Linux, fcntl, F_SETLEASE and signals

[Chris Green]

Hey folks,

Is there anyway for a signal handler in python to get the information
from a 3 argument signal handler rather than just the signal number
and stack frame?

I've got an application where I have to check for F_SETLEASE on a file
in python on Linux 2.4. What this does is tells the kernel to notify
the current process with SIGIO that a particular file descriptor is being
modified by another process.

import fcntl
f = open(".zshrc", "r+")
fcntl.fcntl(f, fcntl.F_SETLEAS E, fcntl.F_WRLCK)

0

Now, when another process opens ".zshrc", I get a SIGIO saying
something happened. The kernel provides the information on what
descriptor changed in a siginfo_t's si_fd field.

Is there anyway to get this from python?

Thanks,
Chris
--
Chris Green <cm*@dok.org>
You now have 14 minutes to reach minimum safe distance.

[Chris Green]

Jeff Epler <je****@unpytho nic.net> writes:

What I don't see here is any handling of threads.
You're right. I'm ignorant of the thread<->signal interaction in
python.

The SIGIO handler might be called at the same time as Python code is
running in another thread. That means the call to getPending can see a
partially modified queue, or that the queue can be modified by a signal
while getPending is running.

If I put a thread-safe mutex around the queue, that should be good
enough? Everything that I've seen has

Py_BEGIN_ALLOW_ THREADS
code
Py_END_ALLOW_TH READS

getPending()
read from queue
interrupt while reading via signal
read from modified queue

Is this where you were recommending Py_AddPendingCa ll? Add the
pending increment when no other fields are taking place?

Are C extensions only accessed by a single thread unless they
Py_BEGIN_ALLOW_ THREADS?

Thanks,
Chris
--
Chris Green <cm*@dok.org>
Warning: time of day goes back, taking countermeasures .

[Chris Green]

Jeff Epler <je****@unpytho nic.net> writes:

What I don't see here is any handling of threads.

http://cmg.dok.org/code/linuxlease-0.3.tar.gz now has the same signal
code roughly as signalmodule.c. The biggest difference is that I
add to my internal queue the pending calls with an argument of a
pointer to the signal handler argument.

I'm not sure that is safe but it seems to work. Ideally, I'd
allocate space for the argument and then queue it.
--
Chris Green <cm*@dok.org>
A good pun is its own reword.