posix threads

hi

i wrote a programm using libpthread unter obsd 3.3.

i create two threads but only one of them is running:

--- snip of source ---
pthread_t th1, th2;
char *mes1="Hello";
char *mes2="World";

if(pthread_create(&th1, NULL, print_message, mes1)!=0)
perror("pthread_create");
pthread_detach(th1);

if(pthread_create(&th2, NULL, print_message, mes2)!=0)
perror("pthread_create");
pthread_detach(th2);
--- snap -------------

the print_message function looks like this:

void *print_message(void *ptr)
{
char *mes=(char*)ptr;
printf("%s\n", mes);
return NULL;
}

If i compile the source with

gcc -o thread thread.c -lpthread

it produces no errors or warnings. but if i execute the binary,
i only get the output "Hello" from the first thread:

$ ./thread
Hello

If i put a sleep(1) behind every pthread_create()-call, i get
the right output:

$ ./thread
Hello
World

But why did this source need a sleep()-call?

On Thu, 06 May 2004 07:10:02 -0700, Stephan Sa? wrote:

> --- snip of source ---
> pthread_t th1, th2;
> char *mes1="Hello";
> char *mes2="World";
>
> if(pthread_create(&th1, NULL, print_message, mes1)!=0)
> perror("pthread_create");
> pthread_detach(th1);
>
> if(pthread_create(&th2, NULL, print_message, mes2)!=0)
> perror("pthread_create");
> pthread_detach(th2);
> --- snap -------------
<snip>
> it produces no errors or warnings. but if i execute the binary,
> i only get the output "Hello" from the first thread:
>
> $ ./thread
> Hello
>
> If i put a sleep(1) behind every pthread_create()-call, i get
> the right output:
>
> $ ./thread
> Hello
> World
>
> But why did this source need a sleep()-call?

I have to guess without seeing the rest of the code, but does the program
exit shortly after the last pthread_detach() ? If so, then the reason why
you never see the second thread's output is because your program
terminates before it ever gets a chance to run.

One solution you could consider is not using pthread_detach(), and then
using pthread_join() on each of the threads after you spawn the last one
-- that will ensure that your program doesn't return until the threads are
finished.

HTH,
--
Eric Enright /"\
sauronAtiptsoftDcom \ / ASCII Ribbon Campaign
X Against HTML E-Mail
Public Key: 0xBEDF636F / \

Eric Enright wrote:
> On Thu, 06 May 2004 07:10:02 -0700, Stephan Sa? wrote:
>
>
>>--- snip of source ---
>>pthread_t th1, th2;
>>char *mes1="Hello";
>>char *mes2="World";
>>
>>if(pthread_create(&th1, NULL, print_message, mes1)!=0)
>> perror("pthread_create");
>>pthread_detach(th1);
>>
>>if(pthread_create(&th2, NULL, print_message, mes2)!=0)
>> perror("pthread_create");
>>pthread_detach(th2);
>>--- snap -------------
>
> <snip>
>
>>it produces no errors or warnings. but if i execute the binary,
>>i only get the output "Hello" from the first thread:
>>
>>$ ./thread
>>Hello
>>
>>If i put a sleep(1) behind every pthread_create()-call, i get
>>the right output:
>>
>>$ ./thread
>>Hello
>>World
>>
>>But why did this source need a sleep()-call?
>
>
> I have to guess without seeing the rest of the code, but does the program
> exit shortly after the last pthread_detach() ? If so, then the reason why
> you never see the second thread's output is because your program
> terminates before it ever gets a chance to run.
>
> One solution you could consider is not using pthread_detach(), and then
> using pthread_join() on each of the threads after you spawn the last one
> -- that will ensure that your program doesn't return until the threads are
> finished.
>
> HTH,
Another possibility is for print_message to flush its print buffer.
Likewise, sight unseen.

MK

Der_gruene_Punkt@gmx.de (Stephan Sa?) wrote in
news:1ef9cfaa.0405060610.e0924ed@posting.google.co m:

> ...
> If i compile the source with
>
> gcc -o thread thread.c -lpthread
> ...

read gcc-local(1), use gcc -pthread instead and try again

--
Peter Strömberg
C2K2 C2K3 ISCCIV02 ISCCIV03