2 * Copyright 2017 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
30 #include <unordered_map>
31 #include <unordered_set>
34 #include <boost/intrusive/list.hpp>
35 #include <boost/utility.hpp>
36 #include <glog/logging.h>
38 #include <folly/CallOnce.h>
39 #include <folly/Executor.h>
40 #include <folly/Function.h>
41 #include <folly/Portability.h>
42 #include <folly/ScopeGuard.h>
43 #include <folly/experimental/ExecutionObserver.h>
44 #include <folly/futures/DrivableExecutor.h>
45 #include <folly/io/async/AsyncTimeout.h>
46 #include <folly/io/async/HHWheelTimer.h>
47 #include <folly/io/async/Request.h>
48 #include <folly/io/async/TimeoutManager.h>
49 #include <folly/portability/Event.h>
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 {
182 // Like FunctionLoopCallback, but saves one allocation. Use with caution.
184 // The caller is responsible for maintaining the lifetime of this callback
185 // until after the point at which the contained function is called.
186 class StackFunctionLoopCallback : public LoopCallback {
188 explicit StackFunctionLoopCallback(Func&& function)
189 : function_(std::move(function)) {}
190 void runLoopCallback() noexcept override {
191 Func(std::move(function_))();
199 * Create a new EventBase object.
201 * @param enableTimeMeasurement Informs whether this event base should measure
202 * time. Disabling it would likely improve
203 * performance, but will disable some features
204 * that relies on time-measurement, including:
205 * observer, max latency and avg loop time.
207 explicit EventBase(bool enableTimeMeasurement = true);
210 * Create a new EventBase object that will use the specified libevent
211 * event_base object to drive the event loop.
213 * The EventBase will take ownership of this event_base, and will call
214 * event_base_free(evb) when the EventBase is destroyed.
216 * @param enableTimeMeasurement Informs whether this event base should measure
217 * time. Disabling it would likely improve
218 * performance, but will disable some features
219 * that relies on time-measurement, including:
220 * observer, max latency and avg loop time.
222 explicit EventBase(event_base* evb, bool enableTimeMeasurement = true);
223 ~EventBase() override;
226 * Runs the event loop.
228 * loop() will loop waiting for I/O or timeouts and invoking EventHandler
229 * and AsyncTimeout callbacks as their events become ready. loop() will
230 * only return when there are no more events remaining to process, or after
231 * terminateLoopSoon() has been called.
233 * loop() may be called again to restart event processing after a previous
234 * call to loop() or loopForever() has returned.
236 * Returns true if the loop completed normally (if it processed all
237 * outstanding requests, or if terminateLoopSoon() was called). If an error
238 * occurs waiting for events, false will be returned.
243 * Wait for some events to become active, run them, then return.
245 * When EVLOOP_NONBLOCK is set in flags, the loop won't block if there
246 * are not any events to process.
248 * This is useful for callers that want to run the loop manually.
250 * Returns the same result as loop().
252 bool loopOnce(int flags = 0);
255 * Runs the event loop.
257 * loopForever() behaves like loop(), except that it keeps running even if
258 * when there are no more user-supplied EventHandlers or AsyncTimeouts
259 * registered. It will only return after terminateLoopSoon() has been
262 * This is useful for callers that want to wait for other threads to call
263 * runInEventBaseThread(), even when there are no other scheduled events.
265 * loopForever() may be called again to restart event processing after a
266 * previous call to loop() or loopForever() has returned.
268 * Throws a std::system_error if an error occurs.
273 * Causes the event loop to exit soon.
275 * This will cause an existing call to loop() or loopForever() to stop event
276 * processing and return, even if there are still events remaining to be
279 * It is safe to call terminateLoopSoon() from another thread to cause loop()
280 * to wake up and return in the EventBase loop thread. terminateLoopSoon()
281 * may also be called from the loop thread itself (for example, a
282 * EventHandler or AsyncTimeout callback may call terminateLoopSoon() to
283 * cause the loop to exit after the callback returns.) If the loop is not
284 * running, this will cause the next call to loop to terminate soon after
285 * starting. If a loop runs out of work (and so terminates on its own)
286 * concurrently with a call to terminateLoopSoon(), this may cause a race
289 * Note that the caller is responsible for ensuring that cleanup of all event
290 * callbacks occurs properly. Since terminateLoopSoon() causes the loop to
291 * exit even when there are pending events present, there may be remaining
292 * callbacks present waiting to be invoked. If the loop is later restarted
293 * pending events will continue to be processed normally, however if the
294 * EventBase is destroyed after calling terminateLoopSoon() it is the
295 * caller's responsibility to ensure that cleanup happens properly even if
296 * some outstanding events are never processed.
298 void terminateLoopSoon();
301 * Adds the given callback to a queue of things run after the current pass
302 * through the event loop completes. Note that if this callback calls
303 * runInLoop() the new callback won't be called until the main event loop
304 * has gone through a cycle.
