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 * This is useful for callers that want to run the loop manually.
151 * Returns the same result as loop().
156 * Runs the event loop.
158 * loopForever() behaves like loop(), except that it keeps running even if
159 * when there are no more user-supplied EventHandlers or AsyncTimeouts
160 * registered. It will only return after terminateLoopSoon() has been
163 * This is useful for callers that want to wait for other threads to call
164 * runInEventBaseThread(), even when there are no other scheduled events.
166 * loopForever() may be called again to restart event processing after a
167 * previous call to loop() or loopForever() has returned.
169 * Throws a std::system_error if an error occurs.
174 * Causes the event loop to exit soon.
176 * This will cause an existing call to loop() or loopForever() to stop event
177 * processing and return, even if there are still events remaining to be
180 * It is safe to call terminateLoopSoon() from another thread to cause loop()
181 * to wake up and return in the EventBase loop thread. terminateLoopSoon()
182 * may also be called from the loop thread itself (for example, a
183 * EventHandler or AsyncTimeout callback may call terminateLoopSoon() to
184 * cause the loop to exit after the callback returns.)
186 * Note that the caller is responsible for ensuring that cleanup of all event
187 * callbacks occurs properly. Since terminateLoopSoon() causes the loop to
188 * exit even when there are pending events present, there may be remaining
189 * callbacks present waiting to be invoked. If the loop is later restarted
190 * pending events will continue to be processed normally, however if the
191 * EventBase is destroyed after calling terminateLoopSoon() it is the
192 * caller's responsibility to ensure that cleanup happens properly even if
193 * some outstanding events are never processed.
195 void terminateLoopSoon();
198 * Adds the given callback to a queue of things run after the current pass
199 * through the event loop completes. Note that if this callback calls
200 * runInLoop() the new callback won't be called until the main event loop
201 * has gone through a cycle.
203 * This method may only be called from the EventBase's thread. This
204 * essentially allows an event handler to schedule an additional callback to
205 * be invoked after it returns.
207 * Use runInEventBaseThread() to schedule functions from another thread.
209 * The thisIteration parameter makes this callback run in this loop
210 * iteration, instead of the next one, even if called from a
211 * runInLoop callback (normal io callbacks that call runInLoop will
212 * always run in this iteration). This was originally added to
213 * support detachEventBase, as a user callback may have called
214 * terminateLoopSoon(), but we want to make sure we detach. Also,
215 * detachEventBase almost always must be called from the base event
216 * loop to ensure the stack is unwound, since most users of
217 * EventBase are not thread safe.
219 * Ideally we would not need thisIteration, and instead just use
220 * runInLoop with loop() (instead of terminateLoopSoon).
222 void runInLoop(LoopCallback* callback, bool thisIteration = false);
225 * Convenience function to call runInLoop() with a std::function.
227 * This creates a LoopCallback object to wrap the std::function, and invoke
228 * the std::function when the loop callback fires. This is slightly more
229 * expensive than defining your own LoopCallback, but more convenient in
230 * areas that aren't performance sensitive where you just want to use
231 * std::bind. (std::bind is fairly slow on even by itself.)
233 * This method may only be called from the EventBase's thread. This
234 * essentially allows an event handler to schedule an additional callback to
235 * be invoked after it returns.
237 * Use runInEventBaseThread() to schedule functions from another thread.
239 void runInLoop(const Cob& c, bool thisIteration = false);
241 void runInLoop(Cob&& c, bool thisIteration = false);
244 * Run the specified function in the EventBase's thread.
246 * This method is thread-safe, and may be called from another thread.
248 * If runInEventBaseThread() is called when the EventBase loop is not
249 * running, the function call will be delayed until the next time the loop is
252 * If runInEventBaseThread() returns true the function has successfully been
253 * scheduled to run in the loop thread. However, if the loop is terminated
254 * (and never later restarted) before it has a chance to run the requested
255 * function, the function may never be run at all. The caller is responsible
256 * for handling this situation correctly if they may terminate the loop with
257 * outstanding runInEventBaseThread() calls pending.
259 * If two calls to runInEventBaseThread() are made from the same thread, the
260 * functions will always be run in the order that they were scheduled.
