7133499: (fc) FileChannel.read not preempted by asynchronous close on OS X

[Alan Bateman]

One of the outstanding issues from the OS X port is that the async close 
of a FileChannel where there are threads blocked doing I/O operation 
does not work, instead close hang (potentially indefinitely, say when 
another thread is blocked waiting for a file lock to be acquired or 
where the file is something like a pipe or other type of file where you 
can block indefinitely). From what I can tell, it wasn't implemented in 
Apple's JDK6 either.

In order to fix this on OS X then close needs to signal all threads that 
are blocked in I/O operations, something we already do on Linux. The 
other part is removing the preClose (the dup2) from the closing of 
FileChannels as it is not needed when you can signal. The webrev with 
the proposed changes is here:

http://cr.openjdk.java.net/~alanb/7133499/webrev/

Fixing this issue means that two tests can be removed from the exclude 
list (there is third test removed from the exclude list too, that 
shouldn't have been there).

-Alan.