[Discussion] There are so much threadpool, can we merge some threadpool into one threadpool?

[yuhang xiu <ca...@gmail.com>]

Hi, all

I noticed that @cvictory made a very good issue[1], I think we can have
more discussion, so I brought it here:

There are so much threadpool that manage only one thread , and this thread
is idle. The threadpool as follow:

*
org.apache.dubbo.metadata.support.AbstractMetadataReport#reportCacheExecutor
for asyn write metadata.
* The HashedWheelTimer is used in Registry retry task.
* Configcenter listen the config changed, and the callback will excuted by
a dependency Executor.
....

There are so much situation that we will use threadpool. I think can we
merge this threadpool to make the threadpool is used by much more situation.

Also we should move some timer task to HashedWheelTimer?

[1] https://github.com/apache/incubator-dubbo/issues/3616