RFR: 8175010: ImageReader is not thread-safe

[Alan Bateman]

On 15/02/2017 13:22, Claes Redestad wrote:

> Hi,
>
> a few intermittent but rare test failures[1] that has appeared
> since the latest jake integration, and since one of the changes
> in there was to make initialization of the system ImageReader
> lazy there appears to be cases where ImageReaders are not
> safely published:
>
> - Ensure ImageReader::open is called only once per Path in
> ImageReaderFactory by using CHM.computeIfAbsent
> - Ensure ImageReader.reader is safely published to a
> final field and signal close using a volatile boolean instead
>
> webrev: http://cr.openjdk.java.net/~redestad/8175010/webrev.02/
> bug: https://bugs.openjdk.java.net/browse/JDK-8175010
ImageReaderFactory looks good.

The changes to ImageReader are okay too, always a bit odd that this code 
throw NPE when the reader was closed. There is still an issue with async 
close of course in that someone could close at the same time as an 
access. However that is a high-level issue for jrtfs, at run-time then 
the image file is opened once and is never closed.

-Alan