6934977: (bf) MappedByteBuffer.load can SIGBUS if file is truncated

[Chris Hegarty]

Alan - The changes looks great.

-Chris.

On 07/21/10 15:36, Alan Bateman wrote:
>
> If the file underlying a mapped byte buffer is truncated then it's
> possible that invoking the MappedByteBuffer's load method will SIGBUS.
> The reason is that the load touches each page in a native method and the
> VM's handler cannot deal with the fault. A second and related issue
> (6799037) is that same native code is reading an int from each page
> without taking alignment into consideration or the possibility that it
> might read beyond the end of the mapping. Yet another issue, is that
> isLoaded fails with an IOException for the case that the mapping doesn't
> start on a multiple of the page size. The load method has a similar
> problem but it doesn't throw IOException because it is ignoring the
> return value from madvise(3C).
>
> The webrev with the proposed changes to fix these issues is here:
> http://cr.openjdk.java.net/~alanb/6934977/webrev
>
> The main change is that load is changed to touch the pages via Unsafe
> and so uses the existing handler.
>
> -Alan.