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RE: semaphores

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....
-----Original Message-----
From: Rob Fanner []
Sent: May 30, 2002 10:10 AM
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.

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