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// Copyright Oliver Kowalke 2013.
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
#ifndef BOOST_FIBERS_ALGO_DETAIL_CHASE_LEV_QUEUE_H
#define BOOST_FIBERS_ALGO_DETAIL_CHASE_LEV_QUEUE_H
#include <atomic>
#include <cstddef>
#include <memory>
#include <type_traits>
#include <vector>
#include <boost/assert.hpp>
#include <boost/config.hpp>
#include <boost/fiber/detail/config.hpp>
#include <boost/fiber/context.hpp>
// David Chase and Yossi Lev. Dynamic circular work-stealing deque.
// In SPAA ’05: Proceedings of the seventeenth annual ACM symposium
// on Parallelism in algorithms and architectures, pages 21–28,
// New York, NY, USA, 2005. ACM.
//
// Nhat Minh Lê, Antoniu Pop, Albert Cohen, and Francesco Zappa Nardelli. 2013.
// Correct and efficient work-stealing for weak memory models.
// In Proceedings of the 18th ACM SIGPLAN symposium on Principles and practice
// of parallel programming (PPoPP '13). ACM, New York, NY, USA, 69-80.
namespace boost {
namespace fibers {
namespace algo {
namespace detail {
class chase_lev_queue {
private:
class circular_buffer {
private:
typedef typename std::aligned_storage< sizeof( context *), alignof( context *) >::type storage_t;
int64_t size_;
context ** items;
chase_lev_queue * queue_;
public:
circular_buffer( int64_t size, chase_lev_queue * queue) noexcept :
size_{ size },
items{ reinterpret_cast< context ** >( new storage_t[size_] ) },
queue_{ queue } {
}
~circular_buffer() {
delete [] reinterpret_cast< storage_t * >( items);
}
int64_t size() const noexcept {
return size_;
}
context * get( int64_t idx) noexcept {
BOOST_ASSERT( 0 <= idx);
return * (items + (idx & (size() - 1)));
}
void put( int64_t idx, context * ctx) noexcept {
BOOST_ASSERT( 0 <= idx);
* (items + (idx & (size() - 1))) = ctx;
}
circular_buffer * grow( int64_t top, int64_t bottom) {
BOOST_ASSERT( 0 <= top);
BOOST_ASSERT( 0 <= bottom);
circular_buffer * buffer = new circular_buffer{ size() * 2, queue_ };
queue_->old_buffers_.push_back( this);
for ( int64_t i = top; i != bottom; ++i) {
buffer->put( i, get( i) );
}
return buffer;
}
};
std::atomic< int64_t > top_{ 0 };
std::atomic< int64_t > bottom_{ 0 };
std::atomic< circular_buffer * > buffer_;
std::vector< circular_buffer * > old_buffers_;
public:
chase_lev_queue() :
buffer_{ new circular_buffer{ 1024, this } } {
old_buffers_.resize( 10);
}
~chase_lev_queue() {
delete buffer_.load( std::memory_order_seq_cst);
for ( circular_buffer * buffer : old_buffers_) {
delete buffer;
}
}
chase_lev_queue( chase_lev_queue const&) = delete;
chase_lev_queue( chase_lev_queue &&) = delete;
chase_lev_queue & operator=( chase_lev_queue const&) = delete;
chase_lev_queue & operator=( chase_lev_queue &&) = delete;
bool empty() const noexcept {
int64_t bottom = bottom_.load( std::memory_order_relaxed);
int64_t top = top_.load( std::memory_order_relaxed);
return bottom <= top;
}
void push( context * ctx) {
int64_t bottom = bottom_.load( std::memory_order_relaxed);
int64_t top = top_.load( std::memory_order_acquire);
circular_buffer * buffer = buffer_.load( std::memory_order_relaxed);
if ( (bottom - top) > buffer->size() - 1) {
// queue is full
buffer = buffer->grow( top, bottom);
buffer_.store( buffer, std::memory_order_release);
}
buffer->put( bottom, ctx);
std::atomic_thread_fence( std::memory_order_release);
bottom_.store( bottom + 1, std::memory_order_relaxed);
}
context * pop() {
int64_t bottom = bottom_.load( std::memory_order_relaxed) - 1;
circular_buffer * buffer = buffer_.load( std::memory_order_relaxed);
bottom_.store( bottom, std::memory_order_relaxed);
std::atomic_thread_fence( std::memory_order_seq_cst);
int64_t top = top_.load( std::memory_order_relaxed);
context * ctx = nullptr;
if ( top <= bottom) {
// queue is not empty
ctx = buffer->get( bottom);
// last element
if ( top == bottom) {
if ( ! top_.compare_exchange_strong( top, top + 1,
std::memory_order_seq_cst, std::memory_order_relaxed) ) {
return nullptr;
}
bottom_.store( bottom + 1, std::memory_order_relaxed);
}
} else {
// queue is empty
bottom_.store( bottom + 1, std::memory_order_relaxed);
}
return ctx;
}
context * steal() {
int64_t top = top_.load( std::memory_order_acquire);
std::atomic_thread_fence( std::memory_order_seq_cst);
int64_t bottom = bottom_.load( std::memory_order_acquire);
context * ctx = nullptr;
if ( top < bottom) {
// queue is not empty
circular_buffer * buffer = buffer_.load( std::memory_order_consume);
ctx = buffer->get( top);
if ( ! top_.compare_exchange_strong( top, top + 1,
std::memory_order_seq_cst, std::memory_order_relaxed) ) {
return nullptr;
}
}
return ctx;
}
};
}}}}
#endif // #define BOOST_FIBERS_ALGO_DETAIL_CHASE_LEV_QUEUE_H
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