VXI11 lock handling by hb020 · Pull Request #633 · pyvisa/pyvisa-py

hb020 · 2026-08-25T10:02:54Z

Why

This allows more compliant lock handling on VXI-11.

Closes VXI-11 lock handling incorrect #583
Executed pre-commit with no errors
The change is fully covered by automated unit tests
Documented in docs/ as appropriate
Added an entry to the CHANGES file

…dling

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codecov · 2026-08-25T10:04:23Z

Codecov Report

❌ Patch coverage is 85.44304% with 23 lines in your changes missing coverage. Please review.
✅ Project coverage is 48.19%. Comparing base (fde650a) to head (0043e6a).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pyvisa_py/tcpip.py	64.15%	17 Missing and 2 partials ⚠️
pyvisa_py/attributes.py	90.90%	0 Missing and 1 partial ⚠️
pyvisa_py/gpib.py	0.00%	1 Missing ⚠️
pyvisa_py/prologix.py	0.00%	1 Missing ⚠️
pyvisa_py/testsuite/test_open_timeout.py	96.15%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #633      +/-   ##
==========================================
+ Coverage   44.78%   48.19%   +3.40%     
==========================================
  Files          31       33       +2     
  Lines        5468     5625     +157     
  Branches      534      545      +11     
==========================================
+ Hits         2449     2711     +262     
+ Misses       2987     2865     -122     
- Partials       32       49      +17

Flag	Coverage Δ
unittests	`48.19% <85.44%> (+3.40%)`	⬆️

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…dling

hb020 · 2026-08-25T19:08:13Z

releasing this for merge. hislip is more effort, will come in a next PR.

MatthieuDartiailh

First quick pass.

MatthieuDartiailh · 2026-08-26T12:44:07Z

+- Request a lock via ``inst.lock_excl()``. This is the most portable. See above.
+- Configure the lock timeout via the PyVISA-Py specific ``rm.visalib.sessions[inst.session].lock_timeout``.  


Why do you need to poke at the internals here ? I would prefer to not encourage such uses.
Since Keysight make use of a non standard attribute to control this parameter, we could do the same. This ways internals are not exposed.

well, it was like that, so I left it. But yes, I prefer the keysight way.

BUT: then we also need to adapt pyvisa, since it is pyvisa that would expose that specific attribute to the user. It is not a standard attribute.

I do not have all the code within easy reach to check but since pyvisa mostly forward directly to the library for get/set attribute we may be able to to define the extra args outside PyVISA.

sure, can be done, the other attributes are 'hard coded' in pyvisa/constants.py. They do not refer to the backends.
Not a big issue, but then we'll have to make sure to catch any mismatching package versions.

I'll work on something. For now, only in pyvisa-py. And making sure it can live with outdated pyvisa.

MatthieuDartiailh · 2026-08-26T12:49:25Z

+            # TODO determine how OP_FLAG_WAIT_BLOCK could be set from the outside.
+            # VPP-4.3 does not provide a clear definition for it.
+            # For now, we derive it from self.lock_timeout.
+            lock_timeout = self.lock_timeout
+            if lock_timeout != constants.VI_TMO_IMMEDIATE:
+                flags |= vxi11.OP_FLAG_WAIT_BLOCK
+


This could be factored out in a helper.

yes, will do

MatthieuDartiailh

I would expect changes to be required for serial and USB for locking when opening. And for those and GPIB since locking does not do anything we should reject non default value.

hb020 · 2026-08-26T16:51:06Z

Implemented VI_KTATTR_LOCKWAIT, removed lock_timeout. It is all limited it to vxi-11

hb020 · 2026-08-26T17:01:44Z

In fact, VPP-4.3 states that all types should support locking, both exclusive locks and shared locks, AND nested locking.

For exclusive locks, VXI-11 and HiSLIP instruments handle that themselves (maybe also vicp and vxi?).
The other instrument interfaces do not support it AFAIK.
Also, shared locking, and nested locking, mean a fair amount of work inside the higher layers of pyvisa-py. Much more than this. Seen potential low return (those who use shared locking, often use large setups, and they use NI-VISA), not sure I will get to that one day.

hb020 · 2026-08-26T17:38:41Z

Now I need to work on the timeout of the remote/local functions

MatthieuDartiailh · 2026-08-26T17:42:42Z

I would expect changes to be required for serial and USB for locking when opening. And for those and GPIB since locking does not do anything we should reject non default value.

I realize this was silly since serial is by definition a unique connection and USBTMC and GPIB are likely the same. I will make another more thorough review but I think are nearly good.

hb020 · 2026-08-26T18:15:35Z

merged.
Preferred order of integration: this PR and only then #626. I might need to do some merging and cleaning for that one, and it is less important.

