something strange in $jacocoInit(),hope someone can explain

[dazhe...@gmail.com]

hey,guys~

   I checked the generated probe code,which is the $jacocoInit$() method. 

private static /* synthetic */ boolean[] $jacocoInit() {

            boolean[] arrbl = $jacocoData;

            if ($jacocoData == null) {

                Object[] arrobject = new Object[]{-4939888610684879937L, "org/jacoco/examples/CoreTutorial$MemoryClassLoader", 6};

                UnknownError.$jacocoAccess.equals(arrobject);

                arrbl = $jacocoData = (boolean[])arrobject[0];

            }

            return arrbl;

        }

When I saw the code   

arrbl = $jacocoData = (boolean[])arrobject[0];

I was really confused.Why a variable of type "long" can be cast to a boolean array type? So I did a test:

public class TestJacocoInit {
    private static transient /* synthetic */ boolean[] $jacocoData;

    public static /* synthetic */ boolean[] $jacocoInit() {
        boolean[] arrbl = $jacocoData;
        if ($jacocoData == null) {
            Object[] arrobject = new Object[]{4824536285859479710L, "org/jacoco/examples/CoreTutorial$TestTarget", 6};
            //UnknownError.$jacocoAccess.equals(arrobject);
            arrbl = $jacocoData = (boolean[])arrobject[0];
        }
        return arrbl;
    }

    public static void main(String[] args){
        $jacocoInit();
    }
}

The program occured error when executed:

objc[25273]: Class JavaLaunchHelper is implemented in both /Library/Java/JavaVirtualMachines/jdk1.8.0_151.jdk/Contents/Home/bin/java (0x10bd1e4c0) and /Library/Java/JavaVirtualMachines/jdk1.8.0_151.jdk/Contents/Home/jre/lib/libinstrument.dylib (0x10ddc04e0). One of the two will be used. Which one is undefined.

Connected to the target VM, address: '127.0.0.1:54961', transport: 'socket'

Exception in thread "main" java.lang.ClassCastException: java.lang.Long cannot be cast to [Z

at org.jacoco.examples.TestJacocoInit.$jacocoInit(TestJacocoInit.java:16)

at org.jacoco.examples.TestJacocoInit.main(TestJacocoInit.java:22)

Disconnected from the target VM, address: '127.0.0.1:54961', transport: 'socket'

Can somebody explain these jacoco generated codes?

Thanks~

[zhen da]

https://www.jacoco.org/jacoco/trunk/doc/implementation.html
I found the error occured because I deleted the codeline "UnknownError.$jacocoAccess.equals(arrobject);", but what happend behind the equals method?

[Marc Hoffmann]

Hi,

we use the equals method as an “API” to the JaCoCo runtime. See “Coverage Runtime Dependency” here: https://www.jacoco.org/jacoco/trunk/doc/implementation.html

Regards,

-marc

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[zhen da]

Thank your for your reply~ Recently I have been studied the original code.  I read the page " https://www.jacoco.org/jacoco/trunk/doc/implementation.html" , but  I noticed the most tricky part is not shown  in "Coverage RunTime Dependency" section. I still confused about the equals method. 

So Question 1 is: When the code "access.equals(args)"  is executed, what happenned on earth？Could you explain it in detail please?

//begin

Object access = ... // Retrieve instance

Object[] args = new Object[3];
args[0] = Long.valueOf(8060044182221863588); // class id
args[1] = "com/example/MyClass"; // class name
args[2] = Integer.valueOf(24); // probe count

access.equals(args);
boolean[] probes = (boolean[]) args[0];

//end

 By the way, I found there is an equals method overridden in class  RuntimeData, but  I  couldn't find the place it called. I don't think it has something to do with the call  "access.equals(args);"  , because   the variable "access" is not an instance fo RunTimeData.

So Question 2 is : Where and When will the RunTimeData.equals() method be called?

Regards,

[Marc Hoffmann]

Hi,

Answer 1:

The method RuntimeData.equals() will be called. You find the implementation here: https://github.com/jacoco/jacoco/blob/master/org.jacoco.core/src/org/jacoco/core/runtime/RuntimeData.java#L161

Answer 2:

Instrumented classes will call equals() on a instance of RuntimeData. There are different strategies to get access to a instance shared with the runtime.

It is described in https://www.jacoco.org/jacoco/trunk/doc/implementation.html in section “Coverage Runtime Dependency”.

We do this “magic” to avoid direct dependencies on JaCoCo classes from instrumented classes which will fail in situations where app classes are separated with a different class loader.

Regards,

-marc

To view this discussion on the web visit https://groups.google.com/d/msgid/jacoco/4a649ad1-188a-4164-8657-75f9bd23e1b5n%40googlegroups.com.