Use singleton reduction functions in count and countLong

[davidmoten]

Every call to Observable.count() and countLong() instantiated a new Func2 which I have now made a singleton in the interests of minimizing GC pressure.

Can anyone in the know confirm for me that there is GC benefit from this one because I assume a sophisticated enough compiler could replace the new Func2 call with a singleton during its optimizations.

If this one is worthwhile then there are heaps more of these in Observable.java and possibly elsewhere.

[akarnokd]

Since we are Java 6+, we can't assume a bunch of optimizations happen so what's left is manual optimization/inlining.

[akarnokd]

I'd instead do this directly with a long counting Subscriber and for int, I'd map it to min(count, Integer.MAX_VALUE) at the end saving the duplications.

[davidmoten]

I guess this is an opportunity to decide what overflow behaviour we desire. I see three options:

1. be consistent with Integer/Long overflow behaviour
2. return Integer.MAX_VALUE/Long.MAX_VALUE on overflow
3. throw an error on overflow

My preference is 3.

[zsxwing]

I think both 2 and 3 will be a breaking change so it's not acceptable. 1 is not a big deal since it's consistent with Java, which all Java users should be familiar with it.

[zsxwing]

@davidmoten thoughts?

[davidmoten]

I'm happy to maintain the existing overflow behaviour so it's not a
breaking change. Given that I think the PR could go in as is.

On Tue, 21 Apr 2015 18:57 Shixiong Zhu [email protected] wrote:

@davidmoten https://github.com/davidmoten thoughts?

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#2880 (comment).

[zsxwing]

Thanks.