On Fri, 1 Dec 2023 13:33:01 GMT, Markus KARG <[email protected]> wrote:
>> Brian Burkhalter has updated the pull request incrementally with one
>> additional commit since the last revision:
>>
>> 8321053: Trust non-FilterOutputStreams in "java." packages
>
> src/java.base/share/classes/java/io/ByteArrayInputStream.java line 221:
>
>> 219: int nbyte = Integer.min(len - nwritten,
>> MAX_TRANSFER_SIZE);
>> 220: if (tmp != null) {
>> 221: System.arraycopy(buf, pos, tmp, 0, nbyte);
>
> I assume the overall performance of transferTo will be faster if we use
> System.arraycopy *only once* in line 215 to create a safe copy of the
> *complete* buf instead of calling it multiple times in a loop to create
> copies *per slice*. In that case we can omit the tmp == null case but simply
> use tmp = buf, making the code in the loop if-free.
There is a tradeoff here between number of invocations of `arraycopy` and
amount of memory allocated for `tmp`. (We have seen this before in #14981 which
I have allowed to languish.) The allocation limit is `MAX_TRANSFER_SIZE` which
is presently 128 kB, so any transfer of size less than this will invoke
`arraycopy` only once already.
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/16893#discussion_r1412626433
