2 * Copyright 2014 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/wangle/Executor.h>
30 #include <boost/intrusive/list.hpp>
31 #include <boost/utility.hpp>
33 #include <event.h> // libevent
40 typedef std::function<void()> Cob;
41 template <typename MessageT>
42 class NotificationQueue;
44 class EventBaseObserver {
46 virtual ~EventBaseObserver() {}
48 virtual uint32_t getSampleRate() const = 0;
50 virtual void loopSample(
51 int64_t busyTime, int64_t idleTime) = 0;
55 * This class is a wrapper for all asynchronous I/O processing functionality
57 * EventBase provides a main loop that notifies EventHandler callback objects
58 * when I/O is ready on a file descriptor, and notifies AsyncTimeout objects
59 * when a specified timeout has expired. More complex, higher-level callback
60 * mechanisms can then be built on top of EventHandler and AsyncTimeout.
62 * A EventBase object can only drive an event loop for a single thread. To
63 * take advantage of multiple CPU cores, most asynchronous I/O servers have one
64 * thread per CPU, and use a separate EventBase for each thread.
66 * In general, most EventBase methods may only be called from the thread
67 * running the EventBase's loop. There are a few exceptions to this rule, for
68 * methods that are explicitly intended to allow communication with a
69 * EventBase from other threads. When it is safe to call a method from
70 * another thread it is explicitly listed in the method comments.
73 private boost::noncopyable, public TimeoutManager, public wangle::Executor
77 * A callback interface to use with runInLoop()
79 * Derive from this class if you need to delay some code execution until the
80 * next iteration of the event loop. This allows you to schedule code to be
81 * invoked from the top-level of the loop, after your immediate callers have
84 * If a LoopCallback object is destroyed while it is scheduled to be run in
85 * the next loop iteration, it will automatically be cancelled.
89 virtual ~LoopCallback() {}
91 virtual void runLoopCallback() noexcept = 0;
92 void cancelLoopCallback() {
96 bool isLoopCallbackScheduled() const {
97 return hook_.is_linked();
101 typedef boost::intrusive::list_member_hook<
102 boost::intrusive::link_mode<boost::intrusive::auto_unlink> > ListHook;
106 typedef boost::intrusive::list<
108 boost::intrusive::member_hook<LoopCallback, ListHook,
109 &LoopCallback::hook_>,
110 boost::intrusive::constant_time_size<false> > List;
112 // EventBase needs access to LoopCallbackList (and therefore to hook_)
113 friend class EventBase;
114 std::shared_ptr<RequestContext> context_;
118 * Create a new EventBase object.
123 * Create a new EventBase object that will use the specified libevent
124 * event_base object to drive the event loop.
126 * The EventBase will take ownership of this event_base, and will call
127 * event_base_free(evb) when the EventBase is destroyed.
129 explicit EventBase(event_base* evb);
133 * Runs the event loop.
135 * loop() will loop waiting for I/O or timeouts and invoking EventHandler
136 * and AsyncTimeout callbacks as their events become ready. loop() will
137 * only return when there are no more events remaining to process, or after
138 * terminateLoopSoon() has been called.
140 * loop() may be called again to restart event processing after a previous
141 * call to loop() or loopForever() has returned.
143 * Returns true if the loop completed normally (if it processed all
144 * outstanding requests, or if terminateLoopSoon() was called). If an error
145 * occurs waiting for events, false will be returned.
150 * Wait for some events to become active, run them, then return.
152 * When EVLOOP_NONBLOCK is set in flags, the loop won't block if there
153 * are not any events to process.
155 * This is useful for callers that want to run the loop manually.
157 * Returns the same result as loop().
159 bool loopOnce(int flags = 0);
162 * Runs the event loop.
164 * loopForever() behaves like loop(), except that it keeps running even if
165 * when there are no more user-supplied EventHandlers or AsyncTimeouts
166 * registered. It will only return after terminateLoopSoon() has been
169 * This is useful for callers that want to wait for other threads to call
170 * runInEventBaseThread(), even when there are no other scheduled events.
172 * loopForever() may be called again to restart event processing after a
173 * previous call to loop() or loopForever() has returned.
175 * Throws a std::system_error if an error occurs.
180 * Causes the event loop to exit soon.
