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https://issues.apache.org/jira/browse/LUCENE-4025?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13265663#comment-13265663
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Shai Erera commented on LUCENE-4025:
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Calling maybeRefresh in an empty loop is not good. You'd want to at least add
some sleep in between calls. And then you need to decide on the sleep interval.
Complicate things.
What's not clear to me is why was this API made non-blocking in the first
place? Did someone complain about it being blocking?
bq. The non-blocking fashion is a big asset here IMO since you can't build a
non-blocking app with blocking components but you can do the other way around.
That's generally a correct statement, but who said that in the context of a
ReferenceManager you want to build a non-blocking app?
Perhaps a maybeRefreshBlocking() will be the best compromise after all. That
method won't return anything and will just block on reopenLock. I'll create a
patch, let's see how it looks first. While I'm at it, I'll rename reopenLock to
refreshLock (reopenLock was from the time it was in SearcherManager).
> ReferenceManager.maybeRefresh should allow the caller to block
> --------------------------------------------------------------
>
> Key: LUCENE-4025
> URL: https://issues.apache.org/jira/browse/LUCENE-4025
> Project: Lucene - Java
> Issue Type: Improvement
> Components: core/search
> Reporter: Shai Erera
> Priority: Minor
> Fix For: 4.0
>
>
> 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:
> {code}
> writer.commit();
> searcherManager.maybeRefresh();
> searcherManager.acquire();
> {code}
> 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?
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