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/io/async/Request.h>
23 #include <folly/wangle/Executor.h>
31 #include <boost/intrusive/list.hpp>
32 #include <boost/utility.hpp>
34 #include <event.h> // libevent
41 typedef std::function<void()> Cob;
42 template <typename MessageT>
43 class NotificationQueue;
45 class EventBaseObserver {
47 virtual ~EventBaseObserver() {}
49 virtual uint32_t getSampleRate() const = 0;
51 virtual void loopSample(
52 int64_t busyTime, int64_t idleTime) = 0;
55 // Helper class that sets and retrieves the EventBase associated with a given
56 // request via RequestContext. See Request.h for that mechanism.
57 class RequestEventBase : public RequestData {
59 static EventBase* get() {
60 auto data = dynamic_cast<RequestEventBase*>(
61 RequestContext::get()->getContextData(kContextDataName));
68 static void set(EventBase* eb) {
69 RequestContext::get()->setContextData(
71 std::unique_ptr<RequestEventBase>(new RequestEventBase(eb)));
75 explicit RequestEventBase(EventBase* eb) : eb_(eb) {}
77 static constexpr const char* kContextDataName{"EventBase"};
81 * This class is a wrapper for all asynchronous I/O processing functionality
83 * EventBase provides a main loop that notifies EventHandler callback objects
84 * when I/O is ready on a file descriptor, and notifies AsyncTimeout objects
85 * when a specified timeout has expired. More complex, higher-level callback
86 * mechanisms can then be built on top of EventHandler and AsyncTimeout.
88 * A EventBase object can only drive an event loop for a single thread. To
89 * take advantage of multiple CPU cores, most asynchronous I/O servers have one
90 * thread per CPU, and use a separate EventBase for each thread.
92 * In general, most EventBase methods may only be called from the thread
93 * running the EventBase's loop. There are a few exceptions to this rule, for
94 * methods that are explicitly intended to allow communication with a
95 * EventBase from other threads. When it is safe to call a method from
96 * another thread it is explicitly listed in the method comments.
99 private boost::noncopyable, public TimeoutManager, public wangle::Executor
103 * A callback interface to use with runInLoop()
105 * Derive from this class if you need to delay some code execution until the
106 * next iteration of the event loop. This allows you to schedule code to be
107 * invoked from the top-level of the loop, after your immediate callers have
110 * If a LoopCallback object is destroyed while it is scheduled to be run in
111 * the next loop iteration, it will automatically be cancelled.
115 virtual ~LoopCallback() {}
117 virtual void runLoopCallback() noexcept = 0;
118 void cancelLoopCallback() {
122 bool isLoopCallbackScheduled() const {
123 return hook_.is_linked();
127 typedef boost::intrusive::list_member_hook<
128 boost::intrusive::link_mode<boost::intrusive::auto_unlink> > ListHook;
132 typedef boost::intrusive::list<
134 boost::intrusive::member_hook<LoopCallback, ListHook,
135 &LoopCallback::hook_>,
136 boost::intrusive::constant_time_size<false> > List;
138 // EventBase needs access to LoopCallbackList (and therefore to hook_)
139 friend class EventBase;
140 std::shared_ptr<RequestContext> context_;
144 * Create a new EventBase object.
149 * Create a new EventBase object that will use the specified libevent
150 * event_base object to drive the event loop.
152 * The EventBase will take ownership of this event_base, and will call
153 * event_base_free(evb) when the EventBase is destroyed.
155 explicit EventBase(event_base* evb);
159 * Runs the event loop.
161 * loop() will loop waiting for I/O or timeouts and invoking EventHandler
162 * and AsyncTimeout callbacks as their events become ready. loop() will
163 * only return when there are no more events remaining to process, or after
164 * terminateLoopSoon() has been called.
166 * loop() may be called again to restart event processing after a previous
167 * call to loop() or loopForever() has returned.
169 * Returns true if the loop completed normally (if it processed all
170 * outstanding requests, or if terminateLoopSoon() was called). If an error
171 * occurs waiting for events, false will be returned.
176 * Wait for some events to become active, run them, then return.
178 * When EVLOOP_NONBLOCK is set in flags, the loop won't block if there
179 * are not any events to process.
181 * This is useful for callers that want to run the loop manually.
183 * Returns the same result as loop().
185 bool loopOnce(int flags = 0);
188 * Runs the event loop.
