Codereview needed for #6929479

[Alan Bateman]

Xueming Shen wrote:
>
> http://cr.openjdk.java.net/~sherman/6929479/webrev/
>
> This is a rfe to add a system property sun.zip.disableMmap to enable 
> the end user to disable the mmap usage in
> Sun's java.util.zip.ZipFile implementaiton (for Solaris and Linux 
> platforms).
>
> Application uses java.util.zip.ZipFile might experience SIGBUS vm 
> crash if the application mistakely over-writes
> zip/jar files that are still being used, for example the application 
> server repeatedly deploy the same jar file into the
> same location again and again while there is still code (running in 
> the same vm)  still accessing this particular zip/
> jar file (access the memory that mmapped the central directory of the 
> zip file). While this is indeed an programming
> error in the offending application, there is situation that the end 
> user really does not have the control of those
> applications and look for a workaround for the crash. With this 
> property set to true (-Dsun.zip.disableMmap=true)
> the sun zipfile implementation reads in the central directory into the 
> memory instead of using mmap.
I've had to debug a few of these so this option should be very useful. I 
wonder if sun.zip.disableMapping would be a slightly better name?

The changes looks reasonable to me - it's just a pity that we can't get 
rid of USE_MMAP (the changes really make this stand out).

-Alan