818ab71a41
From-SVN: r232055
313 lines
9.4 KiB
C++
313 lines
9.4 KiB
C++
// -*- C++ -*-
|
||
|
||
// Copyright (C) 2007-2016 Free Software Foundation, Inc.
|
||
//
|
||
// This file is part of the GNU ISO C++ Library. This library is free
|
||
// software; you can redistribute it and/or modify it under the terms
|
||
// of the GNU General Public License as published by the Free Software
|
||
// Foundation; either version 3, or (at your option) any later
|
||
// version.
|
||
|
||
// This library is distributed in the hope that it will be useful, but
|
||
// WITHOUT ANY WARRANTY; without even the implied warranty of
|
||
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
||
// General Public License for more details.
|
||
|
||
// Under Section 7 of GPL version 3, you are granted additional
|
||
// permissions described in the GCC Runtime Library Exception, version
|
||
// 3.1, as published by the Free Software Foundation.
|
||
|
||
// You should have received a copy of the GNU General Public License and
|
||
// a copy of the GCC Runtime Library Exception along with this program;
|
||
// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
|
||
// <http://www.gnu.org/licenses/>.
|
||
|
||
/** @file parallel/workstealing.h
|
||
* @brief Parallelization of embarrassingly parallel execution by
|
||
* means of work-stealing.
|
||
*
|
||
* Work stealing is described in
|
||
*
|
||
* R. D. Blumofe and C. E. Leiserson.
|
||
* Scheduling multithreaded computations by work stealing.
|
||
* Journal of the ACM, 46(5):720–748, 1999.
|
||
*
|
||
* This file is a GNU parallel extension to the Standard C++ Library.
|
||
*/
|
||
|
||
// Written by Felix Putze.
|
||
|
||
#ifndef _GLIBCXX_PARALLEL_WORKSTEALING_H
|
||
#define _GLIBCXX_PARALLEL_WORKSTEALING_H 1
|
||
|
||
#include <parallel/parallel.h>
|
||
#include <parallel/random_number.h>
|
||
#include <parallel/compatibility.h>
|
||
|
||
namespace __gnu_parallel
|
||
{
|
||
|
||
#define _GLIBCXX_JOB_VOLATILE volatile
|
||
|
||
/** @brief One __job for a certain thread. */
|
||
template<typename _DifferenceTp>
|
||
struct _Job
|
||
{
|
||
typedef _DifferenceTp _DifferenceType;
|
||
|
||
/** @brief First element.
|
||
*
|
||
* Changed by owning and stealing thread. By stealing thread,
|
||
* always incremented. */
|
||
_GLIBCXX_JOB_VOLATILE _DifferenceType _M_first;
|
||
|
||
/** @brief Last element.
|
||
*
|
||
* Changed by owning thread only. */
|
||
_GLIBCXX_JOB_VOLATILE _DifferenceType _M_last;
|
||
|
||
/** @brief Number of elements, i.e. @c _M_last-_M_first+1.
|
||
*
|
||
* Changed by owning thread only. */
|
||
_GLIBCXX_JOB_VOLATILE _DifferenceType _M_load;
|
||
};
|
||
|
||
/** @brief Work stealing algorithm for random access iterators.
|
||
*
|
||
* Uses O(1) additional memory. Synchronization at job lists is
|
||
* done with atomic operations.
|
||
* @param __begin Begin iterator of element sequence.
|
||
* @param __end End iterator of element sequence.
|
||
* @param __op User-supplied functor (comparator, predicate, adding
|
||
* functor, ...).
|
||
* @param __f Functor to @a process an element with __op (depends on
|
||
* desired functionality, e. g. for std::for_each(), ...).
|
||
* @param __r Functor to @a add a single __result to the already
|
||
* processed elements (depends on functionality).
|
||
* @param __base Base value for reduction.
|
||
* @param __output Pointer to position where final result is written to
|
||
* @param __bound Maximum number of elements processed (e. g. for
|
||
* std::count_n()).
|
||
* @return User-supplied functor (that may contain a part of the result).
