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Copy pathspscqueue.h
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172 lines (148 loc) · 4.97 KB
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/*
* https://github.com/Kolkir/cpptask/
* Copyright (c) 2012, Kyrylo Kolodiazhnyi
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS `AS IS'
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
//Idea taken from http://www.1024cores.net/home/lock-free-algorithms/queues/unbounded-spsc-queue
#ifndef _SPSCQUEUE_H_
#define _SPSCQUEUE_H_
#include <cassert>
#include <atomic>
namespace cpptask
{
template<class T>
class SPSCQueue
{
public:
#if defined(_DEBUG) || defined(DEBUG)
SPSCQueue(T defaultValue)
{
Node* n = new Node;
n->value = defaultValue;
n->next.store(nullptr, std::memory_order_relaxed);
head.store(n, std::memory_order_relaxed);
tail = n;
cache_start = cache_mid = n;
}
#endif
SPSCQueue()
{
Node* n = new Node();
n->next.store(nullptr, std::memory_order_relaxed);
head.store(n, std::memory_order_relaxed);
tail = n;
cache_start = cache_mid = n;
}
~SPSCQueue()
{
Node* n = cache_start;
do
{
Node* next = n->next.load(std::memory_order_relaxed);
delete n;
n = next;
}
while (n != nullptr);
}
#if defined(_DEBUG) || defined(DEBUG)
//not thread safe - for testing purposes
template<class IF>
void Iterate(IF func) const
{
auto h = head.load(std::memory_order_relaxed);
Node* n = cache_start;
do
{
func(n->value, n == h, n == tail, n == cache_start, n == cache_mid);
Node* next = n->next.load(std::memory_order_relaxed);
n = next;
} while (n != nullptr);
}
#endif
void Enqueue(T v)
{
Node* n = AllocNode();
n->next = nullptr;
n->value = v;
tail->next.store(n, std::memory_order_release);
tail = n;
}
bool Dequeue(T& v)
{
auto h = head.load(std::memory_order_acquire);
auto h_next = h->next.load(std::memory_order_acquire);
if (h_next != nullptr)
{
v = h_next->value;
head.store(h_next, std::memory_order_release);
return true;
}
else
{
return false;
}
}
SPSCQueue(SPSCQueue const&) = delete;
SPSCQueue& operator = (SPSCQueue const&) = delete;
private:
// internal node structure
struct Node
{
std::atomic<Node*> next;
T value;
};
Node* AllocNode()
{
// cache_start tries to allocate node from internal node cache,
// if attempt fails, allocates node via ::operator new()
if (cache_start != cache_mid)
{
Node* n = cache_start;
cache_start = cache_start->next.load(std::memory_order_acquire);
return n;
}
cache_mid = head.load(std::memory_order_acquire);
if (cache_start != cache_mid)
{
Node* n = cache_start;
cache_start = cache_start->next.load(std::memory_order_acquire);
return n;
}
Node* n = new Node;
return n;
}
// consumer part
// accessed mainly by consumer, infrequently be producer
std::atomic<Node*> head; // head of the queue
// delimiter between consumer part and producer part,
// so that they situated on different cache lines
char cache_line_pad[_CPP_TASK_CACHE_LINE_SIZE_];
// producer part
// accessed only by producer
Node* tail; // tail of the queue
Node* cache_start; // first unused node (head of node cache)
Node* cache_mid; // points somewhere between cache_start and head - minimize accesses to the head node during allocation
};
}
#endif