2 * Copyright 2016 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 <folly/Optional.h>
20 #include <folly/io/async/AsyncTimeout.h>
21 #include <folly/io/async/DelayedDestruction.h>
23 #include <boost/intrusive/list.hpp>
24 #include <glog/logging.h>
34 * Hashed Hierarchical Wheel Timer
36 * We model timers as the number of ticks until the next
37 * due event. We allow 32-bits of space to track this
38 * due interval, and break that into 4 regions of 8 bits.
39 * Each region indexes into a bucket of 256 lists.
41 * Bucket 0 represents those events that are due the soonest.
42 * Each tick causes us to look at the next list in a bucket.
43 * The 0th list in a bucket is special; it means that it is time to
44 * flush the timers from the next higher bucket and schedule them
45 * into a different bucket.
47 * This technique results in a very cheap mechanism for
48 * maintaining time and timers.
50 * Unlike the original timer wheel paper, this implementation does
51 * *not* tick constantly, and instead calculates the exact next wakeup
54 class HHWheelTimer : private folly::AsyncTimeout,
55 public folly::DelayedDestruction {
57 // This type has always been a misnomer, because it is not a unique pointer.
58 using UniquePtr = std::unique_ptr<HHWheelTimer, Destructor>;
59 using SharedPtr = std::shared_ptr<HHWheelTimer>;
61 template <typename... Args>
62 static UniquePtr newTimer(Args&&... args) {
63 return UniquePtr(new HHWheelTimer(std::forward<Args>(args)...));
67 * A callback to be notified when a timeout has expired.
78 * timeoutExpired() is invoked when the timeout has expired.
80 virtual void timeoutExpired() noexcept = 0;
82 /// This callback was canceled. The default implementation is to just
83 /// proxy to `timeoutExpired` but if you care about the difference between
84 /// the timeout finishing or being canceled you can override this.
85 virtual void callbackCanceled() noexcept {
90 * Cancel the timeout, if it is running.
92 * If the timeout is not scheduled, cancelTimeout() does nothing.
94 void cancelTimeout() {
95 if (wheel_ == nullptr) {
96 // We're not scheduled, so there's nothing to do.
103 * Return true if this timeout is currently scheduled, and false otherwise.
105 bool isScheduled() const {
106 return wheel_ != nullptr;
111 * Don't override this unless you're doing a test. This is mainly here so
112 * that we can override it to simulate lag in steady_clock.
114 virtual std::chrono::milliseconds getCurTime() {
115 return std::chrono::duration_cast<std::chrono::milliseconds>(
116 std::chrono::steady_clock::now().time_since_epoch());
120 // Get the time remaining until this timeout expires
121 std::chrono::milliseconds getTimeRemaining(
122 std::chrono::milliseconds now) const {
123 if (now >= expiration_) {
124 return std::chrono::milliseconds(0);
126 return expiration_ - now;
129 void setScheduled(HHWheelTimer* wheel,
130 std::chrono::milliseconds);
131 void cancelTimeoutImpl();
133 HHWheelTimer* wheel_;
134 std::chrono::milliseconds expiration_;
136 typedef boost::intrusive::list_member_hook<
137 boost::intrusive::link_mode<boost::intrusive::auto_unlink> > ListHook;
141 typedef boost::intrusive::list<
143 boost::intrusive::member_hook<Callback, ListHook, &Callback::hook_>,
144 boost::intrusive::constant_time_size<false> > List;
146 std::shared_ptr<RequestContext> context_;
148 // Give HHWheelTimer direct access to our members so it can take care
149 // of scheduling/cancelling.
150 friend class HHWheelTimer;
154 * Create a new HHWheelTimer with the specified interval and the
155 * default timeout value set.
157 * Objects created using this version of constructor can be used
158 * to schedule both variable interval timeouts using
159 * scheduleTimeout(callback, timeout) method, and default
160 * interval timeouts using scheduleTimeout(callback) method.
