shmop_close doesn't delete the memory segment, it just detaches from it.
If you have created the block and need to delete it you must call shmop_delete **BEFORE** calling shmop_close (for reasons outlined in shmop_delete help page notes).
(PHP 4 >= 4.0.4, PHP 5, PHP 7)
shmop_close — Close shared memory block
shmop_close() is used to close a shared memory block.
The shared memory block resource created by shmop_open()
Example #1 Closing shared memory block
This example will close shared memory block identified by $shm_id.