Fix observed hangs with LV measurements for certain situations of service launches

[jonathanmendez]

• This contribution adheres to CONTRIBUTING.md.

What does this Pull Request accomplish?

Fixes AB#2508868 and AB#2464807

Why should this Pull Request be merged?

In the existing implementation of the service startup code, there is a race condition caused by a delay between registering the measurement service with Discovery Service (enabling clients to try to call the measurement service) and registering the user events for handling calls to the measurement service (enabling the measurement service to receive and react to calls). If a client makes a call to the measurement service between those two pieces of code, the measurement service never handles the call and the client waits indefinitely.

The fix moves the event registration before the measurement is registered with Discovery Service. The events are registered and the registration refnum is stored in the service private data to later be wired to the event handler. Through testing, the registration call is sufficient to be ready to handle calls, even if the event handler structure has not been reached yet.

What testing has been done?

Tested the implementation using a reproducing TestStand sequence that repeatedly calls and kills a measurement. Before the fix, a hang would consistently occur within a few minutes. After the fix, I have not observed a hang over many minutes and repeated runs.

[dixonjoel]

Would you be able to post some screenshots for the relevant changes? I'm not sure if I need to look at all these files or if most are just type prop that had to be saved.

[pbirkhol-ni]

Would you be able to post some screenshots for the relevant changes? I'm not sure if I need to look at all these files or if most are just type prop that had to be saved.

I found that the only VIs with real changes are:

• Register gRPC Methods and Messages.vi
• Start Sync.vi

[jonathanmendez]

Would you be able to post some screenshots for the relevant changes? I'm not sure if I need to look at all these files or if most are just type prop that had to be saved.

Yes, I'm working on that now. Unfortunately I ran out of time at my computer as I was posting the PR earlier.

[jonathanmendez]

Here are screenshots for the original changes (before reflecting Paul's review). Only the V1 VIs are shown but the same changes were made to V2.

Class private data:

Register gRPC Methods and Messages:

Start Sync (before/after):

The rest are just recompiles due to adding data to the class.