ConcurrentModificationException in java.util.ServiceLoader (not a multi-thread issue)

[Martin Desruisseaux]

Hello all

java.util.ServiceLoader does not seem to support usage of a second
Iterator in the middle of a previous iteration. The attached Java file
provides two simple tests with a ServiceLoader iterating over two
elements. The first test creates two iterators and invokes their
hasNext() / next() methods in the following order:

  * Iterator 1
  * Iterator 2
  * Iterator 1
  * Iterator 2  -  unexpected end of iteration here.

The second test creates two iterators and invoke the hasNext() methods
on both iterators before to invoke their next() methods. This result is
the following exception (tested on 1.8.0_31-b13):

    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)

(note: to run the test, the attached test.ServiceLoaderTest file needs
to be in the META-INF/services/ directory). I found a Stackoverflow
thread mentioning this issue 4 years ago [1], but apparently without
solution. Should I look for a patch, or is the current behaviour
considered okay (in which case I would suggest to warn the users in the
Javadoc)?


    Martin


[1] http://stackoverflow.com/questions/2593777/serviceloader-double-iterator-issues


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test.ServiceLoaderTest$I1
test.ServiceLoaderTest$I2