Re: RE: sem_trywait never returns EAGAIN

[Patrick Frants <patrick at quintiq dot com>]

2/26/2002 6:49:36 PM, "Bossom, John" <John.Bossom@Cognos.COM> wrote:

>Try checking the value of errno....
>
>Older UNIX methods would return -1 on failure and set errno to the actual
>specific error.

I am working under windows with pthreads-win32 and checking errno gives 0.

Patrick

>
>
>-----Original Message-----
>From: Patrick Frants [mailto:patrick@quintiq.com]
>Sent: February 26, 2002 12:43 PM
>To: pthreads-win32@sourceware.cygnus.com
>Subject: sem_trywait never returns EAGAIN
>
>
>Hi,
>
>From the Linux man pages I concluded that calling sem_trywait on a semaphore
>with a zero count should result in an EAGAIN return value. I get a -1 all
>time 
>time. Intiializing the count with 1 and calling sem_trywait two times
>results in 0 and -1 return codes. Initializing with 0, calling sem_trywait
>results in a -1 return 
>code. Initializing with 0, calling sem_post, and sem_trywait twice results
>in 0 and -1 return codes for the sem_trywait calls.
>
>Are my expectations wrong or is the behaviour of the library wrong?
>
>Here is my sample code:
>
>#include <pthread.h>
>#include <semaphore.h>
>#include <cassert>
>#include <cstdio>
>
>#pragma comment(lib, "pthreadvce")
>
>int main(int argc, char** argv)
>{
>  sem_t s;
>  assert(sem_init(&s, 0, 0) == 0);
>  int result = sem_trywait(&s);
>  if ( result == -1 )
>  {
>    perror("sem_wait"); // No error
>  }
>  else
>  {
>    printf("ok\n");
>  }
>
>  result = sem_post(&s);
>
>  result = sem_trywait(&s);
>  if ( result == -1 )
>  {
>    perror("sem_wait");
>  }
>  else
>  {
>    printf("ok\n");
>  }
>
>  return 0;
>}
>  
>  
>
>	
>--
>Patrick Frants
>Senior Software Engineer
>Quintiq
>patrick@quintiq.com
>www.quintiq.com
>
>
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--
Patrick Frants
Senior Software Engineer
Quintiq
patrick@quintiq.com
www.quintiq.com