2 * Copyright 2016 Facebook, Inc.
4 * Licensed to the Apache Software Foundation (ASF) under one
5 * or more contributor license agreements. See the NOTICE file
6 * distributed with this work for additional information
7 * regarding copyright ownership. The ASF licenses this file
8 * to you under the Apache License, Version 2.0 (the
9 * "License"); you may not use this file except in compliance
10 * with the License. You may obtain a copy of the License at
12 * http://www.apache.org/licenses/LICENSE-2.0
14 * Unless required by applicable law or agreed to in writing,
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21 #include <folly/io/async/HHWheelTimer.h>
22 #include <folly/io/async/Request.h>
24 #include <folly/Optional.h>
25 #include <folly/ScopeGuard.h>
29 using std::chrono::milliseconds;
34 * We want to select the default interval carefully.
35 * An interval of 10ms will give us 10ms * WHEEL_SIZE^WHEEL_BUCKETS
36 * for the largest timeout possible, or about 497 days.
38 * For a lower bound, we want a reasonable limit on local IO, 10ms
41 * A shorter interval also has CPU implications, less than 1ms might
42 * start showing up in cpu perf. Also, it might not be possible to set
43 * tick interval less than 10ms on older kernels.
45 int HHWheelTimer::DEFAULT_TICK_INTERVAL = 10;
47 HHWheelTimer::Callback::~Callback() {
53 void HHWheelTimer::Callback::setScheduled(HHWheelTimer* wheel,
54 std::chrono::milliseconds timeout) {
55 assert(wheel_ == nullptr);
56 assert(expiration_ == milliseconds(0));
60 // Only update the now_ time if we're not in a timeout expired callback
61 if (wheel_->count_ == 0 && !wheel_->processingCallbacksGuard_) {
62 wheel_->now_ = getCurTime();
65 expiration_ = wheel_->now_ + timeout;
68 void HHWheelTimer::Callback::cancelTimeoutImpl() {
69 if (--wheel_->count_ <= 0) {
70 assert(wheel_->count_ == 0);
71 wheel_->AsyncTimeout::cancelTimeout();
76 expiration_ = milliseconds(0);
79 HHWheelTimer::HHWheelTimer(
80 folly::TimeoutManager* timeoutMananger,
81 std::chrono::milliseconds intervalMS,
82 AsyncTimeout::InternalEnum internal,
83 std::chrono::milliseconds defaultTimeoutMS)
84 : AsyncTimeout(timeoutMananger, internal),
85 interval_(intervalMS),
86 defaultTimeout_(defaultTimeoutMS),
89 catchupEveryN_(DEFAULT_CATCHUP_EVERY_N),
90 expirationsSinceCatchup_(0),
91 processingCallbacksGuard_(nullptr) {}
93 HHWheelTimer::~HHWheelTimer() {
94 // Ensure this gets done, but right before destruction finishes.
95 auto destructionPublisherGuard = folly::makeGuard([&] {
96 // Inform the subscriber that this instance is doomed.
97 if (processingCallbacksGuard_) {
98 *processingCallbacksGuard_ = true;
104 void HHWheelTimer::scheduleTimeoutImpl(Callback* callback,
105 std::chrono::milliseconds timeout) {
106 int64_t due = timeToWheelTicks(timeout) + nextTick_;
107 int64_t diff = due - nextTick_;
111 list = &buckets_[0][nextTick_ & WHEEL_MASK];
112 } else if (diff < WHEEL_SIZE) {
113 list = &buckets_[0][due & WHEEL_MASK];
114 } else if (diff < 1 << (2 * WHEEL_BITS)) {
115 list = &buckets_[1][(due >> WHEEL_BITS) & WHEEL_MASK];
116 } else if (diff < 1 << (3 * WHEEL_BITS)) {
117 list = &buckets_[2][(due >> 2 * WHEEL_BITS) & WHEEL_MASK];
119 /* in largest slot */
120 if (diff > LARGEST_SLOT) {
122 due = diff + nextTick_;
124 list = &buckets_[3][(due >> 3 * WHEEL_BITS) & WHEEL_MASK];
126 list->push_back(*callback);
129 void HHWheelTimer::scheduleTimeout(Callback* callback,
130 std::chrono::milliseconds timeout) {
131 // Cancel the callback if it happens to be scheduled already.
