Hello techies,

I am new to LinuxQuestions.org.
I want to use Posix shared memory functions shm_open shm_unlink etc..
to create shared memory logs for some s/w module so there is less I/O.
I want to check , if i kill the process without shm_unlink() does the shared memory object floats in the memory or it is deleted automatically.

Also, which is better interface for shared memory access
POSIX / SysV?

Thanks

Hi,

Can't answer the POSIX version question, but I can for the SystemV - all the linux books I have only talk about SysV IPC (with the exception of saying that POSIX message queues are more flexible in Linux than SysV)

shmget - allocates
shmat - attaches. do this in the parent and there's no need to do it in the children
shmctl - amongst other things, call this to flag for deallocation.
shmdt - detach (NOT deallocate) happens automatically when process inheriting or attaching ends

Deallocation is explicitly required even when the allocating parent and all other attached processes die.

Deallocation happens at reboot(!), or when both of the following are true:
A process has used shmctl to flag the region for delete AND
All processes have detached, either by dying, or by calling shmdt.

I was tempted to flag for delete early, like unlinking a tmp file, but apparently this can have undesirable results platform by platform

Hope that's useful,

Andy T

Oh, and just noticed you posted this in hardware - it'll probably get moved to programming.

Trust me, allocating any kind of application memory in *nix you won't get closer than 8 stack pushes of allocating actual physical memory ;-)