|
||
*/
|
||
template<typename _RAIter,
|
||
typename _Op,
|
||
typename _Fu,
|
||
typename _Red,
|
||
typename _Result>
|
||
_Op
|
||
__for_each_template_random_access_workstealing(_RAIter __begin,
|
||
_RAIter __end, _Op __op,
|
||
_Fu& __f, _Red __r,
|
||
_Result __base,
|
||
_Result& __output,
|
||
typename std::iterator_traits<_RAIter>::difference_type __bound)
|
||
{
|
||
_GLIBCXX_CALL(__end - __begin)
|
||
|
||
typedef std::iterator_traits<_RAIter> _TraitsType;
|
||
typedef typename _TraitsType::difference_type _DifferenceType;
|
||
|
||
const _Settings& __s = _Settings::get();
|
||
|
||
_DifferenceType __chunk_size =
|
||
static_cast<_DifferenceType>(__s.workstealing_chunk_size);
|
||
|
||
// How many jobs?
|
||
_DifferenceType __length = (__bound < 0) ? (__end - __begin) : __bound;
|
||
|
||
// To avoid false sharing in a cache line.
|
||
const int __stride = (__s.cache_line_size * 10
|
||
/ sizeof(_Job<_DifferenceType>) + 1);
|
||
|
||
// Total number of threads currently working.
|
||
_ThreadIndex __busy = 0;
|
||
|
||
_Job<_DifferenceType> *__job;
|
||
|
||
omp_lock_t __output_lock;
|
||
omp_init_lock(&__output_lock);
|
||
|
||
// Write base value to output.
|
||
__output = __base;
|
||
|
||
// No more threads than jobs, at least one thread.
|
||
_ThreadIndex __num_threads = __gnu_parallel::max<_ThreadIndex>
|
||
(1, __gnu_parallel::min<_DifferenceType>(__length,
|
||
__get_max_threads()));
|
||
|
||
# pragma omp parallel shared(__busy) num_threads(__num_threads)
|
||
{
|
||
# pragma omp single
|
||
{
|
||
__num_threads = omp_get_num_threads();
|
||
|
||
// Create job description array.
|
||
__job = new _Job<_DifferenceType>[__num_threads * __stride];
|
||
}
|
||
|
||
// Initialization phase.
|
||
|
||
// Flags for every thread if it is doing productive work.
|
||
bool __iam_working = false;
|
||
|
||
// Thread id.
|
||
_ThreadIndex __iam = omp_get_thread_num();
|
||
|
||
// This job.
|
||
_Job<_DifferenceType>& __my_job = __job[__iam * __stride];
|
||
|
||
// Random number (for work stealing).
|
||
_ThreadIndex __victim;
|
||
|
||
// Local value for reduction.
|
||
_Result __result = _Result();
|
||
|
||
// Number of elements to steal in one attempt.
|
||
_DifferenceType __steal;
|
||
|
||
// Every thread has its own random number generator
|
||
// (modulo __num_threads).
|
||
_RandomNumber __rand_gen(__iam, __num_threads);
|
||
|
||
// This thread is currently working.
|
||
# pragma omp atomic
|
||
++__busy;
|
||
|
||
__iam_working = true;
|
||
|
||
// How many jobs per thread? last thread gets the rest.
|
||
__my_job._M_first = static_cast<_DifferenceType>
|
||
(__iam * (__length / __num_threads));
|
||
|
||
__my_job._M_last = (__iam == (__num_threads - 1)
|
||
? (__length - 1)
|
||
: ((__iam + 1) * (__length / __num_threads) - 1));
|
||
__my_job._M_load = __my_job._M_last - __my_job._M_first + 1;
|
||
|
||
// Init result with _M_first value (to have a base value for reduction)
|
||
if (__my_job._M_first <= __my_job._M_last)
|
||
{
|
||
// Cannot use volatile variable directly.
|
||
_DifferenceType __my_first = __my_job._M_first;
|
||
__result = __f(__op, __begin + __my_first);
|
||
++__my_job._M_first;
|
||
--__my_job._M_load;
|
||
}
|
||
|
||
_RAIter __current;
|
||
|
||
# pragma omp barrier
|
||
|
||
// Actual work phase
|
||
// Work on own or stolen current start
|
||
while (__busy > 0)
|
||
{
|
||
// Work until no productive thread left.
