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/futures/DrivableExecutor.h>
32 #include <boost/intrusive/list.hpp>
33 #include <boost/utility.hpp>
35 #include <event.h> // libevent
42 typedef std::function<void()> Cob;
43 template <typename MessageT>
44 class NotificationQueue;
46 class EventBaseObserver {
48 virtual ~EventBaseObserver() {}
50 virtual uint32_t getSampleRate() const = 0;
52 virtual void loopSample(
53 int64_t busyTime, int64_t idleTime) = 0;
56 // Helper class that sets and retrieves the EventBase associated with a given
57 // request via RequestContext. See Request.h for that mechanism.
58 class RequestEventBase : public RequestData {
60 static EventBase* get() {
61 auto data = dynamic_cast<RequestEventBase*>(
62 RequestContext::get()->getContextData(kContextDataName));
69 static void set(EventBase* eb) {
70 RequestContext::get()->setContextData(
72 std::unique_ptr<RequestEventBase>(new RequestEventBase(eb)));
76 explicit RequestEventBase(EventBase* eb) : eb_(eb) {}
78 static constexpr const char* kContextDataName{"EventBase"};
82 * This class is a wrapper for all asynchronous I/O processing functionality
84 * EventBase provides a main loop that notifies EventHandler callback objects
85 * when I/O is ready on a file descriptor, and notifies AsyncTimeout objects
86 * when a specified timeout has expired. More complex, higher-level callback
87 * mechanisms can then be built on top of EventHandler and AsyncTimeout.
89 * A EventBase object can only drive an event loop for a single thread. To
90 * take advantage of multiple CPU cores, most asynchronous I/O servers have one
91 * thread per CPU, and use a separate EventBase for each thread.
93 * In general, most EventBase methods may only be called from the thread
94 * running the EventBase's loop. There are a few exceptions to this rule, for
95 * methods that are explicitly intended to allow communication with a
96 * EventBase from other threads. When it is safe to call a method from
97 * another thread it is explicitly listed in the method comments.
99 class EventBase : private boost::noncopyable,
100 public TimeoutManager,
101 public DrivableExecutor {
104 * A callback interface to use with runInLoop()
106 * Derive from this class if you need to delay some code execution until the
107 * next iteration of the event loop. This allows you to schedule code to be
108 * invoked from the top-level of the loop, after your immediate callers have
111 * If a LoopCallback object is destroyed while it is scheduled to be run in
112 * the next loop iteration, it will automatically be cancelled.
116 virtual ~LoopCallback() {}
118 virtual void runLoopCallback() noexcept = 0;
119 void cancelLoopCallback() {
123 bool isLoopCallbackScheduled() const {
124 return hook_.is_linked();
128 typedef boost::intrusive::list_member_hook<
129 boost::intrusive::link_mode<boost::intrusive::auto_unlink> > ListHook;
133 typedef boost::intrusive::list<
135 boost::intrusive::member_hook<LoopCallback, ListHook,
136 &LoopCallback::hook_>,
137 boost::intrusive::constant_time_size<false> > List;
139 // EventBase needs access to LoopCallbackList (and therefore to hook_)
140 friend class EventBase;
141 std::shared_ptr<RequestContext> context_;
145 * Create a new EventBase object.
147 * @param enableTimeMeasurement Informs whether this event base should measure
148 * time. Disabling it would likely improve
149 * performance, but will disable some features
150 * that relies on time-measurement, including:
151 * observer, max latency and avg loop time.
153 explicit EventBase(bool enableTimeMeasurement = true);
156 * Create a new EventBase object that will use the specified libevent
157 * event_base object to drive the event loop.
159 * The EventBase will take ownership of this event_base, and will call
160 * event_base_free(evb) when the EventBase is destroyed.
162 * @param enableTimeMeasurement Informs whether this event base should measure
163 * time. Disabling it would likely improve
164 * performance, but will disable some features
165 * that relies on time-measurement, including:
166 * observer, max latency and avg loop time.
168 explicit EventBase(event_base* evb, bool enableTimeMeasurement = true);
172 * Runs the event loop.
174 * loop() will loop waiting for I/O or timeouts and invoking EventHandler
175 * and AsyncTimeout callbacks as their events become ready. loop() will
176 * only return when there are no more events remaining to process, or after
177 * terminateLoopSoon() has been called.
179 * loop() may be called again to restart event processing after a previous
180 * call to loop() or loopForever() has returned.
182 * Returns true if the loop completed normally (if it processed all
183 * outstanding requests, or if terminateLoopSoon() was called). If an error
184 * occurs waiting for events, false will be returned.
