Make thread executor a background thread.

[jamdavi]

The original implementation of XThread created a task on the standard TaskScheduler and did not spin up a parent thread. But instead the XThread container allowed "thread-like" operations to take place. The default TaskScheduler creates background threads by default.

When XThread was replaced with Thread it caused a real .NET thread to be created. This thread was created as a foreground thread which, when an application is terminated, will leave the application waiting on the termination of the thread.

This behavior is different than the original behavior with XThread.

Before, closing the application via Environment.Exit or letting it run to completion would kill all background threads. Now, the only way to terminate the executor thread is to call ShutdownGracefullyAsync. If the application using DotNetty was already calling ShutdownGracefullyAsync then the application would not experience any issues.

DotNetty/src/DotNetty.Common/Concurrency/IEventExecutorGroup.cs

Line 29 in 47f5ec7

Task ShutdownGracefullyAsync();

Foreground and background threads