semaphores using up and down - High Level Programming

ddx08 · #1 (**permalink**) 04-02-2007

been searching around on how to use an up and down function with semaphores but i can't find an example. i looked into using: "semop" but i have no idea how to use it. I have been able to declared the semaphores using semget and initializing them using semctl.

jim mcnamara · #2 (**permalink**) 04-03-2007

Up and down? Do you mean a mutex?

Sempahores can have values other than one and zero. Mutexes are "switches" - either on or off (one or zero).

ddx08 · #3 (**permalink**) 04-03-2007

sorry, forgot to update this. i found out that i needed to create a stuct that would implement the function i wanted. increment the semaphore by 1 or decrease it by 1.

here is where i got the idea
http://docs.linux.cz/programming/c/u...les/semab.html

jim mcnamara · #4 (**permalink**) 04-03-2007

void main() is a terrible idea... noticed it on your link.

matrixmadhan · #5 (**permalink**) 04-03-2007

should be as

Code:

int main() {
 return <n>;
}

I noticed the semaphore resource acquired is not released using

Code:

semctl + IPC_RMID;
soemthing like,
semctl(sem_id, 0, IPC_RMID, <union>);

ddx08 · #6 (**permalink**) 04-03-2007

what i did was just define a number of KEYs equal to the number of semaphores i wanted and then i created 2 struct to create the functions up and down. i didn't use a void main, just main. Why would void main be bad?

you have to release the resources??? how do you do that? aren't they released as soon as the program is done?

matrixmadhan · #7 (**permalink**) 04-03-2007

Quote:

just main.

But Still,

use int main and make the code to return a value !

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