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"};
106 * This class is a wrapper for all asynchronous I/O processing functionality
108 * EventBase provides a main loop that notifies EventHandler callback objects
109 * when I/O is ready on a file descriptor, and notifies AsyncTimeout objects
110 * when a specified timeout has expired. More complex, higher-level callback
111 * mechanisms can then be built on top of EventHandler and AsyncTimeout.
113 * A EventBase object can only drive an event loop for a single thread. To
114 * take advantage of multiple CPU cores, most asynchronous I/O servers have one
115 * thread per CPU, and use a separate EventBase for each thread.
117 * In general, most EventBase methods may only be called from the thread
118 * running the EventBase's loop. There are a few exceptions to this rule, for
119 * methods that are explicitly intended to allow communication with a
120 * EventBase from other threads. When it is safe to call a method from
121 * another thread it is explicitly listed in the method comments.
123 class EventBase : private boost::noncopyable,
124 public TimeoutManager,
125 public DrivableExecutor {
127 using Func = folly::Function<void()>;
130 * A callback interface to use with runInLoop()
132 * Derive from this class if you need to delay some code execution until the
133 * next iteration of the event loop. This allows you to schedule code to be
134 * invoked from the top-level of the loop, after your immediate callers have
137 * If a LoopCallback object is destroyed while it is scheduled to be run in
138 * the next loop iteration, it will automatically be cancelled.
141 : public boost::intrusive::list_base_hook<
142 boost::intrusive::link_mode<boost::intrusive::auto_unlink>> {
144 virtual ~LoopCallback() = default;
146 virtual void runLoopCallback() noexcept = 0;
147 void cancelLoopCallback() {
151 bool isLoopCallbackScheduled() const {
156 typedef boost::intrusive::list<
158 boost::intrusive::constant_time_size<false> > List;
160 // EventBase needs access to LoopCallbackList (and therefore to hook_)
161 friend class EventBase;
162 std::shared_ptr<RequestContext> context_;
166 * Create a new EventBase object.
168 * @param enableTimeMeasurement Informs whether this event base should measure
169 * time. Disabling it would likely improve
170 * performance, but will disable some features
171 * that relies on time-measurement, including:
172 * observer, max latency and avg loop time.
174 explicit EventBase(bool enableTimeMeasurement = true);
177 * Create a new EventBase object that will use the specified libevent
178 * event_base object to drive the event loop.
180 * The EventBase will take ownership of this event_base, and will call
181 * event_base_free(evb) when the EventBase is destroyed.
183 * @param enableTimeMeasurement Informs whether this event base should measure
184 * time. Disabling it would likely improve
185 * performance, but will disable some features
186 * that relies on time-measurement, including:
187 * observer, max latency and avg loop time.
189 explicit EventBase(event_base* evb, bool enableTimeMeasurement = true);
193 * Runs the event loop.
195 * loop() will loop waiting for I/O or timeouts and invoking EventHandler
196 * and AsyncTimeout callbacks as their events become ready. loop() will
197 * only return when there are no more events remaining to process, or after
198 * terminateLoopSoon() has been called.
200 * loop() may be called again to restart event processing after a previous
201 * call to loop() or loopForever() has returned.
203 * Returns true if the loop completed normally (if it processed all
204 * outstanding requests, or if terminateLoopSoon() was called). If an error
205 * occurs waiting for events, false will be returned.
210 * Wait for some events to become active, run them, then return.
212 * When EVLOOP_NONBLOCK is set in flags, the loop won't block if there
213 * are not any events to process.
215 * This is useful for callers that want to run the loop manually.
217 * Returns the same result as loop().
219 bool loopOnce(int flags = 0);
222 * Runs the event loop.
224 * loopForever() behaves like loop(), except that it keeps running even if
225 * when there are no more user-supplied EventHandlers or AsyncTimeouts
226 * registered. It will only return after terminateLoopSoon() has been
229 * This is useful for callers that want to wait for other threads to call
230 * runInEventBaseThread(), even when there are no other scheduled events.
