On Tue, 14 Feb 2012 23:10:11 -0500
Mike Meyer<[email protected]> wrote:
I'd prefer to provide shm_open on Windows if at all possible. The
"sorta-kinda" bothers me. That would also allow for an application to
exit and then resume work stored in a mapped segment (something I've
done before). However, setting this up on Windows isn't something I
can do.
Here is a proof-of-concept for shm_open/shm_unlink on Windows.
Note that shm_unlink opens the file using FILE_FLAG_DELETE_ON_CLOSE
which ensures that subsequent attempts to open the file will not
succeed. However, the directory entry will not disappear till all
handles have been closed.
FILE_ATTRIBUTE_TEMPORARY tells the system we want to try to cache the
file without worrying about flushing.
sbt
import os
import msvcrt
import tempfile
from _multiprocessing import win32
DEV_SHM = tempfile.gettempdir()
GENERIC_READ = win32.GENERIC_READ
GENERIC_WRITE = win32.GENERIC_WRITE
CREATE_NEW = 1
CREATE_ALWAYS = 2
OPEN_EXISTING = 3
OPEN_ALWAYS = 4
TRUNCATE_EXISTING = 5
FILE_SHARE_READ = 1
FILE_SHARE_WRITE = 2
FILE_SHARE_DELETE = 4
FILE_ATTRIBUTE_TEMPORARY = 256
FILE_FLAG_DELETE_ON_CLOSE = 0x04000000
NULL = 0
_CreationDisposition = {
os.O_CREAT | os.O_EXCL: CREATE_NEW,
os.O_CREAT | os.O_TRUNC: CREATE_ALWAYS,
0: OPEN_EXISTING,
os.O_CREAT: OPEN_ALWAYS,
os.O_TRUNC: TRUNCATE_EXISTING
}
_DesiredAccess = {
os.O_RDONLY: GENERIC_READ,
os.O_RDWR: GENERIC_READ | GENERIC_WRITE
}
_OsfDesiredAccess = {
os.O_RDONLY: os.O_RDONLY,
os.O_RDWR: 0
}
def _get_path(name, dev_shm):
name = name.lstrip('/')
if '/' in name or '\\' in name:
raise ValueError('invalid name')
return os.path.join(dev_shm, name)
def shm_open(name, flags, mode, dev_shm=DEV_SHM):
# Opening with FILE_SHARE_READ | FILE_SHARE_WRITE |
# FILE_SHARE_DELETE ensures that other processes can open the file
# and pseudo-unlink it while it is still in use.
path = _get_path(name, dev_shm)
da_flags = flags & (os.O_RDONLY | os.O_RDWR)
cd_flags = flags & ~(os.O_RDONLY | os.O_RDWR)
h = win32.CreateFile(
path, _DesiredAccess[da_flags],
FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE, NULL,
_CreationDisposition[cd_flags], FILE_ATTRIBUTE_TEMPORARY, NULL)
try:
os.chmod(path, mode)
return msvcrt.open_osfhandle(h, _OsfDesiredAccess[da_flags])
except:
win32.CloseHandle(h)
raise
def shm_unlink(name, dev_shm=DEV_SHM):
# Opening with FILE_FLAG_DELETE_ON_CLOSE will make subsequent
# attempts to open the file fail. However, the name is not
# removed from the file system until all handles have been removed.
path = _get_path(name, dev_shm)
h = win32.CreateFile(
path, GENERIC_READ | GENERIC_WRITE,
FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE, NULL,
OPEN_EXISTING,
FILE_ATTRIBUTE_TEMPORARY | FILE_FLAG_DELETE_ON_CLOSE, NULL)
win32.CloseHandle(h)
##
if __name__ == '__main__':
import mmap
MYMAP = "mymmap"
fd = shm_open(MYMAP, os.O_RDWR | os.O_CREAT | os.O_EXCL, 0o600)
m = mmap.mmap(fd, 10)
os.close(fd)
m[:5] = "hello"
fd = shm_open(MYMAP, os.O_RDWR, 0o600)
n = mmap.mmap(fd, 10)
os.close(fd)
n[:] = n[:].upper()
n.close()
assert os.path.exists(_get_path(MYMAP, DEV_SHM))
shm_unlink(MYMAP)
try:
fd = shm_open(MYMAP, os.O_RDWR, 0o600)
except OSError:
pass
else:
raise AssertionError("expected access denied")
print repr(m[:])
m.close()
assert not os.path.exists(_get_path(MYMAP, DEV_SHM))
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