[Description]
If the shmem index doesn't exist, we are bootstrapping: we must be trying to init the shmem index itself. Notice that the ShmemIndexLock is released before the shmem index has been initialized. This should be OK because no other process can be accessing shared memory yet.
[System Processing]
Processing will be aborted.
[Action]
To investigate the cause of the occurrence from the message, and remove cause.