232 * loopForever() may be called again to restart event processing after a
233 * previous call to loop() or loopForever() has returned.
235 * Throws a std::system_error if an error occurs.
240 * Causes the event loop to exit soon.
242 * This will cause an existing call to loop() or loopForever() to stop event
243 * processing and return, even if there are still events remaining to be
246 * It is safe to call terminateLoopSoon() from another thread to cause loop()
247 * to wake up and return in the EventBase loop thread. terminateLoopSoon()
248 * may also be called from the loop thread itself (for example, a
249 * EventHandler or AsyncTimeout callback may call terminateLoopSoon() to
250 * cause the loop to exit after the callback returns.) If the loop is not
251 * running, this will cause the next call to loop to terminate soon after
252 * starting. If a loop runs out of work (and so terminates on its own)
253 * concurrently with a call to terminateLoopSoon(), this may cause a race
256 * Note that the caller is responsible for ensuring that cleanup of all event
257 * callbacks occurs properly. Since terminateLoopSoon() causes the loop to
258 * exit even when there are pending events present, there may be remaining
259 * callbacks present waiting to be invoked. If the loop is later restarted
260 * pending events will continue to be processed normally, however if the
261 * EventBase is destroyed after calling terminateLoopSoon() it is the
262 * caller's responsibility to ensure that cleanup happens properly even if
263 * some outstanding events are never processed.
265 void terminateLoopSoon();
268 * Adds the given callback to a queue of things run after the current pass
269 * through the event loop completes. Note that if this callback calls
270 * runInLoop() the new callback won't be called until the main event loop
271 * has gone through a cycle.
273 * This method may only be called from the EventBase's thread. This
274 * essentially allows an event handler to schedule an additional callback to
275 * be invoked after it returns.
277 * Use runInEventBaseThread() to schedule functions from another thread.
279 * The thisIteration parameter makes this callback run in this loop
280 * iteration, instead of the next one, even if called from a
281 * runInLoop callback (normal io callbacks that call runInLoop will
282 * always run in this iteration). This was originally added to
283 * support detachEventBase, as a user callback may have called
284 * terminateLoopSoon(), but we want to make sure we detach. Also,
285 * detachEventBase almost always must be called from the base event
286 * loop to ensure the stack is unwound, since most users of
287 * EventBase are not thread safe.
289 * Ideally we would not need thisIteration, and instead just use
290 * runInLoop with loop() (instead of terminateLoopSoon).
292 void runInLoop(LoopCallback* callback, bool thisIteration = false);
295 * Convenience function to call runInLoop() with a folly::Function.
297 * This creates a LoopCallback object to wrap the folly::Function, and invoke
298 * the folly::Function when the loop callback fires. This is slightly more
299 * expensive than defining your own LoopCallback, but more convenient in
300 * areas that aren't too performance sensitive.
302 * This method may only be called from the EventBase's thread. This
303 * essentially allows an event handler to schedule an additional callback to
304 * be invoked after it returns.
306 * Use runInEventBaseThread() to schedule functions from another thread.
308 void runInLoop(Func c, bool thisIteration = false);
311 * Adds the given callback to a queue of things run before destruction
312 * of current EventBase.
314 * This allows users of EventBase that run in it, but don't control it,
315 * to be notified before EventBase gets destructed.
317 * Note: will be called from the thread that invoked EventBase destructor,
318 * before the final run of loop callbacks.
320 void runOnDestruction(LoopCallback* callback);
323 * Adds a callback that will run immediately *before* the event loop.
324 * This is very similar to runInLoop(), but will not cause the loop to break:
325 * For example, this callback could be used to get loop times.
327 void runBeforeLoop(LoopCallback* callback);
330 * Run the specified function in the EventBase's thread.
332 * This method is thread-safe, and may be called from another thread.
334 * If runInEventBaseThread() is called when the EventBase loop is not
335 * running, the function call will be delayed until the next time the loop is
338 * If runInEventBaseThread() returns true the function has successfully been
339 * scheduled to run in the loop thread. However, if the loop is terminated
340 * (and never later restarted) before it has a chance to run the requested
341 * function, the function will be run upon the EventBase's destruction.
