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pyvisa / pyvisa-py

A pure python PyVISA backend
https://pyvisa-py.readthedocs.io
MIT License
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Locked resources are easily stolen by other VISA implementation #453

Open Ben3094 opened 2 months ago

Ben3094 commented 2 months ago

When I apply an exclusive lock to a session, the session can be stolen by another session. I tested this using pyvisa with pyvisa-py on one computer and pyvisa with IVI VISA installed on the other computer.

To Reproduce

Steps to reproduce the behavior:

  1. Create a pyvisa resource with exclusive lock on the PC with only pyvisa-py.
  2. Create the same pyvisa resource with exclusive lock on another PC with IVI VISA implementation
  3. The second PC is now connected to the ressource and can write command while it should not
  4. Try to write command from the pyvisa-py PC and it raise an error...
MatthieuDartiailh commented 2 months ago

What kind of session are you using ?

Ben3094 commented 2 months ago

Both are sessions with exclusive lock

MatthieuDartiailh commented 2 months ago

I meant are you using GPIB, TCPIP, USB ?

Ben3094 commented 2 months ago

Sorry, TCPIP.

MatthieuDartiailh commented 2 months ago

Which protocol ? hislip or VXI11 (the default is VXI11 for TCPIP)

Ben3094 commented 2 months ago

I think VXI11 as second to last address word is "inst0".

MatthieuDartiailh commented 2 months ago

It is VXI11. I will need to check the code, I am not sure how locking is handled.

MatthieuDartiailh commented 2 months ago

Checking the VXI11 specs, there is not special option to locking beyond whether or not to block when attempting to acquire the lock. So I do not see what we may be doing wrong. Could you attempt to capture the network traffic when locking using pyvisa-py and using NI ?

Ben3094 commented 2 months ago

I use pyvisa-py on one PC and keysight IO installation on the other. It will take time but I will do it for sure. 😉

MatthieuDartiailh commented 2 months ago

Thanks !!!

Ben3094 commented 2 months ago

It appears that the pyvisa-py PC does not call DEVICE_LOCK as the Keysight IO equipped PC... Both are running the same test code and using the same library (that use pyvisa)... The library is different that the one you see as I add "exclusive_lock" on both PC.

self.__resource__ = DEFAULT_RESOURCE_MANAGER.open_resource(self.Address, timeout=self.__timeout__, access_mode=AccessModes.exclusive_lock)
Ben3094 commented 2 months ago

It seems that highlevel.py open method does not use access_mode argument. https://github.com/pyvisa/pyvisa-py/blob/main/pyvisa_py/highlevel.py#L119 Does it mean that it is not supported for the moment ? If yes, I will try to help to resolve this. 😉

MatthieuDartiailh commented 2 months ago

You are welcome to make a PR. For the specific case at hand, I suggest you start with only supporting exclusive locking. Reading the specs I think shared lock cannot work between VISA libraries. However supporting properly nested locking seems worth it. Let me know if you need any guidance.

arr-ee commented 2 months ago

Note that there is a (partially implemented, lock type is not being respected at the moment) implementation of Session#lock in TCPIPInstrVxi11 and underlying RPC client — might be worth checking if that does what you're looking for, and build from there.

Ben3094 commented 2 months ago

Do you recommand me a document to build the implementation from it ?

MatthieuDartiailh commented 2 months ago

You can have a look at the VISA specification here: https://www.ivifoundation.org/downloads/Architecture%20Specifications/IVIspecstopost10-22-2018/vpp43_2018-10-19.pdf As I said I suggest focusing on exclusive locking with proper support for nested locking (which may or may not require to keep track of the level of nesting on pyvisa-py side since the VXI-11 specs does not mention multiple locking).