On Thu, 2 Sep 2021 11:43:46 GMT, Alan Bateman <al...@openjdk.org> wrote:
>> Using jarIndex for Hibench, there is an unexpected behavior with the
>> exception "Exception in thread "main"
>> org.apache.hadoop.fs.UnsupportedFileSystemException: No FileSystem for
>> scheme "hdfs"".
>>
>> After investigating it, it is related to the usage of ServiceLoader with
>> JarIndex.
>> The below stack shows the issue with JDK11:
>>
>> getResource:1016, URLClassPath$JarLoader (jdk.internal.loader)
>> getResource:937, URLClassPath$JarLoader (jdk.internal.loader)
>> findResource:912, URLClassPath$JarLoader (jdk.internal.loader)
>> next:341, URLClassPath$1 (jdk.internal.loader)
>> hasMoreElements:351, URLClassPath$1 (jdk.internal.loader)
>> hasNext:355, BuiltinClassLoader$1 (jdk.internal.loader)
>> hasMoreElements:363, BuiltinClassLoader$1 (jdk.internal.loader)
>> next:3032, CompoundEnumeration (java.lang)
>> hasMoreElements:3041, CompoundEnumeration (java.lang)
>> nextProviderClass:1203, ServiceLoader$LazyClassPathLookupIterator (java.util)
>> hasNextService:1221, ServiceLoader$LazyClassPathLookupIterator (java.util)
>> hasNext:1265, ServiceLoader$LazyClassPathLookupIterator (java.util)
>> hasNext:1300, ServiceLoader$2 (java.util)
>> hasNext:1385, ServiceLoader$3 (java.util)
>>
>> The below API tries to get all the resources with the same name.
>>
>> public Enumeration<URL> findResources(final String name,
>> final boolean check)
>> ```
>> After using JarIndex, URLClassPath.findResources only returns 1 URL.
>> It is the same as the description in JDK-6957241.
>>
>> The issue still exists in JDK18.
>>
>> Root cause:
>>
>> public Enumeration<URL> findResources(final String name,
>> final boolean check) {
>> return new Enumeration<>() {
>> private int index = 0;
>> private URL url = null;
>>
>> private boolean next() {
>> if (url != null) {
>> return true;
>> } else {
>> Loader loader;
>> while ((loader = getLoader(index++)) != null) {
>> url = loader.findResource(name, check);
>> if (url != null) {
>> return true;
>> }
>> }
>> return false;
>> }
>> }
>> ...
>> };
>> }
>>
>> With the JarIndex, there is only one loader which is corresponding to the
>> jar with the index due to the implementation in JarLoader.getResource(final
>> String name, boolean check, Set<String> visited).
>>
>> Loaders corresponding to other jar packages will not appear in this while.
>> So it only returns 1 instance.
>>
>> To solve the issue, I change the implementation "private boolean next()".
>> If the loader has index, traverse the index and get all the resource from
>> the loader.
>
> @wxiang I think there is at least some support for removing the JAR indexing
> support rather than trying to fix findResources. The issue of what to do with
> the legacy JAR index mechanism came up during JDK 9 in the context of modular
> JARs and also Multi-Release JARs but it was too much to take on at the time.
> Would you be interested in working out the changes to remove it?
@AlanBateman Sure, I am interested in it.
-------------
PR: https://git.openjdk.java.net/jdk/pull/5316
