Return Value of a pthread_create

Question

I am attempting to make the following call,

PID = pthread_create(&t, NULL, schedule_sync(sch,t1), NULL);

schedule_sync returns a value, I would like to be able to grab that value, but from what Ive read about pthread_create, you should pass a "void" function. Is it possible to get the return value of schedule_sync, or am I going to have to modify some kind of parameter passed in?

Thanks for the help!

Answer 1

pthread_create returns an <errno.h> code. It doesn't create a new process so there's no new PID.

To pass a pointer to your function, take its address with &.

pthread_create takes a function of form void *func( void * ).

So assuming schedule_sync is the thread function,

struct schedule_sync_params {
    foo sch;
    bar t1;
    int result;
    pthread_t thread;
} args = { sch, t1 };

int err = pthread_create( &args.thread, NULL, &schedule_sync, &args );
 .....

schedule_sync_params *params_ptr; // not necessary if you still have the struct
err = pthread_join( args.thread, &params_ptr ); // just pass NULL instead
 .....

void *schedule_sync( void *args_v ) {
   shedule_sync_params *args = args_v;
   ....
   args->result = return_value;
   return args;
}

Answer 2

schedule_sync should return void* which can be anything. You can grab the value with pthread_join.

//Function shoulde be look like this
void* schedule_sync(void* someStructureWithArguments);

//Call pthread_create like so
pthread_create(&t, NULL, schedule_sync, locationOfSomeStructureWithArguments);

When thread terminates

pthread_joint(&t, locationToPutReturnValue);

Don't have a development enviroment, so I can't get you the exact sequence just yet, but this will hopefully get you started.