En Thu, 18 Dec 2008 19:46:45 -0200, Aaron Brady <castiro...@gmail.com>
escribió:
On Dec 17, 7:16 pm, "Gabriel Genellina" <gagsl-...@yahoo.com.ar>
wrote:
En Wed, 17 Dec 2008 22:46:32 -0200, Aaron Brady <castiro...@gmail.com>
escribió:
> On Dec 17, 5:05 pm, "Gabriel Genellina" <gagsl-...@yahoo.com.ar>
> wrote:
>> En Wed, 17 Dec 2008 12:21:38 -0200, Jeremy Sanders
>> <jeremy+complangpyt...@jeremysanders.net> escribió:
>> > It would be nice if Python created pipes that are properly
>> inheritable by
>> > default by child processes, as they're mostly used for IPC.
>> I'd say it is a bug in os.pipe implementation; they should be
>> inheritable
>> by default, as in posix (after all, the code is in "posixmodule.c").
> The code looks like this:
> ok = CreatePipe(&read, &write, NULL, 0);
> Py_END_ALLOW_THREADS
> if (!ok)
> return win32_error("CreatePipe", NULL);
> read_fd = _open_osfhandle((Py_intptr_t)read, 0);
> write_fd = _open_osfhandle((Py_intptr_t)write, 1);
> 'If lpPipeAttributes is NULL, the handle cannot be inherited.' You
> could populate a 'SECURITY_ATTRIBUTES' structure, or call
> DuplicateHandle on both of them.
> A patch would look like this:
> SECURITY_ATTRIBUTES sattribs;
> sattribs.nLength = sizeof(sattribs);
> sattribs.lpSecurityDescriptor = NULL;
> sattribs.bInheritHandle = TRUE;
> ok = CreatePipe(&read, &write, &sattribs, 0);
Yes, that's exactly how os.popen does it (in posixmodule.c)
> This still doesn't answer whether the file descriptor return by
> '_open_osfhandle' can be inherited too.
It doesn't matter. The OS only cares about file handles, not C RTL
structures.
Sorry for the multiple posts. File handles are inheritable by child
processes, if the permissions are right. File descriptors are not.
Is there a way that we can get the handles of a pipe into code, so
that we can pass them to a subprocess?
On Windows, file handles are the real OS stuff, the "true" reference to an
open file. File descriptors are not, they exist only to please the C
runtime library. Programs not written in C (directly, or indirectly like
Python) don't care at all about file descriptors. And in case one actually
cares, there is _open_osfhandle in the C RTL (available as
msvcrt.open_osfhandle from Python).
A subprocess may inherit handles from its parent [there are two filters:
the parameter "bInheritHandles" in the CreateProcess call provides global
control, and individual handles can be made inheritable or not, before
creating the new subprocess].
"Anonymous" pipes are good to replace stdin/stdout/stderr, because there
is no need to explicitely communicate the handle value to the subprocess:
one just replaces the corresponding handle with the desired pipe, and the
subprocess might not even notice it.
In case this is not enough, one might pass the handle (as a number) in the
command line, but probably a "named pipe" would be better. As this is not
transparent for the child process, one must explicitely code such things.
Will it take calling
'CreatePipe' from ctypes directly if on Windows? Or can 'os.pipe' be
made to abstract that? If Windows can't inherit descriptors,
'os.pipe' should return handles, and 'os.read' &co. should accept
them.
I think the best way would be to modify os.pipe so it returns inheritable
pipes, as it should have been from the beginning.
It is a fairly large patch.
Not at all, you have already posted most of it.
--
Gabriel Genellina
--
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