Allow user to specify whether pool is LIFO or FIFO

[tomfitzhenry]

Issue: #1184

What do you think about whether this should be configurable via ahc.properties? I initially did this, but I wondered whether there might be implementations of ChannelPool for which LIFO vs FIFO didn't make sense, and by putting LIFO vs FIFO at properties file level, that might be a leaky abstraction.

[slandelle]

What do you think about whether this should be configurable via ahc.properties?

Usage would be very specific/limited as it could only tune the default DefaultChannelPool.
I think this version is sufficient for a first version.

Let's see if users need more (meaning that they would need to be aware of this feature, meaning documentation, which is this project's weakness).

WDYT?

[ghost]

I added this wiki page: https://github.com/AsyncHttpClient/async-http-client/wiki/Connection-pooling

Suggestions welcome!

[slandelle]

@bbc-tomfitzhenry Awesome, thanks!

Some comments:

• You actually have a AsyncHttpClientConfig, not a builder, as you call build
• You could use the helpers from org.asynchttpclient.Dsl (use a static import)
• Beware that if you're having your own timer, you're in charge of shutting it down

[tomfitzhenry]

Fixed docs to use org.asynchttpclient.Dsl. Didn't know about that!

[slandelle]

Thanks!

Didn't know about that!

New in AHC2. When I'm telling you doc is lacking ;-)