Semaphore problem 1

[thumpkidd9]

Hello,

I am having a problem with my semaphores. After using semget(), it always returns a -1. I've read about different ways to initialize it but I dont see what is wrong.

sid1=semget(IPC_PRIVATE,N,0666|IPC_CREAT);   
(sid1==-1)printf("Trouble with semget\n");

is it a syntax error?

Thanks..

 

[Hammer]

Do you have an "if" statement in there?

 

[thumpkidd9]

yes sry, it got cut off and didn't realize. The correct statement reads

if(sid1==-1) printf("Trouble with semget\n")

 

[Hammer]

.. and what does perror("semget"); tell you? Replace the printf() with perror().

 

[chipperMDW]

If you replace the printf statement with

perror(0);

you'll get a better indication of what's wrong.

 

[thumpkidd9]

after replacing printf() with perror(0). I get the message "no space left on device

 

[Hammer]

So, you're out of space then ! Better free some up!

Out of interest, what value does N have at the time of calling semget()?

 

[thumpkidd9]

N is equal to 4. It turns out that I have like 10 open semaphores on this machine. gonna delete them and try again.

 

[Hammer]

... yeah, was just about to post a "try cleaning up the ipc memory" message to you!

 

[chipperMDW]

Sounds like: A semaphore set has to be created but the system limit for the maximum number of semaphore sets (SEMMNI), or the system wide maximum number of semaphores (SEMMNS), would be exceeded.

So you can check those to make sure you know which one is exceeded.


Hammer,

Just so you know, we posted our perror replies at the same time, and when I said "better" in mine, I meant better than the printf, not better than your suggestion.

 

[thumpkidd9]

Yep that was it. semaphores and shared mem working now. Thanks guys.

 

[Hammer]

@chipperMDW : no worries, I knew what you meant! :-D

@thumpkidd9: glad you got it going!