182 * This will cause an existing call to loop() or loopForever() to stop event
183 * processing and return, even if there are still events remaining to be
186 * It is safe to call terminateLoopSoon() from another thread to cause loop()
187 * to wake up and return in the EventBase loop thread. terminateLoopSoon()
188 * may also be called from the loop thread itself (for example, a
189 * EventHandler or AsyncTimeout callback may call terminateLoopSoon() to
190 * cause the loop to exit after the callback returns.) If the loop is not
191 * running, this will cause the next call to loop to terminate soon after
192 * starting. If a loop runs out of work (and so terminates on its own)
193 * concurrently with a call to terminateLoopSoon(), this may cause a race
196 * Note that the caller is responsible for ensuring that cleanup of all event
197 * callbacks occurs properly. Since terminateLoopSoon() causes the loop to
198 * exit even when there are pending events present, there may be remaining
199 * callbacks present waiting to be invoked. If the loop is later restarted
200 * pending events will continue to be processed normally, however if the
201 * EventBase is destroyed after calling terminateLoopSoon() it is the
202 * caller's responsibility to ensure that cleanup happens properly even if
203 * some outstanding events are never processed.
205 void terminateLoopSoon();
208 * Adds the given callback to a queue of things run after the current pass
209 * through the event loop completes. Note that if this callback calls
210 * runInLoop() the new callback won't be called until the main event loop
211 * has gone through a cycle.
213 * This method may only be called from the EventBase's thread. This
214 * essentially allows an event handler to schedule an additional callback to
215 * be invoked after it returns.
217 * Use runInEventBaseThread() to schedule functions from another thread.
219 * The thisIteration parameter makes this callback run in this loop
220 * iteration, instead of the next one, even if called from a
221 * runInLoop callback (normal io callbacks that call runInLoop will
222 * always run in this iteration). This was originally added to
223 * support detachEventBase, as a user callback may have called
224 * terminateLoopSoon(), but we want to make sure we detach. Also,
225 * detachEventBase almost always must be called from the base event
226 * loop to ensure the stack is unwound, since most users of
227 * EventBase are not thread safe.
229 * Ideally we would not need thisIteration, and instead just use
230 * runInLoop with loop() (instead of terminateLoopSoon).
232 void runInLoop(LoopCallback* callback, bool thisIteration = false);
235 * Convenience function to call runInLoop() with a std::function.
237 * This creates a LoopCallback object to wrap the std::function, and invoke
238 * the std::function when the loop callback fires. This is slightly more
239 * expensive than defining your own LoopCallback, but more convenient in
240 * areas that aren't performance sensitive where you just want to use
241 * std::bind. (std::bind is fairly slow on even by itself.)
243 * This method may only be called from the EventBase's thread. This
244 * essentially allows an event handler to schedule an additional callback to
245 * be invoked after it returns.
247 * Use runInEventBaseThread() to schedule functions from another thread.
249 void runInLoop(const Cob& c, bool thisIteration = false);
251 void runInLoop(Cob&& c, bool thisIteration = false);
254 * Adds the given callback to a queue of things run before destruction
255 * of current EventBase.
257 * This allows users of EventBase that run in it, but don't control it,
258 * to be notified before EventBase gets destructed.
260 * Note: will be called from the thread that invoked EventBase destructor,
261 * before the final run of loop callbacks.
263 void runOnDestruction(LoopCallback* callback);
266 * Adds a callback that will run immediately *before* the event loop.
267 * This is very similar to runInLoop(), but will not cause the loop to break:
268 * For example, this callback could be used to get loop times.
270 void runBeforeLoop(LoopCallback* callback);
273 * Run the specified function in the EventBase's thread.
275 * This method is thread-safe, and may be called from another thread.
277 * If runInEventBaseThread() is called when the EventBase loop is not
278 * running, the function call will be delayed until the next time the loop is
281 * If runInEventBaseThread() returns true the function has successfully been
282 * scheduled to run in the loop thread. However, if the loop is terminated
283 * (and never later restarted) before it has a chance to run the requested
284 * function, the function may never be run at all. The caller is responsible
285 * for handling this situation correctly if they may terminate the loop with
286 * outstanding runInEventBaseThread() calls pending.
288 * If two calls to runInEventBaseThread() are made from the same thread, the
289 * functions will always be run in the order that they were scheduled.