343 * If two calls to runInEventBaseThread() are made from the same thread, the
344 * functions will always be run in the order that they were scheduled.
345 * Ordering between functions scheduled from separate threads is not
348 * @param fn The function to run. The function must not throw any
350 * @param arg An argument to pass to the function.
352 * @return Returns true if the function was successfully scheduled, or false
353 * if there was an error scheduling the function.
355 template <typename T>
356 bool runInEventBaseThread(void (*fn)(T*), T* arg);
359 * Run the specified function in the EventBase's thread
361 * This version of runInEventBaseThread() takes a folly::Function object.
362 * Note that this may be less efficient than the version that takes a plain
363 * function pointer and void* argument, if moving the function is expensive
364 * (e.g., if it wraps a lambda which captures some values with expensive move
367 * If the loop is terminated (and never later restarted) before it has a
368 * chance to run the requested function, the function will be run upon the
369 * EventBase's destruction.
371 * The function must not throw any exceptions.
373 bool runInEventBaseThread(Func fn);
376 * Like runInEventBaseThread, but the caller waits for the callback to be
379 template <typename T>
380 bool runInEventBaseThreadAndWait(void (*fn)(T*), T* arg);
383 * Like runInEventBaseThread, but the caller waits for the callback to be
386 bool runInEventBaseThreadAndWait(Func fn);
389 * Like runInEventBaseThreadAndWait, except if the caller is already in the
390 * event base thread, the functor is simply run inline.
392 template <typename T>
393 bool runImmediatelyOrRunInEventBaseThreadAndWait(void (*fn)(T*), T* arg);
396 * Like runInEventBaseThreadAndWait, except if the caller is already in the
397 * event base thread, the functor is simply run inline.
399 bool runImmediatelyOrRunInEventBaseThreadAndWait(Func fn);
402 * Set the maximum desired latency in us and provide a callback which will be
403 * called when that latency is exceeded.
404 * OBS: This functionality depends on time-measurement.
406 void setMaxLatency(int64_t maxLatency, Func maxLatencyCob) {
407 assert(enableTimeMeasurement_);
408 maxLatency_ = maxLatency;
409 maxLatencyCob_ = std::move(maxLatencyCob);
413 * Set smoothing coefficient for loop load average; # of milliseconds
414 * for exp(-1) (1/2.71828...) decay.
416 void setLoadAvgMsec(uint32_t ms);
419 * reset the load average to a desired value
421 void resetLoadAvg(double value = 0.0);
424 * Get the average loop time in microseconds (an exponentially-smoothed ave)
426 double getAvgLoopTime() const {
427 assert(enableTimeMeasurement_);
428 return avgLoopTime_.get();
432 * check if the event base loop is running.
434 bool isRunning() const {
435 return loopThread_.load(std::memory_order_relaxed) != 0;
439 * wait until the event loop starts (after starting the event loop thread).
441 void waitUntilRunning();
443 int getNotificationQueueSize() const;
445 void setMaxReadAtOnce(uint32_t maxAtOnce);
448 * Verify that current thread is the EventBase thread, if the EventBase is
451 bool isInEventBaseThread() const {
452 auto tid = loopThread_.load(std::memory_order_relaxed);
453 return tid == 0 || pthread_equal(tid, pthread_self());
456 bool inRunningEventBaseThread() const {
457 return pthread_equal(
458 loopThread_.load(std::memory_order_relaxed), pthread_self());
461 HHWheelTimer& timer() {
463 wheelTimer_ = HHWheelTimer::newTimer(this);
465 return *wheelTimer_.get();
468 // --------- interface to underlying libevent base ------------
469 // Avoid using these functions if possible. These functions are not
470 // guaranteed to always be present if we ever provide alternative EventBase
471 // implementations that do not use libevent internally.
472 event_base* getLibeventBase() const { return evb_; }
473 static const char* getLibeventVersion();
474 static const char* getLibeventMethod();
477 * only EventHandler/AsyncTimeout subclasses and ourselves should
480 * This is used to mark the beginning of a new loop cycle by the
481 * first handler fired within that cycle.
