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// Copyright Oliver Kowalke 2015.
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// Distributed under the Boost Software License, Version 1.0.
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// (See accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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//
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#ifndef BOOST_FIBERS_DETAIL_SPINLOCK_QUEUE_H
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#define BOOST_FIBERS_DETAIL_SPINLOCK_QUEUE_H
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#include <cstddef>
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#include <cstring>
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#include <mutex>
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#include <boost/config.hpp>
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#include <boost/fiber/context.hpp>
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#include <boost/fiber/detail/config.hpp>
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#include <boost/fiber/detail/spinlock.hpp>
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#ifdef BOOST_HAS_ABI_HEADERS
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# include BOOST_ABI_PREFIX
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#endif
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namespace boost {
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namespace fibers {
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namespace detail {
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class context_spinlock_queue {
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private:
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typedef context * slot_type;
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mutable spinlock splk_{};
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std::size_t pidx_{ 0 };
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std::size_t cidx_{ 0 };
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std::size_t capacity_;
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slot_type * slots_;
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void resize_() {
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slot_type * old_slots = slots_;
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slots_ = new slot_type[2*capacity_];
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std::size_t offset = capacity_ - cidx_;
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std::memcpy( slots_, old_slots + cidx_, offset * sizeof( slot_type) );
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if ( 0 < cidx_) {
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std::memcpy( slots_ + offset, old_slots, pidx_ * sizeof( slot_type) );
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}
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cidx_ = 0;
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pidx_ = capacity_ - 1;
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capacity_ *= 2;
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delete [] old_slots;
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}
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bool is_full_() const noexcept {
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return cidx_ == ((pidx_ + 1) % capacity_);
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}
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bool is_empty_() const noexcept {
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return cidx_ == pidx_;
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}
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public:
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context_spinlock_queue( std::size_t capacity = 4096) :
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capacity_{ capacity } {
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slots_ = new slot_type[capacity_];
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}
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~context_spinlock_queue() {
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delete [] slots_;
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}
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context_spinlock_queue( context_spinlock_queue const&) = delete;
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context_spinlock_queue & operator=( context_spinlock_queue const&) = delete;
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bool empty() const noexcept {
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spinlock_lock lk{ splk_ };
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return is_empty_();
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}
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void push( context * c) {
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spinlock_lock lk{ splk_ };
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if ( is_full_() ) {
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resize_();
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}
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slots_[pidx_] = c;
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pidx_ = (pidx_ + 1) % capacity_;
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}
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context * pop() {
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spinlock_lock lk{ splk_ };
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context * c = nullptr;
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if ( ! is_empty_() ) {
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c = slots_[cidx_];
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cidx_ = (cidx_ + 1) % capacity_;
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}
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return c;
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}
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context * steal() {
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spinlock_lock lk{ splk_ };
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context * c = nullptr;
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if ( ! is_empty_() ) {
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c = slots_[cidx_];
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if ( c->is_context( type::pinned_context) ) {
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return nullptr;
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}
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cidx_ = (cidx_ + 1) % capacity_;
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}
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return c;
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}
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};
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}}}
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#ifdef BOOST_HAS_ABI_HEADERS
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# include BOOST_ABI_SUFFIX
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#endif
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#endif // BOOST_FIBERS_DETAIL_SPINLOCK_QUEUE_H
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