RFR: JDK-8142508: To bring j.u.z.ZipFile's native implementation to Java to remove the expensive jni cost and mmap crash risk
Xueming Shen
xueming.shen at oracle.com
Wed Nov 11 20:22:00 UTC 2015
Hi
Please help review the changes for JDK-8142508 (third try)
Issue: https://bugs.openjdk.java.net/browse/JDK-8142508
webrev: http://cr.openjdk.java.net/~sherman/8142508/webrev
Mainly to address the issues in current j.u.z.ZipFile implementation as listed
below
(1) The ZIP file format support code is in native C (shared with the VM via
ZipFile.c -> zip_util.c). Any entry lookup, creation operation requires multiple
round-trips of expensive jni calls.
(2) The native C implementation which uses mmap to map in the central directory
table appears to be a big risk of vm crash when the underlying jar file gets
overwritten with new contents while it is still being used by other ZipFile. The
crash reports keep coming in even after we have introduced in system flag
to disable it (sun.zip.disableMemoryMapping).
(3) The use of "filename + lastModified()" cache (zip_util.c) appears to be broken
if the timestamp is in low resolution/precision (File.getModified() for example,
might only have "second" ersolution on solaris/linux), and/or the file is being
overwritten.
The clean solution appears to bring the ZIP format support code completely from
native to Java to remove the jni invocation cost and the mmap risk. Also to use
the fileKey and lastModified from java.nio.file.attribute.BasicFileAttributes to have
better/correct cache matching.
Benchmark:
This simple jmh measurement suggests a big boost of the performance of
ZipFile.getEntry()/entries()/getStream() which are basically entry related
accesses (the "open only" has some regression, which is expected as we
switched from the mmap to simply read the cen table in into a byte[])
http://cr.openjdk.java.net/~sherman/8142508/MyBenchmark.java
# JDK9 base
Benchmark Mode Cnt Score Error Units
MyBenchmark.testEntries avgt 50 13.671 ± 0.385 ms/op
MyBenchmark.testGetEntry avgt 50 17.414 ± 0.803 ms/op
MyBenchmark.testGetStream avgt 50 42.398 ± 10.136 ms/op
MyBenchmark.testOpen avgt 50 3.049 ± 0.094 ms/op
MyBenchmark.testRead avgt 50 215.179 ± 9.926 ms/op
MyBenchmark.testReadAll avgt 50 244.422 ± 19.375 ms/op
--------------------------------------------------------------------------------------
# JDK9 ZipFile without jni invocation
Benchmark Mode Cnt Score Error Units
MyBenchmark.testEntries avgt 50 6.436 ± 0.422 ms/op
MyBenchmark.testGetEntry avgt 50 10.021 ± 0.699 ms/op
MyBenchmark.testGetStream avgt 50 38.713 ± 16.687 ms/op
MyBenchmark.testOpen avgt 50 3.288 ± 0.119 ms/op
MyBenchmark.testRead avgt 50 220.653 ± 8.529 ms/op
MyBenchmark.testReadAll avgt 50 249.798 ± 18.438 ms/op
---------------------------------------------------------------------------------------
Test:
http://cr.openjdk.java.net/~sherman/8142508/webrev/test/java/util/zip/ZipFile/TestZipFile.java.html
Verified the new ZipFile runs as expected when the underlying jar/zip file get
deleted/overwritten when the zip still be used. The "old" ZipFile fails to continue
to work but no crash, and the "new" one works correctly on updated zip file
without problem (The test runs a little long, have not decided if it should be
checked in as unit test).
-Sherman
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