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// Copyright Oliver Kowalke 2015.
// 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_SPINLOCK_QUEUE_H
#define BOOST_FIBERS_DETAIL_SPINLOCK_QUEUE_H
#include <cstddef>
#include <cstring>
#include <mutex>
#include <boost/config.hpp>
#include <boost/fiber/context.hpp>
#include <boost/fiber/detail/config.hpp>
#include <boost/fiber/detail/spinlock.hpp>
#ifdef BOOST_HAS_ABI_HEADERS
# include BOOST_ABI_PREFIX
#endif
namespace boost {
namespace fibers {
namespace detail {
class context_spinlock_queue {
private:
typedef context * slot_type;
mutable spinlock splk_{};
std::size_t pidx_{ 0 };
std::size_t cidx_{ 0 };
std::size_t capacity_;
slot_type * slots_;
void resize_() {
slot_type * old_slots = slots_;
slots_ = new slot_type[2*capacity_];
std::size_t offset = capacity_ - cidx_;
std::memcpy( slots_, old_slots + cidx_, offset * sizeof( slot_type) );
if ( 0 < cidx_) {
std::memcpy( slots_ + offset, old_slots, pidx_ * sizeof( slot_type) );
}
cidx_ = 0;
pidx_ = capacity_ - 1;
capacity_ *= 2;
delete [] old_slots;
}
bool is_full_() const noexcept {
return cidx_ == ((pidx_ + 1) % capacity_);
}
bool is_empty_() const noexcept {
return cidx_ == pidx_;
}
public:
context_spinlock_queue( std::size_t capacity = 4096) :
capacity_{ capacity } {
slots_ = new slot_type[capacity_];
}
~context_spinlock_queue() {
delete [] slots_;
}
context_spinlock_queue( context_spinlock_queue const&) = delete;
context_spinlock_queue & operator=( context_spinlock_queue const&) = delete;
bool empty() const noexcept {
spinlock_lock lk{ splk_ };
return is_empty_();
}
void push( context * c) {
spinlock_lock lk{ splk_ };
if ( is_full_() ) {
resize_();
}
slots_[pidx_] = c;
pidx_ = (pidx_ + 1) % capacity_;
}
context * pop() {
spinlock_lock lk{ splk_ };
context * c = nullptr;
if ( ! is_empty_() ) {
c = slots_[cidx_];
cidx_ = (cidx_ + 1) % capacity_;
}
return c;
}
context * steal() {
spinlock_lock lk{ splk_ };
context * c = nullptr;
if ( ! is_empty_() ) {
c = slots_[cidx_];
if ( c->is_context( type::pinned_context) ) {
return nullptr;
}
cidx_ = (cidx_ + 1) % capacity_;
}
return c;
}
};
}}}
#ifdef BOOST_HAS_ABI_HEADERS
# include BOOST_ABI_SUFFIX
#endif
#endif // BOOST_FIBERS_DETAIL_SPINLOCK_QUEUE_H
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