RFR: 8334866: Improve Speed of ElfDecoder source search [v6]

[Kerem Kat]

On Fri, 24 Oct 2025 17:38:35 GMT, Kerem Kat <krk at openjdk.org> wrote:

>> Right now, looking up source file and line number info is slow because we do a full linear scan of the `.debug_aranges` section for every single call. This can be a major bottleneck on large binaries, especially during frequent native stack walking, e.g. while writing an hs_err.
>> 
>> This change fixes that by caching the address ranges on the first lookup, and keeping it in memory for the lifetime of the `DwarfFile` object.
>> 
>> All subsequent lookups on that object now use a binary search instead of the slow linear scan. If caching fails for any reason, it just falls back to the old method.
>
> Kerem Kat has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix comments, delete copy ctor

New benchmark results with 100 threads created:


hyperfine -i -N --warmup=1 -r 20 -L JDK build/release-no-cache/jdk,build/release-cache/jdk -L THREADS 100 '{JDK}/bin/java -Xbatch DerefNullCrash {THREADS}'
Benchmark 1: build/release-no-cache/jdk/bin/java -Xbatch DerefNullCrash 100
  Time (mean ± σ):      4.150 s ±  0.304 s    [User: 5.589 s, System: 2.506 s]
  Range (min … max):    3.804 s …  4.874 s    20 runs

Benchmark 2: build/release-cache/jdk/bin/java DerefNullCrash 100

Warning: Ignoring non-zero exit code.
  Time (mean ± σ):      3.963 s ±  0.065 s    [User: 5.499 s, System: 2.504 s]
  Range (min … max):    3.804 s …  4.062 s    20 runs


Summary
  build/release-cache/jdk/bin/java -Xbatch DerefNullCrash 100 ran
    1.05 ± 0.08 times faster than build/release-no-cache/jdk/bin/java -cp /ws/stress/src/AsprofStressTests/stress-apps -Xbatch DerefNullCrash 100



import java.lang.reflect.Field;
import sun.misc.Unsafe;

public class DerefNullCrash {
    public static void main(String[] args) throws Exception {
        int NUM_THREADS = Integer.parseInt(args[0]);
        for (int i = 0; i < NUM_THREADS; i++) {
            Thread t = new Thread(() -> {
                double res = 0;
                for (;;) {
                    res += Math.random() * Math.cos(res);
                    try {
                        Thread.sleep(1);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            });
            t.start();
        }
        getUnsafe().putLong(0L, 0L);
    }

    private static Unsafe getUnsafe() throws NoSuchFieldException, IllegalAccessException {
        Field f = Unsafe.class.getDeclaredField("theUnsafe");
        f.setAccessible(true);
        return (Unsafe) f.get(null);
    }
}

-------------

PR Comment: https://git.openjdk.org/jdk/pull/27337#issuecomment-3461966366