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// Copyright 2016 The SwiftShader Authors. All Rights Reserved.
//
// 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.
#ifndef rr_MutexLock_hpp
#define rr_MutexLock_hpp
#include "Thread.hpp"
#if defined(__linux__)
// Use a pthread mutex on Linux. Since many processes may use Reactor
// at the same time it's best to just have the scheduler overhead.
#include <pthread.h>
namespace rr
{
class MutexLock
{
public:
MutexLock()
{
pthread_mutex_init(&mutex, NULL);
}
~MutexLock()
{
pthread_mutex_destroy(&mutex);
}
bool attemptLock()
{
return pthread_mutex_trylock(&mutex) == 0;
}
void lock()
{
pthread_mutex_lock(&mutex);
}
void unlock()
{
pthread_mutex_unlock(&mutex);
}
private:
pthread_mutex_t mutex;
};
}
#else // !__linux__
#include <atomic>
namespace rr
{
class BackoffLock
{
public:
BackoffLock()
{
mutex = 0;
}
bool attemptLock()
{
if(!isLocked())
{
if(mutex.exchange(true) == false)
{
return true;
}
}
return false;
}
void lock()
{
int backoff = 1;
while(!attemptLock())
{
if(backoff <= 64)
{
for(int i = 0; i < backoff; i++)
{
nop();
nop();
nop();
nop();
nop();
nop();
nop();
nop();
nop();
nop();
nop();
nop();
nop();
nop();
nop();
nop();
nop();
nop();
nop();
nop();
nop();
nop();
nop();
nop();
nop();
nop();
nop();
nop();
nop();
nop();
nop();
nop();
nop();
nop();
nop();
}
backoff *= 2;
}
else
{
Thread::yield();
backoff = 1;
}
};
}
void unlock()
{
mutex.store(false, std::memory_order_release);
}
bool isLocked()
{
return mutex.load(std::memory_order_acquire);
}
private:
struct
{
// Ensure that the mutex variable is on its own 64-byte cache line to avoid false sharing
// Padding must be public to avoid compiler warnings
volatile int padding1[16];
std::atomic<bool> mutex;
volatile int padding2[15];
};
};
using MutexLock = BackoffLock;
}
#endif // !__linux__
#endif // rr_MutexLock_hpp