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pthread_create question

pthread_create question

pthread_create question

Hey, kinda feels like I'm in over my head here, but trying to learn how to use pthread_create and am having problems with passing in arguments. Right now, I have
 a = pthread_create(&thread1, NULL, MatrixTimes, (Matrixa, 0, i, MAX, Matrixb));

in my code calling pthread create, and

void MatrixTimes(int Matrixa[5][5], int start, int end, int max, int Matrixb[5][5])

as my function prototype. What I can gather from reading and the internet is that I need to create a void pointer and pass my arguements in that way... and that's where I go over my head. I see how it works with one item passed in, but looking to pass in several, 5 to be exact. Any help, or directions to a good pthread tutorial, would be much appreciated. Thanks.

RE: pthread_create question

If you've got multiple arguments, then you need to put them into a struct, then pass a pointer to an instance of that struct.


struct matArgs {
    int Matrixa[5][5];
    int start;
    int end;
    int max;
    int Matrixb[5][5];

Which would be used as


struct matArgs args;
// fill in args
a = pthread_create(&thread1, NULL, MatrixTimesWrapper, &args);

Where MatrixTimesWrapper is something like


void *MatrixTimesWrapper ( void *p ) {
    struct matArgs *m = p;
    MatrixTimes(m->Matrixa, m->start, m->end, m->max, m->Matrixb);
    return NULL;

If you're intending to use the same function over and over, in different threads, with different arguments, then it's a really good idea to use malloc() to allocate each thread-specific instance of matArgs where the threads are created, and call free() inside the thread when it has finished looking at the parameters.

If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.

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