multiprocess.shared_memory.SharedMemory name too long

[gma-uw (gma1)]

From the python documentation example at ​https://docs.python.org/3/library/multiprocessing.shared_memory.html

from multiprocessing import shared_memory
shm_a = shared_memory.SharedMemory(create=True, size=10, name='a'*31)
type(shm_a.buf)
buffer = shm_a.buf
print (len(buffer))
buffer[:4] = bytearray([22, 33, 44, 55])  # Modify multiple at once
buffer[4] = 100                           # Modify single byte at a time
# Attach to an existing shared memory block
shm_b = shared_memory.SharedMemory(shm_a.name)
import array
array.array('b', shm_b.buf[:5])  # Copy the data into a new array.array
shm_b.buf[:5] = b'howdy'  # Modify via shm_b using bytes
bytes(shm_a.buf[:5])      # Access via shm_a
shm_b.close()   # Close each SharedMemory instance
shm_a.close()
shm_a.unlink()  # Call unlink only once to release the shared memory

If name is longer that 30 characters, I get the error: OSError: [Errno 63] File name too long: '/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa'

The documentation ​https://docs.python.org/3/library/multiprocessing.shared_memory.html says nothing about the length of name.

This is on an M1 Mac.

[jmroot (Joshua Root)]

This appears to be an upstream documentation bug if anything. There's a reference in the code to 14 characters being the maximum safe name length at least on FreeBSD: ​https://github.com/python/cpython/blob/3.10/Lib/multiprocessing/shared_memory.py#L29

The underlying posix shared memory API has a name length limit of PSHMNAMLEN, defined in sys/posix_shm.h.