SHMDEFINED

The SHMDEFINED function checks whether a shared symbol exists in shared memory, i.e. in a memory location independent of a given execution context. It return true if it exists, false otherwise.

As unused symbols can be removed from shared memory because of the shm.ttl configuration, a call to SHMDEFINED ensures that, within the same MUTEX call, a call to SHMLOAD on the same symbol name will not fail.