openmp

问题 I am in the process of learning how to use OpenMP in C, and as a HelloWorld exercise I am writing a program to count primes. I then parallelise this as follows: int numprimes = 0; #pragma omp parallel for reduction (+:numprimes) for (i = 1; i <= n; i++) { if (is_prime(i) == true) numprimes ++; } I compile this code using gcc -g -Wall -fopenmp -o primes primes.c -lm ( -lm for the math.h functions I am using). Then I run this code on an Intel® Core™2 Duo CPU E8400 @ 3.00GHz × 2 , and as

问题 A thread that reads a shared variable has first to call flush , and a thread that writes to a shared variable has to call OpenMP flush afterwards, to keep the shared variable in main memory and cache synchronized. How does the flush function know in which direction to flush? It needs to know which of both variables (main memory or cache) is newer. I assume, but I am not sure, that the OS or CPU take care of this somehow. Does someone know? 回答1: flush is not a function - it is an OpenMP

问题 I’m building an R package that has some .c files with code that uses OpenMP, and these C functions are called from .cpp files, but the .cpp files themselves don’t make any use of OpenMP. e.g. cfile.c : int parallel_function(double *x, int n) { int i; #pragma omp parallel for firstprivate(x, n) for (i = 0; i < n; i++){ x[i] *= 2; } } cppfile.cpp : #include <Rcpp.h> using namespace Rcpp; extern “C” { int parallel_function(double *x, int n); } // [[Rcpp::export]] void multiply_by_two

问题 I’m building an R package that has some .c files with code that uses OpenMP, and these C functions are called from .cpp files, but the .cpp files themselves don’t make any use of OpenMP. e.g. cfile.c : int parallel_function(double *x, int n) { int i; #pragma omp parallel for firstprivate(x, n) for (i = 0; i < n; i++){ x[i] *= 2; } } cppfile.cpp : #include <Rcpp.h> using namespace Rcpp; extern “C” { int parallel_function(double *x, int n); } // [[Rcpp::export]] void multiply_by_two

问题 I’m building an R package that has some .c files with code that uses OpenMP, and these C functions are called from .cpp files, but the .cpp files themselves don’t make any use of OpenMP. e.g. cfile.c : int parallel_function(double *x, int n) { int i; #pragma omp parallel for firstprivate(x, n) for (i = 0; i < n; i++){ x[i] *= 2; } } cppfile.cpp : #include <Rcpp.h> using namespace Rcpp; extern “C” { int parallel_function(double *x, int n); } // [[Rcpp::export]] void multiply_by_two

问题 I am using OpenMP and MPI to parallelize some matrix operations in c. Some of the functions operating on the matrix are written in Fortran. The Fortran functions require a buffer array to be passed in which is only used internally in the function. Currently I am allocating buffers in each parallel section similar to the code below. int i = 0; int n = 1024; // Actually this is read from command line double **a = createNbyNMat(n); #pragma omp parallel { double *buf; buf = malloc(sizeof(double)

问题 I am using OpenMP and MPI to parallelize some matrix operations in c. Some of the functions operating on the matrix are written in Fortran. The Fortran functions require a buffer array to be passed in which is only used internally in the function. Currently I am allocating buffers in each parallel section similar to the code below. int i = 0; int n = 1024; // Actually this is read from command line double **a = createNbyNMat(n); #pragma omp parallel { double *buf; buf = malloc(sizeof(double)

问题 I have the following code: void simulation (MD *md){ double sum; #pragma omp parallel private (move) { for(move = 0; move < maxIterations; ++move) { cicleDoMove(md); cicleForces(md); cicleMkekin(md,sum); // ... } } } where : void cicleMkekin(Md *md, double sum){ #pragma omp for reduction(+ : sum) for (i = 0; i < md->mdsize; i++) { sum += mkekin(..); } // .. } I got the following error: "reduction variable 'sum' is private in outer context" The variable sum is shared not private, in fact if I

问题 Does OpenMP support an atomic minimum for C++11? If OpenMP has no portable method: Is there some way of doing it using a x86 or amd64 feature? In the OpenMP specifications I found nothing for C++ but the Fortran version seems to support it. See 2.8.5 of the v3.1 for the details. For C++ it states binop is one of +, *, -, /, &, ^, |, <<, or >>. but for Fortran it states intrinsic_procedure_name is one of MAX, MIN, IAND, IOR, or IEOR. In case you are interested in more context: I am looking for

问题 Does OpenMP support an atomic minimum for C++11? If OpenMP has no portable method: Is there some way of doing it using a x86 or amd64 feature? In the OpenMP specifications I found nothing for C++ but the Fortran version seems to support it. See 2.8.5 of the v3.1 for the details. For C++ it states binop is one of +, *, -, /, &, ^, |, <<, or >>. but for Fortran it states intrinsic_procedure_name is one of MAX, MIN, IAND, IOR, or IEOR. In case you are interested in more context: I am looking for