279 lines
10 KiB
Plaintext
279 lines
10 KiB
Plaintext
// Copyright (C) 2004-2006 The Trustees of Indiana University.
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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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// Authors: Douglas Gregor
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// Andrew Lumsdaine
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#ifndef BOOST_GRAPH_DISTRIBUTED_QUEUE_HPP
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#define BOOST_GRAPH_DISTRIBUTED_QUEUE_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 <boost/graph/parallel/process_group.hpp>
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#include <boost/optional.hpp>
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#include <boost/shared_ptr.hpp>
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#include <vector>
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namespace boost { namespace graph { namespace distributed {
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/// A unary predicate that always returns "true".
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struct always_push
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{
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template<typename T> bool operator()(const T&) const { return true; }
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};
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/** A distributed queue adaptor.
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*
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* Class template @c distributed_queue implements a distributed queue
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* across a process group. The distributed queue is an adaptor over an
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* existing (local) queue, which must model the @ref Buffer
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* concept. Each process stores a distinct copy of the local queue,
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* from which it draws or removes elements via the @ref pop and @ref
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* top members.
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*
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* The value type of the local queue must be a model of the @ref
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* GlobalDescriptor concept. The @ref push operation of the
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* distributed queue passes (via a message) the value to its owning
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* processor. Thus, the elements within a particular local queue are
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* guaranteed to have the process owning that local queue as an owner.
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*
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* Synchronization of distributed queues occurs in the @ref empty and
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* @ref size functions, which will only return "empty" values (true or
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* 0, respectively) when the entire distributed queue is empty. If the
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* local queue is empty but the distributed queue is not, the
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* operation will block until either condition changes. When the @ref
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* size function of a nonempty queue returns, it returns the size of
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* the local queue. These semantics were selected so that sequential
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* code that processes elements in the queue via the following idiom
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* can be parallelized via introduction of a distributed queue:
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*
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* distributed_queue<...> Q;
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* Q.push(x);
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* while (!Q.empty()) {
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* // do something, that may push a value onto Q
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* }
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*
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* In the parallel version, the initial @ref push operation will place
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* the value @c x onto its owner's queue. All processes will
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* synchronize at the call to empty, and only the process owning @c x
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* will be allowed to execute the loop (@ref Q.empty() returns
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* false). This iteration may in turn push values onto other remote
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* queues, so when that process finishes execution of the loop body
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* and all processes synchronize again in @ref empty, more processes
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* may have nonempty local queues to execute. Once all local queues
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* are empty, @ref Q.empty() returns @c false for all processes.
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*
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* The distributed queue can receive messages at two different times:
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* during synchronization and when polling @ref empty. Messages are
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* always received during synchronization, to ensure that accurate
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* local queue sizes can be determines. However, whether @ref empty
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* should poll for messages is specified as an option to the
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* constructor. Polling may be desired when the order in which
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* elements in the queue are processed is not important, because it
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* permits fewer synchronization steps and less communication
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* overhead. However, when more strict ordering guarantees are
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* required, polling may be semantically incorrect. By disabling
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* polling, one ensures that parallel execution using the idiom above
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* will not process an element at a later "level" before an earlier
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* "level".
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*
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* The distributed queue nearly models the @ref Buffer
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* concept. However, the @ref push routine does not necessarily
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* increase the result of @c size() by one (although the size of the
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* global queue does increase by one).
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*/
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template<typename ProcessGroup, typename OwnerMap, typename Buffer,
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typename UnaryPredicate = always_push>
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class distributed_queue
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{
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typedef distributed_queue self_type;
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enum {
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/** Message indicating a remote push. The message contains a
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* single value x of type value_type that is to be pushed on the
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* receiver's queue.
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*/
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msg_push,
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/** Push many elements at once. */
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msg_multipush
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};
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public:
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typedef ProcessGroup process_group_type;
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typedef Buffer buffer_type;
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typedef typename buffer_type::value_type value_type;
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typedef typename buffer_type::size_type size_type;
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/** Construct a new distributed queue.
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*
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* Build a new distributed queue that communicates over the given @p
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* process_group, whose local queue is initialized via @p buffer and
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* which may or may not poll for messages.
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*/
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explicit
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distributed_queue(const ProcessGroup& process_group,
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const OwnerMap& owner,
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const Buffer& buffer,
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bool polling = false);
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/** Construct a new distributed queue.
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*
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* Build a new distributed queue that communicates over the given @p
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* process_group, whose local queue is initialized via @p buffer and
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* which may or may not poll for messages.
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*/
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explicit
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distributed_queue(const ProcessGroup& process_group = ProcessGroup(),
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const OwnerMap& owner = OwnerMap(),
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const Buffer& buffer = Buffer(),
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const UnaryPredicate& pred = UnaryPredicate(),
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bool polling = false);
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/** Construct a new distributed queue.
