3dff28cf9b
Summary: For performance purposes, the lower level routines were changed to use a SystemClock* instead of a std::shared_ptr<SystemClock>. The shared ptr has some performance degradation on certain hardware classes. For most of the system, there is no risk of the pointer being deleted/invalid because the shared_ptr will be stored elsewhere. For example, the ImmutableDBOptions stores the Env which has a std::shared_ptr<SystemClock> in it. The SystemClock* within the ImmutableDBOptions is essentially a "short cut" to gain access to this constant resource. There were a few classes (PeriodicWorkScheduler?) where the "short cut" property did not hold. In those cases, the shared pointer was preserved. Using db_bench readrandom perf_level=3 on my EC2 box, this change performed as well or better than 6.17: 6.17: readrandom : 28.046 micros/op 854902 ops/sec; 61.3 MB/s (355999 of 355999 found) 6.18: readrandom : 32.615 micros/op 735306 ops/sec; 52.7 MB/s (290999 of 290999 found) PR: readrandom : 27.500 micros/op 871909 ops/sec; 62.5 MB/s (367999 of 367999 found) (Note that the times for 6.18 are prior to revert of the SystemClock). Pull Request resolved: https://github.com/facebook/rocksdb/pull/8033 Reviewed By: pdillinger Differential Revision: D27014563 Pulled By: mrambacher fbshipit-source-id: ad0459eba03182e454391b5926bf5cdd45657b67
332 lines
9.5 KiB
C++
332 lines
9.5 KiB
C++
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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//
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#pragma once
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#include <functional>
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#include <memory>
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#include <queue>
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#include <unordered_map>
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#include <utility>
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#include <vector>
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#include "monitoring/instrumented_mutex.h"
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#include "rocksdb/system_clock.h"
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#include "test_util/sync_point.h"
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#include "util/mutexlock.h"
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namespace ROCKSDB_NAMESPACE {
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// A Timer class to handle repeated work.
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//
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// `Start()` and `Shutdown()` are currently not thread-safe. The client must
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// serialize calls to these two member functions.
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//
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// A single timer instance can handle multiple functions via a single thread.
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// It is better to leave long running work to a dedicated thread pool.
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//
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// Timer can be started by calling `Start()`, and ended by calling `Shutdown()`.
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// Work (in terms of a `void function`) can be scheduled by calling `Add` with
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// a unique function name and de-scheduled by calling `Cancel`.
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// Many functions can be added.
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//
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// Impl Details:
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// A heap is used to keep track of when the next timer goes off.
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// A map from a function name to the function keeps track of all the functions.
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class Timer {
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public:
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explicit Timer(SystemClock* clock)
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: clock_(clock),
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mutex_(clock),
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cond_var_(&mutex_),
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running_(false),
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executing_task_(false) {}
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~Timer() { Shutdown(); }
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// Add a new function to run.
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// fn_name has to be identical, otherwise, the new one overrides the existing
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// one, regardless if the function is pending removed (invalid) or not.
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// start_after_us is the initial delay.
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// repeat_every_us is the interval between ending time of the last call and
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// starting time of the next call. For example, repeat_every_us = 2000 and
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// the function takes 1000us to run. If it starts at time [now]us, then it
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// finishes at [now]+1000us, 2nd run starting time will be at [now]+3000us.
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// repeat_every_us == 0 means do not repeat.
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void Add(std::function<void()> fn,
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const std::string& fn_name,
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uint64_t start_after_us,
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uint64_t repeat_every_us) {
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std::unique_ptr<FunctionInfo> fn_info(new FunctionInfo(
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std::move(fn), fn_name, clock_->NowMicros() + start_after_us,
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repeat_every_us));
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{
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InstrumentedMutexLock l(&mutex_);
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auto it = map_.find(fn_name);
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if (it == map_.end()) {
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heap_.push(fn_info.get());
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map_.emplace(std::make_pair(fn_name, std::move(fn_info)));
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} else {
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// If it already exists, overriding it.
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it->second->fn = std::move(fn_info->fn);
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it->second->valid = true;
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it->second->next_run_time_us = clock_->NowMicros() + start_after_us;
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it->second->repeat_every_us = repeat_every_us;
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}
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}
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cond_var_.SignalAll();
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}
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void Cancel(const std::string& fn_name) {
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InstrumentedMutexLock l(&mutex_);
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// Mark the function with fn_name as invalid so that it will not be
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// requeued.
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auto it = map_.find(fn_name);
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if (it != map_.end() && it->second) {
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it->second->Cancel();
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}
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// If the currently running function is fn_name, then we need to wait
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// until it finishes before returning to caller.
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while (!heap_.empty() && executing_task_) {
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FunctionInfo* func_info = heap_.top();
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assert(func_info);
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if (func_info->name == fn_name) {
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WaitForTaskCompleteIfNecessary();
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} else {
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break;
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}
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}
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}
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void CancelAll() {
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InstrumentedMutexLock l(&mutex_);
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CancelAllWithLock();
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}
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// Start the Timer
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bool Start() {
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InstrumentedMutexLock l(&mutex_);
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if (running_) {
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return false;
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}
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running_ = true;
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thread_.reset(new port::Thread(&Timer::Run, this));
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return true;
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}
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// Shutdown the Timer
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bool Shutdown() {
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{
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InstrumentedMutexLock l(&mutex_);
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if (!running_) {
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return false;
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}
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running_ = false;
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CancelAllWithLock();
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cond_var_.SignalAll();
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}
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if (thread_) {
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thread_->join();
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}
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return true;
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}
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bool HasPendingTask() const {
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InstrumentedMutexLock l(&mutex_);
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for (auto it = map_.begin(); it != map_.end(); it++) {
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if (it->second->IsValid()) {
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return true;
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}
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}
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return false;
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}
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#ifndef NDEBUG
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// Wait until Timer starting waiting, call the optional callback, then wait
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// for Timer waiting again.