261 * Ordering between functions scheduled from separate threads is not
264 * @param fn The function to run. The function must not throw any
266 * @param arg An argument to pass to the function.
268 * @return Returns true if the function was successfully scheduled, or false
269 * if there was an error scheduling the function.
272 bool runInEventBaseThread(void (*fn)(T*), T* arg) {
273 return runInEventBaseThread(reinterpret_cast<void (*)(void*)>(fn),
274 reinterpret_cast<void*>(arg));
277 bool runInEventBaseThread(void (*fn)(void*), void* arg);
280 * Run the specified function in the EventBase's thread
282 * This version of runInEventBaseThread() takes a std::function object.
283 * Note that this is less efficient than the version that takes a plain
284 * function pointer and void* argument, as it has to allocate memory to copy
285 * the std::function object.
287 * If the EventBase loop is terminated before it has a chance to run this
288 * function, the allocated memory will be leaked. The caller is responsible
289 * for ensuring that the EventBase loop is not terminated before this
292 * The function must not throw any exceptions.
294 bool runInEventBaseThread(const Cob& fn);
297 * Runs the given Cob at some time after the specified number of
298 * milliseconds. (No guarantees exactly when.)
300 * @return true iff the cob was successfully registered.
305 TimeoutManager::InternalEnum = TimeoutManager::InternalEnum::NORMAL);
308 * Set the maximum desired latency in us and provide a callback which will be
309 * called when that latency is exceeded.
311 void setMaxLatency(int64_t maxLatency, const Cob& maxLatencyCob) {
312 maxLatency_ = maxLatency;
313 maxLatencyCob_ = maxLatencyCob;
317 * Set smoothing coefficient for loop load average; # of milliseconds
318 * for exp(-1) (1/2.71828...) decay.
320 void setLoadAvgMsec(uint32_t ms);
323 * reset the load average to a desired value
325 void resetLoadAvg(double value = 0.0);
328 * Get the average loop time in microseconds (an exponentially-smoothed ave)
330 double getAvgLoopTime() const {
331 return avgLoopTime_.get();
335 * check if the event base loop is running.
337 bool isRunning() const {
338 return loopThread_.load(std::memory_order_relaxed) != 0;
342 * wait until the event loop starts (after starting the event loop thread).
344 void waitUntilRunning();
346 int getNotificationQueueSize() const;
349 * Verify that current thread is the EventBase thread, if the EventBase is
352 bool isInEventBaseThread() const {
353 auto tid = loopThread_.load(std::memory_order_relaxed);
354 return tid == 0 || pthread_equal(tid, pthread_self());
357 bool inRunningEventBaseThread() const {
358 return pthread_equal(
359 loopThread_.load(std::memory_order_relaxed), pthread_self());
362 // --------- interface to underlying libevent base ------------
363 // Avoid using these functions if possible. These functions are not
364 // guaranteed to always be present if we ever provide alternative EventBase
365 // implementations that do not use libevent internally.
366 event_base* getLibeventBase() const { return evb_; }
367 static const char* getLibeventVersion() { return event_get_version(); }
368 static const char* getLibeventMethod() { return event_get_method(); }
371 * only EventHandler/AsyncTimeout subclasses and ourselves should
374 * This is used to mark the beginning of a new loop cycle by the
375 * first handler fired within that cycle.
378 bool bumpHandlingTime();
380 class SmoothLoopTime {
382 explicit SmoothLoopTime(uint64_t timeInterval)
383 : expCoeff_(-1.0/timeInterval)
385 , oldBusyLeftover_(0) {
386 VLOG(11) << "expCoeff_ " << expCoeff_ << " " << __PRETTY_FUNCTION__;
389 void setTimeInterval(uint64_t timeInterval);
390 void reset(double value = 0.0);
392 void addSample(int64_t idle, int64_t busy);
398 void dampen(double factor) {
405 int64_t oldBusyLeftover_;
409 const std::shared_ptr<EventBaseObserver>& observer) {
410 observer_ = observer;
413 const std::shared_ptr<EventBaseObserver>& getObserver() {
418 * Set the name of the thread that runs this event base.
