ConcurrentModificationException

[asfimport]

Chris (Bug 16304):
The problem seems to be the HashTree which is a HashMap. This is a major
problem when there are multiple threads and the script is large. If a thread
should get this error then the thread is done. Then the test will not be
correct. I tried a few things. I tried synchronizing on the HashTree in
TestCompiler, but that didn't work. I then went to 'public void
traverse(HashTreeTraverser visitor)' in HashTree. I tried synchronizing on
list() and visitor that didn't work. Then I created a static object and
synchronized the object and that has been working. This slows down the
performance of setting up the test before it executes the test script. Since I
don't have a full understanding of the program, my guess there is a better
place. If anybody has another suggestion, let me know and I will give it a try.

This happens on NT and Linux.

java.util.ConcurrentModificationException
     at java.util.HashMap$HashIterator.nextEntry(HashMap.java:750)
     at java.util.HashMap$KeyIterator.next(HashMap.java:786)
     at org.apache.jmeter.threads.TestCompiler.hasFunctions(TestCompiler.java:498)
     at org.apache.jmeter.threads.TestCompiler.saveSamplerConfigs(TestCompiler.java:196)
     at org.apache.jmeter.threads.TestCompiler.subtractNode(TestCompiler.java:158)
     at org.apache.jorphan.collections.HashTree.traverseInto(HashTree.java:908)
     at org.apache.jorphan.collections.HashTree.traverseInto(HashTree.java:902)
     at org.apache.jorphan.collections.HashTree.traverseInto(HashTree.java:902)
     at org.apache.jorphan.collections.HashTree.traverseInto(HashTree.java:902)
     at org.apache.jorphan.collections.HashTree.traverse(HashTree.java:886)
     at org.apache.jmeter.threads.JMeterThread.run(JMeterThread.java:125)
     at java.lang.Thread.run(Thread.java:536)

Severity: major
OS: Linux

[asfimport]

Mike Stover (migrated from Bugzilla):
I just committed a change to org.apache.jmeter.testelement.AbstractTestElement
that changed the new HashMap() to Collections.synchronizedMap(new HashMap()). I
think this should help fix this problem, and not slow things down overly much.

It's still not perfect, since to do a synchronized map correctly, you're
supposed to manually synchronize iteration code, but since the Map is a private
variable of AbstractTestElement, this is currently possible in other classes.
One way to fix this would be to add a method to the TestElement interface, such as:

getSyncObject()

which would return the synchronized Map, so developers could write code such as:

Iterater iter = testElement.getPropertyNames().iterator();
synchronized(testElement.getSyncObject())
{
while(iter.hasNext())
{
Object item = iter.next();
//do stuff safely
}
}

It seems inelegant to me, but I'm not sure what a good alternative is. Using
Hashtable is not viable, since Map's can hold null values, and Hashtables can't,
and JMeter saves null values.

[asfimport]

Chris (migrated from Bugzilla):
I retried this with 1.8.1 and the problem is still there.