82 lines
2.7 KiB
C++
82 lines
2.7 KiB
C++
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/*
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* Copyright (c) Facebook, Inc. and its affiliates.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include <folly/futures/ThreadWheelTimekeeper.h>
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#include <folly/futures/WTCallback.h>
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#include <folly/Chrono.h>
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#include <folly/Singleton.h>
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#include <folly/futures/Future.h>
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#include <future>
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namespace folly {
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namespace {
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Singleton<ThreadWheelTimekeeper> timekeeperSingleton_;
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}
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ThreadWheelTimekeeper::ThreadWheelTimekeeper()
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: thread_([this] { eventBase_.loopForever(); }),
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wheelTimer_(
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HHWheelTimer::newTimer(&eventBase_, std::chrono::milliseconds(1))) {
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eventBase_.waitUntilRunning();
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eventBase_.runInEventBaseThread([this] {
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// 15 characters max
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eventBase_.setName("FutureTimekeepr");
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});
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}
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ThreadWheelTimekeeper::~ThreadWheelTimekeeper() {
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eventBase_.runInEventBaseThreadAndWait([this] {
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wheelTimer_->cancelAll();
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eventBase_.terminateLoopSoon();
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});
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thread_.join();
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}
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SemiFuture<Unit> ThreadWheelTimekeeper::after(HighResDuration dur) {
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auto cob = WTCallback<HHWheelTimer>::create(&eventBase_);
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auto f = cob->getSemiFuture();
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//
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// Even shared_ptr of cob is captured in lambda this is still somewhat *racy*
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// because it will be released once timeout is scheduled. So technically there
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// is no gurantee that EventBase thread can safely call timeout callback.
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// However due to fact that we are having circular reference here:
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// WTCallback->Promise->Core->WTCallbak, so three of them won't go away until
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// we break the circular reference. The break happens either in
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// WTCallback::timeoutExpired or WTCallback::interruptHandler. Former means
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// timeout callback is being safely executed. Latter captures shared_ptr of
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// WTCallback again in another lambda for canceling timeout. The moment
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// canceling timeout is executed in EventBase thread, the actual timeout
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// callback has either been executed, or will never be executed. So we are
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// fine here.
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//
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eventBase_.runInEventBaseThread([this, cob, dur] {
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wheelTimer_->scheduleTimeout(cob.get(), folly::chrono::ceil<Duration>(dur));
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});
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return f;
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}
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namespace detail {
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std::shared_ptr<Timekeeper> getTimekeeperSingleton() {
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return timekeeperSingleton_.try_get();
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}
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} // namespace detail
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} // namespace folly
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