ResourceManager.open_resource() does not time out when trying to connect to TCP resource

Hello, I am passing open_timeout parameter when connecting to a non-connected device’s resource name like this:

resource_manager.open_resource("TCPIP0::10.0.20.20::inst0::INSTR", open_timeout=100)

so I expect it to throw timeout error after just 100 milliseconds but it waits for about 5 seconds until a VisaIOError is thrown.

PyVisa version: 1.9.1 Visa backend: NI Python version: 3.6 64-bit

What might be the problem?

[MatthieuDartiailh]

I can reproduce. However it seems to be a bad documentation issue on PyVisa side since the VISA specification says (page 85 about viOpen):

If the accessMode parameter requests a lock, then this parameter specifies the absolute time period (in milliseconds) that the resource waits to get unlocked before this operation returns an error.

Hence in the absence of any lock, this timeout does not have any effect. We need to fix PyVISA documentation and possibly pyvisa-py implementation to conform to this (but this is lower priority).

[MatthieuDartiailh]

Closed by #451