rocksdb/util/timer.h

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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
//
#pragma once
#include <functional>
#include <memory>
#include <queue>
#include <unordered_map>
#include <utility>
#include <vector>
#include "monitoring/instrumented_mutex.h"
#include "rocksdb/system_clock.h"
#include "test_util/sync_point.h"
#include "util/mutexlock.h"
namespace ROCKSDB_NAMESPACE {
// A Timer class to handle repeated work.
//
// `Start()` and `Shutdown()` are currently not thread-safe. The client must
// serialize calls to these two member functions.
//
// A single timer instance can handle multiple functions via a single thread.
// It is better to leave long running work to a dedicated thread pool.
//
// Timer can be started by calling `Start()`, and ended by calling `Shutdown()`.
// Work (in terms of a `void function`) can be scheduled by calling `Add` with
// a unique function name and de-scheduled by calling `Cancel`.
// Many functions can be added.
//
// Impl Details:
// A heap is used to keep track of when the next timer goes off.
// A map from a function name to the function keeps track of all the functions.
class Timer {
public:
explicit Timer(SystemClock* clock)
: clock_(clock),
mutex_(clock),
cond_var_(&mutex_),
running_(false),
executing_task_(false) {}
~Timer() { Shutdown(); }
// Add a new function to run.
// fn_name has to be identical, otherwise it will fail to add and return false
// start_after_us is the initial delay.
// repeat_every_us is the interval between ending time of the last call and
// starting time of the next call. For example, repeat_every_us = 2000 and
// the function takes 1000us to run. If it starts at time [now]us, then it
// finishes at [now]+1000us, 2nd run starting time will be at [now]+3000us.
// repeat_every_us == 0 means do not repeat.
bool Add(std::function<void()> fn, const std::string& fn_name,
uint64_t start_after_us, uint64_t repeat_every_us) {
auto fn_info = std::make_unique<FunctionInfo>(std::move(fn), fn_name, 0,
repeat_every_us);
InstrumentedMutexLock l(&mutex_);
// Assign time within mutex to make sure the next_run_time is larger than
// the current running one
fn_info->next_run_time_us = clock_->NowMicros() + start_after_us;
// the new task start time should never before the current task executing
// time, as the executing task can only be running if it's next_run_time_us
// is due (<= clock_->NowMicros()).
if (executing_task_ &&
fn_info->next_run_time_us < heap_.top()->next_run_time_us) {
return false;
}
auto it = map_.find(fn_name);
if (it == map_.end()) {
heap_.push(fn_info.get());
map_.try_emplace(fn_name, std::move(fn_info));
} else {
// timer doesn't support duplicated function name
return false;
}
cond_var_.SignalAll();
return true;
}
void Cancel(const std::string& fn_name) {
InstrumentedMutexLock l(&mutex_);
// Mark the function with fn_name as invalid so that it will not be
// requeued.
auto it = map_.find(fn_name);
if (it != map_.end() && it->second) {
it->second->Cancel();
}
// If the currently running function is fn_name, then we need to wait
// until it finishes before returning to caller.
while (!heap_.empty() && executing_task_) {
FunctionInfo* func_info = heap_.top();
assert(func_info);
if (func_info->name == fn_name) {
WaitForTaskCompleteIfNecessary();
} else {
break;
}
}
}
void CancelAll() {
InstrumentedMutexLock l(&mutex_);
CancelAllWithLock();
}
// Start the Timer
bool Start() {
InstrumentedMutexLock l(&mutex_);
if (running_) {
return false;
}
running_ = true;
thread_ = std::make_unique<port::Thread>(&Timer::Run, this);
return true;
}
// Shutdown the Timer
bool Shutdown() {
{
InstrumentedMutexLock l(&mutex_);
if (!running_) {
return false;
}
running_ = false;
CancelAllWithLock();
cond_var_.SignalAll();
}
if (thread_) {
thread_->join();
}
return true;
}
bool HasPendingTask() const {
InstrumentedMutexLock l(&mutex_);
for (const auto& fn_info : map_) {
if (fn_info.second->IsValid()) {
return true;
}
}
return false;
}
#ifndef NDEBUG
// Wait until Timer starting waiting, call the optional callback, then wait
// for Timer waiting again.
// Tests can provide a custom Clock object to mock time, and use the callback
// here to bump current time and trigger Timer. See timer_test for example.
