Named Semaphores

3 Jun 2005

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(also posted on unix-porting...)
If this is posted to the wrong list, please let me know of a more
appropriate listing.  I am porting a unix program that utilizes named
pthreads to lock certain things in one program, and in another "child"
program, it sees if it locks for certain tests.

I'd like to preface this by saying we are using the 10.2.8 SDK.

Since we do not have named pthreads, I am using named semaphores because
they are system-wide, and we are only doing locks & try locks.  However,
when I set up my two programs, they do not recognize each other's semaphore
IDs.  Some of the IDs even over lap.  Here is a snippet of pseudo code I am
going by...

class NamedSemaphores
{
  public:
  // Constructor / Destructor
    NamedSemaphores( const char *name_ = 0 )
    {
      // See if it exists first
      _semaphoreID = ::sem_open( name_, 0 );

      printf("semid = %i\n", (int)_semaphoreID );

      if ( ( int )_semaphoreID == SEM_FAILED )
      {
        // Otherwise, create it
        _semaphoreID = ::sem_open( name_, O_CREAT, 0777, 0 );
      }

      if ( ( int )_semaphoreID == SEM_FAILED )
      {
        printf( "SEM_FAILED\n" );
      }
    }

...continues with more class functions...

  private:
    sem_t       *_semaphoreID;
}

I had to edit that really quick, so the syntax may contain a typo or
something.  At any rate, both programs are pretty much identical, and they
are both calling a:

NamedSemaphores     *mySemaphore;
MySemaphore = new NamedSemaphores( "TEST" );

Obviously I am not using that string, but more like 5 different strings.
Program A might return semaphoreID's of:  4, 5, 6, 7, and 8.  Program B
might return semaphoreID's of 7, 8, 9, 10, and 11.  They do not recognize
identical strings, and they also overlap certain semaphoreIDs.

Any clues as to what might be happening?

Mark Stultz
United Developers
mstultz@udgames.com

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