// -*- C++ -*-
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// Copyright (C) 2007 Douglas Gregor <doug.gregor@gmail.com>
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// Use, modification and distribution is subject to the Boost Software
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// License, Version 1.0. (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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#ifndef BOOST_GRAPH_DISTRIBUTED_TAG_ALLOCATOR_HPP
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#define BOOST_GRAPH_DISTRIBUTED_TAG_ALLOCATOR_HPP
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#ifndef BOOST_GRAPH_USE_MPI
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#error "Parallel BGL files should not be included unless <boost/graph/use_mpi.hpp> has been included"
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#endif
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#include <vector>
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namespace boost { namespace graph { namespace distributed { namespace detail {
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/**
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* \brief The tag allocator allows clients to request unique tags that
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* can be used for one-time communications.
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*
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* The tag allocator hands out tag values from a predefined maximum
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* (given in the constructor) moving downward. Tags are provided one
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* at a time via a @c token. When the @c token goes out of scope, the
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* tag is returned and may be reallocated. These tags should be used,
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* for example, for one-time communication of values.
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*/
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class tag_allocator {
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public:
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class token;
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friend class token;
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/**
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* Construct a new tag allocator that provides unique tags starting
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* with the value @p top_tag and moving lower, as necessary.
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*/
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explicit tag_allocator(int top_tag) : bottom(top_tag) { }
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/**
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* Retrieve a new tag. The token itself holds onto the tag, which
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* will be released when the token is destroyed.
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*/
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token get_tag();
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private:
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int bottom;
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std::vector<int> freed;
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};
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/**
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* A token used to represent an allocated tag.
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*/
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class tag_allocator::token {
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public:
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/// Transfer ownership of the tag from @p other.
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token(const token& other);
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/// De-allocate the tag, if this token still owns it.
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~token();
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/// Retrieve the tag allocated for this task.
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operator int() const { return tag_; }
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private:
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/// Create a token with a specific tag from the given tag_allocator
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token(tag_allocator* allocator, int tag)
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: allocator(allocator), tag_(tag) { }
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/// Undefined: tokens are not copy-assignable
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token& operator=(const token&);
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/// The allocator from which this tag was allocated.
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tag_allocator* allocator;
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/// The stored tag flag. If -1, this token does not own the tag.
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mutable int tag_;
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friend class tag_allocator;
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};
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} } } } // end namespace boost::graph::distributed::detail
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#endif // BOOST_GRAPH_DISTRIBUTED_TAG_ALLOCATOR_HPP
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