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Some Python ctypes-based POSIX shared memory functions
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import ctypes | |
import mmap | |
import os | |
import stat | |
import sys | |
try: | |
unicode | |
except NameError: | |
unicode = str | |
rtld = ctypes.cdll.LoadLibrary(None) | |
_shm_open = rtld.shm_open | |
_shm_unlink = rtld.shm_unlink | |
def shm_open(name): | |
if isinstance(name, bytes): | |
name = ctypes.create_string_buffer(name) | |
elif isinstance(name, unicode): | |
name = ctypes.create_unicode_buffer(name) | |
else: | |
raise TypeError("`name` must be `bytes` or `unicode`") | |
result = _shm_open( | |
name, | |
ctypes.c_int(os.O_RDWR | os.O_CREAT | os.O_EXCL), | |
ctypes.c_ushort(stat.S_IRUSR | stat.S_IWUSR) | |
) | |
if result == -1: | |
raise RuntimeError(os.strerror(ctypes.get_errno())) | |
return result | |
def shm_unlink(name): | |
if isinstance(name, bytes): | |
name = ctypes.create_string_buffer(name) | |
elif isinstance(name, unicode): | |
name = ctypes.create_unicode_buffer(name) | |
else: | |
raise TypeError("`name` must be `bytes` or `unicode`") | |
result = _shm_unlink(name) | |
if result == -1: | |
raise RuntimeError(os.strerror(ctypes.get_errno())) |
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import os | |
import mmap | |
import numpy as np | |
from shm import * | |
fid = shm_open("arr") | |
size = 10 | |
os.ftruncate(fid, size) # Skipped by processes reusing the memory | |
m = mmap.mmap(fid, size) | |
a = np.frombuffer(m, dtype=np.uint8) |
On Linux, something like this is preferable since the kernel will auto-close it (shm_open
requires a corresponding shm_unlink
, otherwise it leaks an open "file" at /dev/shm/
):
import os
import mmap
def get_shared(size=1024, name="shared_memory"):
fd = os.memfd_create(name)
os.ftruncate(fd, size)
m = mmap.mmap(fd, size)
os.close(fd)
return m
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The string buffer handling here is slightly confusing. Can't we directly pass in an encoded name (i.e. bytes), at least if we set argtypes for the functions?