A DESCRIPTION OF THE REQUEST :
sun.nio.ch.SelChImpl is presently unsupported. This interface is used to demark an AbstractSelectableChannel as being able to be registered against an sun.nio.ch.SelectorImpl.

I propose that sun.nio.ch.SelChImpl becomes supported as a part of Java NIO, perhaps as a part of java.nio.channels.spi. A better name should also be determined for SelChImpl.

JUSTIFICATION :
Supporting sun.nio.ch.SelChImpl would allow third parties to provide a SelectableChannel implementation that can leverage the existing Selector infrastructure. For example, to implement a Unix Domain Socket as per https://github.com/jnr/jnr-unixsocket, a kQueue/epoll Selector implementation has also been provided. This is duplication that could be avoided given that Java NIO already has such an implementation.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
java.nio.channels.Selector sel = java.nio.channels.Selector.open();

// Use the "sel" selector with a third party channel e.g.

jnr.unixsocket.UnixServerSocketChannel channel =
  jnr.unixsocket.UnixServerSocketChannel.open();
channel.register(sel, java.nio.channels.SelectionKey.OP_ACCEPT);

ACTUAL -
java.nio.channels.IllegalSelectorException is thrown given that jnr.unixsocket.UnixServerSocketChannel does not implement sun.nio.ch.SelChImpl - which it could, but would then be unsupported.

CUSTOMER SUBMITTED WORKAROUND :
Libraries such as JNR provide their own selector implementation. This circumvents the issue but duplicates code that could be leveraged.