Subj : Re: returning arguments
To   : comp.programming.threads
From : Huub
Date : Mon Jun 27 2005 08:49 pm

loic-dev@gmx.net wrote:
> Salut Huub,
> 
> 
> 
>>I know this isn't compilable code, but it's just to give an idea. My
>>question(s):
>>- Do threads *have* to be void?
> 
> 
>>From a pure semantic point of view, thread should be function returning
> a void*, that is a pointer to something.
> 
> 
> 
>>- Can I pass on return values directly from the thread?
> 
> 
> Yes, this is possible if the returned type can pad on a void*, that is
> its size is <= sizeof(void*).
> 
> For instance to return an integer, assuming that
> sizeof(int)<=sizeof(void*), then you can proceed as follows:
> 
> void*
> thread (void* args)
> {
> int result;
> ...
> return (void*) result;
> }
> 
> and where you're joining the thread:
> void *retp;
> int   retv;
> ...
> rc   = pthread_join (thread_id, &retp);
> assert (rc==0);
> retv = (int) retp;
> 
> 
> 
>>- If not, how do I pass them on?
> 
> 
> If you need to return a type that is bigger than a void*, you can
> proceed as follows:
> 
> In the thread:
> - allocate the type on the heap using e.g. malloc
> - return a pointer to the type located on the heap
> 
> void*
> thread (void* args)
> {
> void* retp;
> ...
> retp = malloc (sizeof(myType);
> // fills-up (*retp)
> ...
> return retp;
> }
> 
> where you're joining the thread:
> - reads the type
> - free the heap
> 
> void *retp;
> ...
> rc   = pthread_join (thread_id, &retp);
> // read *(retp)
> ...
> free (retp); 
> 
> 
> HTH,
> Loic.
> 
Thank you.

.