189 * Wait for some events to become active, run them, then return.
191 * When EVLOOP_NONBLOCK is set in flags, the loop won't block if there
192 * are not any events to process.
194 * This is useful for callers that want to run the loop manually.
196 * Returns the same result as loop().
198 bool loopOnce(int flags = 0);
201 * Runs the event loop.
203 * loopForever() behaves like loop(), except that it keeps running even if
204 * when there are no more user-supplied EventHandlers or AsyncTimeouts
205 * registered. It will only return after terminateLoopSoon() has been
208 * This is useful for callers that want to wait for other threads to call
209 * runInEventBaseThread(), even when there are no other scheduled events.
211 * loopForever() may be called again to restart event processing after a
212 * previous call to loop() or loopForever() has returned.
214 * Throws a std::system_error if an error occurs.
219 * Causes the event loop to exit soon.
221 * This will cause an existing call to loop() or loopForever() to stop event
222 * processing and return, even if there are still events remaining to be
225 * It is safe to call terminateLoopSoon() from another thread to cause loop()
226 * to wake up and return in the EventBase loop thread. terminateLoopSoon()
227 * may also be called from the loop thread itself (for example, a
228 * EventHandler or AsyncTimeout callback may call terminateLoopSoon() to
229 * cause the loop to exit after the callback returns.) If the loop is not
230 * running, this will cause the next call to loop to terminate soon after
231 * starting. If a loop runs out of work (and so terminates on its own)
232 * concurrently with a call to terminateLoopSoon(), this may cause a race
235 * Note that the caller is responsible for ensuring that cleanup of all event
236 * callbacks occurs properly. Since terminateLoopSoon() causes the loop to
237 * exit even when there are pending events present, there may be remaining
238 * callbacks present waiting to be invoked. If the loop is later restarted
239 * pending events will continue to be processed normally, however if the
240 * EventBase is destroyed after calling terminateLoopSoon() it is the
241 * caller's responsibility to ensure that cleanup happens properly even if
242 * some outstanding events are never processed.
244 void terminateLoopSoon();
247 * Adds the given callback to a queue of things run after the current pass
248 * through the event loop completes. Note that if this callback calls
249 * runInLoop() the new callback won't be called until the main event loop
250 * has gone through a cycle.
252 * This method may only be called from the EventBase's thread. This
253 * essentially allows an event handler to schedule an additional callback to
254 * be invoked after it returns.
256 * Use runInEventBaseThread() to schedule functions from another thread.
258 * The thisIteration parameter makes this callback run in this loop
259 * iteration, instead of the next one, even if called from a
260 * runInLoop callback (normal io callbacks that call runInLoop will
261 * always run in this iteration). This was originally added to
262 * support detachEventBase, as a user callback may have called
263 * terminateLoopSoon(), but we want to make sure we detach. Also,
264 * detachEventBase almost always must be called from the base event
265 * loop to ensure the stack is unwound, since most users of
266 * EventBase are not thread safe.
268 * Ideally we would not need thisIteration, and instead just use
269 * runInLoop with loop() (instead of terminateLoopSoon).
271 void runInLoop(LoopCallback* callback, bool thisIteration = false);
274 * Convenience function to call runInLoop() with a std::function.
276 * This creates a LoopCallback object to wrap the std::function, and invoke
277 * the std::function when the loop callback fires. This is slightly more
278 * expensive than defining your own LoopCallback, but more convenient in
279 * areas that aren't performance sensitive where you just want to use
280 * std::bind. (std::bind is fairly slow on even by itself.)
282 * This method may only be called from the EventBase's thread. This
283 * essentially allows an event handler to schedule an additional callback to
284 * be invoked after it returns.
286 * Use runInEventBaseThread() to schedule functions from another thread.
288 void runInLoop(const Cob& c, bool thisIteration = false);
290 void runInLoop(Cob&& c, bool thisIteration = false);
293 * Adds the given callback to a queue of things run before destruction
294 * of current EventBase.
296 * This allows users of EventBase that run in it, but don't control it,
297 * to be notified before EventBase gets destructed.
299 * Note: will be called from the thread that invoked EventBase destructor,
300 * before the final run of loop callbacks.
302 void runOnDestruction(LoopCallback* callback);
305 * Adds a callback that will run immediately *before* the event loop.
306 * This is very similar to runInLoop(), but will not cause the loop to break:
307 * For example, this callback could be used to get loop times.
309 void runBeforeLoop(LoopCallback* callback);
312 * Run the specified function in the EventBase's thread.