MatthieuDartiailh

Some small comments

MatthieuDartiailh · 2026-08-26T17:24:33Z

+        flags = 0
+        flags, lock_timeout = self._adapt_flags_and_lock_timeout(flags)
+
        # XXX make this nicer (either validate protocol or pass it)


Not sure this comment still applies

corrected comment

MatthieuDartiailh · 2026-08-28T12:16:36Z

+    ``VI_KTATTR_LOCKWAIT`` may not be available yet in pyvisa. In that case, you could do this:
+
+    >>> import pyvisa
+    >>> rm = pyvisa.ResourceManager('@py')
+    >>> inst = rm.open_resource('TCPIP::192.168.1.100::INSTR')
+    >>>
+    >>> # Define the raw hex constant for VI_KTATTR_LOCKWAIT
+    >>> VI_KTATTR_LOCKWAIT = 0x0FFF002BL
+    >>>
+    >>> # Set lockwait to True (VI_TRUE = 1)
+    >>> inst.set_attribute(VI_KTATTR_LOCKWAIT, 1)
+    >>> # Read back the attribute value
+    >>> lockwait_val = inst.get_attribute(VI_KTATTR_LOCKWAIT)
+    >>> print("Lockwait state:", lockwait_val)
+    >>>
+    >>> # Do your operations


Why do you need this since we force set this attribute?

Otherwise you get this: NameError: name 'VI_KTATTR_LOCKWAIT' is not defined

It needs to be added to pyvisa.constants

clarified faq

oops. you're right. WIll correct the faq.

MatthieuDartiailh · 2026-08-28T12:52:06Z

    #: Time to wait in ms before erroring with a timeout when trying to acquire a lock
-    lock_timeout: int = 10000
+    # 0 = immediate, >0 = wait for that many milliseconds
+    # This is used for most operations (mainly except open_resource and lock_excl)
+    #
+    # NI-VISA and R&S VISA do not expose any of this.
+    # Keysight exposes the Keysight-specific VISA ViBoolean local (per-session) attribute VI_KTATTR_LOCKWAIT
+    #   When False, when already locked, immediately returns VI_ERROR_RSRC_LOCKED
+    #   When True, uses lock timeout = session timeout interval. When locked and timed out, returns VI_ERROR_TMO
+    # lock_timeout: int = 0


This whole paragraph seems out of place.

yes, will remove the comments

hb020 and others added 18 commits August 21, 2026 18:16

lock on open

e8da4ea

add test for locks

2a24ca1

add tests

a92fa8f

expand tests

f128a99

Merge branch 'main' of github.com:hb020/pyvisa-py into vxi11-lock-han…

3d3aebd

…dling

device_lock corrected

5533c87

add lock check in existing required vxi11 functions

e21bffe

add doc

dadded1

clarify code doc

7a6fdfe

doc update

330ae7f

improve doc

dedccb3

integrate lock_timeout

e732098

more doc

f8db6d8

return codes to be corrected

62f2557

slowly better

0c826af

Merge branch 'main' of github.com:hb020/pyvisa-py into vxi11-lock-han…

4ea23ae

…dling

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5b8b53e

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added PR #

9f6d778

hb020 marked this pull request as draft August 25, 2026 10:05

hb020 added 5 commits August 25, 2026 12:11

correct ruff

0407e59

add more tests

1358e20

finishing vxi-11

ddaad9f

Merge branch 'main' of github.com:hb020/pyvisa-py into vxi11-lock-han…

47381aa

…dling

doc

46b86e7

hb020 marked this pull request as ready for review August 25, 2026 19:08

hb020 mentioned this pull request Aug 26, 2026

Add remote/local handling for VXI-11 and HiSLIP #636

Merged

5 tasks

MatthieuDartiailh reviewed Aug 26, 2026

View reviewed changes

concentrate flags and lock timeout

77c55dd

MatthieuDartiailh reviewed Aug 26, 2026

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move to VI_KTATTR_LOCKWAIT

9339f95

hb020 added 2 commits August 26, 2026 18:55

mypy patch

c8a45f3

ruff mismatch

3f0b6ce

hb020 and others added 2 commits August 26, 2026 19:15

faq update

11528ea

Merge branch 'main' into vxi11-lock-handling

c51c633

merge remote/local

12f7dba

improved doc

fc24c4c

MatthieuDartiailh reviewed Aug 28, 2026

View reviewed changes

hb020 added 3 commits August 28, 2026 15:37

comment clean up

696f0f8

clarify faq

6b5afa5

faq correction

0043e6a

MatthieuDartiailh merged commit 328408f into pyvisa:main Aug 28, 2026
18 checks passed

hb020 deleted the vxi11-lock-handling branch August 28, 2026 20:17

		- Request a lock via ``inst.lock_excl()``. This is the most portable. See above.
		- Configure the lock timeout via the PyVISA-Py specific ``rm.visalib.sessions[inst.session].lock_timeout``.

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