Generational ZGC parsing logic assumes only one collection is happening at any given time

[akiselev98]

Generational ZGC runs two garbage collectors concurrently (major and minor). The current implementation of ZGCParser assumes that at any given time, there can be at most one cycle happening.

When a minor collection starts before the major collection has finished, the information from the major collection is lost.

Example GC log snippet

sample-gc.log

Sequence of events:

• Major collection (GC 13) starts
• GC 13 performs young generation collection
• Minor collection (GC 14)
• Minor collection (GC 15), and there's some log lines from GC 13 mixed in
• GC 13 finishes

When I ran this through the library, it loses track of GC 13 entirely.

I know you guys were planning to release a new version soon-ish, and wanted to make sure this was on your radar.