314 * This method is thread-safe, and may be called from another thread.
316 * If runInEventBaseThread() is called when the EventBase loop is not
317 * running, the function call will be delayed until the next time the loop is
320 * If runInEventBaseThread() returns true the function has successfully been
321 * scheduled to run in the loop thread. However, if the loop is terminated
322 * (and never later restarted) before it has a chance to run the requested
323 * function, the function will be run upon the EventBase's destruction.
325 * If two calls to runInEventBaseThread() are made from the same thread, the
326 * functions will always be run in the order that they were scheduled.
327 * Ordering between functions scheduled from separate threads is not
330 * @param fn The function to run. The function must not throw any
332 * @param arg An argument to pass to the function.
334 * @return Returns true if the function was successfully scheduled, or false
335 * if there was an error scheduling the function.
338 bool runInEventBaseThread(void (*fn)(T*), T* arg) {
339 return runInEventBaseThread(reinterpret_cast<void (*)(void*)>(fn),
340 reinterpret_cast<void*>(arg));
343 bool runInEventBaseThread(void (*fn)(void*), void* arg);
346 * Run the specified function in the EventBase's thread
348 * This version of runInEventBaseThread() takes a std::function object.
349 * Note that this is less efficient than the version that takes a plain
350 * function pointer and void* argument, as it has to allocate memory to copy
351 * the std::function object.
353 * If the loop is terminated (and never later restarted) before it has a
354 * chance to run the requested function, the function will be run upon the
355 * EventBase's destruction.
357 * The function must not throw any exceptions.
359 bool runInEventBaseThread(const Cob& fn);
362 * Like runInEventBaseThread, but the caller waits for the callback to be
366 bool runInEventBaseThreadAndWait(void (*fn)(T*), T* arg) {
367 return runInEventBaseThreadAndWait(reinterpret_cast<void (*)(void*)>(fn),
368 reinterpret_cast<void*>(arg));
372 * Like runInEventBaseThread, but the caller waits for the callback to be
375 bool runInEventBaseThreadAndWait(void (*fn)(void*), void* arg) {
376 return runInEventBaseThreadAndWait(std::bind(fn, arg));
380 * Like runInEventBaseThread, but the caller waits for the callback to be
383 bool runInEventBaseThreadAndWait(const Cob& fn);
386 * Runs the given Cob at some time after the specified number of
387 * milliseconds. (No guarantees exactly when.)
389 * Throws a std::system_error if an error occurs.
394 TimeoutManager::InternalEnum in = TimeoutManager::InternalEnum::NORMAL);
397 * @see tryRunAfterDelay for more details
399 * @return true iff the cob was successfully registered.
402 bool tryRunAfterDelay(
405 TimeoutManager::InternalEnum in = TimeoutManager::InternalEnum::NORMAL);
408 * Set the maximum desired latency in us and provide a callback which will be
409 * called when that latency is exceeded.
410 * OBS: This functionality depends on time-measurement.
412 void setMaxLatency(int64_t maxLatency, const Cob& maxLatencyCob) {
413 assert(enableTimeMeasurement_);
414 maxLatency_ = maxLatency;
415 maxLatencyCob_ = maxLatencyCob;
420 * Set smoothing coefficient for loop load average; # of milliseconds
421 * for exp(-1) (1/2.71828...) decay.
423 void setLoadAvgMsec(uint32_t ms);
426 * reset the load average to a desired value
428 void resetLoadAvg(double value = 0.0);
431 * Get the average loop time in microseconds (an exponentially-smoothed ave)
433 double getAvgLoopTime() const {
434 assert(enableTimeMeasurement_);
435 return avgLoopTime_.get();
439 * check if the event base loop is running.
441 bool isRunning() const {
442 return loopThread_.load(std::memory_order_relaxed) != 0;
446 * wait until the event loop starts (after starting the event loop thread).
448 void waitUntilRunning();
450 int getNotificationQueueSize() const;
452 void setMaxReadAtOnce(uint32_t maxAtOnce);
455 * Verify that current thread is the EventBase thread, if the EventBase is
458 bool isInEventBaseThread() const {
459 auto tid = loopThread_.load(std::memory_order_relaxed);
460 return tid == 0 || pthread_equal(tid, pthread_self());
463 bool inRunningEventBaseThread() const {
464 return pthread_equal(
465 loopThread_.load(std::memory_order_relaxed), pthread_self());
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 bool bumpHandlingTime() override;
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 * Set the name of the thread that runs this event base.
526 void setName(const std::string& name);
529 * Returns the name of the thread that runs this event base.
