8012019: (fs) Thread.interrupt triggers hang in FileChannelImpl.pread (win)

[Alan Bateman]

The FileChannel read/write methods that take a position are currently 
synchronized on Windows due ReadFile/WriteFile changing the global file 
position. This is something that will need to be looked again because it 
is a long standing (since jdk1.4) scalability issue.

In the mean-time, it turns out that there is potential for deadlock on 
Windows when a position sensitive method is interrupted at around the 
time that a position insensitive method is executing. It's been there 
for some time but only reported recently. The problem is that a position 
sensitive method has the positionLock and if interrupted will close the 
channel causing it to wait until all threads have finished their I/O 
operations. With position insensitive methods then the positionLock is 
acquired as part of the I/O operation, hence the deadlock.

The fix is very simple and just changes the two FileChannel methods to 
acquire positionLock (if needed) before doing the I/O operations. This 
means dropping the lock parameter from the IOUtil read/write methods so 
there are more files changed that might be obvious. The webrev with the 
changes is here:

http://cr.openjdk.java.net/~alanb/8012019/webrev/

-Alan.