484 void bumpHandlingTime() override final;
486 class SmoothLoopTime {
488 explicit SmoothLoopTime(uint64_t timeInterval)
489 : expCoeff_(-1.0/timeInterval)
491 , oldBusyLeftover_(0) {
492 VLOG(11) << "expCoeff_ " << expCoeff_ << " " << __PRETTY_FUNCTION__;
495 void setTimeInterval(uint64_t timeInterval);
496 void reset(double value = 0.0);
498 void addSample(int64_t idle, int64_t busy);
504 void dampen(double factor) {
511 int64_t oldBusyLeftover_;
514 void setObserver(const std::shared_ptr<EventBaseObserver>& observer) {
515 assert(enableTimeMeasurement_);
516 observer_ = observer;
519 const std::shared_ptr<EventBaseObserver>& getObserver() {
524 * Setup execution observation/instrumentation for every EventHandler
525 * executed in this EventBase.
527 * @param executionObserver EventHandle's execution observer.
529 void setExecutionObserver(ExecutionObserver* observer) {
530 executionObserver_ = observer;
534 * Gets the execution observer associated with this EventBase.
536 ExecutionObserver* getExecutionObserver() {
537 return executionObserver_;
541 * Set the name of the thread that runs this event base.
543 void setName(const std::string& name);
546 * Returns the name of the thread that runs this event base.
548 const std::string& getName();
550 /// Implements the Executor interface
551 void add(Cob fn) override {
552 // runInEventBaseThread() takes a const&,
553 // so no point in doing std::move here.
554 runInEventBaseThread(std::move(fn));
557 /// Implements the DrivableExecutor interface
558 void drive() override {
559 // We can't use loopKeepAlive() here since LoopKeepAlive token can only be
560 // released inside a loop.
561 ++loopKeepAliveCount_;
563 --loopKeepAliveCount_;
568 struct LoopKeepAliveDeleter {
569 void operator()(EventBase* evb) {
570 DCHECK(evb->isInEventBaseThread());
571 evb->loopKeepAliveCount_--;
574 using LoopKeepAlive = std::unique_ptr<EventBase, LoopKeepAliveDeleter>;
576 /// Returns you a handle which make loop() behave like loopForever() until
577 /// destroyed. loop() will return to its original behavior only when all
578 /// loop keep-alives are released. Loop holder is safe to release only from
579 /// EventBase thread.
581 /// May return no op LoopKeepAlive if loopForever() is already running.
582 LoopKeepAlive loopKeepAlive() {
583 DCHECK(isInEventBaseThread());
584 loopKeepAliveCount_++;
585 return LoopKeepAlive(this);
588 // Thread-safe version of loopKeepAlive()
589 LoopKeepAlive loopKeepAliveAtomic() {
590 if (inRunningEventBaseThread()) {
591 return loopKeepAlive();
593 loopKeepAliveCountAtomic_.fetch_add(1, std::memory_order_relaxed);
594 return LoopKeepAlive(this);
598 void attachTimeoutManager(
600 TimeoutManager::InternalEnum internal) override final;
602 void detachTimeoutManager(AsyncTimeout* obj) override final;
604 bool scheduleTimeout(AsyncTimeout* obj, TimeoutManager::timeout_type timeout)
607 void cancelTimeout(AsyncTimeout* obj) override final;
609 bool isInTimeoutManagerThread() override final {
610 return isInEventBaseThread();
614 void applyLoopKeepAlive();
616 ssize_t loopKeepAliveCount();
619 * Helper function that tells us whether we have already handled
620 * some event/timeout/callback in this loop iteration.