531 const std::string& getName();
533 /// Implements the Executor interface
534 void add(Cob fn) override {
535 // runInEventBaseThread() takes a const&,
536 // so no point in doing std::move here.
537 runInEventBaseThread(fn);
540 /// Implements the DrivableExecutor interface
541 void drive() override {
548 void attachTimeoutManager(AsyncTimeout* obj,
549 TimeoutManager::InternalEnum internal) override;
551 void detachTimeoutManager(AsyncTimeout* obj) override;
553 bool scheduleTimeout(AsyncTimeout* obj, std::chrono::milliseconds timeout)
556 void cancelTimeout(AsyncTimeout* obj) override;
558 bool isInTimeoutManagerThread() override {
559 return isInEventBaseThread();
562 // Helper class used to short circuit runInEventBaseThread
563 class RunInLoopCallback : public LoopCallback {
565 RunInLoopCallback(void (*fn)(void*), void* arg);
566 void runLoopCallback() noexcept;
574 * Helper function that tells us whether we have already handled
575 * some event/timeout/callback in this loop iteration.
577 bool nothingHandledYet();
579 // --------- libevent callbacks (not for client use) ------------
581 static void runFunctionPtr(std::function<void()>* fn);
583 // small object used as a callback arg with enough info to execute the
584 // appropriate client-provided Cob
585 class CobTimeout : public AsyncTimeout {
587 CobTimeout(EventBase* b, const Cob& c, TimeoutManager::InternalEnum in)
588 : AsyncTimeout(b, in), cob_(c) {}
590 virtual void timeoutExpired() noexcept;
596 typedef boost::intrusive::list_member_hook<
597 boost::intrusive::link_mode<boost::intrusive::auto_unlink> > ListHook;
601 typedef boost::intrusive::list<
603 boost::intrusive::member_hook<CobTimeout, ListHook, &CobTimeout::hook>,
604 boost::intrusive::constant_time_size<false> > List;
607 typedef LoopCallback::List LoopCallbackList;
608 class FunctionRunner;
610 bool loopBody(int flags = 0);
612 // executes any callbacks queued by runInLoop(); returns false if none found
613 bool runLoopCallbacks(bool setContext = true);
615 void initNotificationQueue();
617 CobTimeout::List pendingCobTimeouts_;
619 LoopCallbackList loopCallbacks_;
620 LoopCallbackList runBeforeLoopCallbacks_;
621 LoopCallbackList onDestructionCallbacks_;
623 // This will be null most of the time, but point to currentCallbacks
624 // if we are in the middle of running loop callbacks, such that
625 // runInLoop(..., true) will always run in the current loop
627 LoopCallbackList* runOnceCallbacks_;
629 // stop_ is set by terminateLoopSoon() and is used by the main loop
630 // to determine if it should exit
633 // The ID of the thread running the main loop.
634 // 0 if loop is not running.
635 // Note: POSIX doesn't guarantee that 0 is an invalid pthread_t (or
636 // even that atomic<pthread_t> is valid), but that's how it is
637 // everywhere (at least on Linux, FreeBSD, and OSX).
638 std::atomic<pthread_t> loopThread_;
640 // pointer to underlying event_base class doing the heavy lifting
643 // A notification queue for runInEventBaseThread() to use
644 // to send function requests to the EventBase thread.
645 std::unique_ptr<NotificationQueue<std::pair<void (*)(void*), void*>>> queue_;
646 std::unique_ptr<FunctionRunner> fnRunner_;
648 // limit for latency in microseconds (0 disables)
651 // exponentially-smoothed average loop time for latency-limiting
652 SmoothLoopTime avgLoopTime_;
654 // smoothed loop time used to invoke latency callbacks; differs from
655 // avgLoopTime_ in that it's scaled down after triggering a callback
656 // to reduce spamminess
657 SmoothLoopTime maxLatencyLoopTime_;
659 // callback called when latency limit is exceeded
662 // Enables/disables time measurements in loopBody(). if disabled, the
663 // following functionality that relies on time-measurement, will not
664 // be supported: avg loop time, observer and max latency.
665 const bool enableTimeMeasurement_;
667 // we'll wait this long before running deferred callbacks if the event
669 static const int kDEFAULT_IDLE_WAIT_USEC = 20000; // 20ms
671 // Wrap-around loop counter to detect beginning of each loop
672 uint64_t nextLoopCnt_;
673 uint64_t latestLoopCnt_;
676 // Observer to export counters
677 std::shared_ptr<EventBaseObserver> observer_;
678 uint32_t observerSampleCount_;
680 // Name of the thread running this EventBase