8220394: bufferedStream does not honor size limit

[Langer, Christoph]

Hi Thomas,

this change looks good to me.

Best regards
Christoph

> -----Original Message-----
> From: hotspot-runtime-dev <hotspot-runtime-dev-
> bounces at openjdk.java.net> On Behalf Of Thomas Stüfe
> Sent: Mittwoch, 22. Mai 2019 11:25
> To: Hotspot dev runtime <hotspot-runtime-dev at openjdk.java.net>; David
> Holmes <david.holmes at oracle.com>
> Subject: Re: 8220394: bufferedStream does not honor size limit
>
> Hi all,
>
> third round:
> http://cr.openjdk.java.net/~stuefe/webrevs/8220394-bufferedstream-
> does-not-honor-size-limit/webrev.02/webrev/
>
> I also added a gtest test case for bufferedStream. It tests the static
> variant, the dynamic variant without truncation and with truncation. The
> last test, testing with truncation, is commented out - to run this test,
> you need to manually enable it first. This is because it uses a lot of
> memory (100M) in release and in debug it would crash as expected.
>
> Cheers, Thomas
>
>
>
>
> On Tue, May 21, 2019 at 4:18 PM Thomas Stüfe <thomas.stuefe at gmail.com>
> wrote:
>
> > Hi,
> >
> > new webrev with the following changes:
> >
> > - reworked comment to make it more concise and clear
> > - the cap where we assert now is guaranteed to be larger than the buffer
> > maximum.
> >
> >
> > http://cr.openjdk.java.net/~stuefe/webrevs/8220394-bufferedstream-
> does-not-honor-size-limit/webrev.01/webrev/
> >
> > Thanks, Thomas
> >
> >
> >
> > On Tue, May 14, 2019 at 12:25 PM Thomas Stüfe
> <thomas.stuefe at gmail.com>
> > wrote:
> >
> >>
> >>    Hi all,
> >>
> >>
> >> Bug: https://bugs.openjdk.java.net/browse/JDK-8220394
> >> cr:
> >> http://cr.openjdk.java.net/~stuefe/webrevs/8220394-bufferedstream-
> does-not-honor-size-limit/webrev.00/webrev/
> >>
> >> I redid the patch for this in a minimal form. The first version I posted
> >> in March but after consideration I found it too invasive.
> >>
> >> Short story: bufferedStream is misused as a
> >> outputStream-with-dynamic-buffer in a number of places - misused since
> we
> >> have stringStream for that.
> >>
> >> It has something looking like a maximum buffer size cap but that is
> >> actually a flush-trigger for child classes of bufferesStream.
> >> bufferedStream::flush itself is a noop.
> >>
> >> That means that printing to this stream may cause high memory footprint
> >> or native OOM since the upper limit is not honored. In runaway printing
> >> coding this can tear down the process.
> >>
> >> This patch is a stopgap - when we reach the buffer limit - but not below
> >> 100M - we will assert(debug) or truncate (release).
> >>
> >> I am careful here since I do not know if there are situations where more
> >> than buffer-limit bytes are written today and suddenly enforcing this limit
> >> now would cause errors. I think 100M is safe to be considered "too
> much".
> >>
> >> The real correct solution should be that all callers use stringStream and
> >> handle truncation. This patch is small and could be, if necessary, ported
> >> down to older releases easily.
> >>
> >> Thanks, Thomas
> >>
> >>
> >>