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// Copyright (C) 2014 The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#pragma once
#include "base/Compiler.h"
#include "base/Lock.h"
#include "base/System.h"
#include <algorithm>
#include <inttypes.h>
#ifdef _WIN32
#include <windows.h>
#else
#include <pthread.h>
#endif
#include <assert.h>
namespace android {
namespace base {
// A class that implements a condition variable, which can be used in
// association with a Lock to blocking-wait for specific conditions.
// Useful to implement various synchronization data structures.
class ConditionVariable {
public:
// A set of functions to efficiently unlock the lock used with
// the current condition variable and signal or broadcast it.
//
// The functions are needed because on some platforms (Posix) it's more
// efficient to signal the variable before unlocking mutex, while on others
// (Windows) it's exactly the opposite. Functions implement the best way
// for each platform and abstract it out from the user.
void signalAndUnlock(StaticLock* lock);
void signalAndUnlock(AutoLock* lock);
void broadcastAndUnlock(StaticLock* lock);
void broadcastAndUnlock(AutoLock* lock);
void wait(AutoLock* userLock) {
assert(userLock->mLocked);
wait(&userLock->mLock);
}
//
// Convenience functions to get rid of the loop in condition variable usage
// Instead of hand-writing a loop, e.g.
//
// while (mRefCount < 3) {
// mCv.wait(&mLock);
// }
//
// use the following two wait() overloads:
//
// mCv.wait(&mLock, [this]() { return mRefCount >= 3; });
//
// Parameters:
// |lock| - a Lock or AutoLock pointer used with the condition variable.
// |pred| - a functor predicate that's compatible with "bool pred()"
// signature and returns a condition when one should stop waiting.
//
template <class Predicate>
void wait(StaticLock* lock, Predicate pred) {
while (!pred()) {
this->wait(lock);
}
}
template <class Predicate>
void wait(AutoLock* lock, Predicate pred) {
this->wait(&lock->mLock, pred);
}
#ifdef _WIN32
ConditionVariable() {
::InitializeConditionVariable(&mCond);
}
// There's no special function to destroy CONDITION_VARIABLE in Windows.
~ConditionVariable() = default;
// Wait until the condition variable is signaled. Note that spurious
// wakeups are always a possibility, so always check the condition
// in a loop, i.e. do:
//
// while (!condition) { condVar.wait(&lock); }
//
// instead of:
//
// if (!condition) { condVar.wait(&lock); }
//
void wait(StaticLock* userLock) {
::SleepConditionVariableSRW(&mCond, &userLock->mLock, INFINITE, 0);
}
bool timedWait(StaticLock *userLock, uint64_t waitUntilUs) {
const auto now = android::base::getUnixTimeUs();
const auto timeout =
std::max<uint64_t>(0, waitUntilUs - now) / 1000;
return ::SleepConditionVariableSRW(
&mCond, &userLock->mLock, timeout, 0) != 0;
}
// Signal that a condition was reached. This will wake at least (and
// preferrably) one waiting thread that is blocked on wait().
void signal() {
::WakeConditionVariable(&mCond);
}
// Like signal(), but wakes all of the waiting threads.
void broadcast() {
::WakeAllConditionVariable(&mCond);
}
private:
CONDITION_VARIABLE mCond;
#else // !_WIN32
// Note: on Posix systems, make it a naive wrapper around pthread_cond_t.
ConditionVariable() {
pthread_cond_init(&mCond, NULL);
}
~ConditionVariable() {
pthread_cond_destroy(&mCond);
}
void wait(StaticLock* userLock) {
pthread_cond_wait(&mCond, &userLock->mLock);
}
bool timedWait(StaticLock* userLock, uint64_t waitUntilUs) {
timespec abstime;
abstime.tv_sec = waitUntilUs / 1000000LL;
abstime.tv_nsec = (waitUntilUs % 1000000LL) * 1000;
return pthread_cond_timedwait(&mCond, &userLock->mLock, &abstime) == 0;
}
void signal() {
pthread_cond_signal(&mCond);
}
void broadcast() {
pthread_cond_broadcast(&mCond);
}
private:
pthread_cond_t mCond;
#endif // !_WIN32
DISALLOW_COPY_ASSIGN_AND_MOVE(ConditionVariable);
};
#ifdef _WIN32
inline void ConditionVariable::signalAndUnlock(StaticLock* lock) {
lock->unlock();
signal();
}
inline void ConditionVariable::signalAndUnlock(AutoLock* lock) {
lock->unlock();
signal();
}
inline void ConditionVariable::broadcastAndUnlock(StaticLock* lock) {
lock->unlock();
broadcast();
}
inline void ConditionVariable::broadcastAndUnlock(AutoLock* lock) {
lock->unlock();
broadcast();
}
#else // !_WIN32
inline void ConditionVariable::signalAndUnlock(StaticLock* lock) {
signal();
lock->unlock();
}
inline void ConditionVariable::signalAndUnlock(AutoLock* lock) {
signal();
lock->unlock();
}
inline void ConditionVariable::broadcastAndUnlock(StaticLock* lock) {
broadcast();
lock->unlock();
}
inline void ConditionVariable::broadcastAndUnlock(AutoLock* lock) {
broadcast();
lock->unlock();
}
#endif // !_WIN32
} // namespace base
} // namespace android
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