Java11: Static variable appears to be difference instance even though it's in the same class.

[YusukeTobo]

Investigative information

Repro steps

Provide the steps required to reproduce the problem:

1. Create Function.java below.

package com.azure.yutobo.func;

import com.microsoft.azure.functions.ExecutionContext;
import com.microsoft.azure.functions.HttpMethod;
import com.microsoft.azure.functions.HttpRequestMessage;
import com.microsoft.azure.functions.HttpResponseMessage;
import com.microsoft.azure.functions.HttpStatus;
import com.microsoft.azure.functions.annotation.AuthorizationLevel;
import com.microsoft.azure.functions.annotation.FunctionName;
import com.microsoft.azure.functions.annotation.HttpTrigger;

import java.util.Optional;

public class Function {
    static final Person person  = new Person();

    @FunctionName("foo")
    public HttpResponseMessage foo(
            @HttpTrigger(
                name = "req",
                methods = {HttpMethod.GET, HttpMethod.POST},
                authLevel = AuthorizationLevel.ANONYMOUS)
                HttpRequestMessage<Optional<String>> request,
            final ExecutionContext context) {
        context.getLogger().info("foo processed a request.");
        return request.createResponseBuilder(HttpStatus.OK).body("Foo: " + person.).build();
    }

    @FunctionName("bar")
    public HttpResponseMessage bar(
            @HttpTrigger(
                name = "req",
                methods = {HttpMethod.GET, HttpMethod.POST},
                authLevel = AuthorizationLevel.ANONYMOUS)
                HttpRequestMessage<Optional<String>> request,
            final ExecutionContext context) {
        context.getLogger().info("bar processed a request.");
        return request.createResponseBuilder(HttpStatus.OK).body("Bar: " + person).build();
    }
}

package com.azure.yutobo.func;

class Person {
    String name = "";
    int age = 18;

    Person() {}

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + age;
        result = prime * result + ((name == null) ? 0 : name.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Person other = (Person) obj;
        if (age != other.age)
            return false;
        if (name == null) {
            if (other.name != null)
                return false;
        } else if (!name.equals(other.name))
            return false;
        return true;
    }

    @Override
    public String toString() {
        return "Person [age=" + age + ", name=" + name + "]";
    }
}

2. access Foo & Bar endpoints.

Expected behavior

Foo & Bar methods show the same output because they share the same class variable.

Actual behavior

Foo & Bar methods show the different output like below.

I found that there are separate class variables of Function.class in the heap.

And, Function.class loaded twince by the different URLClassLoader.
Apparently, you don't check whether Function.class is already loaded or not.

Known workarounds

I couldn't find workarounds.

Impact

• There appears to be no ways to share the class variable even methods are in the same class.
• I think we can't make Double-checked locked instance to get Singleton in multi-thread environment.

[TsuyoshiUshio]

I found that it is reproduced on Java 11 but not for Java 8.

Function.java

package com.fabrikam;

import com.microsoft.azure.functions.ExecutionContext;
import com.microsoft.azure.functions.HttpMethod;
import com.microsoft.azure.functions.HttpRequestMessage;
import com.microsoft.azure.functions.HttpResponseMessage;
import com.microsoft.azure.functions.HttpStatus;
import com.microsoft.azure.functions.annotation.AuthorizationLevel;
import com.microsoft.azure.functions.annotation.FunctionName;
import com.microsoft.azure.functions.annotation.HttpTrigger;

import java.util.Optional;

/**
 * Azure Functions with HTTP Trigger.
 */
public class Function {

    private static int count = 0;
    private static final Person person = new Person();
    /**
     * This function listens at endpoint "/api/HttpExample". Two ways to invoke it using "curl" command in bash:
     * 1. curl -d "HTTP Body" {your host}/api/HttpExample
     * 2. curl "{your host}/api/HttpExample?name=HTTP%20Query"
     */
    @FunctionName("HttpExample1")
    public HttpResponseMessage run1(
            @HttpTrigger(
                name = "req",
                methods = {HttpMethod.GET, HttpMethod.POST},
                authLevel = AuthorizationLevel.ANONYMOUS)
                HttpRequestMessage<Optional<String>> request,
            final ExecutionContext context) {
        context.getLogger().info("Java HTTP trigger 1 processed a request.");
            count++;
            return request.createResponseBuilder(HttpStatus.OK).body("Foo count:" + count + ":" + person).build();
    }

    @FunctionName("HttpExample2")
    public HttpResponseMessage run2(
            @HttpTrigger(
                    name = "req",
                    methods = {HttpMethod.GET, HttpMethod.POST},
                    authLevel = AuthorizationLevel.ANONYMOUS)
                    HttpRequestMessage<Optional<String>> request,
            final ExecutionContext context) {
        context.getLogger().info("Java HTTP2 trigger processed a request.");
        count++;
        return request.createResponseBuilder(HttpStatus.OK).body("Bar" + count + ":" + person).build();
    }
}

Person.java

package com.fabrikam;

public class Person {
    String name = "";
    int age = 18;

    Person() {}

}

[YusukeTobo]

Thank you for your help. As you found, I ran my function in local Java11. When I tried it in local Java8, I also didn't reproduced this issue(please see the following screenshot).

[YusukeTobo]

Allow me follow-up. It's reproduced in Azure on Java11 stack.

As you may know, Java8, Java11 utilize the different class loader.
https://github.com/Azure/azure-functions-java-worker/blob/dev/src/main/java/com/microsoft/azure/functions/worker/reflect/FactoryClassLoader.java

I would be glad if I could help you.

[amamounelsayed]

Thank you so much @YusukeTobo and @TsuyoshiUshio
So the issue is with Java 11 the static variables are not shared among all functions in the same class, it is just shared between all instances for the same function.

As showed in @TsuyoshiUshio example, the run1 function will share static variable different than run2 function. But all run1 threads wil share the same static variable, the same for run2 function.