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>
29 #include <boost/intrusive/list.hpp>
30 #include <boost/utility.hpp>
32 #include <event.h> // libevent
39 typedef std::function<void()> Cob;
40 template <typename MessageT>
41 class NotificationQueue;
43 class EventBaseObserver {
45 virtual ~EventBaseObserver() {}
47 virtual uint32_t getSampleRate() const = 0;
49 virtual void loopSample(
50 int64_t busyTime, int64_t idleTime) = 0;
54 * This class is a wrapper for all asynchronous I/O processing functionality
56 * EventBase provides a main loop that notifies EventHandler callback objects
57 * when I/O is ready on a file descriptor, and notifies AsyncTimeout objects
58 * when a specified timeout has expired. More complex, higher-level callback
59 * mechanisms can then be built on top of EventHandler and AsyncTimeout.
61 * A EventBase object can only drive an event loop for a single thread. To
62 * take advantage of multiple CPU cores, most asynchronous I/O servers have one
63 * thread per CPU, and use a separate EventBase for each thread.
65 * In general, most EventBase methods may only be called from the thread
66 * running the EventBase's loop. There are a few exceptions to this rule, for
67 * methods that are explicitly intended to allow communication with a
68 * EventBase from other threads. When it is safe to call a method from
69 * another thread it is explicitly listed in the method comments.
71 class EventBase : private boost::noncopyable, public TimeoutManager {
74 * A callback interface to use with runInLoop()
76 * Derive from this class if you need to delay some code execution until the
77 * next iteration of the event loop. This allows you to schedule code to be
78 * invoked from the top-level of the loop, after your immediate callers have
81 * If a LoopCallback object is destroyed while it is scheduled to be run in
82 * the next loop iteration, it will automatically be cancelled.
86 virtual ~LoopCallback() {}
88 virtual void runLoopCallback() noexcept = 0;
89 void cancelLoopCallback() {
93 bool isLoopCallbackScheduled() const {
94 return hook_.is_linked();
98 typedef boost::intrusive::list_member_hook<
99 boost::intrusive::link_mode<boost::intrusive::auto_unlink> > ListHook;
103 typedef boost::intrusive::list<
105 boost::intrusive::member_hook<LoopCallback, ListHook,
106 &LoopCallback::hook_>,
107 boost::intrusive::constant_time_size<false> > List;
109 // EventBase needs access to LoopCallbackList (and therefore to hook_)
110 friend class EventBase;
111 std::shared_ptr<RequestContext> context_;
115 * Create a new EventBase object.
120 * Create a new EventBase object that will use the specified libevent
121 * event_base object to drive the event loop.
123 * The EventBase will take ownership of this event_base, and will call
124 * event_base_free(evb) when the EventBase is destroyed.
126 explicit EventBase(event_base* evb);
130 * Runs the event loop.
132 * loop() will loop waiting for I/O or timeouts and invoking EventHandler
133 * and AsyncTimeout callbacks as their events become ready. loop() will
134 * only return when there are no more events remaining to process, or after
135 * terminateLoopSoon() has been called.
137 * loop() may be called again to restart event processing after a previous
138 * call to loop() or loopForever() has returned.
140 * Returns true if the loop completed normally (if it processed all
141 * outstanding requests, or if terminateLoopSoon() was called). If an error
142 * occurs waiting for events, false will be returned.
147 * Wait for some events to become active, run them, then return.
149 * When EVLOOP_NONBLOCK is set in flags, the loop won't block if there
150 * are not any events to process.
152 * This is useful for callers that want to run the loop manually.
154 * Returns the same result as loop().
156 bool loopOnce(int flags = 0);
159 * Runs the event loop.
161 * loopForever() behaves like loop(), except that it keeps running even if
162 * when there are no more user-supplied EventHandlers or AsyncTimeouts
163 * registered. It will only return after terminateLoopSoon() has been
166 * This is useful for callers that want to wait for other threads to call
167 * runInEventBaseThread(), even when there are no other scheduled events.
169 * loopForever() may be called again to restart event processing after a
170 * previous call to loop() or loopForever() has returned.
172 * Throws a std::system_error if an error occurs.
