Hi, can I please have a review for the following small enhancement which improves the speed of reading from ZipFile.getInputStream() by ~5%:
http://cr.openjdk.java.net/~simonis/webrevs/2020/8244659/ https://bugs.openjdk.java.net/browse/JDK-8244659 ZipFile.getInputStream() tries to find a good size for sizing the internal buffer of the underlying InflaterInputStream. This buffer is used to read the compressed data from the associated InputStream. Unfortunately, ZipFile.getInputStream() uses CENLEN (i.e. the uncompressed size of a ZipEntry) instead of CENSIZ (i.e. the compressed size of a ZipEntry) to configure the input buffer and thus unnecessarily wastes memory, because the corresponding, compressed input data is at most CENSIZ bytes long. After fixing this and doing some benchmarks, I realized that a much bigger problem is the continuous allocation of new, temporary input buffers for each new input stream. Assuming that a zip files usually has hundreds if not thousands of ZipEntries, I think it makes sense to cache these input buffers. Fortunately, ZipFile already has a built-in mechanism for such caching which it uses for caching the Inflaters needed for each new input stream. In order to cache the buffers as well, I had to add a new , package-private constructor to InflaterInputStream. I'm not sure if it makes sense to make this new constructor public, to enable other users of InflaterInputStream to pre-allocate the buffer. If you think so, I'd be happy to do that change and open a CSR for this issue. Adding a cache for input stream buffers increases the speed of reading ZipEntries from an InputStream by roughly 5% (see benchmark results below). More importantly, it also decreases the memory consumption for each call to ZipFile.getInputStream() which can be quite significant if many ZipEntries are read from a ZipFile. One visible effect of caching the input buffers is that the manual JTreg test java/util/zip/ZipFile/TestZipFile.java, which regularly failed on my desktop with an OutOfMemoryError before, now reliably passes (this tests calls ZipFile.getInputStream() excessively). I've experimented with different buffer sizes (even with buffer sizes depending on the size of the compressed ZipEntries), but couldn't see any difference so I decided to go with a default buffer size of 65536 which already was the maximal buffer size in use before my change. I've also added a shortcut to Inflater which prevents us doing a native call down to libz's inflate() method every time we call Inflater.inflate() with "input == ZipUtils.defaultBuf" which is the default for every newly created Inflater and for Inflaters after "Inflater.reset()" has been called on them. Following some JMH benchmark results which show the time and memory used to read all bytes from a ZipEntry before and after this change. The 'size' parameter denotes the uncompressed size of the corresponding ZipEntries. In the "BEFORE" numbers, when looking at the "gc.alloc.rate.norm" values, you can see the anomaly caused by using CENLEN instead of CENSIZ in ZipFile.getInputStream(). I.e. getInputStream() chooses to big buffers because it looks at the uncompressed ZipEntry sizes which are ~ 6 times bigger than the compressed sizes. Also, the old implementation capped buffers bigger than 65536 to 8192 bytes. The memory savings for a call to getInputStream() are obviously the effect of repetadly calling getInputStream() on the same zip file (becuase only in that case, the caching of the input buffers pays of). But as I wrote before, I think it is common to have mor then a