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/*========================== omp_num_threads.hpp ============================
* include openmp and provide a function to compute a smart number of threads
*
* Hugo Raguet 2018
*===========================================================================*/
#pragma once
#ifdef _OPENMP
#include <omp.h>
#include <cstdint> // requires C++11, needed for uintmax_t
/* rough minimum number of operations per thread */
#ifndef MIN_OPS_PER_THREAD
#define MIN_OPS_PER_THREAD 10000
#endif
/* num_ops is a rough estimation of the total number of operations
* max_threads is the maximum number of jobs performed in parallel */
static inline int compute_num_threads(uintmax_t num_ops,
uintmax_t max_threads)
{
uintmax_t num_threads = num_ops/MIN_OPS_PER_THREAD;
if (num_threads > (unsigned) omp_get_max_threads()){
num_threads = omp_get_max_threads();
}
if (num_threads > (unsigned) omp_get_num_procs()){
num_threads = omp_get_num_procs();
}
if (num_threads > max_threads){ num_threads = max_threads; }
return num_threads > 1 ? num_threads : 1;
}
/* overload for max_threads defaulting to num_ops */
static inline int compute_num_threads(uintmax_t num_ops)
{ return compute_num_threads(num_ops, num_ops); }
#define NUM_THREADS(...) \
num_threads(compute_num_threads((uintmax_t) __VA_ARGS__))
#else /* provide default definitions for basic openmp queries */
static inline int omp_get_num_procs(){ return 1; }
static inline int omp_get_thread_num(){ return 0; }
static inline int omp_get_max_threads(){ return 1; }
static inline void omp_set_num_threads(int){ /* do nothing */ }
static inline int compute_num_threads(int num_ops, int max_threads = 1)
{ return 1; }
#endif
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