190 * loopForever() behaves like loop(), except that it keeps running even if
191 * when there are no more user-supplied EventHandlers or AsyncTimeouts
192 * registered. It will only return after terminateLoopSoon() has been
195 * This is useful for callers that want to wait for other threads to call
196 * runInEventBaseThread(), even when there are no other scheduled events.
198 * loopForever() may be called again to restart event processing after a
199 * previous call to loop() or loopForever() has returned.
201 * Throws a std::system_error if an error occurs.
206 * Causes the event loop to exit soon.
208 * This will cause an existing call to loop() or loopForever() to stop event
209 * processing and return, even if there are still events remaining to be
212 * It is safe to call terminateLoopSoon() from another thread to cause loop()
213 * to wake up and return in the EventBase loop thread. terminateLoopSoon()
214 * may also be called from the loop thread itself (for example, a
215 * EventHandler or AsyncTimeout callback may call terminateLoopSoon() to
216 * cause the loop to exit after the callback returns.) If the loop is not
217 * running, this will cause the next call to loop to terminate soon after
218 * starting. If a loop runs out of work (and so terminates on its own)
219 * concurrently with a call to terminateLoopSoon(), this may cause a race
222 * Note that the caller is responsible for ensuring that cleanup of all event
223 * callbacks occurs properly. Since terminateLoopSoon() causes the loop to
224 * exit even when there are pending events present, there may be remaining
225 * callbacks present waiting to be invoked. If the loop is later restarted
226 * pending events will continue to be processed normally, however if the
227 * EventBase is destroyed after calling terminateLoopSoon() it is the
228 * caller's responsibility to ensure that cleanup happens properly even if
229 * some outstanding events are never processed.
231 void terminateLoopSoon();
234 * Adds the given callback to a queue of things run after the current pass
235 * through the event loop completes. Note that if this callback calls
236 * runInLoop() the new callback won't be called until the main event loop
237 * has gone through a cycle.
239 * This method may only be called from the EventBase's thread. This
240 * essentially allows an event handler to schedule an additional callback to
241 * be invoked after it returns.
243 * Use runInEventBaseThread() to schedule functions from another thread.
245 * The thisIteration parameter makes this callback run in this loop
246 * iteration, instead of the next one, even if called from a
247 * runInLoop callback (normal io callbacks that call runInLoop will
248 * always run in this iteration). This was originally added to
249 * support detachEventBase, as a user callback may have called
250 * terminateLoopSoon(), but we want to make sure we detach. Also,
251 * detachEventBase almost always must be called from the base event
252 * loop to ensure the stack is unwound, since most users of
253 * EventBase are not thread safe.
255 * Ideally we would not need thisIteration, and instead just use
256 * runInLoop with loop() (instead of terminateLoopSoon).
258 void runInLoop(LoopCallback* callback, bool thisIteration = false);
261 * Convenience function to call runInLoop() with a std::function.
263 * This creates a LoopCallback object to wrap the std::function, and invoke
264 * the std::function when the loop callback fires. This is slightly more
265 * expensive than defining your own LoopCallback, but more convenient in
266 * areas that aren't performance sensitive where you just want to use
267 * std::bind. (std::bind is fairly slow on even by itself.)
269 * This method may only be called from the EventBase's thread. This
270 * essentially allows an event handler to schedule an additional callback to
271 * be invoked after it returns.
273 * Use runInEventBaseThread() to schedule functions from another thread.
275 void runInLoop(const Cob& c, bool thisIteration = false);
277 void runInLoop(Cob&& c, bool thisIteration = false);
280 * Adds the given callback to a queue of things run before destruction
281 * of current EventBase.
283 * This allows users of EventBase that run in it, but don't control it,
284 * to be notified before EventBase gets destructed.
286 * Note: will be called from the thread that invoked EventBase destructor,
287 * before the final run of loop callbacks.
289 void runOnDestruction(LoopCallback* callback);
292 * Adds a callback that will run immediately *before* the event loop.
293 * This is very similar to runInLoop(), but will not cause the loop to break:
294 * For example, this callback could be used to get loop times.
296 void runBeforeLoop(LoopCallback* callback);
299 * Run the specified function in the EventBase's thread.
301 * This method is thread-safe, and may be called from another thread.