622 bool nothingHandledYet() const noexcept;
624 typedef LoopCallback::List LoopCallbackList;
625 class FunctionRunner;
627 bool loopBody(int flags = 0);
629 // executes any callbacks queued by runInLoop(); returns false if none found
630 bool runLoopCallbacks();
632 void initNotificationQueue();
634 // should only be accessed through public getter
635 HHWheelTimer::UniquePtr wheelTimer_;
637 LoopCallbackList loopCallbacks_;
638 LoopCallbackList runBeforeLoopCallbacks_;
639 LoopCallbackList onDestructionCallbacks_;
641 // This will be null most of the time, but point to currentCallbacks
642 // if we are in the middle of running loop callbacks, such that
643 // runInLoop(..., true) will always run in the current loop
645 LoopCallbackList* runOnceCallbacks_;
647 // stop_ is set by terminateLoopSoon() and is used by the main loop
648 // to determine if it should exit
649 std::atomic<bool> stop_;
651 // The ID of the thread running the main loop.
652 // 0 if loop is not running.
653 // Note: POSIX doesn't guarantee that 0 is an invalid pthread_t (or
654 // even that atomic<pthread_t> is valid), but that's how it is
655 // everywhere (at least on Linux, FreeBSD, and OSX).
656 std::atomic<pthread_t> loopThread_;
658 // pointer to underlying event_base class doing the heavy lifting
661 // A notification queue for runInEventBaseThread() to use
662 // to send function requests to the EventBase thread.
663 std::unique_ptr<NotificationQueue<Func>> queue_;
664 std::unique_ptr<FunctionRunner> fnRunner_;
665 ssize_t loopKeepAliveCount_{0};
666 std::atomic<ssize_t> loopKeepAliveCountAtomic_{0};
667 bool loopKeepAliveActive_{false};
669 // limit for latency in microseconds (0 disables)
672 // exponentially-smoothed average loop time for latency-limiting
673 SmoothLoopTime avgLoopTime_;
675 // smoothed loop time used to invoke latency callbacks; differs from
676 // avgLoopTime_ in that it's scaled down after triggering a callback
677 // to reduce spamminess
678 SmoothLoopTime maxLatencyLoopTime_;
680 // callback called when latency limit is exceeded
683 // Enables/disables time measurements in loopBody(). if disabled, the
684 // following functionality that relies on time-measurement, will not
685 // be supported: avg loop time, observer and max latency.
686 const bool enableTimeMeasurement_;
688 // we'll wait this long before running deferred callbacks if the event
690 static const int kDEFAULT_IDLE_WAIT_USEC = 20000; // 20ms
692 // Wrap-around loop counter to detect beginning of each loop
693 uint64_t nextLoopCnt_;
694 uint64_t latestLoopCnt_;
696 // Prevent undefined behavior from invoking event_base_loop() reentrantly.
697 // This is needed since many projects use libevent-1.4, which lacks commit
698 // b557b175c00dc462c1fce25f6e7dd67121d2c001 from
699 // https://github.com/libevent/libevent/.
700 bool invokingLoop_{false};
702 // Observer to export counters
703 std::shared_ptr<EventBaseObserver> observer_;
704 uint32_t observerSampleCount_;
706 // EventHandler's execution observer.
707 ExecutionObserver* executionObserver_;
709 // Name of the thread running this EventBase
712 // allow runOnDestruction() to be called from any threads
713 std::mutex onDestructionCallbacksMutex_;
715 // see EventBaseLocal
716 friend class detail::EventBaseLocalBase;
717 template <typename T> friend class EventBaseLocal;
718 std::mutex localStorageMutex_;
719 std::unordered_map<uint64_t, std::shared_ptr<void>> localStorage_;
720 std::unordered_set<detail::EventBaseLocalBaseBase*> localStorageToDtor_;
723 template <typename T>
724 bool EventBase::runInEventBaseThread(void (*fn)(T*), T* arg) {
725 return runInEventBaseThread([=] { fn(arg); });
728 template <typename T>
729 bool EventBase::runInEventBaseThreadAndWait(void (*fn)(T*), T* arg) {
730 return runInEventBaseThreadAndWait([=] { fn(arg); });
733 template <typename T>
734 bool EventBase::runImmediatelyOrRunInEventBaseThreadAndWait(
737 return runImmediatelyOrRunInEventBaseThreadAndWait([=] { fn(arg); });