Imported Upstream version 1.63.0upstream/1.63.0

Change-Id: Iac85556a04b7e58d63ba636dedb0986e3555714a
Signed-off-by: DongHun Kwak <dh0128.kwak@samsung.com>

1 files changed, 98 insertions, 0 deletions

diff --git a/boost/fiber/detail/context_mpsc_queue.hpp b/boost/fiber/detail/context_mpsc_queue.hpp
new file mode 100644
index 0000000000..f7e664659c
--- /dev/null
+++ b/boost/fiber/detail/context_mpsc_queue.hpp
@@ -0,0 +1,98 @@
+
+//          Copyright Dmitry Vyukov 2010-2011.
+//          Copyright Oliver Kowalke 2016.
+// 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)
+//
+// based on Dmitry Vyukov's intrusive MPSC queue
+// http://www.1024cores.net/home/lock-free-algorithms/queues/intrusive-mpsc-node-based-queue
+// https://groups.google.com/forum/#!topic/lock-free/aFHvZhu1G-0
+
+#ifndef BOOST_FIBERS_DETAIL_CONTEXT_MPSC_QUEUE_H
+#define BOOST_FIBERS_DETAIL_CONTEXT_MPSC_QUEUE_H
+
+#include <atomic>
+#include <memory>
+#include <type_traits>
+
+#include <boost/assert.hpp>
+#include <boost/config.hpp>
+
+#include <boost/fiber/context.hpp>
+#include <boost/fiber/detail/config.hpp>
+
+#ifdef BOOST_HAS_ABI_HEADERS
+#  include BOOST_ABI_PREFIX
+#endif
+
+namespace boost {
+namespace fibers {
+namespace detail {
+
+// a MPSC queue
+// multiple threads push ready fibers (belonging to local scheduler)
+// (thread) local scheduler pops fibers
+class context_mpsc_queue {
+private:
+    // not default constructor for context - use aligned_storage instead
+    alignas(cache_alignment) std::aligned_storage< sizeof( context), alignof( context) >::type  storage_{};
+    context                                         *   dummy_;
+    alignas(cache_alignment) std::atomic< context * >   head_;
+    alignas(cache_alignment) context                *   tail_;
+    char                                                pad_[cacheline_length];
+
+public:
+    context_mpsc_queue() :
+        dummy_{ reinterpret_cast< context * >( std::addressof( storage_) ) },
+        head_{ dummy_ },
+        tail_{ dummy_ } {
+        dummy_->remote_nxt_.store( nullptr, std::memory_order_release);
+    }
+
+    context_mpsc_queue( context_mpsc_queue const&) = delete;
+    context_mpsc_queue & operator=( context_mpsc_queue const&) = delete;
+
+    void push( context * ctx) noexcept {
+        BOOST_ASSERT( nullptr != ctx);
+        ctx->remote_nxt_.store( nullptr, std::memory_order_release);
+        context * prev = head_.exchange( ctx, std::memory_order_acq_rel);
+        prev->remote_nxt_.store( ctx, std::memory_order_release);
+    }
+
+    context * pop() noexcept {
+        context * tail = tail_;
+        context * next = tail->remote_nxt_.load( std::memory_order_acquire);
+        if ( dummy_ == tail) {
+            if ( nullptr == next) {
+                return nullptr;
+            }
+            tail_ = next;
+            tail = next;
+            next = next->remote_nxt_.load( std::memory_order_acquire);;
+        }
+        if ( nullptr != next) {
+            tail_ = next;
+            return tail;
+        }
+        context * head = head_.load( std::memory_order_acquire);
+        if ( tail != head) {
+            return nullptr;
+        }
+        push( dummy_);
+        next = tail->remote_nxt_.load( std::memory_order_acquire);
+        if ( nullptr != next) {
+            tail_= next;
+            return tail;
+        }
+        return nullptr;
+    }
+};
+
+}}}
+
+#ifdef BOOST_HAS_ABI_HEADERS
+#  include BOOST_ABI_SUFFIX
+#endif
+
+#endif // BOOST_FIBERS_DETAIL_CONTEXT_MPSC_QUEUE_H