ReferenceManager.maybeRefresh() returns a boolean today, specifying whether the maybeRefresh logic was executed by the caller or not. If it's false, it means that another thread is currently refreshing and the call returns immediately.
I think that that's inconvenient to the caller. I.e., if you wanted to do something like:
It'd be better if you could guarantee that when the maybeRefresh() call returned, the follow on acquire() will return a refreshed IndexSearcher. Even if you omit the commit instruction, it'd be good if you can guarantee that.
I don't quite see the benefit of having the caller thread not block if there's another thread currently refreshing. In, I believe, most cases, you'd anyway have just one thread calling maybeRefresh(). Even if not, the only benefit of not blocking is if you have commit() followed by maybeRefresh() logic done by some threads, while other threads acquire searchers - maybe then you wouldn't care if another thread is currently doing the refresh?
Actually, I tend to think that not blocking is buggy? I mean, what if two threads do commit() + maybeRefresh(). The first thread finishes commit, enters maybeRefresh(), acquires the lock and reopens the Reader. Then the second thread does its commit(), enters maybeRefresh, fails to obtain the lock and exits. Its changes won't be exposed by SM until the next maybeRefresh() is called.
So it looks to me like current logic may be buggy in that sense?