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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_DETAIL_CONTEXT_SPMC_QUEUE_H
#define BOOST_FIBERS_DETAIL_CONTEXT_SPMC_QUEUE_H
#include <atomic>
#include <cstddef>
#include <cstdint>
#include <memory>
#include <type_traits>
#include <utility>
#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 detail {
class context_spmc_queue {
private:
class array {
private:
typedef std::atomic< context * > atomic_type;
typedef std::aligned_storage<
sizeof( atomic_type), cache_alignment
>::type storage_type;
std::size_t size_;
storage_type * storage_;
public:
array( std::size_t size) :
size_{ size },
storage_{ new storage_type[size_] } {
for ( std::size_t i = 0; i < size_; ++i) {
::new ( static_cast< void * >( std::addressof( storage_[i]) ) ) atomic_type{ nullptr };
}
}
~array() {
for ( std::size_t i = 0; i < size_; ++i) {
reinterpret_cast< atomic_type * >( std::addressof( storage_[i]) )->~atomic_type();
}
delete [] storage_;
}
std::size_t size() const noexcept {
return size_;
}
void push( std::size_t bottom, context * ctx) noexcept {
reinterpret_cast< atomic_type * >(
std::addressof( storage_[bottom % size_]) )
->store( ctx, std::memory_order_relaxed);
}
context * pop( std::size_t top) noexcept {
return reinterpret_cast< atomic_type * >(
std::addressof( storage_[top % size_]) )
->load( std::memory_order_relaxed);
}
array * resize( std::size_t bottom, std::size_t top) {
std::unique_ptr< array > tmp{ new array{ 2 * size_ } };
for ( std::size_t i = top; i != bottom; ++i) {
tmp->push( i, pop( i) );
}
return tmp.release();
}
};
alignas(cache_alignment) std::atomic< std::size_t > top_{ 0 };
alignas(cache_alignment) std::atomic< std::size_t > bottom_{ 0 };
alignas(cache_alignment) std::atomic< array * > array_;
std::vector< array * > old_arrays_{};
char padding_[cacheline_length];
public:
context_spmc_queue() :
array_{ new array{ 1024 } } {
old_arrays_.reserve( 32);
}
~context_spmc_queue() {
for ( array * a : old_arrays_) {
delete a;
}
delete array_.load();
}
context_spmc_queue( context_spmc_queue const&) = delete;
context_spmc_queue & operator=( context_spmc_queue const&) = delete;
bool empty() const noexcept {
std::size_t bottom{ bottom_.load( std::memory_order_relaxed) };
std::size_t top{ top_.load( std::memory_order_relaxed) };
return bottom <= top;
}
void push( context * ctx) {
std::size_t bottom{ bottom_.load( std::memory_order_relaxed) };
std::size_t top{ top_.load( std::memory_order_acquire) };
array * a{ array_.load( std::memory_order_relaxed) };
if ( (a->size() - 1) < (bottom - top) ) {
// queue is full
// resize
array * tmp{ a->resize( bottom, top) };
old_arrays_.push_back( a);
std::swap( a, tmp);
array_.store( a, std::memory_order_relaxed);
}
a->push( bottom, ctx);
std::atomic_thread_fence( std::memory_order_release);
bottom_.store( bottom + 1, std::memory_order_relaxed);
}
context * pop() {
std::size_t top{ top_.load( std::memory_order_acquire) };
std::atomic_thread_fence( std::memory_order_seq_cst);
std::size_t bottom{ bottom_.load( std::memory_order_acquire) };
context * ctx{ nullptr };
if ( top < bottom) {
// queue is not empty
array * a{ array_.load( std::memory_order_consume) };
ctx = a->pop( top);
if ( ctx->is_context( type::pinned_context) ||
! top_.compare_exchange_strong( top, top + 1,
std::memory_order_seq_cst,
std::memory_order_relaxed) ) {
// lose the race
return nullptr;
}
}
return ctx;
}
};
}}}
#endif // BOOST_FIBERS_DETAIL_CONTEXT_SPMC_QUEUE_H
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