132 callback->cancelTimeout();
134 callback->context_ = RequestContext::saveContext();
136 if (count_ == 0 && !processingCallbacksGuard_) {
137 this->AsyncTimeout::scheduleTimeout(interval_.count());
140 callback->setScheduled(this, timeout);
141 scheduleTimeoutImpl(callback, timeout);
145 void HHWheelTimer::scheduleTimeout(Callback* callback) {
146 CHECK(std::chrono::milliseconds(-1) != defaultTimeout_)
147 << "Default timeout was not initialized";
148 scheduleTimeout(callback, defaultTimeout_);
151 bool HHWheelTimer::cascadeTimers(int bucket, int tick) {
153 cbs.swap(buckets_[bucket][tick]);
154 while (!cbs.empty()) {
155 auto* cb = &cbs.front();
157 scheduleTimeoutImpl(cb, cb->getTimeRemaining(now_));
160 // If tick is zero, timeoutExpired will cascade the next bucket.
164 void HHWheelTimer::timeoutExpired() noexcept {
165 // If the last smart pointer for "this" is reset inside the callback's
166 // timeoutExpired(), then the guard will detect that it is time to bail from
168 auto isDestroyed = false;
169 // If scheduleTimeout is called from a callback in this function, it may
170 // cause inconsistencies in the state of this object. As such, we need
171 // to treat these calls slightly differently.
172 CHECK(!processingCallbacksGuard_);
173 processingCallbacksGuard_ = &isDestroyed;
174 auto reEntryGuard = folly::makeGuard([&] {
176 processingCallbacksGuard_ = nullptr;
180 // timeoutExpired() can only be invoked directly from the event base loop.
181 // It should never be invoked recursively.
183 milliseconds catchup = now_ + interval_;
184 // If catchup is enabled, we may have missed multiple intervals, use
185 // currentTime() to check exactly.
186 if (++expirationsSinceCatchup_ >= catchupEveryN_) {
187 catchup = std::chrono::duration_cast<milliseconds>(
188 std::chrono::steady_clock::now().time_since_epoch());
189 expirationsSinceCatchup_ = 0;
191 while (now_ < catchup) {
194 int idx = nextTick_ & WHEEL_MASK;
197 if (cascadeTimers(1, (nextTick_ >> WHEEL_BITS) & WHEEL_MASK) &&
198 cascadeTimers(2, (nextTick_ >> (2 * WHEEL_BITS)) & WHEEL_MASK)) {
199 cascadeTimers(3, (nextTick_ >> (3 * WHEEL_BITS)) & WHEEL_MASK);
204 CallbackList* cbs = &buckets_[0][idx];
205 while (!cbs->empty()) {
206 auto* cb = &cbs->front();
209 cb->wheel_ = nullptr;
210 cb->expiration_ = milliseconds(0);
211 RequestContextScopeGuard rctx(cb->context_);
212 cb->timeoutExpired();
214 // The HHWheelTimer itself has been destroyed. The other callbacks
215 // will have been cancelled from the destructor. Bail before causing
222 this->AsyncTimeout::scheduleTimeout(interval_.count());
226 size_t HHWheelTimer::cancelAll() {
230 const uint64_t numElements = WHEEL_BUCKETS * WHEEL_SIZE;
231 auto maxBuckets = std::min(numElements, count_);
232 auto buckets = folly::make_unique<CallbackList[]>(maxBuckets);
233 size_t countBuckets = 0;
234 for (auto& tick : buckets_) {
235 for (auto& bucket : tick) {
236 if (bucket.empty()) {
239 for (auto& cb : bucket) {
242 std::swap(bucket, buckets[countBuckets++]);
243 if (count >= count_) {
249 for (size_t i = 0; i < countBuckets; ++i) {
250 auto& bucket = buckets[i];
251 while (!bucket.empty()) {
252 auto& cb = bucket.front();
254 cb.callbackCanceled();