2 * Copyright 2015 Facebook, Inc.
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8 * to you under the Apache License, Version 2.0 (the
9 * "License"); you may not use this file except in compliance
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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));
58 wheelGuard_ = DestructorGuard(wheel);
61 // Only update the now_ time if we're not in a timeout expired callback
62 if (wheel_->count_ == 0 && !wheel_->processingCallbacksGuard_) {
63 wheel_->now_ = getCurTime();
66 expiration_ = wheel_->now_ + timeout;
69 void HHWheelTimer::Callback::cancelTimeoutImpl() {
70 if (--wheel_->count_ <= 0) {
71 assert(wheel_->count_ == 0);
72 wheel_->AsyncTimeout::cancelTimeout();
77 wheelGuard_ = folly::none;
78 expiration_ = milliseconds(0);
81 HHWheelTimer::HHWheelTimer(folly::EventBase* eventBase,
82 std::chrono::milliseconds intervalMS,
83 AsyncTimeout::InternalEnum internal,
84 std::chrono::milliseconds defaultTimeoutMS)
85 : AsyncTimeout(eventBase, internal)
86 , interval_(intervalMS)
87 , defaultTimeout_(defaultTimeoutMS)
90 , catchupEveryN_(DEFAULT_CATCHUP_EVERY_N)
91 , expirationsSinceCatchup_(0)
92 , processingCallbacksGuard_(false)
96 HHWheelTimer::~HHWheelTimer() {
100 void HHWheelTimer::destroy() {
103 DelayedDestruction::destroy();
106 void HHWheelTimer::scheduleTimeoutImpl(Callback* callback,
107 std::chrono::milliseconds timeout) {
108 int64_t due = timeToWheelTicks(timeout) + nextTick_;
109 int64_t diff = due - nextTick_;
113 list = &buckets_[0][nextTick_ & WHEEL_MASK];
114 } else if (diff < WHEEL_SIZE) {
115 list = &buckets_[0][due & WHEEL_MASK];
116 } else if (diff < 1 << (2 * WHEEL_BITS)) {
117 list = &buckets_[1][(due >> WHEEL_BITS) & WHEEL_MASK];
118 } else if (diff < 1 << (3 * WHEEL_BITS)) {
119 list = &buckets_[2][(due >> 2 * WHEEL_BITS) & WHEEL_MASK];
121 /* in largest slot */
122 if (diff > LARGEST_SLOT) {
124 due = diff + nextTick_;
126 list = &buckets_[3][(due >> 3 * WHEEL_BITS) & WHEEL_MASK];
128 list->push_back(*callback);
131 void HHWheelTimer::scheduleTimeout(Callback* callback,
132 std::chrono::milliseconds timeout) {
133 // Cancel the callback if it happens to be scheduled already.
134 callback->cancelTimeout();
136 callback->context_ = RequestContext::saveContext();
138 if (count_ == 0 && !processingCallbacksGuard_) {
139 this->AsyncTimeout::scheduleTimeout(interval_.count());
142 callback->setScheduled(this, timeout);
143 scheduleTimeoutImpl(callback, timeout);
147 void HHWheelTimer::scheduleTimeout(Callback* callback) {
148 CHECK(std::chrono::milliseconds(-1) != defaultTimeout_)
149 << "Default timeout was not initialized";
150 scheduleTimeout(callback, defaultTimeout_);
153 bool HHWheelTimer::cascadeTimers(int bucket, int tick) {
155 cbs.swap(buckets_[bucket][tick]);
156 while (!cbs.empty()) {
157 auto* cb = &cbs.front();
159 scheduleTimeoutImpl(cb, cb->getTimeRemaining(now_));
162 // If tick is zero, timeoutExpired will cascade the next bucket.
166 void HHWheelTimer::timeoutExpired() noexcept {
167 // If destroy() is called inside timeoutExpired(), delay actual destruction
168 // until timeoutExpired() returns
169 DestructorGuard dg(this);
170 // If scheduleTimeout is called from a callback in this function, it may
171 // cause inconsistencies in the state of this object. As such, we need
172 // to treat these calls slightly differently.
173 processingCallbacksGuard_ = true;
174 auto reEntryGuard = folly::makeGuard([&] {
175 processingCallbacksGuard_ = false;
178 // timeoutExpired() can only be invoked directly from the event base loop.
179 // It should never be invoked recursively.
181 milliseconds catchup = now_ + interval_;
182 // If catchup is enabled, we may have missed multiple intervals, use
183 // currentTime() to check exactly.
184 if (++expirationsSinceCatchup_ >= catchupEveryN_) {
185 catchup = std::chrono::duration_cast<milliseconds>(
186 std::chrono::steady_clock::now().time_since_epoch());
187 expirationsSinceCatchup_ = 0;
189 while (now_ < catchup) {
192 int idx = nextTick_ & WHEEL_MASK;
195 if (cascadeTimers(1, (nextTick_ >> WHEEL_BITS) & WHEEL_MASK) &&
196 cascadeTimers(2, (nextTick_ >> (2 * WHEEL_BITS)) & WHEEL_MASK)) {
197 cascadeTimers(3, (nextTick_ >> (3 * WHEEL_BITS)) & WHEEL_MASK);
202 CallbackList* cbs = &buckets_[0][idx];
203 while (!cbs->empty()) {
204 auto* cb = &cbs->front();
207 cb->wheel_ = nullptr;
208 cb->expiration_ = milliseconds(0);
210 RequestContext::setContext(cb->context_);
211 cb->timeoutExpired();
212 RequestContext::setContext(old_ctx);
216 this->AsyncTimeout::scheduleTimeout(interval_.count());
220 size_t HHWheelTimer::cancelAll() {
224 decltype(buckets_) buckets;
226 // Work around std::swap() bug in libc++
228 // http://llvm.org/bugs/show_bug.cgi?id=22106
230 for (size_t i = 0; i < WHEEL_BUCKETS; ++i) {
231 for (size_t ii = 0; ii < WHEEL_SIZE; ++ii) {
232 std::swap(buckets_[i][ii], buckets[i][ii]);
236 std::swap(buckets, buckets_);
239 for (auto& tick : buckets) {
240 for (auto& bucket : tick) {
241 while (!bucket.empty()) {
242 auto& cb = bucket.front();
244 cb.callbackCanceled();