420 void setName(const std::string& name);
423 * Returns the name of the thread that runs this event base.
425 const std::string& getName();
430 void attachTimeoutManager(AsyncTimeout* obj,
431 TimeoutManager::InternalEnum internal);
433 void detachTimeoutManager(AsyncTimeout* obj);
435 bool scheduleTimeout(AsyncTimeout* obj, std::chrono::milliseconds timeout);
437 void cancelTimeout(AsyncTimeout* obj);
439 bool isInTimeoutManagerThread() {
440 return isInEventBaseThread();
443 // Helper class used to short circuit runInEventBaseThread
444 class RunInLoopCallback : public LoopCallback {
446 RunInLoopCallback(void (*fn)(void*), void* arg);
447 void runLoopCallback() noexcept;
455 * Helper function that tells us whether we have already handled
456 * some event/timeout/callback in this loop iteration.
458 bool nothingHandledYet();
460 // --------- libevent callbacks (not for client use) ------------
462 static void runFunctionPtr(std::function<void()>* fn);
464 // small object used as a callback arg with enough info to execute the
465 // appropriate client-provided Cob
466 class CobTimeout : public AsyncTimeout {
468 CobTimeout(EventBase* b, const Cob& c, TimeoutManager::InternalEnum in)
469 : AsyncTimeout(b, in), cob_(c) {}
471 virtual void timeoutExpired() noexcept;
477 typedef boost::intrusive::list_member_hook<
478 boost::intrusive::link_mode<boost::intrusive::auto_unlink> > ListHook;
482 typedef boost::intrusive::list<
484 boost::intrusive::member_hook<CobTimeout, ListHook, &CobTimeout::hook>,
485 boost::intrusive::constant_time_size<false> > List;
488 typedef LoopCallback::List LoopCallbackList;
489 class FunctionRunner;
491 bool loopBody(bool once = false);
493 // executes any callbacks queued by runInLoop(); returns false if none found
494 bool runLoopCallbacks(bool setContext = true);
496 void initNotificationQueue();
498 CobTimeout::List pendingCobTimeouts_;
500 LoopCallbackList loopCallbacks_;
502 // This will be null most of the time, but point to currentCallbacks
503 // if we are in the middle of running loop callbacks, such that
504 // runInLoop(..., true) will always run in the current loop
506 LoopCallbackList* runOnceCallbacks_;
508 // stop_ is set by terminateLoopSoon() and is used by the main loop
509 // to determine if it should exit
512 // The ID of the thread running the main loop.
513 // 0 if loop is not running.
514 // Note: POSIX doesn't guarantee that 0 is an invalid pthread_t (or
515 // even that atomic<pthread_t> is valid), but that's how it is
516 // everywhere (at least on Linux, FreeBSD, and OSX).
517 std::atomic<pthread_t> loopThread_;
519 // pointer to underlying event_base class doing the heavy lifting
522 // A notification queue for runInEventBaseThread() to use
523 // to send function requests to the EventBase thread.
524 std::unique_ptr<NotificationQueue<std::pair<void (*)(void*), void*>>> queue_;
525 std::unique_ptr<FunctionRunner> fnRunner_;
527 // limit for latency in microseconds (0 disables)
530 // exponentially-smoothed average loop time for latency-limiting
531 SmoothLoopTime avgLoopTime_;
533 // smoothed loop time used to invoke latency callbacks; differs from
534 // avgLoopTime_ in that it's scaled down after triggering a callback
535 // to reduce spamminess
536 SmoothLoopTime maxLatencyLoopTime_;
538 // callback called when latency limit is exceeded
541 // we'll wait this long before running deferred callbacks if the event
543 static const int kDEFAULT_IDLE_WAIT_USEC = 20000; // 20ms
545 // Wrap-around loop counter to detect beginning of each loop
546 uint64_t nextLoopCnt_;
547 uint64_t latestLoopCnt_;
550 // Observer to export counters
551 std::shared_ptr<EventBaseObserver> observer_;
552 uint32_t observerSampleCount_;
554 // Name of the thread running this EventBase