https://issues.apache.org/bugzilla/show_bug.cgi?id=55827
Bug ID: 55827
Summary: Iteration over a view on a synchronized collection
without obtaining a lock on the collection
Product: JMeter
Version: 2.10
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P2
Component: Main
Assignee: [email protected]
Reporter: [email protected]
We ran our static analysis tool ThreadSafe [1] on version 2.10 of JMeter, which
appeared to uncover a couple of concurrency issues. One of the most interesting
was the possibility of an unsynchronised iteration over a synchronised
collection in the class 'AbstractTestElement'.
The relevant line is 499:
Iterator<Map.Entry<String, JMeterProperty>> iter =
propMap.entrySet().iterator();
where the propMap field always contains a synchronised collection created at
line 57 in the same file.
The JDK documentation for Collections.synchronizedMap states that:
> It is imperative that the user manually synchronize on the
> returned map when iterating over any of its collection views:
>
> Map m = Collections.synchronizedMap(new HashMap());
> ...
> Set s = m.keySet(); // Needn't be in synchronized block
> ...
> synchronized (m) { // Synchronizing on m, not s!
> Iterator i = s.iterator(); // Must be in synchronized block
> while (i.hasNext())
> foo(i.next());
> }
>
> Failure to follow this advice may result in non-deterministic behavior.
It appears that the code on line 499 does not correctly synchronize on propMap,
leading to the possibility of the non-deterministic behaviour the JDK
documentation warns about.
We're not sure that this can actually result in a user-visible bug, but we
thought you'd like to know.
We are also planning to use this finding as an example of Android-related
concurrency mistakes in an article about ThreadSafe. Obviously, if you, as the
developers of JMeter, have any objections to our using this as an example, then
we won't.
[1] ThreadSafe is a static analysis tool for Java concurrency, developed by
Contemplate Ltd.:
http://www.contemplateltd.com/
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