How to use channel groups from custom implementation?

[Alan Bateman]

Gili wrote:
> Hi,
>
> It's not clear how to make use of AsynchronousChannelGroup. The user invokes
> open(AsynchronousChannelGroup) on my custom AsynchronousByteChannel. What
> next? How am I supposed to gain access to the underlying Executor used to
> invoke the CompletionHandlers? How am I supposed to gain access to the
> default channel group if he invokes open()?
>   
Channels in the same group share resources such as I/O event or 
completion ports. All the details on demultiplexing are highly 
provider/implementation specific and there isn't any supported way to 
attach a new channel type to an existing provider implementation. It's a 
similar to what we have with Selector where someone can't develop a 
SelectableChannel implementation and have it work with the default 
provider. Instead the replacement unit is the complete ball of wax that 
is the SelectorProvider or AsynchronousChannelProvider and the 
associated channel types.

That said, for experimental purposes then it may be useful to know our 
AsynchronousChannelGroup implementation implements Executor so there is 
a means (albeit not supported) to execute tasks on the thread pool. 
Whether this is efficient or not depends will depend on the type of 
thread pool. With a fixed thread pool then all threads are normally 
blocked waiting on I/O events and so if you execute some arbitrary task 
then one of these threads will require to be woken up in order to 
execute the task.

The default channel group cannot be shutdown so this is why there isn't 
a method to get a reference to it.

-Alan