Ipc

[hkullana]

hi i want to develop a simple program:

int main()
{
int sharedvariable = 0;
int pid = fork();

if(pid != 0)
{
cout << "i am the parent process and it will increment the value of sharedvariable by 5" << endl;
while(true)
{
...

sharedvariable+=5;
cout << "parent process increments the sharedvariable by 5 and the new value is: " << sharedvariable << endl;
...
}
}

else
{
cout << "i am the child process and it will decrement the value of sharedvariable by 3" << endl;

while(true)
{
...
sharedvariable -= 3;
cout << "child process decrements the sharedvariable by 3 and the new value is: " <<sharedvariable<< endl;
...
}
}
}

in the above what i want to do is simple. I want two processes (not threads). The two processes share a variable called "sharedvariable". Parent process increments the sharedvariable by 5 and the child process decrements the sharedvariable by 3. But two of them reaches sharedvariable not in the same time. So in the "..." parts of the code i think i should use semaphores. So; when parent process want to reach sharedvariable but if currently child process is modifying the sharedvariable, parent process should sleep until the child process releases the semaphore. also it is same for the child process visa versa. Can you please help me to finish the code or can you please provide some useful links about IPC and semaphores.

thank you,
hkullana

[wje_lf]

This is most likely homework, and we obviously can't do your homework for you, but here are some links to get you started:

man semctl
man semget
man semop
man shmat
man shmctl
man shmdt
man shmget

Hope this helps.