290 * Ordering between functions scheduled from separate threads is not
293 * @param fn The function to run. The function must not throw any
295 * @param arg An argument to pass to the function.
297 * @return Returns true if the function was successfully scheduled, or false
298 * if there was an error scheduling the function.
301 bool runInEventBaseThread(void (*fn)(T*), T* arg) {
302 return runInEventBaseThread(reinterpret_cast<void (*)(void*)>(fn),
303 reinterpret_cast<void*>(arg));
306 bool runInEventBaseThread(void (*fn)(void*), void* arg);
309 * Run the specified function in the EventBase's thread
311 * This version of runInEventBaseThread() takes a std::function object.
312 * Note that this is less efficient than the version that takes a plain
313 * function pointer and void* argument, as it has to allocate memory to copy
314 * the std::function object.
316 * If the EventBase loop is terminated before it has a chance to run this
317 * function, the allocated memory will be leaked. The caller is responsible
318 * for ensuring that the EventBase loop is not terminated before this
321 * The function must not throw any exceptions.
323 bool runInEventBaseThread(const Cob& fn);
326 * Runs the given Cob at some time after the specified number of
327 * milliseconds. (No guarantees exactly when.)
329 * @return true iff the cob was successfully registered.
334 TimeoutManager::InternalEnum = TimeoutManager::InternalEnum::NORMAL);
337 * Set the maximum desired latency in us and provide a callback which will be
338 * called when that latency is exceeded.
340 void setMaxLatency(int64_t maxLatency, const Cob& maxLatencyCob) {
341 maxLatency_ = maxLatency;
342 maxLatencyCob_ = maxLatencyCob;
346 * Set smoothing coefficient for loop load average; # of milliseconds
347 * for exp(-1) (1/2.71828...) decay.
349 void setLoadAvgMsec(uint32_t ms);
352 * reset the load average to a desired value
354 void resetLoadAvg(double value = 0.0);
357 * Get the average loop time in microseconds (an exponentially-smoothed ave)
359 double getAvgLoopTime() const {
360 return avgLoopTime_.get();
364 * check if the event base loop is running.
366 bool isRunning() const {
367 return loopThread_.load(std::memory_order_relaxed) != 0;
371 * wait until the event loop starts (after starting the event loop thread).
373 void waitUntilRunning();
375 int getNotificationQueueSize() const;
377 void setMaxReadAtOnce(uint32_t maxAtOnce);
380 * Verify that current thread is the EventBase thread, if the EventBase is
383 bool isInEventBaseThread() const {
384 auto tid = loopThread_.load(std::memory_order_relaxed);
385 return tid == 0 || pthread_equal(tid, pthread_self());
388 bool inRunningEventBaseThread() const {
389 return pthread_equal(
390 loopThread_.load(std::memory_order_relaxed), pthread_self());
393 // --------- interface to underlying libevent base ------------
394 // Avoid using these functions if possible. These functions are not
395 // guaranteed to always be present if we ever provide alternative EventBase
396 // implementations that do not use libevent internally.
397 event_base* getLibeventBase() const { return evb_; }
398 static const char* getLibeventVersion();
399 static const char* getLibeventMethod();
402 * only EventHandler/AsyncTimeout subclasses and ourselves should
405 * This is used to mark the beginning of a new loop cycle by the
406 * first handler fired within that cycle.
409 bool bumpHandlingTime();
411 class SmoothLoopTime {
413 explicit SmoothLoopTime(uint64_t timeInterval)
414 : expCoeff_(-1.0/timeInterval)
416 , oldBusyLeftover_(0) {
417 VLOG(11) << "expCoeff_ " << expCoeff_ << " " << __PRETTY_FUNCTION__;
420 void setTimeInterval(uint64_t timeInterval);
421 void reset(double value = 0.0);
423 void addSample(int64_t idle, int64_t busy);
429 void dampen(double factor) {
436 int64_t oldBusyLeftover_;
440 const std::shared_ptr<EventBaseObserver>& observer) {
441 observer_ = observer;
444 const std::shared_ptr<EventBaseObserver>& getObserver() {
449 * Set the name of the thread that runs this event base.
451 void setName(const std::string& name);
454 * Returns the name of the thread that runs this event base.