306 * This method may only be called from the EventBase's thread. This
307 * essentially allows an event handler to schedule an additional callback to
308 * be invoked after it returns.
310 * Use runInEventBaseThread() to schedule functions from another thread.
312 * The thisIteration parameter makes this callback run in this loop
313 * iteration, instead of the next one, even if called from a
314 * runInLoop callback (normal io callbacks that call runInLoop will
315 * always run in this iteration). This was originally added to
316 * support detachEventBase, as a user callback may have called
317 * terminateLoopSoon(), but we want to make sure we detach. Also,
318 * detachEventBase almost always must be called from the base event
319 * loop to ensure the stack is unwound, since most users of
320 * EventBase are not thread safe.
322 * Ideally we would not need thisIteration, and instead just use
323 * runInLoop with loop() (instead of terminateLoopSoon).
325 void runInLoop(LoopCallback* callback, bool thisIteration = false);
328 * Convenience function to call runInLoop() with a folly::Function.
330 * This creates a LoopCallback object to wrap the folly::Function, and invoke
331 * the folly::Function when the loop callback fires. This is slightly more
332 * expensive than defining your own LoopCallback, but more convenient in
333 * areas that aren't too performance sensitive.
335 * This method may only be called from the EventBase's thread. This
336 * essentially allows an event handler to schedule an additional callback to
337 * be invoked after it returns.
339 * Use runInEventBaseThread() to schedule functions from another thread.
341 void runInLoop(Func c, bool thisIteration = false);
344 * Adds the given callback to a queue of things run before destruction
345 * of current EventBase.
347 * This allows users of EventBase that run in it, but don't control it,
348 * to be notified before EventBase gets destructed.
350 * Note: will be called from the thread that invoked EventBase destructor,
351 * before the final run of loop callbacks.
353 void runOnDestruction(LoopCallback* callback);
356 * Adds a callback that will run immediately *before* the event loop.
357 * This is very similar to runInLoop(), but will not cause the loop to break:
358 * For example, this callback could be used to get loop times.
360 void runBeforeLoop(LoopCallback* callback);
363 * Run the specified function in the EventBase's thread.
365 * This method is thread-safe, and may be called from another thread.
367 * If runInEventBaseThread() is called when the EventBase loop is not
368 * running, the function call will be delayed until the next time the loop is
371 * If runInEventBaseThread() returns true the function has successfully been
372 * scheduled to run in the loop thread. However, if the loop is terminated
373 * (and never later restarted) before it has a chance to run the requested
374 * function, the function will be run upon the EventBase's destruction.
376 * If two calls to runInEventBaseThread() are made from the same thread, the
377 * functions will always be run in the order that they were scheduled.
378 * Ordering between functions scheduled from separate threads is not
381 * @param fn The function to run. The function must not throw any
383 * @param arg An argument to pass to the function.
385 * @return Returns true if the function was successfully scheduled, or false
386 * if there was an error scheduling the function.
388 template <typename T>
389 bool runInEventBaseThread(void (*fn)(T*), T* arg);
392 * Run the specified function in the EventBase's thread
394 * This version of runInEventBaseThread() takes a folly::Function object.
395 * Note that this may be less efficient than the version that takes a plain
396 * function pointer and void* argument, if moving the function is expensive
397 * (e.g., if it wraps a lambda which captures some values with expensive move
400 * If the loop is terminated (and never later restarted) before it has a
401 * chance to run the requested function, the function will be run upon the
402 * EventBase's destruction.
404 * The function must not throw any exceptions.
406 bool runInEventBaseThread(Func fn);
409 * Like runInEventBaseThread, but the caller waits for the callback to be
412 template <typename T>
413 bool runInEventBaseThreadAndWait(void (*fn)(T*), T* arg);
416 * Like runInEventBaseThread, but the caller waits for the callback to be
419 bool runInEventBaseThreadAndWait(Func fn);
422 * Like runInEventBaseThreadAndWait, except if the caller is already in the
423 * event base thread, the functor is simply run inline.
425 template <typename T>
426 bool runImmediatelyOrRunInEventBaseThreadAndWait(void (*fn)(T*), T* arg);
429 * Like runInEventBaseThreadAndWait, except if the caller is already in the
430 * event base thread, the functor is simply run inline.
432 bool runImmediatelyOrRunInEventBaseThreadAndWait(Func fn);
435 * Set the maximum desired latency in us and provide a callback which will be
436 * called when that latency is exceeded.
437 * OBS: This functionality depends on time-measurement.
439 void setMaxLatency(std::chrono::microseconds maxLatency, Func maxLatencyCob) {
440 assert(enableTimeMeasurement_);
441 maxLatency_ = maxLatency;
442 maxLatencyCob_ = std::move(maxLatencyCob);
446 * Set smoothing coefficient for loop load average; # of milliseconds
447 * for exp(-1) (1/2.71828...) decay.
