87 lines
2.0 KiB
C++
87 lines
2.0 KiB
C++
/*
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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/system/Pid.h>
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#include <atomic>
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#include <glog/logging.h>
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#include <folly/detail/AtFork.h>
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namespace folly {
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namespace {
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enum class State : uint8_t { INVALID, LOCKED, VALID };
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class PidState {
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std::atomic<State> value_{State::INVALID};
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public:
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FOLLY_ALWAYS_INLINE State load() noexcept {
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return value_.load(std::memory_order_acquire);
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}
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void store(State state) noexcept {
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value_.store(state, std::memory_order_release);
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}
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bool cas(State& expected, State newstate) noexcept {
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return value_.compare_exchange_strong(
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expected,
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newstate,
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std::memory_order_relaxed,
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std::memory_order_relaxed);
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}
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}; // PidState
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class PidCache {
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PidState state_;
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pid_t pid_;
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public:
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FOLLY_ALWAYS_INLINE pid_t get() {
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DCHECK(!valid() || pid_ == getpid());
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return valid() ? pid_ : init();
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}
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private:
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bool valid() { return state_.load() == State::VALID; }
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FOLLY_COLD pid_t init() {
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pid_t pid = getpid();
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auto s = state_.load();
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if (s == State::INVALID && state_.cas(s, State::LOCKED)) {
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folly::detail::AtFork::registerHandler(
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this, [] { return true; }, [] {}, [this] { pid_ = getpid(); });
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pid_ = pid;
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state_.store(State::VALID);
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}
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return pid;
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}
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}; // PidCache
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static PidCache cache_;
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} // namespace
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pid_t get_cached_pid() {
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return cache_.get();
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}
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} // namespace folly
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