Re: Python bindings and a suggestion for improvement

Hi Frank, thanks for the reply. Attached is the patch that introduces a
safe Gpib.Gpib.close() which will ensure proper cleanup. Please take a look.

Cheers,
Tomislav


On Wed, Nov 28, 2018 at 11:15 AM Frank Mori Hess <[email protected]> wrote:

> On Tue, Nov 27, 2018 at 4:19 PM Tomislav Ivek <[email protected]>
> wrote:
> >
> > The pure-Python VISA backend pyvisa-py has recently stumbled upon a
> double-close situation with linux-gpib's Python class Gpib.Gpib:
> https://github.com/pyvisa/pyvisa-py/pull/171 This bug is related to a
> design point in Gpib.Gpib which cleans up its GPIB handle only on Python's
> GC cycle. This is not guaranteed to run when the programmer expects it to
> and in extreme cases might even leak resources. It appears Gpib.Gpib has no
> other user-facing method to close its GPIB handle.
> >
> > This can be resolved by adding a Gpib.close() method for user-controlled
> cleanup. I hav ealready tested the fix in gpib_ctypes, a cross-platform
> GPIB binding that aims to be compatible with linux-gpib (
> https://pypi.org/project/gpib-ctypes/). I would be happy to send a patch
> for linux-gpib's Python lib.
> >
> > Please let me know what you think about that.
>
>
> I'm no python expert, but your change sounds reasonable to me.
>

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Index: linux-gpib-user/language/python/Gpib.py
===================================================================
--- linux-gpib-user/language/python/Gpib.py	(revision 1766)
+++ linux-gpib-user/language/python/Gpib.py	(working copy)
@@ -28,13 +28,17 @@
 
 	# automatically close descriptor when instance is deleted
 	def __del__(self):
-		if self._own:
-			gpib.close(self.id)
+		self.close()
 
 	def __repr__(self):
 		return "%s(%d)" % (self.__class__.__name__, self.id)
 
 
+	def close(self):
+		if self._own:
+			gpib.close(self.id)
+			self._own = False
+
 	def command(self,str):
 		gpib.command(self.id, str)