|
||
# pragma omp flush(__busy)
|
||
|
||
// Thread has own work to do
|
||
while (__my_job._M_first <= __my_job._M_last)
|
||
{
|
||
// fetch-and-add call
|
||
// Reserve current job block (size __chunk_size) in my queue.
|
||
_DifferenceType __current_job =
|
||
__fetch_and_add<_DifferenceType>(&(__my_job._M_first),
|
||
__chunk_size);
|
||
|
||
// Update _M_load, to make the three values consistent,
|
||
// _M_first might have been changed in the meantime
|
||
__my_job._M_load = __my_job._M_last - __my_job._M_first + 1;
|
||
for (_DifferenceType __job_counter = 0;
|
||
__job_counter < __chunk_size
|
||
&& __current_job <= __my_job._M_last;
|
||
++__job_counter)
|
||
{
|
||
// Yes: process it!
|
||
__current = __begin + __current_job;
|
||
++__current_job;
|
||
|
||
// Do actual work.
|
||
__result = __r(__result, __f(__op, __current));
|
||
}
|
||
|
||
# pragma omp flush(__busy)
|
||
}
|
||
|
||
// After reaching this point, a thread's __job list is empty.
|
||
if (__iam_working)
|
||
{
|
||
// This thread no longer has work.
|
||
# pragma omp atomic
|
||
--__busy;
|
||
|
||
__iam_working = false;
|
||
}
|
||
|
||
_DifferenceType __supposed_first, __supposed_last,
|
||
__supposed_load;
|
||
do
|
||
{
|
||
// Find random nonempty deque (not own), do consistency check.
|
||
__yield();
|
||
# pragma omp flush(__busy)
|
||
__victim = __rand_gen();
|
||
__supposed_first = __job[__victim * __stride]._M_first;
|
||
__supposed_last = __job[__victim * __stride]._M_last;
|
||
__supposed_load = __job[__victim * __stride]._M_load;
|
||
}
|
||
while (__busy > 0
|
||
&& ((__supposed_load <= 0)
|
||
|| ((__supposed_first + __supposed_load - 1)
|
||
!= __supposed_last)));
|
||
|
||
if (__busy == 0)
|
||
break;
|
||
|
||
if (__supposed_load > 0)
|
||
{
|
||
// Has work and work to do.
|
||
// Number of elements to steal (at least one).
|
||
__steal = (__supposed_load < 2) ? 1 : __supposed_load / 2;
|
||
|
||
// Push __victim's current start forward.
|
||
_DifferenceType __stolen_first =
|
||
__fetch_and_add<_DifferenceType>
|
||
(&(__job[__victim * __stride]._M_first), __steal);
|
||
_DifferenceType __stolen_try = (__stolen_first + __steal
|
||
- _DifferenceType(1));
|
||
|
||
__my_job._M_first = __stolen_first;
|
||
__my_job._M_last = __gnu_parallel::min(__stolen_try,
|
||
__supposed_last);
|
||
__my_job._M_load = __my_job._M_last - __my_job._M_first + 1;
|
||
|
||
// Has potential work again.
|
||
# pragma omp atomic
|
||
++__busy;
|
||
__iam_working = true;
|
||
|
||
# pragma omp flush(__busy)
|
||
}
|
||
# pragma omp flush(__busy)
|
||
} // end while __busy > 0
|
||
// Add accumulated result to output.
|
||
omp_set_lock(&__output_lock);
|
||
__output = __r(__output, __result);
|
||
omp_unset_lock(&__output_lock);
|
||
}
|
||
|
||
delete[] __job;
|
||
|
||
// Points to last element processed (needed as return value for
|
||
// some algorithms like transform)
|
||
__f._M_finish_iterator = __begin + __length;
|
||
|
||
omp_destroy_lock(&__output_lock);
|
||
|
||
return __op;
|
||
}
|
||
} // end namespace
|
||
|
||
#endif /* _GLIBCXX_PARALLEL_WORKSTEALING_H */
|