few entries in a zip file and even if not, the overhead of caching is minimal compared to the situation we had before the change. Thank you and best regards, Volker = BEFORE 8244659 = Benchmark (size) Mode Cnt Score Error Units ZipFileGetInputStream.readAllBytes 1024 avgt 3 13.577 ± 0.540 us/op ZipFileGetInputStream.readAllBytes:·gc.alloc.rate.norm 1024 avgt 3 1872.673 ± 0.317 B/op ZipFileGetInputStream.readAllBytes:·gc.count 1024 avgt 3 57.000 counts ZipFileGetInputStream.readAllBytes:·gc.time 1024 avgt 3 15.000 ms ZipFileGetInputStream.readAllBytes 4096 avgt 3 20.938 ± 0.577 us/op ZipFileGetInputStream.readAllBytes:·gc.alloc.rate.norm 4096 avgt 3 4945.793 ± 0.493 B/op ZipFileGetInputStream.readAllBytes:·gc.count 4096 avgt 3 102.000 counts ZipFileGetInputStream.readAllBytes:·gc.time 4096 avgt 3 25.000 ms ZipFileGetInputStream.readAllBytes 16384 avgt 3 51.348 ± 2.600 us/op ZipFileGetInputStream.readAllBytes:·gc.alloc.rate.norm 16384 avgt 3 17238.030 ± 3.183 B/op ZipFileGetInputStream.readAllBytes:·gc.count 16384 avgt 3 144.000 counts ZipFileGetInputStream.readAllBytes:·gc.time 16384 avgt 3 33.000 ms ZipFileGetInputStream.readAllBytes 65536 avgt 3 203.082 ± 7.046 us/op ZipFileGetInputStream.readAllBytes:·gc.alloc.rate.norm 65536 avgt 3 9035.475 ± 7.426 B/op ZipFileGetInputStream.readAllBytes:·gc.count 65536 avgt 3 18.000 counts ZipFileGetInputStream.readAllBytes:·gc.time 65536 avgt 3 5.000 ms ZipFileGetInputStream.readAllBytes 262144 avgt 3 801.928 ± 22.474 us/op ZipFileGetInputStream.readAllBytes:·gc.alloc.rate.norm 262144 avgt 3 9034.192 ± 0.047 B/op ZipFileGetInputStream.readAllBytes:·gc.count 262144 avgt 3 3.000 counts ZipFileGetInputStream.readAllBytes:·gc.time 262144 avgt 3 1.000 ms ZipFileGetInputStream.readAllBytes 1048576 avgt 3 3154.747 ± 57.588 us/op ZipFileGetInputStream.readAllBytes:·gc.alloc.rate.norm 1048576 avgt 3 9032.194 ± 0.004 B/op ZipFileGetInputStream.readAllBytes:·gc.count 1048576 avgt 3 ≈ 0 counts = AFTER 8244659 = Benchmark (size) Mode Cnt Score Error Units ZipFileGetInputStream.readAllBytes 1024 avgt 3 13.031 ± 0.452 us/op ZipFileGetInputStream.readAllBytes:·gc.alloc.rate.norm 1024 avgt 3 824.311 ± 0.027 B/op ZipFileGetInputStream.readAllBytes:·gc.count 1024 avgt 3 27.000 counts ZipFileGetInputStream.readAllBytes:·gc.time 1024 avgt 3 7.000 ms ZipFileGetInputStream.readAllBytes 4096 avgt 3 20.018 ± 0.805 us/op ZipFileGetInputStream.readAllBytes:·gc.alloc.rate.norm 4096 avgt 3 824.289 ± 0.722 B/op ZipFileGetInputStream.readAllBytes:·gc.count 4096 avgt 3 15.000 counts ZipFileGetInputStream.readAllBytes:·gc.time 4096 avgt 3 4.000 ms ZipFileGetInputStream.readAllBytes 16384 avgt 3 48.916 ± 1.140 us/op ZipFileGetInputStream.readAllBytes:·gc.alloc.rate.norm 16384 avgt 3 824.263 ± 0.008 B/op ZipFileGetInputStream.readAllBytes:·gc.count 16384 avgt 3 6.000 counts ZipFileGetInputStream.readAllBytes:·gc.time 16384 avgt 3 1.000 ms ZipFileGetInputStream.readAllBytes 65536 avgt 3 192.815 ± 4.102 us/op ZipFileGetInputStream.readAllBytes:·gc.alloc.rate.norm 65536 avgt 3 824.012 ± 0.001 B/op ZipFileGetInputStream.readAllBytes:·gc.count 65536 avgt 3 ≈ 0 counts ZipFileGetInputStream.readAllBytes 262144 avgt 3 755.713 ± 42.408 us/op ZipFileGetInputStream.readAllBytes:·gc.alloc.rate.norm 262144 avgt 3 824.047 ± 0.003 B/op ZipFileGetInputStream.readAllBytes:·gc.count 262144 avgt 3 ≈ 0 counts ZipFileGetInputStream.readAllBytes 1048576 avgt 3 2989.236 ± 8.808 us/op ZipFileGetInputStream.readAllBytes:·gc.alloc.rate.norm 1048576 avgt 3 824.184 ± 0.002 B/op ZipFileGetInputStream.readAllBytes:·gc.count 1048576 avgt 3 ≈ 0 counts