303 * If runInEventBaseThread() is called when the EventBase loop is not
304 * running, the function call will be delayed until the next time the loop is
307 * If runInEventBaseThread() returns true the function has successfully been
308 * scheduled to run in the loop thread. However, if the loop is terminated
309 * (and never later restarted) before it has a chance to run the requested
310 * function, the function will be run upon the EventBase's destruction.
312 * If two calls to runInEventBaseThread() are made from the same thread, the
313 * functions will always be run in the order that they were scheduled.
314 * Ordering between functions scheduled from separate threads is not
317 * @param fn The function to run. The function must not throw any
319 * @param arg An argument to pass to the function.
321 * @return Returns true if the function was successfully scheduled, or false
322 * if there was an error scheduling the function.
325 bool runInEventBaseThread(void (*fn)(T*), T* arg) {
326 return runInEventBaseThread(reinterpret_cast<void (*)(void*)>(fn),
327 reinterpret_cast<void*>(arg));
330 bool runInEventBaseThread(void (*fn)(void*), void* arg);
333 * Run the specified function in the EventBase's thread
335 * This version of runInEventBaseThread() takes a std::function object.
336 * Note that this is less efficient than the version that takes a plain
337 * function pointer and void* argument, as it has to allocate memory to copy
338 * the std::function object.
340 * If the loop is terminated (and never later restarted) before it has a
341 * chance to run the requested function, the function will be run upon the
342 * EventBase's destruction.
344 * The function must not throw any exceptions.
346 bool runInEventBaseThread(const Cob& fn);
349 * Runs the given Cob at some time after the specified number of
350 * milliseconds. (No guarantees exactly when.)
352 * @return true iff the cob was successfully registered.
357 TimeoutManager::InternalEnum = TimeoutManager::InternalEnum::NORMAL);
360 * Set the maximum desired latency in us and provide a callback which will be
361 * called when that latency is exceeded.
363 void setMaxLatency(int64_t maxLatency, const Cob& maxLatencyCob) {
364 maxLatency_ = maxLatency;
365 maxLatencyCob_ = maxLatencyCob;
369 * Set smoothing coefficient for loop load average; # of milliseconds
370 * for exp(-1) (1/2.71828...) decay.
372 void setLoadAvgMsec(uint32_t ms);
375 * reset the load average to a desired value
377 void resetLoadAvg(double value = 0.0);
380 * Get the average loop time in microseconds (an exponentially-smoothed ave)
382 double getAvgLoopTime() const {
383 return avgLoopTime_.get();
387 * check if the event base loop is running.
389 bool isRunning() const {
390 return loopThread_.load(std::memory_order_relaxed) != 0;
394 * wait until the event loop starts (after starting the event loop thread).
396 void waitUntilRunning();
398 int getNotificationQueueSize() const;
400 void setMaxReadAtOnce(uint32_t maxAtOnce);
403 * Verify that current thread is the EventBase thread, if the EventBase is
406 bool isInEventBaseThread() const {
407 auto tid = loopThread_.load(std::memory_order_relaxed);
408 return tid == 0 || pthread_equal(tid, pthread_self());
411 bool inRunningEventBaseThread() const {
412 return pthread_equal(
413 loopThread_.load(std::memory_order_relaxed), pthread_self());
416 // --------- interface to underlying libevent base ------------
417 // Avoid using these functions if possible. These functions are not
418 // guaranteed to always be present if we ever provide alternative EventBase
419 // implementations that do not use libevent internally.
420 event_base* getLibeventBase() const { return evb_; }
421 static const char* getLibeventVersion();
422 static const char* getLibeventMethod();
425 * only EventHandler/AsyncTimeout subclasses and ourselves should
428 * This is used to mark the beginning of a new loop cycle by the
429 * first handler fired within that cycle.
432 bool bumpHandlingTime();
434 class SmoothLoopTime {
436 explicit SmoothLoopTime(uint64_t timeInterval)
437 : expCoeff_(-1.0/timeInterval)
439 , oldBusyLeftover_(0) {
440 VLOG(11) << "expCoeff_ " << expCoeff_ << " " << __PRETTY_FUNCTION__;
443 void setTimeInterval(uint64_t timeInterval);
444 void reset(double value = 0.0);
446 void addSample(int64_t idle, int64_t busy);
452 void dampen(double factor) {
459 int64_t oldBusyLeftover_;
463 const std::shared_ptr<EventBaseObserver>& observer) {
464 observer_ = observer;
467 const std::shared_ptr<EventBaseObserver>& getObserver() {
472 * Set the name of the thread that runs this event base.