162 static int DEFAULT_TICK_INTERVAL;
163 explicit HHWheelTimer(
164 folly::TimeoutManager* timeoutManager,
165 std::chrono::milliseconds intervalMS =
166 std::chrono::milliseconds(DEFAULT_TICK_INTERVAL),
167 AsyncTimeout::InternalEnum internal = AsyncTimeout::InternalEnum::NORMAL,
168 std::chrono::milliseconds defaultTimeoutMS =
169 std::chrono::milliseconds(-1));
172 * Cancel all outstanding timeouts
174 * @returns the number of timeouts that were cancelled.
179 * Get the tick interval for this HHWheelTimer.
181 * Returns the tick interval in milliseconds.
183 std::chrono::milliseconds getTickInterval() const {
188 * Get the default timeout interval for this HHWheelTimer.
190 * Returns the timeout interval in milliseconds.
192 std::chrono::milliseconds getDefaultTimeout() const {
193 return defaultTimeout_;
197 * Schedule the specified Callback to be invoked after the
198 * specified timeout interval.
200 * If the callback is already scheduled, this cancels the existing timeout
201 * before scheduling the new timeout.
203 void scheduleTimeout(Callback* callback,
204 std::chrono::milliseconds timeout);
205 void scheduleTimeoutImpl(Callback* callback,
206 std::chrono::milliseconds timeout);
209 * Schedule the specified Callback to be invoked after the
210 * default timeout interval.
212 * If the callback is already scheduled, this cancels the existing timeout
213 * before scheduling the new timeout.
215 * This method uses CHECK() to make sure that the default timeout was
216 * specified on the object initialization.
218 void scheduleTimeout(Callback* callback);
221 void scheduleTimeoutFn(F fn, std::chrono::milliseconds timeout) {
222 struct Wrapper : Callback {
223 Wrapper(F f) : fn_(std::move(f)) {}
224 void timeoutExpired() noexcept override {
227 } catch (std::exception const& e) {
228 LOG(ERROR) << "HHWheelTimer timeout callback threw an exception: "
231 LOG(ERROR) << "HHWheelTimer timeout callback threw a non-exception.";
237 Wrapper* w = new Wrapper(std::move(fn));
238 scheduleTimeout(w, timeout);
242 * Return the number of currently pending timeouts
244 uint64_t count() const {
248 bool isDetachable() const {
249 return !folly::AsyncTimeout::isScheduled();
252 using folly::AsyncTimeout::attachEventBase;
253 using folly::AsyncTimeout::detachEventBase;
254 using folly::AsyncTimeout::getTimeoutManager;
258 * Protected destructor.
260 * Use destroy() instead. See the comments in DelayedDestruction for more
263 virtual ~HHWheelTimer();
266 // Forbidden copy constructor and assignment operator
267 HHWheelTimer(HHWheelTimer const &) = delete;
268 HHWheelTimer& operator=(HHWheelTimer const &) = delete;
270 // Methods inherited from AsyncTimeout
271 virtual void timeoutExpired() noexcept;
273 std::chrono::milliseconds interval_;
274 std::chrono::milliseconds defaultTimeout_;
276 static constexpr int WHEEL_BUCKETS = 4;
277 static constexpr int WHEEL_BITS = 8;
278 static constexpr unsigned int WHEEL_SIZE = (1 << WHEEL_BITS);
279 static constexpr unsigned int WHEEL_MASK = (WHEEL_SIZE - 1);
280 static constexpr uint32_t LARGEST_SLOT = 0xffffffffUL;
282 typedef Callback::List CallbackList;
283 CallbackList buckets_[WHEEL_BUCKETS][WHEEL_SIZE];
285 int64_t timeToWheelTicks(std::chrono::milliseconds t) {
286 return t.count() / interval_.count();
289 bool cascadeTimers(int bucket, int tick);
293 std::chrono::milliseconds startTime_;
295 int64_t calcNextTick();
297 void scheduleNextTimeout();
299 bool* processingCallbacksGuard_;
300 CallbackList timeouts; // Timeouts queued to run
302 std::chrono::milliseconds getCurTime() {
303 return std::chrono::duration_cast<std::chrono::milliseconds>(
304 std::chrono::steady_clock::now().time_since_epoch());