RFR: 8175010: ImageReader is not thread-safe

[Jim Laskey (Oracle)]

+1

> On Feb 15, 2017, at 9:22 AM, Claes Redestad <claes.redestad at oracle.com> 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
> 
> Testing shows no issues (which admittedly doesn't mean we're
> actually solving the root cause for JDK-8174817), and performance
> numbers from adding a volatile read indicate that any overhead
> is lost in the noise on ImageReader-heavy workloads.
> 
> Thanks!
> 
> /Claes
> 
> [1] https://bugs.openjdk.java.net/browse/JDK-8174817