Make pg_local:member_died/2 more resilient

[michaelklishin]

Proposed Changes

This makes pg_local:member_died/2 more defensive and resilient, avoiding failed assertions where they aren't productive or helpful in troubleshooting.

See #1699 for background.

Types of Changes

• Bug fix (non-breaking change which fixes issue pg_local:member_died/1 should be more resilient #1699)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation (correction or otherwise)
• Cosmetics (whitespace, appearance)

Checklist

• I have read the CONTRIBUTING.md document
• I have signed the CA (see https://cla.pivotal.io/sign/rabbitmq)
• All tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in related repositories

Further Comments

[#160530707]

[dcorbacho]

Do we really need this lookup if we always call leave_all_groups with the same Pid? The three case clauses do exactly the same. Or am I missing something?

[michaelklishin]

This code is many years old so I can only guess the intent here. I think it tries to assert that the ref/pid combination is known. I'd leave it as is for now, this is not a hot code path event.

[michaelklishin]

The clauses simply demonstrate what 3 scenarios are possible. We can combine the latter two.