Destroying IPC Resources
IPC resources can outlive your process. When a process terminates for any reason, all files are closed and its shared memory is detached, but its IPC resources will continue to exist. If IPC resources are no longer required, they must be explicitly destroyed.
There are system calls to perform this function:
msgctl(3) for message queues
semctl(2) for semaphores
shmctl(2) for shared memory
The following chapters cover the specifics of these operations. There are, however, some system-wide implications of destroying IPC resources that should be noted here.
When a message queue or a semaphore set is destroyed, they are destroyed immediately. Since IPC resources are not opened like files, they do not stay open until closed. ...
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