dolphin/Source/Core/Common/SPSCQueue.h
Michael M b58f8d19ab Rename Common::FifoQueue to Common::SPSCQueue
Since all queues are FIFO data structures, the name wasn't informative
as to why you'd use it over a normal queue. I originally thought it had
something to do with the hardware graphics FIFO.

This renames it using the common acronym SPSC, which stands for
single-producer single-consumer, and is most commonly used to talk about
lock-free data structures, both of which this is.
2017-08-23 17:00:52 -07:00

111 lines
2.3 KiB
C++

// Copyright 2010 Dolphin Emulator Project
// Licensed under GPLv2+
// Refer to the license.txt file included.
#pragma once
// a simple lockless thread-safe,
// single producer, single consumer queue
#include <algorithm>
#include <atomic>
#include <cstddef>
#include "Common/CommonTypes.h"
namespace Common
{
template <typename T, bool NeedSize = true>
class SPSCQueue
{
public:
SPSCQueue() : m_size(0) { m_write_ptr = m_read_ptr = new ElementPtr(); }
~SPSCQueue()
{
// this will empty out the whole queue
delete m_read_ptr;
}
u32 Size() const
{
static_assert(NeedSize, "using Size() on SPSCQueue without NeedSize");
return m_size.load();
}
bool Empty() const { return !m_read_ptr->next.load(); }
T& Front() const { return m_read_ptr->current; }
template <typename Arg>
void Push(Arg&& t)
{
// create the element, add it to the queue
m_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();
m_write_ptr->next.store(new_ptr, std::memory_order_release);
m_write_ptr = new_ptr;
if (NeedSize)
m_size++;
}
void Pop()
{
if (NeedSize)
m_size--;
ElementPtr* tmpptr = m_read_ptr;
// advance the read pointer
m_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;
if (NeedSize)
m_size--;
ElementPtr* tmpptr = m_read_ptr;
m_read_ptr = tmpptr->next.load(std::memory_order_acquire);
t = std::move(tmpptr->current);
tmpptr->next.store(nullptr);
delete tmpptr;
return true;
}
// not thread-safe
void Clear()
{
m_size.store(0);
delete m_read_ptr;
m_write_ptr = m_read_ptr = new ElementPtr();
}
private:
// stores a pointer to element
// and a pointer to the next ElementPtr
class ElementPtr
{
public:
ElementPtr() : next(nullptr) {}
~ElementPtr()
{
ElementPtr* next_ptr = next.load();
if (next_ptr)
delete next_ptr;
}
T current;
std::atomic<ElementPtr*> next;
};
ElementPtr* m_write_ptr;
ElementPtr* m_read_ptr;
std::atomic<u32> m_size;
};
}