openmp

问题 I'm reading the book An introduction to parallel programming by Peter S. Pacheco. In Section 5.6.2, it gave an interesting discussion about reducing the fork/join overhead. Consider the odd-even transposition sort algorithm: for(phase=0; phase < n; phase++){ if(phase is even){ # pragma omp parallel for default(none) shared(n) private(i) for(i=1; i<n; i+=2){//meat} } else{ # pragma omp parallel for default(none) shared(n) private(i) for(i=1; i<n-1; i+=2){//meat} } } The author argues that the

问题 My problem is related to the one discussed here: Is there a way that OpenMP can operate on Qt spanwed threads? Upon trying to run my Qt-based program under Mac OS that has an OpenMP clause in a secondary thread, it crashed. After browsing through the web, now I understand that it is caused by a bug in the rather old version (4.2) of gcc supplied by Apple. Then I downloaded the latest 4.6 version of gcc from http://hpc.sourceforge.net and tried to compile the project, but I got the following

问题 I am trying to get a hybrid OpenMP / MPI job to run so that OpenMP threads are separated by core (only one thread per core). I have seen other answers which use numa-ctl and bash scripts to set environment variables, and I don't want to do this. I would like to be able to do this only by setting OMP_NUM_THREADS and or OMP_PROC_BIND and mpiexec options on the command line. I have tried the following - let's say I want 2 MPI processes that each have 2 OpenMP threads, and each of the threads are

问题 I have a program which uses POSIX timer ( timer_create() ). Essentially the program sets a timer and starts performing some lengthy (potentially infinite) computation. When the timer expires and a signal handler is called, the handler prints the best result yet that has been computed and quits the program. I consider doing the computation in parallel using OpenMP, because it should speed it up. In pthreads, there are special functions for example for setting signal masks for my threads or so.

问题 I am a newbie in programming with OpenMp. I wrote a simple c program to multiply matrix with a vector. Unfortunately, by comparing executing time I found that the OpenMP is much slower than the Sequential way. Here is my code (Here the matrix is N*N int, vector is N int, result is N long long): #pragma omp parallel for private(i,j) shared(matrix,vector,result,m_size) for(i=0;i<m_size;i++) { for(j=0;j<m_size;j++) { result[i]+=matrix[i][j]*vector[j]; } } And this is the code for sequential way:

问题 There is a thread (clang-omp in Xcode under El Capitan) discussing the possibilities of running OpenMP under El Capitan which was Xcode 7 I assume. I am wondering if it is possible to do it Xcode 8. I have tried both methods mentioned in the thread clang-omp in Xcode under El Capitan, but neither worked for Xcode 8. Considering it was between 2015 - 2016, I assume they work for Xcode 7. Following the setup steps allow me to run OpenMP in command line but not in Xcode 8 (get clang: error:

问题 There is a thread (clang-omp in Xcode under El Capitan) discussing the possibilities of running OpenMP under El Capitan which was Xcode 7 I assume. I am wondering if it is possible to do it Xcode 8. I have tried both methods mentioned in the thread clang-omp in Xcode under El Capitan, but neither worked for Xcode 8. Considering it was between 2015 - 2016, I assume they work for Xcode 7. Following the setup steps allow me to run OpenMP in command line but not in Xcode 8 (get clang: error:

问题 Is the C++ code below legal, or is there a problem with my compiler? The code was complied into a shared library using gcc version 4.4.6 20110731 (Red Hat 4.4.6-3) (GCC) and openMP and then called via R 2.15.2. int it=0; #pragma omp parallel sections shared(it) { #pragma omp section { std::cout<<"Entering section A"<<std::endl; for(it=0;it<10;it++) { std::cout<<"Iteration "<<it<<std::endl; } std::cout<<"Leaving section A with it="<<it<<std::endl; } #pragma omp section { std::cout<<"Entering

问题 I've been struggling a weird problem the last few days. We create some libraries using GCC 4.8 which link some of their dependencies statically - eg. log4cplus or boost. For these libraries we have created Python bindings using boost-python. Every time such a library used TLS (like log4cplus does in it's static initialization or stdlibc++ does when throwing an exception - not only during initialization phase) the whole thing crashed in a segfault - and every time the address of the thread

问题 I am experimenting with OpenMP. I wrote some code to check its performance. On a 4-core single Intel CPU with Kubuntu 11.04, the following program compiled with OpenMP is around 20 times slower than the program compiled without OpenMP. Why? I compiled it by g++ -g -O2 -funroll-loops -fomit-frame-pointer -march=native -fopenmp #include <math.h> #include <iostream> using namespace std; int main () { long double i=0; long double k=0.7; #pragma omp parallel for reduction(+:i) for(int t=1; t