Attributes not synced at kernel exit if there is a pending exception

[lriesebos]

Bug Report

One-Line Summary

No attribute syncing when kernel exits with an exception.

Issue Details

Steps to Reproduce

See the following example code:

class MyExperiment(EnvExperiment):

    def build(self):
        self.setattr_device('core')
        self.attr_sync_var = 0

    def run(self):
        try:
            self._run()
        except RuntimeError:
            pass
        assert self.attr_sync_var == 1

    @kernel
    def _run(self):
        self.attr_sync_var += 1
        raise RuntimeError

Expected Behavior

The assertion passes. The same as what would happen if the RuntimeError was not raised because the exception raised after the variable was modified.

Actual (undesired) Behavior

The assertion fails. Because of the RuntimeError, the kernel exits with a "pending" exception. I expect that is the cause. The logs show that attribute synchronization (from the kernel to the host) is not performed. Hence, attr_sync_var is still 0. Exception propagation still works fine.

This behavior is at least seen in ARTIQ 6 and 7. I have not tested 8. If there is agreement that this behavior is incorrect then I would like backporting of this fix to be considered for versions down to ARTIQ 6 if possible but at least 7 (current old stable).

Your System (omit irrelevant parts)

• Operating System: Ubuntu
• ARTIQ version: 7.8211

[lriesebos]

@sbourdeauducq any opinions about this? intended behavior, or a bug?

[jordens]

It's incorrect behavior but changing it in stable releases is not worth the breakage.