//
// Note: only support one caller of this method.
void TEST_WaitForRun(const std::function<void()>& callback = nullptr) {
InstrumentedMutexLock l(&mutex_);
// It act as a spin lock
while (executing_task_ ||
(!heap_.empty() &&
heap_.top()->next_run_time_us <= clock_->NowMicros())) {
cond_var_.TimedWait(clock_->NowMicros() + 1000);
}
if (callback != nullptr) {
callback();
}
cond_var_.SignalAll();
do {
cond_var_.TimedWait(clock_->NowMicros() + 1000);
} while (executing_task_ ||
(!heap_.empty() &&
heap_.top()->next_run_time_us <= clock_->NowMicros()));
}
size_t TEST_GetPendingTaskNum() const {
InstrumentedMutexLock l(&mutex_);
size_t ret = 0;
for (const auto& fn_info : map_) {
if (fn_info.second->IsValid()) {
ret++;
}
}
return ret;
}
#endif // NDEBUG
private:
void Run() {
InstrumentedMutexLock l(&mutex_);
while (running_) {
if (heap_.empty()) {
// wait
TEST_SYNC_POINT("Timer::Run::Waiting");
cond_var_.Wait();
continue;
}
FunctionInfo* current_fn = heap_.top();
assert(current_fn);
if (!current_fn->IsValid()) {
heap_.pop();
map_.erase(current_fn->name);
continue;
}
if (current_fn->next_run_time_us <= clock_->NowMicros()) {
// make a copy of the function so it won't be changed after
// mutex_.unlock.
std::function<void()> fn = current_fn->fn;
executing_task_ = true;
mutex_.Unlock();
// Execute the work
fn();
mutex_.Lock();
executing_task_ = false;
cond_var_.SignalAll();
// Remove the work from the heap once it is done executing, make sure
// it's the same function after executing the work while mutex is
// released.
// Note that we are just removing the pointer from the heap. Its
// memory is still managed in the map (as it holds a unique ptr).
// So current_fn is still a valid ptr.
assert(heap_.top() == current_fn);
heap_.pop();
// current_fn may be cancelled already.
if (current_fn->IsValid() && current_fn->repeat_every_us > 0) {
assert(running_);
current_fn->next_run_time_us =
clock_->NowMicros() + current_fn->repeat_every_us;
// Schedule new work into the heap with new time.
heap_.push(current_fn);
} else {
// if current_fn is cancelled or no need to repeat, remove it from the
// map to avoid leak.
map_.erase(current_fn->name);
}
} else {
cond_var_.TimedWait(current_fn->next_run_time_us);
}
}
}
void CancelAllWithLock() {
mutex_.AssertHeld();
if (map_.empty() && heap_.empty()) {
return;
}
// With mutex_ held, set all tasks to invalid so that they will not be
// re-queued.
for (auto& elem : map_) {
auto& func_info = elem.second;
assert(func_info);
func_info->Cancel();
}
// WaitForTaskCompleteIfNecessary() may release mutex_
WaitForTaskCompleteIfNecessary();
while (!heap_.empty()) {
heap_.pop();
}
map_.clear();
}
// A wrapper around std::function to keep track when it should run next
// and at what frequency.
struct FunctionInfo {
// the actual work
std::function<void()> fn;
// name of the function
std::string name;
// when the function should run next
uint64_t next_run_time_us;
// repeat interval
uint64_t repeat_every_us;
// controls whether this function is valid.
// A function is valid upon construction and until someone explicitly
// calls `Cancel()`.
bool valid;
FunctionInfo(std::function<void()>&& _fn, std::string _name,
const uint64_t _next_run_time_us, uint64_t _repeat_every_us)
: fn(std::move(_fn)),
name(std::move(_name)),
next_run_time_us(_next_run_time_us),
repeat_every_us(_repeat_every_us),
valid(true) {}
void Cancel() {
valid = false;
}
bool IsValid() const { return valid; }
};
void WaitForTaskCompleteIfNecessary() {
mutex_.AssertHeld();
while (executing_task_) {
TEST_SYNC_POINT("Timer::WaitForTaskCompleteIfNecessary:TaskExecuting");
cond_var_.Wait();
}
}
struct RunTimeOrder {
bool operator()(const FunctionInfo* f1,
const FunctionInfo* f2) {
return f1->next_run_time_us > f2->next_run_time_us;
}
};
SystemClock* clock_;
// This mutex controls both the heap_ and the map_. It needs to be held for
// making any changes in them.
mutable InstrumentedMutex mutex_;
InstrumentedCondVar cond_var_;
std::unique_ptr<port::Thread> thread_;
bool running_;
bool executing_task_;
std::priority_queue<FunctionInfo*,
std::vector<FunctionInfo*>,
RunTimeOrder> heap_;
// In addition to providing a mapping from a function name to a function,
// it is also responsible for memory management.
std::unordered_map<std::string, std::unique_ptr<FunctionInfo>> map_;
};
} // namespace ROCKSDB_NAMESPACE