456 const std::string& getName();
458 /// Implements the wangle::Executor interface
459 void add(Cob fn) override {
460 // runInEventBaseThread() takes a const&,
461 // so no point in doing std::move here.
462 runInEventBaseThread(fn);
468 void attachTimeoutManager(AsyncTimeout* obj,
469 TimeoutManager::InternalEnum internal);
471 void detachTimeoutManager(AsyncTimeout* obj);
473 bool scheduleTimeout(AsyncTimeout* obj, std::chrono::milliseconds timeout);
475 void cancelTimeout(AsyncTimeout* obj);
477 bool isInTimeoutManagerThread() {
478 return isInEventBaseThread();
481 // Helper class used to short circuit runInEventBaseThread
482 class RunInLoopCallback : public LoopCallback {
484 RunInLoopCallback(void (*fn)(void*), void* arg);
485 void runLoopCallback() noexcept;
493 * Helper function that tells us whether we have already handled
494 * some event/timeout/callback in this loop iteration.
496 bool nothingHandledYet();
498 // --------- libevent callbacks (not for client use) ------------
500 static void runFunctionPtr(std::function<void()>* fn);
502 // small object used as a callback arg with enough info to execute the
503 // appropriate client-provided Cob
504 class CobTimeout : public AsyncTimeout {
506 CobTimeout(EventBase* b, const Cob& c, TimeoutManager::InternalEnum in)
507 : AsyncTimeout(b, in), cob_(c) {}
509 virtual void timeoutExpired() noexcept;
515 typedef boost::intrusive::list_member_hook<
516 boost::intrusive::link_mode<boost::intrusive::auto_unlink> > ListHook;
520 typedef boost::intrusive::list<
522 boost::intrusive::member_hook<CobTimeout, ListHook, &CobTimeout::hook>,
523 boost::intrusive::constant_time_size<false> > List;
526 typedef LoopCallback::List LoopCallbackList;
527 class FunctionRunner;
529 bool loopBody(int flags = 0);
531 // executes any callbacks queued by runInLoop(); returns false if none found
532 bool runLoopCallbacks(bool setContext = true);
534 void initNotificationQueue();
536 CobTimeout::List pendingCobTimeouts_;
538 LoopCallbackList loopCallbacks_;
539 LoopCallbackList runBeforeLoopCallbacks_;
540 LoopCallbackList onDestructionCallbacks_;
542 // This will be null most of the time, but point to currentCallbacks
543 // if we are in the middle of running loop callbacks, such that
544 // runInLoop(..., true) will always run in the current loop
546 LoopCallbackList* runOnceCallbacks_;
548 // stop_ is set by terminateLoopSoon() and is used by the main loop
549 // to determine if it should exit
552 // The ID of the thread running the main loop.
553 // 0 if loop is not running.
554 // Note: POSIX doesn't guarantee that 0 is an invalid pthread_t (or
555 // even that atomic<pthread_t> is valid), but that's how it is
556 // everywhere (at least on Linux, FreeBSD, and OSX).
557 std::atomic<pthread_t> loopThread_;
559 // pointer to underlying event_base class doing the heavy lifting
562 // A notification queue for runInEventBaseThread() to use
563 // to send function requests to the EventBase thread.
564 std::unique_ptr<NotificationQueue<std::pair<void (*)(void*), void*>>> queue_;
565 std::unique_ptr<FunctionRunner> fnRunner_;
567 // limit for latency in microseconds (0 disables)
570 // exponentially-smoothed average loop time for latency-limiting
571 SmoothLoopTime avgLoopTime_;
573 // smoothed loop time used to invoke latency callbacks; differs from
574 // avgLoopTime_ in that it's scaled down after triggering a callback
575 // to reduce spamminess
576 SmoothLoopTime maxLatencyLoopTime_;
578 // callback called when latency limit is exceeded
581 // we'll wait this long before running deferred callbacks if the event
583 static const int kDEFAULT_IDLE_WAIT_USEC = 20000; // 20ms
585 // Wrap-around loop counter to detect beginning of each loop
586 uint64_t nextLoopCnt_;
587 uint64_t latestLoopCnt_;
590 // Observer to export counters
591 std::shared_ptr<EventBaseObserver> observer_;
592 uint32_t observerSampleCount_;
594 // Name of the thread running this EventBase