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 * Runs the event loop.
149 * loopForever() behaves like loop(), except that it keeps running even if
150 * when there are no more user-supplied EventHandlers or AsyncTimeouts
151 * registered. It will only return after terminateLoopSoon() has been
154 * This is useful for callers that want to wait for other threads to call
155 * runInEventBaseThread(), even when there are no other scheduled events.
157 * loopForever() may be called again to restart event processing after a
158 * previous call to loop() or loopForever() has returned.
160 * Throws a std::system_error if an error occurs.
165 * Causes the event loop to exit soon.
167 * This will cause an existing call to loop() or loopForever() to stop event
168 * processing and return, even if there are still events remaining to be
171 * It is safe to call terminateLoopSoon() from another thread to cause loop()
172 * to wake up and return in the EventBase loop thread. terminateLoopSoon()
173 * may also be called from the loop thread itself (for example, a
174 * EventHandler or AsyncTimeout callback may call terminateLoopSoon() to
175 * cause the loop to exit after the callback returns.)
177 * Note that the caller is responsible for ensuring that cleanup of all event
178 * callbacks occurs properly. Since terminateLoopSoon() causes the loop to
179 * exit even when there are pending events present, there may be remaining
180 * callbacks present waiting to be invoked. If the loop is later restarted
181 * pending events will continue to be processed normally, however if the
182 * EventBase is destroyed after calling terminateLoopSoon() it is the
183 * caller's responsibility to ensure that cleanup happens properly even if
184 * some outstanding events are never processed.
186 void terminateLoopSoon();
189 * Adds the given callback to a queue of things run after the current pass
190 * through the event loop completes. Note that if this callback calls
191 * runInLoop() the new callback won't be called until the main event loop
192 * has gone through a cycle.
194 * This method may only be called from the EventBase's thread. This
195 * essentially allows an event handler to schedule an additional callback to
196 * be invoked after it returns.
198 * Use runInEventBaseThread() to schedule functions from another thread.
200 * The thisIteration parameter makes this callback run in this loop
201 * iteration, instead of the next one, even if called from a
202 * runInLoop callback (normal io callbacks that call runInLoop will
203 * always run in this iteration). This was originally added to
204 * support detachEventBase, as a user callback may have called
205 * terminateLoopSoon(), but we want to make sure we detach. Also,
206 * detachEventBase almost always must be called from the base event
207 * loop to ensure the stack is unwound, since most users of
208 * EventBase are not thread safe.
210 * Ideally we would not need thisIteration, and instead just use
211 * runInLoop with loop() (instead of terminateLoopSoon).
213 void runInLoop(LoopCallback* callback, bool thisIteration = false);
216 * Convenience function to call runInLoop() with a std::function.
218 * This creates a LoopCallback object to wrap the std::function, and invoke
219 * the std::function when the loop callback fires. This is slightly more
220 * expensive than defining your own LoopCallback, but more convenient in
221 * areas that aren't performance sensitive where you just want to use
222 * std::bind. (std::bind is fairly slow on even by itself.)
224 * This method may only be called from the EventBase's thread. This
225 * essentially allows an event handler to schedule an additional callback to
226 * be invoked after it returns.
228 * Use runInEventBaseThread() to schedule functions from another thread.
230 void runInLoop(const Cob& c, bool thisIteration = false);
232 void runInLoop(Cob&& c, bool thisIteration = false);
235 * Run the specified function in the EventBase's thread.
237 * This method is thread-safe, and may be called from another thread.
239 * If runInEventBaseThread() is called when the EventBase loop is not
240 * running, the function call will be delayed until the next time the loop is
243 * If runInEventBaseThread() returns true the function has successfully been
244 * scheduled to run in the loop thread. However, if the loop is terminated
245 * (and never later restarted) before it has a chance to run the requested
246 * function, the function may never be run at all. The caller is responsible
247 * for handling this situation correctly if they may terminate the loop with
248 * outstanding runInEventBaseThread() calls pending.
250 * If two calls to runInEventBaseThread() are made from the same thread, the
251 * functions will always be run in the order that they were scheduled.