177 * Causes the event loop to exit soon.
179 * This will cause an existing call to loop() or loopForever() to stop event
180 * processing and return, even if there are still events remaining to be
183 * It is safe to call terminateLoopSoon() from another thread to cause loop()
184 * to wake up and return in the EventBase loop thread. terminateLoopSoon()
185 * may also be called from the loop thread itself (for example, a
186 * EventHandler or AsyncTimeout callback may call terminateLoopSoon() to
187 * cause the loop to exit after the callback returns.) If the loop is not
188 * running, this will cause the next call to loop to terminate soon after
189 * starting. If a loop runs out of work (and so terminates on its own)
190 * concurrently with a call to terminateLoopSoon(), this may cause a race
193 * Note that the caller is responsible for ensuring that cleanup of all event
194 * callbacks occurs properly. Since terminateLoopSoon() causes the loop to
195 * exit even when there are pending events present, there may be remaining
196 * callbacks present waiting to be invoked. If the loop is later restarted
197 * pending events will continue to be processed normally, however if the
198 * EventBase is destroyed after calling terminateLoopSoon() it is the
199 * caller's responsibility to ensure that cleanup happens properly even if
200 * some outstanding events are never processed.
202 void terminateLoopSoon();
205 * Adds the given callback to a queue of things run after the current pass
206 * through the event loop completes. Note that if this callback calls
207 * runInLoop() the new callback won't be called until the main event loop
208 * has gone through a cycle.
210 * This method may only be called from the EventBase's thread. This
211 * essentially allows an event handler to schedule an additional callback to
212 * be invoked after it returns.
214 * Use runInEventBaseThread() to schedule functions from another thread.
216 * The thisIteration parameter makes this callback run in this loop
217 * iteration, instead of the next one, even if called from a
218 * runInLoop callback (normal io callbacks that call runInLoop will
219 * always run in this iteration). This was originally added to
220 * support detachEventBase, as a user callback may have called
221 * terminateLoopSoon(), but we want to make sure we detach. Also,
222 * detachEventBase almost always must be called from the base event
223 * loop to ensure the stack is unwound, since most users of
224 * EventBase are not thread safe.
226 * Ideally we would not need thisIteration, and instead just use
227 * runInLoop with loop() (instead of terminateLoopSoon).
229 void runInLoop(LoopCallback* callback, bool thisIteration = false);
232 * Convenience function to call runInLoop() with a std::function.
234 * This creates a LoopCallback object to wrap the std::function, and invoke
235 * the std::function when the loop callback fires. This is slightly more
236 * expensive than defining your own LoopCallback, but more convenient in
237 * areas that aren't performance sensitive where you just want to use
238 * std::bind. (std::bind is fairly slow on even by itself.)
240 * This method may only be called from the EventBase's thread. This
241 * essentially allows an event handler to schedule an additional callback to
242 * be invoked after it returns.
244 * Use runInEventBaseThread() to schedule functions from another thread.
246 void runInLoop(const Cob& c, bool thisIteration = false);
248 void runInLoop(Cob&& c, bool thisIteration = false);
251 * Adds the given callback to a queue of things run before destruction
252 * of current EventBase.
254 * This allows users of EventBase that run in it, but don't control it,
255 * to be notified before EventBase gets destructed.
257 * Note: will be called from the thread that invoked EventBase destructor,
258 * before the final run of loop callbacks.
260 void runOnDestruction(LoopCallback* callback);
262 void runBeforeLoop(LoopCallback* callback);
265 * Run the specified function in the EventBase's thread.
267 * This method is thread-safe, and may be called from another thread.
269 * If runInEventBaseThread() is called when the EventBase loop is not
270 * running, the function call will be delayed until the next time the loop is
273 * If runInEventBaseThread() returns true the function has successfully been
274 * scheduled to run in the loop thread. However, if the loop is terminated
275 * (and never later restarted) before it has a chance to run the requested
276 * function, the function may never be run at all. The caller is responsible
277 * for handling this situation correctly if they may terminate the loop with
278 * outstanding runInEventBaseThread() calls pending.
280 * If two calls to runInEventBaseThread() are made from the same thread, the
281 * functions will always be run in the order that they were scheduled.