449 void setLoadAvgMsec(std::chrono::milliseconds ms);
452 * reset the load average to a desired value
454 void resetLoadAvg(double value = 0.0);
457 * Get the average loop time in microseconds (an exponentially-smoothed ave)
459 double getAvgLoopTime() const {
460 assert(enableTimeMeasurement_);
461 return avgLoopTime_.get();
465 * check if the event base loop is running.
467 bool isRunning() const {
468 return loopThread_.load(std::memory_order_relaxed) != std::thread::id();
472 * wait until the event loop starts (after starting the event loop thread).
474 void waitUntilRunning();
476 size_t getNotificationQueueSize() const;
478 void setMaxReadAtOnce(uint32_t maxAtOnce);
481 * Verify that current thread is the EventBase thread, if the EventBase is
484 bool isInEventBaseThread() const {
485 auto tid = loopThread_.load(std::memory_order_relaxed);
486 return tid == std::thread::id() || tid == std::this_thread::get_id();
489 bool inRunningEventBaseThread() const {
490 return loopThread_.load(std::memory_order_relaxed) ==
491 std::this_thread::get_id();
495 * Equivalent to CHECK(isInEventBaseThread()) (and assert/DCHECK for
496 * dcheckIsInEventBaseThread), but it prints more information on
499 void checkIsInEventBaseThread() const;
500 void dcheckIsInEventBaseThread() const {
502 checkIsInEventBaseThread();
506 HHWheelTimer& timer() {
508 wheelTimer_ = HHWheelTimer::newTimer(this);
510 return *wheelTimer_.get();
513 // --------- interface to underlying libevent base ------------
514 // Avoid using these functions if possible. These functions are not
515 // guaranteed to always be present if we ever provide alternative EventBase
516 // implementations that do not use libevent internally.
517 event_base* getLibeventBase() const { return evb_; }
518 static const char* getLibeventVersion();
519 static const char* getLibeventMethod();
522 * only EventHandler/AsyncTimeout subclasses and ourselves should
525 * This is used to mark the beginning of a new loop cycle by the
526 * first handler fired within that cycle.
529 void bumpHandlingTime() final;
531 class SmoothLoopTime {
533 explicit SmoothLoopTime(std::chrono::microseconds timeInterval)
534 : expCoeff_(-1.0 / timeInterval.count()),
536 oldBusyLeftover_(0) {
537 VLOG(11) << "expCoeff_ " << expCoeff_ << " " << __PRETTY_FUNCTION__;
540 void setTimeInterval(std::chrono::microseconds timeInterval);
541 void reset(double value = 0.0);
544 std::chrono::microseconds idle,
545 std::chrono::microseconds busy);
551 void dampen(double factor) {
558 std::chrono::microseconds oldBusyLeftover_;
561 void setObserver(const std::shared_ptr<EventBaseObserver>& observer) {
562 assert(enableTimeMeasurement_);
563 observer_ = observer;
566 const std::shared_ptr<EventBaseObserver>& getObserver() {
571 * Setup execution observation/instrumentation for every EventHandler
572 * executed in this EventBase.
574 * @param executionObserver EventHandle's execution observer.
576 void setExecutionObserver(ExecutionObserver* observer) {
577 executionObserver_ = observer;
581 * Gets the execution observer associated with this EventBase.
583 ExecutionObserver* getExecutionObserver() {
584 return executionObserver_;
588 * Set the name of the thread that runs this event base.
590 void setName(const std::string& name);
593 * Returns the name of the thread that runs this event base.
595 const std::string& getName();
597 /// Implements the Executor interface
598 void add(Cob fn) override {
599 // runInEventBaseThread() takes a const&,
600 // so no point in doing std::move here.
601 runInEventBaseThread(std::move(fn));
604 /// Implements the DrivableExecutor interface
605 void drive() override {
606 ++loopKeepAliveCount_;
608 --loopKeepAliveCount_;
613 /// Returns you a handle which make loop() behave like loopForever() until
614 /// destroyed. loop() will return to its original behavior only when all
615 /// loop keep-alives are released.
616 KeepAlive getKeepAliveToken() override {
618 return makeKeepAlive();
622 void attachTimeoutManager(
624 TimeoutManager::InternalEnum internal) final;
626 void detachTimeoutManager(AsyncTimeout* obj) final;
628 bool scheduleTimeout(AsyncTimeout* obj, TimeoutManager::timeout_type timeout)
631 void cancelTimeout(AsyncTimeout* obj) final;
633 bool isInTimeoutManagerThread() final {
634 return isInEventBaseThread();
637 // Returns a VirtualEventBase attached to this EventBase. Can be used to
638 // pass to APIs which expect VirtualEventBase. This VirtualEventBase will be
639 // destroyed together with the EventBase.