252 * Ordering between functions scheduled from separate threads is not
255 * @param fn The function to run. The function must not throw any
257 * @param arg An argument to pass to the function.
259 * @return Returns true if the function was successfully scheduled, or false
260 * if there was an error scheduling the function.
263 bool runInEventBaseThread(void (*fn)(T*), T* arg) {
264 return runInEventBaseThread(reinterpret_cast<void (*)(void*)>(fn),
265 reinterpret_cast<void*>(arg));
268 bool runInEventBaseThread(void (*fn)(void*), void* arg);
271 * Run the specified function in the EventBase's thread
273 * This version of runInEventBaseThread() takes a std::function object.
274 * Note that this is less efficient than the version that takes a plain
275 * function pointer and void* argument, as it has to allocate memory to copy
276 * the std::function object.
278 * If the EventBase loop is terminated before it has a chance to run this
279 * function, the allocated memory will be leaked. The caller is responsible
280 * for ensuring that the EventBase loop is not terminated before this
283 * The function must not throw any exceptions.
285 bool runInEventBaseThread(const Cob& fn);
288 * Runs the given Cob at some time after the specified number of
289 * milliseconds. (No guarantees exactly when.)
291 * @return true iff the cob was successfully registered.
296 TimeoutManager::InternalEnum = TimeoutManager::InternalEnum::NORMAL);
299 * Set the maximum desired latency in us and provide a callback which will be
300 * called when that latency is exceeded.
302 void setMaxLatency(int64_t maxLatency, const Cob& maxLatencyCob) {
303 maxLatency_ = maxLatency;
304 maxLatencyCob_ = maxLatencyCob;
308 * Set smoothing coefficient for loop load average; # of milliseconds
309 * for exp(-1) (1/2.71828...) decay.
311 void setLoadAvgMsec(uint32_t ms);
314 * reset the load average to a desired value
316 void resetLoadAvg(double value = 0.0);
319 * Get the average loop time in microseconds (an exponentially-smoothed ave)
321 double getAvgLoopTime() const {
322 return avgLoopTime_.get();
326 * check if the event base loop is running.
328 bool isRunning() const {
329 return loopThread_.load(std::memory_order_relaxed) != 0;
333 * wait until the event loop starts (after starting the event loop thread).
335 void waitUntilRunning();
337 int getNotificationQueueSize() const;
340 * Verify that current thread is the EventBase thread, if the EventBase is
343 bool isInEventBaseThread() const {
344 auto tid = loopThread_.load(std::memory_order_relaxed);
345 return tid == 0 || pthread_equal(tid, pthread_self());
348 bool inRunningEventBaseThread() const {
349 return pthread_equal(
350 loopThread_.load(std::memory_order_relaxed), pthread_self());
353 // --------- interface to underlying libevent base ------------
354 // Avoid using these functions if possible. These functions are not
355 // guaranteed to always be present if we ever provide alternative EventBase
356 // implementations that do not use libevent internally.
357 event_base* getLibeventBase() const { return evb_; }
358 static const char* getLibeventVersion() { return event_get_version(); }
359 static const char* getLibeventMethod() { return event_get_method(); }
362 * only EventHandler/AsyncTimeout subclasses and ourselves should
365 * This is used to mark the beginning of a new loop cycle by the
366 * first handler fired within that cycle.
369 bool bumpHandlingTime();
371 class SmoothLoopTime {
373 explicit SmoothLoopTime(uint64_t timeInterval)
374 : expCoeff_(-1.0/timeInterval)
376 , oldBusyLeftover_(0) {
377 VLOG(11) << "expCoeff_ " << expCoeff_ << " " << __PRETTY_FUNCTION__;
380 void setTimeInterval(uint64_t timeInterval);
381 void reset(double value = 0.0);
383 void addSample(int64_t idle, int64_t busy);
389 void dampen(double factor) {
396 int64_t oldBusyLeftover_;
400 const std::shared_ptr<EventBaseObserver>& observer) {
401 observer_ = observer;
404 const std::shared_ptr<EventBaseObserver>& getObserver() {
409 * Set the name of the thread that runs this event base.