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*
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* Build a new distributed queue that communicates over the given @p
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* process_group, whose local queue is default-initalized and which
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* may or may not poll for messages.
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*/
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distributed_queue(const ProcessGroup& process_group, const OwnerMap& owner,
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const UnaryPredicate& pred, bool polling = false);
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/** Virtual destructor required with virtual functions.
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*
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*/
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virtual ~distributed_queue() {}
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/** Push an element onto the distributed queue.
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*
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* The element will be sent to its owner process to be added to that
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* process's local queue. If polling is enabled for this queue and
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* the owner process is the current process, the value will be
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* immediately pushed onto the local queue.
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*
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* Complexity: O(1) messages of size O(sizeof(value_type)) will be
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* transmitted.
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*/
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void push(const value_type& x);
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/** Pop an element off the local queue.
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*
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* @p @c !empty()
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*/
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void pop() { buffer.pop(); }
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/**
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* Return the element at the top of the local queue.
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*
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* @p @c !empty()
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*/
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value_type& top() { return buffer.top(); }
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/**
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* \overload
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*/
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const value_type& top() const { return buffer.top(); }
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/** Determine if the queue is empty.
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*
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* When the local queue is nonempty, returns @c true. If the local
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* queue is empty, synchronizes with all other processes in the
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* process group until either (1) the local queue is nonempty
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* (returns @c true) (2) the entire distributed queue is empty
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* (returns @c false).
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*/
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bool empty() const;
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/** Determine the size of the local queue.
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*
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* The behavior of this routine is equivalent to the behavior of
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* @ref empty, except that when @ref empty returns true this
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* function returns the size of the local queue and when @ref empty
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* returns false this function returns zero.
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*/
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size_type size() const;
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// private:
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/** Synchronize the distributed queue and determine if all queues
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* are empty.
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*
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* \returns \c true when all local queues are empty, or false if at least
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* one of the local queues is nonempty.
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* Defined as virtual for derived classes like depth_limited_distributed_queue.
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*/
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virtual bool do_synchronize() const;
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private:
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// Setup triggers
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void setup_triggers();
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// Message handlers
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void
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handle_push(int source, int tag, const value_type& value,
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trigger_receive_context);
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void
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handle_multipush(int source, int tag, const std::vector<value_type>& values,
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trigger_receive_context);
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mutable ProcessGroup process_group;
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OwnerMap owner;
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mutable Buffer buffer;
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UnaryPredicate pred;
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bool polling;
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typedef std::vector<value_type> outgoing_buffer_t;
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typedef std::vector<outgoing_buffer_t> outgoing_buffers_t;
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shared_ptr<outgoing_buffers_t> outgoing_buffers;
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};
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/// Helper macro containing the normal names for the template
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/// parameters to distributed_queue.
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#define BOOST_DISTRIBUTED_QUEUE_PARMS \
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typename ProcessGroup, typename OwnerMap, typename Buffer, \
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typename UnaryPredicate
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/// Helper macro containing the normal template-id for
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/// distributed_queue.
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#define BOOST_DISTRIBUTED_QUEUE_TYPE \
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distributed_queue<ProcessGroup, OwnerMap, Buffer, UnaryPredicate>
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/** Synchronize all processes involved with the given distributed queue.
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*
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* This function will synchronize all of the local queues for a given
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* distributed queue, by ensuring that no additional messages are in
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* transit. It is rarely required by the user, because most
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* synchronization of distributed queues occurs via the @c empty or @c
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* size methods.
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*/
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template<BOOST_DISTRIBUTED_QUEUE_PARMS>
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inline void
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synchronize(const BOOST_DISTRIBUTED_QUEUE_TYPE& Q)
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{ Q.do_synchronize(); }
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/// Construct a new distributed queue.
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template<typename ProcessGroup, typename OwnerMap, typename Buffer>
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inline distributed_queue<ProcessGroup, OwnerMap, Buffer>
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make_distributed_queue(const ProcessGroup& process_group,
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const OwnerMap& owner,
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const Buffer& buffer,
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bool polling = false)
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{
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typedef distributed_queue<ProcessGroup, OwnerMap, Buffer> result_type;
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return result_type(process_group, owner, buffer, polling);
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}
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} } } // end namespace boost::graph::distributed
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#include <boost/graph/distributed/detail/queue.ipp>
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#undef BOOST_DISTRIBUTED_QUEUE_TYPE
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#undef BOOST_DISTRIBUTED_QUEUE_PARMS
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#endif // BOOST_GRAPH_DISTRIBUTED_QUEUE_HPP
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