RE: semaphores

["Bossom, John" <John.Bossom@Cognos.COM>]

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sem_getvalue()? 
 
I don't see that in the standard (POSIX.1b (POSIX 1003.1b-1993))... I assume
this
has been added to the pthreads-win32 implementation as an extension (Ross?)
 
Perhaps there is a bug in that new method.
 
However, try looping over sem_trywait and count the # of times it returns 0.
It should return EAGAIN
when the semaphore count is zero.
 
Sorry, I can't help you with the sem_getvalue....
 
Note that since the sem_ calls are from an earlier standard, that when they
fail they are supposed
to return -1 and set errno to the actual error number....
 
John.

-----Original Message-----
From: Rob Fanner [mailto:rfanner@stonethree.com]
Sent: May 30, 2002 10:10 AM
To: pthreads-win32@sources.redhat.com
Subject: semaphores


I'm new to using pthreads-win32 (SNAPSHOT 2002-03-02), and I have to port 
a program from Linux to Windows 2000. A bug has somehow crept into my 
code, and I've narrowed the problem area down to a code fragment similar 
to the following:
 
#include <semaphore.h>
#include <cassert>
#include <iostream>
 
using namespace std;
 
int main()
{
   /**
    * We want to check wether a semaphore can be initialised
    * with a value.
    */
   
   // a semaphore
   sem_t psem;
 
   // initialise it with value 10
   assert(sem_init(&psem,0,10) == 0);                       // ASSERT NO 1
   // if the semaphore initialisation was ok, the sem
   // should now have the value 10
   int ret = 0;
   assert(sem_getvalue(&psem,&ret) == 0);               // ASSERT NO 2
   // if no errors occured then value is now in the 
   // integer ret
   cout << endl << "sem_getvalue() returns value " << ret << endl << flush;
 
   return 0;
}
 
I'm using MS VC++ 6.0, and I'm linking with the precompiled pthreadVCE.lib
library.
At runtime, the first assert() passes OK, but second fails.
I have no idea why this fails (hopefully it's simply a newby error, and not
a bug in 
the pthreads-win32 lib), but it does.
 
Thanks
Rob


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