CODEWITHSUNDEEP
cpthreads
Renju Liu
Renju Liu

Reputation: 55

Create pthread with the function of multiple arguments

If I am going to create a pthread for the following function.

Assume everything is properly delared.

pthread_create(&threadId, &attr, (void * (*)(void*))function, //what should be the arguments for here??);
int a = 0;
int b = 1;
//c and d are global variables.

void function(int a, int b){
    c = a;
    d = b;
}

Upvotes: 4

Views: 13603

Answers (2)

caf
caf

Reputation: 239341

The pthread thread function always takes one void * argument and returns a void * value. If you want to pass two arguments, you must wrap them in a struct - for example:

struct thread_args {
    int a;
    int b;
};

void *function(void *);

struct thread_args *args = malloc(sizeof *args);

if (args != NULL)
{
    args->a = 0;
    args->b = 1;
    pthread_create(&threadId, &attr, &function, args);
}

and for the thread function itself:

void *function(void *argp)
{
    struct thread_args *args = argp;

    int c = args->a;
    int d = args->b;

    free(args);

    /* ... */

You don't need to use malloc() and free(), but you must somehow ensure that the original thread doesn't deallocate or re-use the thread arguments struct until the called thread has finished with it.

Upvotes: 3

Peter Crabtree
Peter Crabtree

Reputation: 929

This does not work. function() has to take exactly one argument. That's why you have to do this:

(void * ()(void))

You're telling your compiler "no, seriously, this function only takes one argument", which of course it doesn't.

What you have to do instead is pass a single argument (say a pointer to a struct) which gets you the information you need.

Edit: See here for an example: number of arguments for a function in pthread

Upvotes: 5

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