graph_parallel/include/boost/graph/distributed/queue.hpp
2009-07-29 02:54:07 +00:00

279 lines
10 KiB
C++

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