JDK-8352891 Performance improvements to ByteArrayOutputStream

[Alan Bateman]

On 28/03/2025 13:05, Engebretson, John wrote:
>
> Hi all!  This message is to discuss the proposal for a public class 
> that is faster/cheaper than ByteArrayOutputStream.  Details are on the 
> ticket [1] so I will only summarize here:
>
> - ByteArrayOutputStream is slower than the provided alternative, and 
> wastes memory bandwidth and allocation.
>
> - The new alternative cannot replace ByteArrayOutputStream because 
> BAOS exposes two implementation-specific fields.
>
> - The problem is broadly present, and different solutions exist in 
> Spring, Tomcat, multiple applications inside my company, and 
> undoubtedly elsewhere.
>
> - There are places within the JDK that will benefit from the improved 
> performance.
>
>
There are many possible directions and APIs that could be explored here, 
lots of fun.

The JBS issue seems to all about BAOS performance, esp. due to it 
maintaining a contiguous array and needing to resize. Rather than 
introduce a subclass into the API then maybe you instead explore adding 
a static factory that returns a BAOS with a different implementation. 
For a long time we've been mulling over adding a factory method to get a 
BAOS that isn't thread safe (the undocumented synchronization dates from 
JDK 1.0 and too risky to change after 30 years of usage). It would also 
be feasible to have BOAS use a different implementation when used 
directly vs. when subclassed although that wouldn't be pretty.

-Alan
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