[SIS-193] Remove the workaround for ServiceLoader bug

• Type: Task
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 0.6, 0.7, 0.8, 1.0, 1.1, 1.2, 1.3
• Fix Version/s: 1.4
• Component/s: Referencing
• Labels: JDK9
• Assignee: Martin Desruisseaux
• Reporter: Martin Desruisseaux
• Created: 27/Feb/15 12:08
• Updated: 03/Oct/23 08:42
• Resolved: 23/Sep/23 10:26

Description

As of 1.8.0_31-b13, java.util.ServiceLoader does not support usage of a second Iterator in the middle of a previous iteration. The following Java code provides two simple tests with a ServiceLoader iterating over two elements.

import java.util.Iterator;
import java.util.ServiceLoader;

public class ServiceLoaderTest {
    public static class I1 extends ServiceLoaderTest {}  // A dummy provider.
    public static class I2 extends ServiceLoaderTest {}  // An other provider.

    public static void main(String[] args) {
        test1();
        test2();
    }

    private static void test1() {
        System.out.println();
        System.out.println("---- TEST 1 ----");
        ServiceLoader<ServiceLoaderTest> loader = ServiceLoader.load(ServiceLoaderTest.class);

        Iterator<ServiceLoaderTest> it1 = loader.iterator();
        System.out.println("it1.hasNext() = " + it1.hasNext());
        System.out.println("it1.next()    = " + it1.next());

        Iterator<ServiceLoaderTest> it2 = loader.iterator();
        System.out.println("it2.hasNext() = " + it2.hasNext());
        System.out.println("it2.next()    = " + it2.next());

        System.out.println("it1.hasNext() = " + it1.hasNext());
        System.out.println("it1.next()    = " + it1.next());

        System.out.println("it2.hasNext() = " + it2.hasNext());  // Expected "true" here, but get "false".
    }

    private static void test2() {
        System.out.println();
        System.out.println("---- TEST 2 ----");
        ServiceLoader<ServiceLoaderTest> loader = ServiceLoader.load(ServiceLoaderTest.class);

        Iterator<ServiceLoaderTest> it1 = loader.iterator();
        System.out.println("it1.hasNext() = " + it1.hasNext());
        System.out.println("it1.next()    = " + it1.next());

        Iterator<ServiceLoaderTest> it2 = loader.iterator();
        System.out.println("it1.hasNext() = " + it1.hasNext());
        System.out.println("it2.hasNext() = " + it2.hasNext());
        System.out.println("it1.next()    = " + it1.next());
        System.out.println("it2.next()    = " + it2.next());  // ConcurrentModificationException here.
    }
}

The second test throws the following exception:

    Exception in thread "main" java.util.ConcurrentModificationException
    	at java.util.LinkedHashMap$LinkedHashIterator.nextNode(LinkedHashMap.java:711)
    	at java.util.LinkedHashMap$LinkedEntryIterator.next(LinkedHashMap.java:744)
    	at java.util.LinkedHashMap$LinkedEntryIterator.next(LinkedHashMap.java:742)
    	at java.util.ServiceLoader$1.next(ServiceLoader.java:479)
    	at test.ServiceLoaderTest.test2(ServiceLoaderTest.java:47)
    	at test.ServiceLoaderTest.main(ServiceLoaderTest.java:12)

The workaround applied in Apache SIS has been to add a LazySet internal class which wraps an Iterable and caches its values. But this is a little bit unfortunate since ServiceLoader already caches its values.

ServiceLoader is probably going to be significantly rewritten in JDK9 as a side effect of the Jigsaw project. So we should revisit if our LazySet workaround is still needed on a JDK9 branch.

Issue Links

• depends upon: SIS-561 Upgrade to Java 11