On Thu, 19 Dec 2024 18:14:39 GMT, Severin Gehwolf <sgehw...@openjdk.org> wrote:
> Please review this fairly simple change to improve how the > `JimageDiffGenerator` works. The original implementation is pretty naive and > read all bytes into memory and then compared them. This improved version only > reads bytes on a bound buffer into memory compares those bytes and if equal > continues on to reading the next bytes (`2k` at most) at a time. Previously > it was `2*N` (where `N` is the file size of a file in bytes) part of the JDK. > Ouch. > > There is still the off-chance of reading a full file into memory when the > generator detects a change, but this shouldn't happen for large files since > the total diff should be around `600K` as of today. > > This also reverts changes from > [JDK-8344036](https://bugs.openjdk.org/browse/JDK-8344036) other than the > `/timeout` change to the test, which is preserved as I think this bump is no > longer needed. > > Testing: > - [x] GHA > - [x] jlink tests on a fastdebug build with > `--with-native-debug-symbols=internal` (so as to have a large libjvm.so). > - [x] Manual reproducer from the bug which fails with OOM before the patch > and passes after > > Thoughts? src/jdk.jlink/share/classes/jdk/tools/jlink/internal/runtimelink/JimageDiffGenerator.java line 134: > 132: while ((bytesRead1 = is1.read(buf1)) != -1 && > 133: (bytesRead2 = is2.read(buf2)) != -1) { > 134: if (bytesRead1 != bytesRead2) { This test seems to assume there won't be any short reads. That might be true in practice, but for defensive programming reasons it would be safer to use `readNBytes()` instead of `read()`. src/jdk.jlink/share/classes/jdk/tools/jlink/internal/runtimelink/JimageDiffGenerator.java line 137: > 135: return false; > 136: } > 137: if (bytesRead1 == buf1.length) { This can be simplified by using [`Arrays.equals(byte[],int,int,byte[],int,int)`](https://docs.oracle.com/en/java/javase/22/docs/api/java.base/java/util/Arrays.html#equals(byte%5B%5D,int,int,byte%5B%5D,int,int)) for both cases. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/22835#discussion_r1907828139 PR Review Comment: https://git.openjdk.org/jdk/pull/22835#discussion_r1907830279