282 * Ordering between functions scheduled from separate threads is not
285 * @param fn The function to run. The function must not throw any
287 * @param arg An argument to pass to the function.
289 * @return Returns true if the function was successfully scheduled, or false
290 * if there was an error scheduling the function.
293 bool runInEventBaseThread(void (*fn)(T*), T* arg) {
294 return runInEventBaseThread(reinterpret_cast<void (*)(void*)>(fn),
295 reinterpret_cast<void*>(arg));
298 bool runInEventBaseThread(void (*fn)(void*), void* arg);
301 * Run the specified function in the EventBase's thread
303 * This version of runInEventBaseThread() takes a std::function object.
304 * Note that this is less efficient than the version that takes a plain
305 * function pointer and void* argument, as it has to allocate memory to copy
306 * the std::function object.
308 * If the EventBase loop is terminated before it has a chance to run this
309 * function, the allocated memory will be leaked. The caller is responsible
310 * for ensuring that the EventBase loop is not terminated before this
313 * The function must not throw any exceptions.
315 bool runInEventBaseThread(const Cob& fn);
318 * Runs the given Cob at some time after the specified number of
319 * milliseconds. (No guarantees exactly when.)
321 * @return true iff the cob was successfully registered.
326 TimeoutManager::InternalEnum = TimeoutManager::InternalEnum::NORMAL);
329 * Set the maximum desired latency in us and provide a callback which will be
330 * called when that latency is exceeded.
332 void setMaxLatency(int64_t maxLatency, const Cob& maxLatencyCob) {
333 maxLatency_ = maxLatency;
334 maxLatencyCob_ = maxLatencyCob;
338 * Set smoothing coefficient for loop load average; # of milliseconds
339 * for exp(-1) (1/2.71828...) decay.
341 void setLoadAvgMsec(uint32_t ms);
344 * reset the load average to a desired value
346 void resetLoadAvg(double value = 0.0);
349 * Get the average loop time in microseconds (an exponentially-smoothed ave)
351 double getAvgLoopTime() const {
352 return avgLoopTime_.get();
356 * check if the event base loop is running.
358 bool isRunning() const {
359 return loopThread_.load(std::memory_order_relaxed) != 0;
363 * wait until the event loop starts (after starting the event loop thread).
365 void waitUntilRunning();
367 int getNotificationQueueSize() const;
369 void setMaxReadAtOnce(uint32_t maxAtOnce);
372 * Verify that current thread is the EventBase thread, if the EventBase is
375 bool isInEventBaseThread() const {
376 auto tid = loopThread_.load(std::memory_order_relaxed);
377 return tid == 0 || pthread_equal(tid, pthread_self());
380 bool inRunningEventBaseThread() const {
381 return pthread_equal(
382 loopThread_.load(std::memory_order_relaxed), pthread_self());
385 // --------- interface to underlying libevent base ------------
386 // Avoid using these functions if possible. These functions are not
387 // guaranteed to always be present if we ever provide alternative EventBase
388 // implementations that do not use libevent internally.
389 event_base* getLibeventBase() const { return evb_; }
390 static const char* getLibeventVersion();
391 static const char* getLibeventMethod();
394 * only EventHandler/AsyncTimeout subclasses and ourselves should
397 * This is used to mark the beginning of a new loop cycle by the
398 * first handler fired within that cycle.
401 bool bumpHandlingTime();
403 class SmoothLoopTime {
405 explicit SmoothLoopTime(uint64_t timeInterval)
406 : expCoeff_(-1.0/timeInterval)
408 , oldBusyLeftover_(0) {
409 VLOG(11) << "expCoeff_ " << expCoeff_ << " " << __PRETTY_FUNCTION__;
412 void setTimeInterval(uint64_t timeInterval);
413 void reset(double value = 0.0);
415 void addSample(int64_t idle, int64_t busy);
421 void dampen(double factor) {
428 int64_t oldBusyLeftover_;
432 const std::shared_ptr<EventBaseObserver>& observer) {
433 observer_ = observer;
436 const std::shared_ptr<EventBaseObserver>& getObserver() {
441 * Set the name of the thread that runs this event base.
