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From "Martin Desruisseaux (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (SIS-193) Remove the workaround for ServiceLoader bug
Date Fri, 20 Jul 2018 10:41:00 GMT

     [ https://issues.apache.org/jira/browse/SIS-193?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Martin Desruisseaux updated SIS-193:
------------------------------------
    Fix Version/s:     (was: 1.0)
                   1.1

> Remove the workaround for ServiceLoader bug
> -------------------------------------------
>
>                 Key: SIS-193
>                 URL: https://issues.apache.org/jira/browse/SIS-193
>             Project: Spatial Information Systems
>          Issue Type: Task
>          Components: Referencing
>    Affects Versions: 0.6, 0.7, 0.8
>            Reporter: Martin Desruisseaux
>            Assignee: Martin Desruisseaux
>            Priority: Minor
>              Labels: JDK9
>             Fix For: 1.1
>
>
> 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.
> {code:java}
> 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.
>     }
> }
> {code}
> The second test throws the following exception:
> {noformat}
>     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)
> {noformat}
> 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.



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