Deadlock in REST.java

[catsncode]

Hello and thanks so much for the great library. I know you said that it is not thread safe, but do you have any ideas on how I can make it so? It's very strange because I've been using the library for around a year with no problems. Now, all of a sudden I'm getting these deadlocks in REST.java where it is synchronizing on the mutex object. I tried synchronizing the whole method, but no luck. Hopefully someone smarter than myself can give me a little advice.

Thanks!

PS - I'm running my gallery on Tomcat in Linux with Java 7.

[catsncode]

FYI - I took the synchorized (mutex) lines out of REST.java and it seems to be working fine now. I do a lot of caching in my gallery code, so the REST.java is not called all that much really. I'm sure there was a reason to synchronize that code, but I'm just not sure what it was. I would still like to understand that if anyone else knows. Thanks!

[boncey]

Hi, it looks like the DocumentBuilder is not thread-safe hence the synchronization.
That code predates me taking over the library, I'd probably have just instantiated a builder each time. It's slower but simpler and means the class would then be thread-safe.

I don't get much time to work on this project at the moment but suggest that you might want to instantiate a DocumentBuilder within the method if you decide to take out the mutex wrapper.
I don't think there's any other mutable state in that class but I only have a quick look at it.

[catsncode]

Thanks so much for the advice! I modified the code as you suggested. Is it ok to just have one instance of DocumentBuilderFactory, or should I do a new instance of that each time as well?

[boncey]

It looks like it's also not thread-safe so don't set one as a field either, just keep it a local variable.
http://stackoverflow.com/questions/9828254/is-documentbuilderfactory-thread-safe-in-java-5

[catsncode]

Ok, thanks again for the help!