443 void setName(const std::string& name);
446 * Returns the name of the thread that runs this event base.
448 const std::string& getName();
453 void attachTimeoutManager(AsyncTimeout* obj,
454 TimeoutManager::InternalEnum internal);
456 void detachTimeoutManager(AsyncTimeout* obj);
458 bool scheduleTimeout(AsyncTimeout* obj, std::chrono::milliseconds timeout);
460 void cancelTimeout(AsyncTimeout* obj);
462 bool isInTimeoutManagerThread() {
463 return isInEventBaseThread();
466 // Helper class used to short circuit runInEventBaseThread
467 class RunInLoopCallback : public LoopCallback {
469 RunInLoopCallback(void (*fn)(void*), void* arg);
470 void runLoopCallback() noexcept;
478 * Helper function that tells us whether we have already handled
479 * some event/timeout/callback in this loop iteration.
481 bool nothingHandledYet();
483 // --------- libevent callbacks (not for client use) ------------
485 static void runFunctionPtr(std::function<void()>* fn);
487 // small object used as a callback arg with enough info to execute the
488 // appropriate client-provided Cob
489 class CobTimeout : public AsyncTimeout {
491 CobTimeout(EventBase* b, const Cob& c, TimeoutManager::InternalEnum in)
492 : AsyncTimeout(b, in), cob_(c) {}
494 virtual void timeoutExpired() noexcept;
500 typedef boost::intrusive::list_member_hook<
501 boost::intrusive::link_mode<boost::intrusive::auto_unlink> > ListHook;
505 typedef boost::intrusive::list<
507 boost::intrusive::member_hook<CobTimeout, ListHook, &CobTimeout::hook>,
508 boost::intrusive::constant_time_size<false> > List;
511 typedef LoopCallback::List LoopCallbackList;
512 class FunctionRunner;
514 bool loopBody(int flags = 0);
516 // executes any callbacks queued by runInLoop(); returns false if none found
517 bool runLoopCallbacks(bool setContext = true);
519 void initNotificationQueue();
521 CobTimeout::List pendingCobTimeouts_;
523 LoopCallbackList loopCallbacks_;
524 LoopCallbackList noWaitLoopCallbacks_;
525 LoopCallbackList onDestructionCallbacks_;
527 // This will be null most of the time, but point to currentCallbacks
528 // if we are in the middle of running loop callbacks, such that
529 // runInLoop(..., true) will always run in the current loop
531 LoopCallbackList* runOnceCallbacks_;
533 // stop_ is set by terminateLoopSoon() and is used by the main loop
534 // to determine if it should exit
537 // The ID of the thread running the main loop.
538 // 0 if loop is not running.
539 // Note: POSIX doesn't guarantee that 0 is an invalid pthread_t (or
540 // even that atomic<pthread_t> is valid), but that's how it is
541 // everywhere (at least on Linux, FreeBSD, and OSX).
542 std::atomic<pthread_t> loopThread_;
544 // pointer to underlying event_base class doing the heavy lifting
547 // A notification queue for runInEventBaseThread() to use
548 // to send function requests to the EventBase thread.
549 std::unique_ptr<NotificationQueue<std::pair<void (*)(void*), void*>>> queue_;
550 std::unique_ptr<FunctionRunner> fnRunner_;
552 // limit for latency in microseconds (0 disables)
555 // exponentially-smoothed average loop time for latency-limiting
556 SmoothLoopTime avgLoopTime_;
558 // smoothed loop time used to invoke latency callbacks; differs from
559 // avgLoopTime_ in that it's scaled down after triggering a callback
560 // to reduce spamminess
561 SmoothLoopTime maxLatencyLoopTime_;
563 // callback called when latency limit is exceeded
566 // we'll wait this long before running deferred callbacks if the event
568 static const int kDEFAULT_IDLE_WAIT_USEC = 20000; // 20ms
570 // Wrap-around loop counter to detect beginning of each loop
571 uint64_t nextLoopCnt_;
572 uint64_t latestLoopCnt_;
575 // Observer to export counters
576 std::shared_ptr<EventBaseObserver> observer_;
577 uint32_t observerSampleCount_;
579 // Name of the thread running this EventBase