On 05/06/2012 11:00, Rémi Forax wrote:
One of my student find a bug in the implementation of Scanner,
that allows you to use a non blocking channel as input of a Scanner.
The Scanner uses Channels.newReader() to create a Reader
from a channel which itself create a StreamDecoder.
In that case, StreamDecoder.impReader() goes into an infinite loop
because impReader() calls readBytes() that does nothing
if channel.read() returns zero.
The javadoc of Channels.newReader() clearly states that
it should throw a IllegalBlockingModeException but
there is no code that checks that.
I think a way to solve the problem is to insert a code
that check the blocking state in Channels.newWriter().
if (ch instanceof SelectableChannel) {
SelectableChannel sc = (SelectableChannel)ch;
if (!sc.isBlocking())
throw new IllegalBlockingModeException();
}
}
This could be fixed in Channels.newReader or in StreamDecoder, the
former would be consistent with Channels.newWriter. I guess you know
this already, but you will need to synchronize on the selectable
channel's blockingLock to ensure that the blocking mode doesn't change.
I've created a bug for this:
7174305: (ch) Channels.newReader doesn't throw IllegalBlockingMode if
channel is configured non-blocking
-Alan.
