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// Copyright 2010 Dolphin Emulator Project
// Licensed under GPLv2+
// Refer to the license.txt file included.
#pragma once
// a simple lockless thread-safe,
// single reader, single writer queue
#include <atomic>
#include <condition_variable>
#include <cstddef>
#include <mutex>
#include <utility>
namespace Common {
template <typename T>
class SPSCQueue {
public:
SPSCQueue() {
write_ptr = read_ptr = new ElementPtr();
}
~SPSCQueue() {
// this will empty out the whole queue
delete read_ptr;
}
std::size_t Size() const {
return size.load();
}
bool Empty() const {
return Size() == 0;
}
T& Front() const {
return read_ptr->current;
}
template <typename Arg>
void Push(Arg&& t) {
// create the element, add it to the queue
write_ptr->current = std::forward<Arg>(t);
// set the next pointer to a new element ptr
// then advance the write pointer
ElementPtr* new_ptr = new ElementPtr();
write_ptr->next.store(new_ptr, std::memory_order_release);
write_ptr = new_ptr;
const size_t previous_size{size++};
// Acquire the mutex and then immediately release it as a fence.
// TODO(bunnei): This can be replaced with C++20 waitable atomics when properly supported.
// See discussion on https://github.com/yuzu-emu/yuzu/pull/3173 for details.
if (previous_size == 0) {
std::lock_guard lock{cv_mutex};
}
cv.notify_one();
}
void Pop() {
--size;
ElementPtr* tmpptr = read_ptr;
// advance the read pointer
read_ptr = tmpptr->next.load();
// set the next element to nullptr to stop the recursive deletion
tmpptr->next.store(nullptr);
delete tmpptr; // this also deletes the element
}
bool Pop(T& t) {
if (Empty())
return false;
--size;
ElementPtr* tmpptr = read_ptr;
read_ptr = tmpptr->next.load(std::memory_order_acquire);
t = std::move(tmpptr->current);
tmpptr->next.store(nullptr);
delete tmpptr;
return true;
}
T PopWait() {
if (Empty()) {
std::unique_lock lock{cv_mutex};
cv.wait(lock, [this]() { return !Empty(); });
}
T t;
Pop(t);
return t;
}
// not thread-safe
void Clear() {
size.store(0);
delete read_ptr;
write_ptr = read_ptr = new ElementPtr();
}
private:
// stores a pointer to element
// and a pointer to the next ElementPtr
class ElementPtr {
public:
ElementPtr() {}
~ElementPtr() {
ElementPtr* next_ptr = next.load();
if (next_ptr)
delete next_ptr;
}
T current;
std::atomic<ElementPtr*> next{nullptr};
};
ElementPtr* write_ptr;
ElementPtr* read_ptr;
std::atomic_size_t size{0};
std::mutex cv_mutex;
std::condition_variable cv;
};
// a simple thread-safe,
// single reader, multiple writer queue
template <typename T>
class MPSCQueue {
public:
std::size_t Size() const {
return spsc_queue.Size();
}
bool Empty() const {
return spsc_queue.Empty();
}
T& Front() const {
return spsc_queue.Front();
}
template <typename Arg>
void Push(Arg&& t) {
std::lock_guard lock{write_lock};
spsc_queue.Push(t);
}
void Pop() {
return spsc_queue.Pop();
}
bool Pop(T& t) {
return spsc_queue.Pop(t);
}
T PopWait() {
return spsc_queue.PopWait();
}
// not thread-safe
void Clear() {
spsc_queue.Clear();
}
private:
SPSCQueue<T> spsc_queue;
std::mutex write_lock;
};
} // namespace Common
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