Ignore WAKEUP_TASK in SingleThreadEventExecutor.PollTask

[yyjdelete]

Without this, it may lead to an infinite loop.

[yyjdelete]

I didn't find a way to create an test for this. It an concurrency issue and only happen in rare case.

Shutdown will never finished if an task is enqueued during CleanupAndTerminate(). If there is any tasks left, RunAllTasks will return true and call WakeUp(true), and WakeUp(true) will enqueue an WAKEUP_TASK and it makes the next call to RunAllTasks still return true.

DotNetty/src/DotNetty.Common/Concurrency/SingleThreadEventExecutor.cs

Lines 115 to 119 in a9d0723

	while (!this.ConfirmShutdown())
	{
	this.RunAllTasks(this.preciseBreakoutInterval);
	}
	this.CleanupAndTerminate(true);

DotNetty/src/DotNetty.Common/Concurrency/SingleThreadEventExecutor.cs

Lines 375 to 381 in a9d0723

	while (true)
	{
	if (this.ConfirmShutdown())
	{
	break;
	}
	}

DotNetty/src/DotNetty.Common/Concurrency/SingleThreadEventExecutor.cs

Lines 317 to 328 in a9d0723

	if (this.RunAllTasks() || this.RunShutdownHooks())
	{
	if (this.IsShutdown)
	{
	// Executor shut down - no new tasks anymore.
	return true;
	}
	// There were tasks in the queue. Wait a little bit more until no tasks are queued for the quiet period.
	this.WakeUp(true);
	return false;
	}