641 // Any number of VirtualEventBases instances may be independently constructed,
642 // which are backed by this EventBase. This method should be only used if you
643 // don't need to manage the life time of the VirtualEventBase used.
644 folly::VirtualEventBase& getVirtualEventBase();
647 void keepAliveAcquire() override {
648 if (inRunningEventBaseThread()) {
649 loopKeepAliveCount_++;
651 loopKeepAliveCountAtomic_.fetch_add(1, std::memory_order_relaxed);
655 void keepAliveRelease() override {
656 if (!inRunningEventBaseThread()) {
657 return add([=] { keepAliveRelease(); });
659 loopKeepAliveCount_--;
663 void applyLoopKeepAlive();
665 ssize_t loopKeepAliveCount();
668 * Helper function that tells us whether we have already handled
669 * some event/timeout/callback in this loop iteration.
671 bool nothingHandledYet() const noexcept;
673 typedef LoopCallback::List LoopCallbackList;
674 class FunctionRunner;
676 bool loopBody(int flags = 0);
678 // executes any callbacks queued by runInLoop(); returns false if none found
679 bool runLoopCallbacks();
681 void initNotificationQueue();
683 // should only be accessed through public getter
684 HHWheelTimer::UniquePtr wheelTimer_;
686 LoopCallbackList loopCallbacks_;
687 LoopCallbackList runBeforeLoopCallbacks_;
688 LoopCallbackList onDestructionCallbacks_;
690 // This will be null most of the time, but point to currentCallbacks
691 // if we are in the middle of running loop callbacks, such that
692 // runInLoop(..., true) will always run in the current loop
694 LoopCallbackList* runOnceCallbacks_;
696 // stop_ is set by terminateLoopSoon() and is used by the main loop
697 // to determine if it should exit
698 std::atomic<bool> stop_;
700 // The ID of the thread running the main loop.
701 // std::thread::id{} if loop is not running.
702 std::atomic<std::thread::id> loopThread_;
704 // pointer to underlying event_base class doing the heavy lifting
707 // A notification queue for runInEventBaseThread() to use
708 // to send function requests to the EventBase thread.
709 std::unique_ptr<NotificationQueue<Func>> queue_;
710 std::unique_ptr<FunctionRunner> fnRunner_;
711 ssize_t loopKeepAliveCount_{0};
712 std::atomic<ssize_t> loopKeepAliveCountAtomic_{0};
713 bool loopKeepAliveActive_{false};
715 // limit for latency in microseconds (0 disables)
716 std::chrono::microseconds maxLatency_;
718 // exponentially-smoothed average loop time for latency-limiting
719 SmoothLoopTime avgLoopTime_;
721 // smoothed loop time used to invoke latency callbacks; differs from
722 // avgLoopTime_ in that it's scaled down after triggering a callback
723 // to reduce spamminess
724 SmoothLoopTime maxLatencyLoopTime_;
726 // callback called when latency limit is exceeded
729 // Enables/disables time measurements in loopBody(). if disabled, the
730 // following functionality that relies on time-measurement, will not
731 // be supported: avg loop time, observer and max latency.
732 const bool enableTimeMeasurement_;
734 // Wrap-around loop counter to detect beginning of each loop
735 uint64_t nextLoopCnt_;
736 uint64_t latestLoopCnt_;
737 std::chrono::steady_clock::time_point startWork_;
738 // Prevent undefined behavior from invoking event_base_loop() reentrantly.
739 // This is needed since many projects use libevent-1.4, which lacks commit
740 // b557b175c00dc462c1fce25f6e7dd67121d2c001 from
741 // https://github.com/libevent/libevent/.
742 bool invokingLoop_{false};
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 // see EventBaseLocal
758 friend class detail::EventBaseLocalBase;
759 template <typename T> friend class EventBaseLocal;
760 std::unordered_map<uint64_t, std::shared_ptr<void>> localStorage_;
761 std::unordered_set<detail::EventBaseLocalBaseBase*> localStorageToDtor_;
763 folly::once_flag virtualEventBaseInitFlag_;
764 std::unique_ptr<VirtualEventBase> virtualEventBase_;
767 template <typename T>
768 bool EventBase::runInEventBaseThread(void (*fn)(T*), T* arg) {
769 return runInEventBaseThread([=] { fn(arg); });
772 template <typename T>
773 bool EventBase::runInEventBaseThreadAndWait(void (*fn)(T*), T* arg) {
774 return runInEventBaseThreadAndWait([=] { fn(arg); });
777 template <typename T>
778 bool EventBase::runImmediatelyOrRunInEventBaseThreadAndWait(
781 return runImmediatelyOrRunInEventBaseThreadAndWait([=] { fn(arg); });