Linux semaphores. (semget & semop)

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2 total messages Started by Bart Trojanowski Fri, 03 Jul 1998 00:00

#3926

Author: Bart Trojanowski
Date: Fri, 03 Jul 1998 00:00

38 lines
1526 bytes

Hello, I have run into a problem with semaphores.  The task that I am
building cannot be thread based so I need to create a system semaphore for
synchronization.

I tried this...

----

struct sembuf sem_wait = { 0, -1, 0 };  // also tried { 0, -1, IPC_NOWAIT
};

...

if( (waitLock = semget( key, 1, IPC_CREAT ) ) == -1)
	perror("semget problem:");

...
// setup alarm handler
// setup timer here
...

if( semop( waitLock, &sem_wait, 1 ) == -1 )
	perror("semop problem:");

----
where key is either IPC_PRIVATE or 0x1FF (9 bits of 1's).

Both give me an error on semop of "Permission denied".  I noticed that this
runs under root, so I have concluded that I have my permissions set
incorrectly.  How do I set them properly?

Well I should say that it didn't give me an error, not that it worked under
root.  Another problem I have now is that  the alarm handler does not get
called when I block on the sema.  It would seem that the alarm is disabled.
 Is that so?

thank you.

Re: Linux semaphores. (semget & semop)

#3927

Author: Lance DeHerrera
Date: Thu, 09 Jul 1998 00:00

8 lines
793 bytes

After compiling the program under linux try this:

1. chmod a+x program name
after this is complete Ls the directory and mv the a.out file to the program
name.

hope this helps!!!!!!

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