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// Tests can provide a custom Clock object to mock time, and use the callback
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// here to bump current time and trigger Timer. See timer_test for example.
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//
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// Note: only support one caller of this method.
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void TEST_WaitForRun(std::function<void()> callback = nullptr) {
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InstrumentedMutexLock l(&mutex_);
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// It act as a spin lock
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while (executing_task_ ||
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(!heap_.empty() &&
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heap_.top()->next_run_time_us <= clock_->NowMicros())) {
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cond_var_.TimedWait(clock_->NowMicros() + 1000);
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}
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if (callback != nullptr) {
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callback();
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}
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cond_var_.SignalAll();
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do {
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cond_var_.TimedWait(clock_->NowMicros() + 1000);
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} while (executing_task_ ||
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(!heap_.empty() &&
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heap_.top()->next_run_time_us <= clock_->NowMicros()));
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}
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size_t TEST_GetPendingTaskNum() const {
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InstrumentedMutexLock l(&mutex_);
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size_t ret = 0;
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for (auto it = map_.begin(); it != map_.end(); it++) {
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if (it->second->IsValid()) {
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ret++;
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}
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}
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return ret;
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}
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#endif // NDEBUG
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private:
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void Run() {
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InstrumentedMutexLock l(&mutex_);
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while (running_) {
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if (heap_.empty()) {
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// wait
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TEST_SYNC_POINT("Timer::Run::Waiting");
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cond_var_.Wait();
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continue;
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}
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FunctionInfo* current_fn = heap_.top();
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assert(current_fn);
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if (!current_fn->IsValid()) {
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heap_.pop();
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map_.erase(current_fn->name);
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continue;
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}
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if (current_fn->next_run_time_us <= clock_->NowMicros()) {
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// make a copy of the function so it won't be changed after
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// mutex_.unlock.
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std::function<void()> fn = current_fn->fn;
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executing_task_ = true;
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mutex_.Unlock();
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// Execute the work
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fn();
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mutex_.Lock();
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executing_task_ = false;
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cond_var_.SignalAll();
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// Remove the work from the heap once it is done executing.
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// Note that we are just removing the pointer from the heap. Its
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// memory is still managed in the map (as it holds a unique ptr).
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// So current_fn is still a valid ptr.
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heap_.pop();
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// current_fn may be cancelled already.
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if (current_fn->IsValid() && current_fn->repeat_every_us > 0) {
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assert(running_);
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current_fn->next_run_time_us =
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clock_->NowMicros() + current_fn->repeat_every_us;
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// Schedule new work into the heap with new time.
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heap_.push(current_fn);
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}
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} else {
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cond_var_.TimedWait(current_fn->next_run_time_us);
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}
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}
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}
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void CancelAllWithLock() {
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mutex_.AssertHeld();
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if (map_.empty() && heap_.empty()) {
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return;
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}
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// With mutex_ held, set all tasks to invalid so that they will not be
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// re-queued.
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for (auto& elem : map_) {
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auto& func_info = elem.second;
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assert(func_info);
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func_info->Cancel();
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}
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// WaitForTaskCompleteIfNecessary() may release mutex_
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WaitForTaskCompleteIfNecessary();
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while (!heap_.empty()) {
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heap_.pop();
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}
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map_.clear();
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}
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// A wrapper around std::function to keep track when it should run next
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// and at what frequency.
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struct FunctionInfo {
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// the actual work
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std::function<void()> fn;
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// name of the function
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std::string name;
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// when the function should run next
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uint64_t next_run_time_us;
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// repeat interval
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uint64_t repeat_every_us;
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// controls whether this function is valid.
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// A function is valid upon construction and until someone explicitly
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// calls `Cancel()`.
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bool valid;
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FunctionInfo(std::function<void()>&& _fn, const std::string& _name,
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const uint64_t _next_run_time_us, uint64_t _repeat_every_us)
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: fn(std::move(_fn)),
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name(_name),
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next_run_time_us(_next_run_time_us),
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repeat_every_us(_repeat_every_us),
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valid(true) {}
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void Cancel() {
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valid = false;
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}
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bool IsValid() const { return valid; }
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};
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void WaitForTaskCompleteIfNecessary() {
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mutex_.AssertHeld();
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while (executing_task_) {
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TEST_SYNC_POINT("Timer::WaitForTaskCompleteIfNecessary:TaskExecuting");
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cond_var_.Wait();
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}
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}
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struct RunTimeOrder {
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bool operator()(const FunctionInfo* f1,
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const FunctionInfo* f2) {
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return f1->next_run_time_us > f2->next_run_time_us;
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}
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};
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SystemClock* clock_;
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// This mutex controls both the heap_ and the map_. It needs to be held for
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// making any changes in them.
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mutable InstrumentedMutex mutex_;
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InstrumentedCondVar cond_var_;
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std::unique_ptr<port::Thread> thread_;
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bool running_;
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bool executing_task_;
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std::priority_queue<FunctionInfo*,
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std::vector<FunctionInfo*>,
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RunTimeOrder> heap_;
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// In addition to providing a mapping from a function name to a function,
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// it is also responsible for memory management.
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std::unordered_map<std::string, std::unique_ptr<FunctionInfo>> map_;
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};
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} // namespace ROCKSDB_NAMESPACE
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