Segmentation Fault on CDLL reloading

[Marcus.CM]

Hi,

I use the following ctype to load a .so library in Linux.

vr = ctypes.CDLL(sstr)

And the following to release it so that i can reload the library without
quiting the python script.

_ctypes.dlclose(vr._handle)

These calls are guarded by a writer lock and access to it guarded by a
reader lock which i got from recipe :
http://code.activestate.com/recipes/413393/

The problem is during the re-loading of the library occasionally the
python script will abort with "Segmentation Fault". This is like 1 out
of 10 times it can happen and that
is good enough to kill the application.

Is there any reason to this or how to do i prevent it?


Marcus .CM

 

[Diez B. Roggisch]

Hi,

I use the following ctype to load a .so library in Linux.

vr = ctypes.CDLL(sstr)
And the following to release it so that i can reload the library without
quiting the python script.

_ctypes.dlclose(vr._handle)

These calls are guarded by a writer lock and access to it guarded by a
reader lock which i got from recipe :

The problem is during the re-loading of the library
occasionally the python script will abort with "Segmentation Fault".
This is like 1 out of 10 times it can happen and that
is good enough to kill the application.

Is there any reason to this or how to do i prevent it?

Short answer: yes, there is a reason, no, you can't prevent it.

Of course there is a reason for this. Segfaults don't happen by
chance... And one can't prevent segfaults from killing the interpreter,
because the OS is responsible for that.

Now what would I do?

- don't care. Or does the DLL frequently change when the program is
deployed? Or to ask different: why do you need unloading/reloading at all?

- debug it. Write a script that exposes the behavior. The fire up GDB
with python, do "set args <myscript>" and run. When the segfault occurs,
look into the traceback with "bt". If the problem is in the DLL-code,
see what's causing it. If it's in ctypes (or the python-interpreter) -
well, there is a ctypes mailing lisk to ask for help.

Diez