474 void setName(const std::string& name);
477 * Returns the name of the thread that runs this event base.
479 const std::string& getName();
481 /// Implements the wangle::Executor interface
482 void add(Cob fn) override {
483 // runInEventBaseThread() takes a const&,
484 // so no point in doing std::move here.
485 runInEventBaseThread(fn);
491 void attachTimeoutManager(AsyncTimeout* obj,
492 TimeoutManager::InternalEnum internal);
494 void detachTimeoutManager(AsyncTimeout* obj);
496 bool scheduleTimeout(AsyncTimeout* obj, std::chrono::milliseconds timeout);
498 void cancelTimeout(AsyncTimeout* obj);
500 bool isInTimeoutManagerThread() {
501 return isInEventBaseThread();
504 // Helper class used to short circuit runInEventBaseThread
505 class RunInLoopCallback : public LoopCallback {
507 RunInLoopCallback(void (*fn)(void*), void* arg);
508 void runLoopCallback() noexcept;
516 * Helper function that tells us whether we have already handled
517 * some event/timeout/callback in this loop iteration.
519 bool nothingHandledYet();
521 // --------- libevent callbacks (not for client use) ------------
523 static void runFunctionPtr(std::function<void()>* fn);
525 // small object used as a callback arg with enough info to execute the
526 // appropriate client-provided Cob
527 class CobTimeout : public AsyncTimeout {
529 CobTimeout(EventBase* b, const Cob& c, TimeoutManager::InternalEnum in)
530 : AsyncTimeout(b, in), cob_(c) {}
532 virtual void timeoutExpired() noexcept;
538 typedef boost::intrusive::list_member_hook<
539 boost::intrusive::link_mode<boost::intrusive::auto_unlink> > ListHook;
543 typedef boost::intrusive::list<
545 boost::intrusive::member_hook<CobTimeout, ListHook, &CobTimeout::hook>,
546 boost::intrusive::constant_time_size<false> > List;
549 typedef LoopCallback::List LoopCallbackList;
550 class FunctionRunner;
552 bool loopBody(int flags = 0);
554 // executes any callbacks queued by runInLoop(); returns false if none found
555 bool runLoopCallbacks(bool setContext = true);
557 void initNotificationQueue();
559 CobTimeout::List pendingCobTimeouts_;
561 LoopCallbackList loopCallbacks_;
562 LoopCallbackList runBeforeLoopCallbacks_;
563 LoopCallbackList onDestructionCallbacks_;
565 // This will be null most of the time, but point to currentCallbacks
566 // if we are in the middle of running loop callbacks, such that
567 // runInLoop(..., true) will always run in the current loop
569 LoopCallbackList* runOnceCallbacks_;
571 // stop_ is set by terminateLoopSoon() and is used by the main loop
572 // to determine if it should exit
575 // The ID of the thread running the main loop.
576 // 0 if loop is not running.
577 // Note: POSIX doesn't guarantee that 0 is an invalid pthread_t (or
578 // even that atomic<pthread_t> is valid), but that's how it is
579 // everywhere (at least on Linux, FreeBSD, and OSX).
580 std::atomic<pthread_t> loopThread_;
582 // pointer to underlying event_base class doing the heavy lifting
585 // A notification queue for runInEventBaseThread() to use
586 // to send function requests to the EventBase thread.
587 std::unique_ptr<NotificationQueue<std::pair<void (*)(void*), void*>>> queue_;
588 std::unique_ptr<FunctionRunner> fnRunner_;
590 // limit for latency in microseconds (0 disables)
593 // exponentially-smoothed average loop time for latency-limiting
594 SmoothLoopTime avgLoopTime_;
596 // smoothed loop time used to invoke latency callbacks; differs from
597 // avgLoopTime_ in that it's scaled down after triggering a callback
598 // to reduce spamminess
599 SmoothLoopTime maxLatencyLoopTime_;
601 // callback called when latency limit is exceeded
604 // we'll wait this long before running deferred callbacks if the event
606 static const int kDEFAULT_IDLE_WAIT_USEC = 20000; // 20ms
608 // Wrap-around loop counter to detect beginning of each loop
609 uint64_t nextLoopCnt_;
610 uint64_t latestLoopCnt_;
613 // Observer to export counters
614 std::shared_ptr<EventBaseObserver> observer_;
615 uint32_t observerSampleCount_;
617 // Name of the thread running this EventBase