Programmatically create a blocking task executor with a custom thread size

Currently, the number of threads of a blocking task executor could be configured only by Flags.numCommonBlockingTaskThreads(). If a user who avoid using flags, he or she has to manually copy the factory code.

I think we can add a new builder method to ServerBuilder that takes the number of threads.

public ServerBuilder blockingTaskExecutor(int numThreads) {
    return ...;
}

[trustin]

One question I have is: do we really need a dedicated builder method in ServerBuilder? Would it be better providing a utility class for this purpose, like we did in EventLoops?

[trustin]

Sounds good to me all in all. How about introducing a builder API so we don’t have to have too many overloaded methods?