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Keep number of threads in a global variable separate from global OMP config #6152

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Keep number of threads in a global variable separate from global OMP config #6152

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13 changes: 5 additions & 8 deletions include/LightGBM/utils/openmp_wrapper.h
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Original file line number Diff line number Diff line change
Expand Up @@ -17,20 +17,17 @@
#include <stdexcept>
#include <vector>

static int lgb_global_omp_threads = omp_get_max_threads();
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I've been testing an approach like this over on my fork (jameslamb#55) and I don't think just having static int in a header here will work.

I found that when I did that, everything that included openmp_wrapper.h got its own copy of that integer, and that therefore updates like this:

LightGBM/src/c_api.cpp

Line 316 in 8ed371c

OMP_SET_NUM_THREADS(config_.num_threads);

did not propagate through everywhere.


inline int OMP_NUM_THREADS() {
int ret = 1;
#pragma omp parallel
#pragma omp master
{ ret = omp_get_num_threads(); }
return ret;
return lgb_global_omp_threads;
}

inline void OMP_SET_NUM_THREADS(int num_threads) {
static const int default_omp_num_threads = OMP_NUM_THREADS();
if (num_threads > 0) {
omp_set_num_threads(num_threads);
lgb_global_omp_threads = num_threads;
} else {
omp_set_num_threads(default_omp_num_threads);
lgb_global_omp_threads = omp_get_max_threads();
}
}

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