openmp

问题 I'm trying to use openmp in cython. I need to do two things in cython: i) use the #pragma omp single{} scope in my cython code. ii) use the #pragma omp barrier{} Does anyone know how to do this in cython? Here are more details. I have a nogil cdef-function my_fun() which I call in an omp for-loop: from cython.parallel cimport prange cimport openmp cdef int i with nogil: for i in prange(10,schedule='static', num_threads=10): my_func(i) Inside my_func I need to place a barrier to wait for all

问题 I would like to take advantage of OpenMP to make my task parallel. I need to subtract the same quantity to all the elements of an array and write the result in another vector. Both arrays are dynamically allocated with malloc and the first one is filled with values from a file. Each element is of type uint64_t . #pragma omp parallel for for (uint64_t i = 0; i < size; ++i) { new_vec[i] = vec[i] - shift; } Where shift is the fixed value I want to remove from every element of vec . size is the

问题 I am trying to test Pi calculation problem with OpenMP. I have this code: #pragma omp parallel private(i, x, y, myid) shared(n) reduction(+:numIn) num_threads(NUM_THREADS) { printf("Thread ID is: %d\n", omp_get_thread_num()); myid = omp_get_thread_num(); printf("Thread myid is: %d\n", myid); for(i = myid*(n/NUM_THREADS); i < (myid+1)*(n/NUM_THREADS); i++) { //for(i = 0; i < n; i++) { x = (double)rand()/RAND_MAX; y = (double)rand()/RAND_MAX; if (x*x + y*y <= 1) numIn++; } printf("Thread ID is:

问题 I have parallelized image convolution and lu factorization using OpenMP and Intel TBB. I am testing it on 1-8 cores. But when I try it on 1 core in OPenMP and TBB by specifying one thread using set_num_threads(1), and task_scheduler_init InitTBB(1) respectively for example; TBB performance shows some small degradation compared to sequential code due to TBB overhead, but surprisingly OpenMP doesnt show any overhead on single core and performs exactly equal to sequential code (using Intel O3

问题 I have this piece of code that is parallelized. int i,n; double area,pi,x; area=0.0; #pragma omp parallel for private(x) reduction (+:area) for(i=0; i<n; i++){ x= (i+0.5)/n; area+= 4.0/(1.0+x*x); } pi = area/n; It is said that the reduction will remove the race condition that could happen if we didn't use a reduction. Still I'm wondering do we need to add lastprivate for area since its used outside the parallel loop and will not be visible outside of it. Else does the reduction cover this as

问题 I am trying to parallelize a for-loop which scans std::map. Below is my toy program: #include <iostream> #include <cstdio> #include <map> #include <string> #include <cassert> #include <omp.h> #define NUM 100000 using namespace std; int main() { omp_set_num_threads(16); int realThreads = 0; string arr[] = {"0", "1", "2"}; std::map<int, string> myMap; for(int i=0; i<NUM; ++i) myMap[i] = arr[i % 3]; string is[NUM]; #pragma omp parallel for for(map<int, string>::iterator it = myMap.begin(); it !=

问题 I have a very basic question (maybe stupid) regarding shared variables in OpenMP. Consider the following code: void main() { int numthreads; #pragma omp parallel default(none) shared(numthreads) { numthreads = omp_get_num_threads(); printf("%d\n",numthreads); } } Now the value of numthreads is the same for all threads. is there a possibility that since various threads are writing the same value to the same variable , the value might get garbled/mangled ? Or is this operation on a primitive

问题 Both of reduction and collapse clauses in OMP confuses me, some points raised popped into my head Why reduction doesn't work with minus? as in the limitation listed here Is there any work around to achieve minus? How does a unary operator work, i.e. x++ or x--? is the -- or ++ applied to each partial result? or only once at the creation of the global result? both cases are totally different. About the collapse.. could we apply collapse on a nested loops but have some lines of code in between

问题 I'm doing some time trials on my code, and logically it seems really easy to parallelize with OpenMP as each trial is independent of the others. As it stands, my code looks something like this: for(int size = 30; size < 50; ++size) { #pragma omp parallel for for(int trial = 0; trial < 8; ++trial) { time_t start, end; //initializations time(&start); //perform computation time(&end); output << size << "\t" << difftime(end,start) << endl; } output << endl; } I have a sneaking suspicion that this

问题 According to valgrind, I can induce a memory leak when compiling a simple hello-world program with OpenMP. This doesn't make sense, because the hello-world program does not intentionally use any OpenMP functionality. Suppose the program below is named hi.c and compiled according to $ gcc -o hi hi.c GCC version 4.8.3 #include <stdio.h> int main( void ) { printf( "hi\n" ); return 1; } We should expect a leak report from valgrind to verify the obvious: there are no leaks. My observations agree