
679 LoopCallbackList onDestructionCallbacks_;
681 // This will be null most of the time, but point to currentCallbacks
682 // if we are in the middle of running loop callbacks, such that
683 // runInLoop(..., true) will always run in the current loop
685 LoopCallbackList* runOnceCallbacks_;
687 // stop_ is set by terminateLoopSoon() and is used by the main loop
688 // to determine if it should exit
689 std::atomic<bool> stop_;
691 // The ID of the thread running the main loop.
692 // 0 if loop is not running.
693 // Note: POSIX doesn't guarantee that 0 is an invalid pthread_t (or
694 // even that atomic<pthread_t> is valid), but that's how it is
695 // everywhere (at least on Linux, FreeBSD, and OSX).
696 std::atomic<pthread_t> loopThread_;
698 // pointer to underlying event_base class doing the heavy lifting
701 // A notification queue for runInEventBaseThread() to use
702 // to send function requests to the EventBase thread.
703 std::unique_ptr<NotificationQueue<std::pair<void (*)(void*), void*>>> queue_;
704 std::unique_ptr<FunctionRunner> fnRunner_;
706 // limit for latency in microseconds (0 disables)
709 // exponentially-smoothed average loop time for latency-limiting
710 SmoothLoopTime avgLoopTime_;
712 // smoothed loop time used to invoke latency callbacks; differs from
713 // avgLoopTime_ in that it's scaled down after triggering a callback
714 // to reduce spamminess
715 SmoothLoopTime maxLatencyLoopTime_;
717 // callback called when latency limit is exceeded
720 // Enables/disables time measurements in loopBody(). if disabled, the
721 // following functionality that relies on time-measurement, will not
722 // be supported: avg loop time, observer and max latency.
723 const bool enableTimeMeasurement_;
725 // we'll wait this long before running deferred callbacks if the event
727 static const int kDEFAULT_IDLE_WAIT_USEC = 20000; // 20ms
729 // Wrap-around loop counter to detect beginning of each loop
730 uint64_t nextLoopCnt_;
731 uint64_t latestLoopCnt_;
734 // Observer to export counters
735 std::shared_ptr<EventBaseObserver> observer_;
736 uint32_t observerSampleCount_;
738 // EventHandler's execution observer.
739 ExecutionObserver* executionObserver_;
741 // Name of the thread running this EventBase
744 // allow runOnDestruction() to be called from any threads
745 std::mutex onDestructionCallbacksMutex_;
747 // see EventBaseLocal
748 friend class detail::EventBaseLocalBase;
749 template <typename T> friend class EventBaseLocal;
750 std::mutex localStorageMutex_;
751 std::unordered_map<uint64_t, std::shared_ptr<void>> localStorage_;
752 std::unordered_set<detail::EventBaseLocalBaseBase*> localStorageToDtor_;