Is it necessary always to set the core pool size in HystrixThreadPoolDefault.touchConfig()

[yanglifan]

While creating a HystrixCommand, a thread pool will be acquired and HystrixThreadPoolDefault.touchConfig() will be executed by default. In HystrixThreadPoolDefault.touchConfig(), threadPool.setCorePoolSize(dynamicCoreSize) will be executed.

In Java 6, threadPool.setCorePoolSize(dynamicCoreSize) will execute a lock operation all the time. That is negative for the performance and sometimes in the high load scenario will cause a live lock issue.

In Java 7 & 8, if the max size is greater than the core size (it is not the default scenario, but someone can have the custom thread pool), the idle worker threads will be interrupted. I think it is unnecessary if the core pool size is not changed.

So I think before execute setCorePoolSize, the new core pool size should be compared the original one to decide the necessity of the execution of setCorePoolSize

[mattrjacobs]

I didn't know either of those facts - thanks for bringing this up! Your proposal sounds like a good one. Are you interested in submitting a PR? I'm happy to review, if so. Otherwise, I can get to it before I cut the next release.

[yanglifan]

I have created a PR

[yanglifan]

The change was very simple but it caused the CI to be failed. I will check the reason, but it will be great if you could have a look.

[mattrjacobs]

Merged PR, looking at flaky unit tests now