411 void setName(const std::string& name);
414 * Returns the name of the thread that runs this event base.
416 const std::string& getName();
421 void attachTimeoutManager(AsyncTimeout* obj,
422 TimeoutManager::InternalEnum internal);
424 void detachTimeoutManager(AsyncTimeout* obj);
426 bool scheduleTimeout(AsyncTimeout* obj, std::chrono::milliseconds timeout);
428 void cancelTimeout(AsyncTimeout* obj);
430 bool isInTimeoutManagerThread() {
431 return isInEventBaseThread();
434 // Helper class used to short circuit runInEventBaseThread
435 class RunInLoopCallback : public LoopCallback {
437 RunInLoopCallback(void (*fn)(void*), void* arg);
438 void runLoopCallback() noexcept;
446 * Helper function that tells us whether we have already handled
447 * some event/timeout/callback in this loop iteration.
449 bool nothingHandledYet();
451 // --------- libevent callbacks (not for client use) ------------
453 static void runFunctionPtr(std::function<void()>* fn);
455 // small object used as a callback arg with enough info to execute the
456 // appropriate client-provided Cob
457 class CobTimeout : public AsyncTimeout {
459 CobTimeout(EventBase* b, const Cob& c, TimeoutManager::InternalEnum in)
460 : AsyncTimeout(b, in), cob_(c) {}
462 virtual void timeoutExpired() noexcept;
468 typedef boost::intrusive::list_member_hook<
469 boost::intrusive::link_mode<boost::intrusive::auto_unlink> > ListHook;
473 typedef boost::intrusive::list<
475 boost::intrusive::member_hook<CobTimeout, ListHook, &CobTimeout::hook>,
476 boost::intrusive::constant_time_size<false> > List;
479 typedef LoopCallback::List LoopCallbackList;
480 class FunctionRunner;
482 // executes any callbacks queued by runInLoop(); returns false if none found
483 bool runLoopCallbacks(bool setContext = true);
485 void initNotificationQueue();
487 CobTimeout::List pendingCobTimeouts_;
489 LoopCallbackList loopCallbacks_;
491 // This will be null most of the time, but point to currentCallbacks
492 // if we are in the middle of running loop callbacks, such that
493 // runInLoop(..., true) will always run in the current loop
495 LoopCallbackList* runOnceCallbacks_;
497 // stop_ is set by terminateLoopSoon() and is used by the main loop
498 // to determine if it should exit
501 // The ID of the thread running the main loop.
502 // 0 if loop is not running.
503 // Note: POSIX doesn't guarantee that 0 is an invalid pthread_t (or
504 // even that atomic<pthread_t> is valid), but that's how it is
505 // everywhere (at least on Linux, FreeBSD, and OSX).
506 std::atomic<pthread_t> loopThread_;
508 // pointer to underlying event_base class doing the heavy lifting
511 // A notification queue for runInEventBaseThread() to use
512 // to send function requests to the EventBase thread.
513 std::unique_ptr<NotificationQueue<std::pair<void (*)(void*), void*>>> queue_;
514 std::unique_ptr<FunctionRunner> fnRunner_;
516 // limit for latency in microseconds (0 disables)
519 // exponentially-smoothed average loop time for latency-limiting
520 SmoothLoopTime avgLoopTime_;
522 // smoothed loop time used to invoke latency callbacks; differs from
523 // avgLoopTime_ in that it's scaled down after triggering a callback
524 // to reduce spamminess
525 SmoothLoopTime maxLatencyLoopTime_;
527 // callback called when latency limit is exceeded
530 // we'll wait this long before running deferred callbacks if the event
532 static const int kDEFAULT_IDLE_WAIT_USEC = 20000; // 20ms
534 // Wrap-around loop counter to detect beginning of each loop
535 uint64_t nextLoopCnt_;
536 uint64_t latestLoopCnt_;
539 // Observer to export counters
540 std::shared_ptr<EventBaseObserver> observer_;
541 uint32_t observerSampleCount_;
543 // Name of the thread running this EventBase