rednaxelafx

exclude Main main
dontinline Main doTest
compileonly Main doTest
compileonly FxIntrinsics *

rednaxelafx

public class HelloWorld {
    private static int foo() {
      return 42;
    }

    private static void bar() {
    }

    public static void main(String[] args) throws Exception {
      foo();

rednaxelafx

# LMF class generated at runtime, dumped via
# <Scala 2.12.2>/bin/scala -cp . -Djdk.internal.lambda.dumpProxyClasses=dumpclasses Bar

$ javap -verbose -private -c -s -l 'Bar$$$Lambda$101.class'
Classfile /private/tmp/dumpclasses/Bar$$$Lambda$101.class
  Last modified Apr 30, 2020; size 695 bytes
  MD5 checksum 419f2634b1acdf7f40ba0bb7c22eabf4
final class Bar$$$Lambda$101 implements scala.runtime.java8.JFunction0$mcV$sp,scala.Serializable
  minor version: 0
  major version: 52

rednaxelafx

import java.util.*;

public class TestVec {
  public static int[] doTest(int[] xs, int[] ys) {
    if (xs.length != ys.length) return null;
    int[] zs = new int[xs.length];
    for (int i = 0; i < xs.length; i++) {
      zs[i] = xs[i] * ys[i];
    }
    return zs;

rednaxelafx

rednaxelafx@fx-laptop:~$ jps
7013 Jps
6946 GroovyStarter
rednaxelafx@fx-laptop:~$ cd /proc/6946
rednaxelafx@fx-laptop:/proc/6946$ ls
attr             cpuset   latency    mountstats   root       statm
auxv             cwd      limits     net          sched      status
cgroup           environ  loginuid   numa_maps    schedstat  syscall
clear_refs       exe      maps       oom_adj      sessionid  task
cmdline          fd       mem        oom_score    smaps      wchan

rednaxelafx

$ cat > OOM.java 
import java.util.*;

public class OOM {
  public static void main(String[] args) throws Exception {
    ArrayList list = new ArrayList();
    while (true) { list.add(new byte[20000]); }
  }
}

rednaxelafx

diff -r 4d8787136e08 src/share/vm/c1/c1_Canonicalizer.cpp
--- a/src/share/vm/c1/c1_Canonicalizer.cpp	Fri May 25 11:39:13 2012 -0700
+++ b/src/share/vm/c1/c1_Canonicalizer.cpp	Wed May 30 03:21:56 2012 +0800
@@ -451,6 +451,28 @@
     }
     break;
   }
+  case vmIntrinsics::_isInstance          : {
+    assert(x->number_of_arguments() == 2, "wrong type");
+

rednaxelafx

class A {
  Object aObj;
  int aInt;
}

class B extends A {
  Object bObj;
  int bInt;
  float fFloat;
}

rednaxelafx

There's a GC start/end event in JVM TI: http://docs.oracle.com/javase/7/docs/platform/jvmti/jvmti.html#GarbageCollectionStart It's been around for quite a while. Can be used in JDK 6. Can't execute Java code in the callback. The VM is in its stop-the-world phase when the event is sent.

From the document:

This event is sent while the VM is still stopped, thus the event handler must not use JNI functions and must not use JVM TI functions except those which specifically allow such use (see the raw monitor, memory management, and environment local storage functions).

The places that issue this event:

rednaxelafx

Java source code:
k = i + j;

May compile to Java bytecode:
iload_0 
iload_1 
iadd 
istore_2

And may turn into Dalvik VM code: