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+//
+// detail/call_stack.hpp
+// ~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2012 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// 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_ASIO_DETAIL_CALL_STACK_HPP
+#define BOOST_ASIO_DETAIL_CALL_STACK_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <boost/asio/detail/config.hpp>
+#include <boost/asio/detail/noncopyable.hpp>
+#include <boost/asio/detail/tss_ptr.hpp>
+
+#include <boost/asio/detail/push_options.hpp>
+
+namespace boost {
+namespace asio {
+namespace detail {
+
+// Helper class to determine whether or not the current thread is inside an
+// invocation of io_service::run() for a specified io_service object.
+template <typename Key, typename Value = unsigned char>
+class call_stack
+{
+public:
+ // Context class automatically pushes the key/value pair on to the stack.
+ class context
+ : private noncopyable
+ {
+ public:
+ // Push the key on to the stack.
+ explicit context(Key* k)
+ : key_(k),
+ next_(call_stack<Key, Value>::top_)
+ {
+ value_ = reinterpret_cast<unsigned char*>(this);
+ call_stack<Key, Value>::top_ = this;
+ }
+
+ // Push the key/value pair on to the stack.
+ context(Key* k, Value& v)
+ : key_(k),
+ value_(&v),
+ next_(call_stack<Key, Value>::top_)
+ {
+ call_stack<Key, Value>::top_ = this;
+ }
+
+ // Pop the key/value pair from the stack.
+ ~context()
+ {
+ call_stack<Key, Value>::top_ = next_;
+ }
+
+ // Find the next context with the same key.
+ Value* next_by_key() const
+ {
+ context* elem = next_;
+ while (elem)
+ {
+ if (elem->key_ == key_)
+ return elem->value_;
+ elem = elem->next_;
+ }
+ return 0;
+ }
+
+ private:
+ friend class call_stack<Key, Value>;
+
+ // The key associated with the context.
+ Key* key_;
+
+ // The value associated with the context.
+ Value* value_;
+
+ // The next element in the stack.
+ context* next_;
+ };
+
+ friend class context;
+
+ // Determine whether the specified owner is on the stack. Returns address of
+ // key if present, 0 otherwise.
+ static Value* contains(Key* k)
+ {
+ context* elem = top_;
+ while (elem)
+ {
+ if (elem->key_ == k)
+ return elem->value_;
+ elem = elem->next_;
+ }
+ return 0;
+ }
+
+private:
+ // The top of the stack of calls for the current thread.
+ static tss_ptr<context> top_;
+};
+
+template <typename Key, typename Value>
+tss_ptr<typename call_stack<Key, Value>::context>
+call_stack<Key, Value>::top_;
+
+} // namespace detail
+} // namespace asio
+} // namespace boost
+
+#include <boost/asio/detail/pop_options.hpp>
+
+#endif // BOOST_ASIO_DETAIL_CALL_STACK_HPP