RFR 8080640: Reduce copying when reading JAR/ZIP entries
staffan.friberg at oracle.com
Thu May 21 18:00:41 UTC 2015
On 05/21/2015 09:48 AM, Staffan Friberg wrote:
> On 05/20/2015 10:57 AM, Xueming Shen wrote:
>> On 05/18/2015 06:44 PM, Staffan Friberg wrote:
>>> Wanted to get reviews and feedback on this performance improvement
>>> for reading from JAR/ZIP files during classloading by reducing
>>> unnecessary copying and reading the entry in one go instead of in
>>> small portions. This shows a significant improvement when reading a
>>> single entry and for a large application with 10k classes and 500+
>>> JAR files it improved the startup time by 4%.
>>> For more details on the background and performance results please
>>> see the RFE entry.
>>> RFE - https://bugs.openjdk.java.net/browse/JDK-8080640
>>> WEBREV - http://cr.openjdk.java.net/~sfriberg/JDK-8080640/webrev.0
>> Hi Staffan,
>> If I did not miss something here, from your use scenario it appears
>> to me the only thing you really
>> need here to help boost your performance is
>> byte ZipFile.getAllBytes(ZipEntry ze);
>> You are allocating a byte at use side and wrapping it with a
>> ByteBuffer if the size is small enough,
>> otherwise, you letting the ZipFile to allocate a big enough one for
>> you. It does not look like you
>> can re-use that byte (has to be wrapped by the ByteArrayInputStream
>> and return), why do you
>> need two different methods here? The logic would be much easier to
>> simply let the ZipFile to allocate
>> the needed buffer with appropriate size, fill the bytes and return,
>> with a "OOME" if the entry size
>> is bigger than 2g.
>> The only thing we use from the input ze is its name, get the
>> size/csize from the jzentry, I don't think
>> jzentry.csize/size can be "unknown", they are from the "cen" table.
>> If the real/final use of the bytes is to wrap it with a
>> ByteArrayInputStream,why bother using ByteBuffer
>> here? Shouldn't a direct byte with exactly the size of the entry
>> server better.
> Hi Sherman,
> Thanks for the comments. I agree, was starting out with bytebuffer
> because I was hoping to be able to cache things where the buffer was
> being used, but since the buffer is past along further I couldn't
> figure out a clean way to do it.
> Will rewrite it to simply just return a buffer, and only wrap it in
> the Resource class getByteBuffer.
> What would be your thought on updating the ZipFile.getInputStream to
> return ByteArrayInputStream for small entries? Currently I do that
> work outside in two places and moving it would potentially speed up
> others reading small entries as well.
Just realized that my use of ByteArrayInputStream would miss Jar
verification if enabled so the way to go hear would be to add it if
possible to the ZipFile.getInputStream.
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