On Wed, 16 Feb 2022 09:30:46 GMT, Volker Simonis <simo...@openjdk.org> wrote:
> Currently, `InflaterInputStream::read()` first does a native call to the
> underlying zlib `inflate()` function and only afterwards checks if the
> inflater requires input (i.e. `Inflater::needsInput()`) or has finished
> inflating (`Inflater::finished()`). This leads to an unnecessary native call
> to `inflate()` when `InflaterInputStream::read()` is invoked for the very
> first time because `Inflater::fill()` hasn't been called and another
> unnecessary native call to detect the end of the stream. For small
> streams/files which completely fit into the output buffer passed to
> `InflaterInputStream::read()` we can therefore save two out of three native
> calls. The attached micro benchmark shows that this results in a 5%-10%
> performance improvement for zip files of sizes between 4096 to 256 bytes
> (notice that in common jars like Tomcat, Spring-Boot, Maven, Jackson, etc.
> about 60-80% of the classes are smaller than 4096 bytes).
>
>
> before JDK-8281962
> ------------------
> Benchmark (size) Mode Cnt Score
> Error Units
> InflaterInputStreams.inflaterInputStreamRead 256 avgt 5 2.571 ±
> 0.120 us/op
> InflaterInputStreams.inflaterInputStreamRead 512 avgt 5 2.861 ±
> 0.064 us/op
> InflaterInputStreams.inflaterInputStreamRead 4096 avgt 5 5.110 ±
> 0.278 us/op
>
> after JDK-8281962
> -----------------
> Benchmark (size) Mode Cnt Score
> Error Units
> InflaterInputStreams.inflaterInputStreamRead 256 avgt 5 2.332 ±
> 0.081 us/op
> InflaterInputStreams.inflaterInputStreamRead 512 avgt 5 2.691 ±
> 0.293 us/op
> InflaterInputStreams.inflaterInputStreamRead 4096 avgt 5 4.812 ±
> 1.038 us/op
>
>
> Tested with the JTreg zip/jar/zipfs and the JCK zip/jar tests.
>
> As a side effect, this change also fixes an issue with alternative zlib
> implementations like zlib-Chromium or zlib-Cloudflare which pad the inflated
> bytes with a specif byte pattern at the end of the output for debugging
> purpose. This breaks code patterns like the following:
>
>
> int readcount = 0;
> while ((bytesRead = inflaterInputStream.read(data, 0, bufferSize)) != -1) {
> outputStream.write(data, 0, bytesRead);
> readCount++;
> }
> if (readCount == 1) {
> return data; // <---- first bytes might be overwritten
> }
> return outputStream.toByteArray();
>
>
> Even if the whole data fits into the `data` array during the first call to
> `inflaterInputStream.read()`, we still need a second call to
> `inflaterInputStream.read()` in order to detect the end of the inflater
> stream. If this second call calls into the native `inflate()` function of
> Cloudflare/Chromium's zlib version, this will still write some padding bytes
> at the beginning of the `data` array and overwrite the previously read data.
> This issue has been reported in Spring [1] and ASM [2] when using these
> libraries with Cloudflares zlib version (by setting `LD_LIBRARY_PATH`
> accordingly).
>
> [1] https://github.com/spring-projects/spring-framework/issues/27429
> [2] https://gitlab.ow2.org/asm/asm/-/issues/317955
This change is probably okay but will require study to see if there are any
side effects (sadly, this area has a history of side effects being reported
months and years after a change). Would you mind holding off integrating this
change until it has been reviewed by someone that works in the area?
-------------
PR: https://git.openjdk.java.net/jdk/pull/7492
