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// Copyright 2019 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.
// This file contains a number of synchronization primitives for concurrency.
//
// You may be tempted to change this code to unlock the mutex before calling
// std::condition_variable::notify_[one,all]. Please read
// https://issuetracker.google.com/issues/133135427 before making this sort of
// change.
#ifndef sw_Synchronization_hpp
#define sw_Synchronization_hpp
#include "Debug.hpp"
#include <assert.h>
#include <chrono>
#include <condition_variable>
#include <queue>
#include "marl/event.h"
#include "marl/mutex.h"
#include "marl/waitgroup.h"
namespace sw {
// CountedEvent is an event that is signalled when the internal counter is
// decremented and reaches zero.
// The counter is incremented with calls to add() and decremented with calls to
// done().
class CountedEvent
{
public:
// Constructs the CountedEvent with the initial signalled state set to the
// provided value.
CountedEvent(bool signalled = false)
: ev(marl::Event::Mode::Manual, signalled)
{}
// add() increments the internal counter.
// add() must not be called when the event is already signalled.
void add() const
{
ASSERT(!ev.isSignalled());
wg.add();
}
// done() decrements the internal counter, signalling the event if the new
// counter value is zero.
// done() must not be called when the event is already signalled.
void done() const
{
ASSERT(!ev.isSignalled());
if(wg.done())
{
ev.signal();
}
}
// reset() clears the signal state.
// done() must not be called when the internal counter is non-zero.
void reset() const
{
ev.clear();
}
// signalled() returns the current signal state.
bool signalled() const
{
return ev.isSignalled();
}
// wait() waits until the event is signalled.
void wait() const
{
ev.wait();
}
// wait() waits until the event is signalled or the timeout is reached.
// If the timeout was reached, then wait() return false.
template<class CLOCK, class DURATION>
bool wait(const std::chrono::time_point<CLOCK, DURATION> &timeout) const
{
return ev.wait_until(timeout);
}
// event() returns the internal marl event.
const marl::Event &event() { return ev; }
private:
const marl::WaitGroup wg;
const marl::Event ev;
};
// Chan is a thread-safe FIFO queue of type T.
// Chan takes its name after Golang's chan.
template<typename T>
class Chan
{
public:
Chan();
// take returns the next item in the chan, blocking until an item is
// available.
T take();
// tryTake returns a <T, bool> pair.
// If the chan is not empty, then the next item and true are returned.
// If the chan is empty, then a default-initialized T and false are returned.
std::pair<T, bool> tryTake();
// put places an item into the chan, blocking if the chan is bounded and
// full.
void put(const T &v);
// Returns the number of items in the chan.
// Note: that this may change as soon as the function returns, so should
// only be used for debugging.
size_t count();
private:
marl::mutex mutex;
std::queue<T> queue GUARDED_BY(mutex);
std::condition_variable added;
};
template<typename T>
Chan<T>::Chan()
{}
template<typename T>
T Chan<T>::take()
{
marl::lock lock(mutex);
// Wait for item to be added.
lock.wait(added, [this]() REQUIRES(mutex) { return queue.size() > 0; });
T out = queue.front();
queue.pop();
return out;
}
template<typename T>
std::pair<T, bool> Chan<T>::tryTake()
{
marl::lock lock(mutex);
if(queue.size() == 0)
{
return std::make_pair(T{}, false);
}
T out = queue.front();
queue.pop();
return std::make_pair(out, true);
}
template<typename T>
void Chan<T>::put(const T &item)
{
marl::lock lock(mutex);
queue.push(item);
added.notify_one();
}
template<typename T>
size_t Chan<T>::count()
{
marl::lock lock(mutex);
return queue.size();
}
} // namespace sw
#endif // sw_Synchronization_hpp