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_;
137 typedef boost::intrusive::list_member_hook<
138 boost::intrusive::link_mode<boost::intrusive::auto_unlink> > ListHook;
142 typedef boost::intrusive::list<
144 boost::intrusive::member_hook<Callback, ListHook, &Callback::hook_>,
145 boost::intrusive::constant_time_size<false> > List;
147 std::shared_ptr<RequestContext> context_;
149 // Give HHWheelTimer direct access to our members so it can take care
150 // of scheduling/cancelling.
151 friend class HHWheelTimer;
155 * Create a new HHWheelTimer with the specified interval and the
156 * default timeout value set.
158 * Objects created using this version of constructor can be used
159 * to schedule both variable interval timeouts using
160 * scheduleTimeout(callback, timeout) method, and default
161 * interval timeouts using scheduleTimeout(callback) method.
163 static int DEFAULT_TICK_INTERVAL;
164 explicit HHWheelTimer(
165 folly::TimeoutManager* timeoutManager,
166 std::chrono::milliseconds intervalMS =
167 std::chrono::milliseconds(DEFAULT_TICK_INTERVAL),
168 AsyncTimeout::InternalEnum internal = AsyncTimeout::InternalEnum::NORMAL,
169 std::chrono::milliseconds defaultTimeoutMS =
170 std::chrono::milliseconds(-1));
173 * Cancel all outstanding timeouts
175 * @returns the number of timeouts that were cancelled.
180 * Get the tick interval for this HHWheelTimer.
182 * Returns the tick interval in milliseconds.
184 std::chrono::milliseconds getTickInterval() const {
189 * Get the default timeout interval for this HHWheelTimer.
191 * Returns the timeout interval in milliseconds.
193 std::chrono::milliseconds getDefaultTimeout() const {
194 return defaultTimeout_;
198 * Schedule the specified Callback to be invoked after the
199 * specified timeout interval.
201 * If the callback is already scheduled, this cancels the existing timeout
202 * before scheduling the new timeout.
204 void scheduleTimeout(Callback* callback,
205 std::chrono::milliseconds timeout);
206 void scheduleTimeoutImpl(Callback* callback,
207 std::chrono::milliseconds timeout);
210 * Schedule the specified Callback to be invoked after the
211 * default timeout interval.
213 * If the callback is already scheduled, this cancels the existing timeout
214 * before scheduling the new timeout.
216 * This method uses CHECK() to make sure that the default timeout was
217 * specified on the object initialization.
219 void scheduleTimeout(Callback* callback);
222 void scheduleTimeoutFn(F fn, std::chrono::milliseconds timeout) {
223 struct Wrapper : Callback {
224 Wrapper(F f) : fn_(std::move(f)) {}
225 void timeoutExpired() noexcept override {
228 } catch (std::exception const& e) {
229 LOG(ERROR) << "HHWheelTimer timeout callback threw an exception: "
232 LOG(ERROR) << "HHWheelTimer timeout callback threw a non-exception.";
238 Wrapper* w = new Wrapper(std::move(fn));
239 scheduleTimeout(w, timeout);
243 * Return the number of currently pending timeouts
245 uint64_t count() const {
249 bool isDetachable() const {
250 return !folly::AsyncTimeout::isScheduled();
253 using folly::AsyncTimeout::attachEventBase;
254 using folly::AsyncTimeout::detachEventBase;
255 using folly::AsyncTimeout::getTimeoutManager;
259 * Protected destructor.
261 * Use destroy() instead. See the comments in DelayedDestruction for more
264 virtual ~HHWheelTimer();
267 // Forbidden copy constructor and assignment operator
268 HHWheelTimer(HHWheelTimer const &) = delete;
269 HHWheelTimer& operator=(HHWheelTimer const &) = delete;
271 // Methods inherited from AsyncTimeout
272 virtual void timeoutExpired() noexcept;
274 std::chrono::milliseconds interval_;
275 std::chrono::milliseconds defaultTimeout_;
277 static constexpr int WHEEL_BUCKETS = 4;
278 static constexpr int WHEEL_BITS = 8;
279 static constexpr unsigned int WHEEL_SIZE = (1 << WHEEL_BITS);
280 static constexpr unsigned int WHEEL_MASK = (WHEEL_SIZE - 1);
281 static constexpr uint32_t LARGEST_SLOT = 0xffffffffUL;
283 typedef Callback::List CallbackList;
284 CallbackList buckets_[WHEEL_BUCKETS][WHEEL_SIZE];
285 std::vector<uint64_t> bitmap_;
287 int64_t timeToWheelTicks(std::chrono::milliseconds t) {
288 return t.count() / interval_.count();
291 bool cascadeTimers(int bucket, int tick);
295 std::chrono::milliseconds startTime_;
297 int64_t calcNextTick();
299 void scheduleNextTimeout();
301 bool* processingCallbacksGuard_;
302 CallbackList timeouts; // Timeouts queued to run
304 std::chrono::milliseconds getCurTime() {
305 return std::chrono::duration_cast<std::chrono::milliseconds>(
306 std::chrono::steady_clock::now().time_since_epoch());