<clinit> sometimes will not be invoked when calling static methods at first.

[ZekerZhayard]

openjdk version "1.8.0_282"
OpenJDK Runtime Environment (build 1.8.0_282-b08)
Eclipse OpenJ9 VM (build openj9-0.24.0, JRE 1.8.0 Windows 8.1 amd64-64-Bit 20210120_560 (JIT enabled, AOT enabled)
OpenJ9   - 345e1b09e
OMR      - 741e94ea8
JCL      - ab07c6a8fd based on jdk8u282-b08)

Considering test cases below:

• Test Case 1

import java.util.Arrays;
import java.util.function.Consumer;

import sun.misc.SharedSecrets;
import sun.reflect.ConstantPool;

public class Main {
    public static void main(String[] args) {
        Consumer<Object> consumer = Test::test;
        ConstantPool cp = SharedSecrets.getJavaLangAccess().getConstantPool(consumer.getClass());
        for (int i = cp.getSize() - 1; i >= 0; i--) {
            try {
                System.out.println("index: " + i + ", method: " + cp.getMethodAtIfLoaded(i) + ", info: " + Arrays.toString(cp.getMemberRefInfoAt(i)));
            } catch (Throwable ignored) {

            }
        }
        Test.test(null);
        System.out.println(Test.a);
    }

    public static class Test {
        public static boolean a = false;

        static {
            System.out.println("<clinit> was invoked");
            throwException();
        }

        public static void throwException() {
            throw new RuntimeException();
        }

        public static void test(Object o) {
            System.out.println("test was invoked");
        }
    }
}

In this case, Test class will throw an exception in <clinit>, then run with OpenJ9 and Hotspot respectively. The result is:

--- OpenJ9 ---
index: 5, method: null, info: [Main$Test, test, (Ljava/lang/Object;)V]
index: 2, method: public java.lang.Object(), info: [java/lang/Object, <init>, ()V]
test was invoked
<clinit> was invoked
Exception in thread "main" java.lang.ExceptionInInitializerError
	at java.lang.J9VMInternals.ensureError(J9VMInternals.java:146)
	at java.lang.J9VMInternals.recordInitializationFailure(J9VMInternals.java:135)
	at Main.main(Main.java:19)
Caused by: java.lang.RuntimeException
	at Main$Test.throwException(Main.java:31)
	at Main$Test.<clinit>(Main.java:27)
	... 1 more

--- Hotspot ---
index: 18, method: public static void Main$Test.test(java.lang.Object), info: [Main$Test, test, (Ljava/lang/Object;)V]
index: 10, method: public java.lang.Object(), info: [java/lang/Object, <init>, ()V]
<clinit> was invoked
Exception in thread "main" java.lang.ExceptionInInitializerError
	at Main.main(Main.java:18)
Caused by: java.lang.RuntimeException
	at Main$Test.throwException(Main.java:31)
	at Main$Test.<clinit>(Main.java:27)
	... 1 more

We will find that, with OpenJ9, <clinit> won't be invoked when Test.test being invoked and until Test.a was acquired.

We can also find that OpenJ9 can't get the method by cp.getMethodAtIfLoaded(i) but Hotspot can.

• Test Case 2

If we change cp.getMethodAtIfLoaded(i) to cp.getMethodAt(i), there will be more different behaviors between OpenJ9 and Hotspot

import java.util.Arrays;
import java.util.function.Consumer;

import sun.misc.SharedSecrets;
import sun.reflect.ConstantPool;

public class Main {
    public static void main(String[] args) {
        Consumer<Object> consumer = Test::test;
        ConstantPool cp = SharedSecrets.getJavaLangAccess().getConstantPool(consumer.getClass());
        for (int i = cp.getSize() - 1; i >= 0; i--) {
            try {
                System.out.println("index: " + i + ", method: " + cp.getMethodAt(i) + ", info: " + Arrays.toString(cp.getMemberRefInfoAt(i)));
            } catch (Throwable ignored) {

            }
        }
        Test.test(null);
        System.out.println(Test.a);
    }

    public static class Test {
        public static boolean a = false;

        static {
            System.out.println("<clinit> was invoked");
            throwException();
        }

        public static void throwException() {
            throw new RuntimeException();
        }

        public static void test(Object o) {
            System.out.println("test was invoked");
        }
    }
}

Result:

--- OpenJ9 ---
<clinit> was invoked
index: 5, method: null, info: [Main$Test, test, (Ljava/lang/Object;)V]
index: 2, method: public java.lang.Object(), info: [java/lang/Object, <init>, ()V]
test was invoked
Exception in thread "main" java.lang.NoClassDefFoundError: Main$Test (initialization failure)
	at java.lang.J9VMInternals.initializationAlreadyFailed(J9VMInternals.java:96)
	at Main.main(Main.java:19)
Caused by: java.lang.RuntimeException
	at Main$Test.throwException(Main.java:31)
	at Main$Test.<clinit>(Main.java:27)
	at sun.reflect.ConstantPool.getMethodAt0(Native Method)
	at sun.reflect.ConstantPool.getMethodAt(ConstantPool.java:41)
	at Main.main(Main.java:13)

--- Hotspot ---
index: 18, method: public static void Main$Test.test(java.lang.Object), info: [Main$Test, test, (Ljava/lang/Object;)V]
index: 10, method: public java.lang.Object(), info: [java/lang/Object, <init>, ()V]
<clinit> was invoked
Exception in thread "main" java.lang.ExceptionInInitializerError
	at Main.main(Main.java:18)
Caused by: java.lang.RuntimeException
	at Main$Test.throwException(Main.java:31)
	at Main$Test.<clinit>(Main.java:27)
	... 1 more

We will find that <clinit> was invoked at cp.getMethodAt(i) with OpenJ9 and still unable to get the Test.test method.

• Test Case 3

If Test class no longer throws an exception:

import java.util.Arrays;
import java.util.function.Consumer;

import sun.misc.SharedSecrets;
import sun.reflect.ConstantPool;

public class Main {
    public static void main(String[] args) {
        Consumer<Object> consumer = Test::test;
        ConstantPool cp = SharedSecrets.getJavaLangAccess().getConstantPool(consumer.getClass());
        for (int i = cp.getSize() - 1; i >= 0; i--) {
            try {
                System.out.println("index: " + i + ", method: " + cp.getMethodAt(i) + ", info: " + Arrays.toString(cp.getMemberRefInfoAt(i)));
            } catch (Throwable ignored) {

            }
        }
        Test.test(null);
        System.out.println(Test.a);
    }

    public static class Test {
        public static boolean a = false;

        public static void test(Object o) {
            System.out.println("test was invoked");
        }
    }
}

Result:

--- OpenJ9 ---
<clinit> was invoked
index: 5, method: public static void Main$Test.test(java.lang.Object), info: [Main$Test, test, (Ljava/lang/Object;)V]
index: 2, method: public java.lang.Object(), info: [java/lang/Object, <init>, ()V]
test was invoked
false

--- Hotspot ---
index: 18, method: public static void Main$Test.test(java.lang.Object), info: [Main$Test, test, (Ljava/lang/Object;)V]
index: 10, method: public java.lang.Object(), info: [java/lang/Object, <init>, ()V]
<clinit> was invoked
test was invoked
false

In this case, OpenJ9 can get test method correctly, but <clinit> was still invoked earlier than Hotspot.

[pshipton]

@tajila fyi

[gacholio]

The issue in test 1 appears to be that the ConstantPool code is resolving the static method without running the <clinit>. This fails because the <clinit> check for invokestatic is done in the resolve called from initialStaticMethod, which does not run if the method has been resolved.

[gacholio]

Nope, that's not it - it appears to be somehow caused by the Test::test - removing that makes it work as expected.

[gacholio]

The entry is resolved by this:

#0  resolveStaticMethodRef (vmStruct=0x16700, ramCP=0x130ab0, cpIndex=2, resolveFlags=1024)
    at resolvesupport.cpp:649
#1  0x00007ffff5bdc15b in resolveMethodHandleRefInto (vmThread=0x16700, ramCP=0x130ab0, cpIndex=10, 
    resolveFlags=1024, ramCPEntry=0x130b50) at resolvesupport.cpp:2005
#2  0x00007ffff5bdc435 in resolveMethodHandleRef (vmThread=0x16700, ramCP=0x130ab0, cpIndex=10, resolveFlags=1024)
    at resolvesupport.cpp:2077
#3  0x00007fffef18c760 in Java_java_lang_invoke_MethodHandleResolver_getCPMethodHandleAt (env=0x16700, 
    unusedClass=0x65a30, constantPoolOop=0xbe660, cpIndex=10) at common/sun_reflect_ConstantPool.c:758

https://github.com/eclipse/openj9/blob/d780e8d8b86e7c62a1f80411d71bec436574f0f2/runtime/jcl/common/sun_reflect_ConstantPool.c#L755-L758

[gacholio]

I have all of the testcases working as expected, but the code needs some reworking before it can be committed.