Apologies, human error – here’s the message I intended:
Thank you! I’ve updated the PR accordingly and summarized the benchmarks in
the description. Here’s the short version:
* For small payloads, unsynchronized and optimized versions are 2-4x faster
than base
* For large payloads, optimized version is 3x faster than base or
unsynchronized
I discovered a capacity-related incompatibility between ByteArrayOutputStream
and MemoryOutputStream: the size() method returns int, but MemoryOutputStream
can exceed that value. I added range checking to size() and a new sizeAsLong()
method… but it really makes me wonder MemoryOutputStream belongs as a subclass
of ByteArrayOutputStream. It now has two significant incompatibilities:
ignoring the protected fields, and size restrictions.
John
From: Engebretson, John
Sent: Wednesday, April 2, 2025 12:58 PM
To: 'Alan Bateman' <alan.bate...@oracle.com>; Markus KARG
<mar...@headcrashing.eu>; core-libs-dev@openjdk.org
Subject: RE: [EXTERNAL] JDK-8352891 Performance improvements to
ByteArrayOutputStream
Thank you! I’ve updated the PR accordingly and summarized the benchmarks in
the description. Here’s the short version:
From: Alan Bateman <alan.bate...@oracle.com<mailto:alan.bate...@oracle.com>>
Sent: Wednesday, April 2, 2025 5:52 AM
To: Engebretson, John <jeng...@amazon.com<mailto:jeng...@amazon.com>>; Markus
KARG <mar...@headcrashing.eu<mailto:mar...@headcrashing.eu>>;
core-libs-dev@openjdk.org<mailto:core-libs-dev@openjdk.org>
Subject: RE: [EXTERNAL] JDK-8352891 Performance improvements to
ByteArrayOutputStream
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On 31/03/2025 16:51, Engebretson, John wrote:
Alan – is this what you have in mind:
ByteArrayOutputStream.getInstance() // returns existing class
ByteArrayOutputStream.getUnsynchronizedInstance() // returns subclass of BAOS
that overrides the synchronization
ByteArrayOutputStream.get<Scalable|Memory|Fast|Segmented>Instance() // returns
the new class
BAOS has been synchronized since JDK 1.0. While undocumented, it's possible
that existing code depends on this 30 year behavior so I think we are stuck
with it.
The removal of biased locking has spurred on a few complaints that the class is
needlessly synchronized. A static factory to return an unsynchronized BOAS
would help but only if it isn't used with code that assumes all operations are
synchronized. So I think we will have to look at the API docs for this.
It's not clear that we need to have several implementation with different
performance tradeoffs. So I think part of the exploration will be to see what
usages perform better or worse, and whether having a parameter to specify the
initial size or some hint of the max size would help the discussion.
-Alan
