[jira] [Created] (NETBEANS-106) NB classloaders should use fine grained locking

["lbruun (JIRA)" <ji...@apache.org>]

lbruun created NETBEANS-106:
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             Summary: NB classloaders should use fine grained locking
                 Key: NETBEANS-106
                 URL: https://issues.apache.org/jira/browse/NETBEANS-106
             Project: NetBeans
          Issue Type: Bug
            Reporter: lbruun


In order to avoid issues such as NETBEANS-58 the NB classloaders should use fine grained locking. (possibly only needed on System Classloader)

Background:  At the time when the NB classloaders were created the general consensus at the time was that a proper classloader used locking at the level of the classloader itself. This was also how the classloaders in the JDK worked. However, in Java 7 this [changed|https://docs.oracle.com/javase/7/docs/technotes/guides/lang/cl-mt.html]. The JDK classloaders started using more fine grained locking. But the NB classloaders didn't follow suit. (it is not exactly an inheritable feature)

This means we are now in a situation were deadlocks occur in NB code which cannot be reproduced with only the JDK. One such case is JDK-8068184 which causes a severe freeze in NetBeans. We cannot expect the JDK folks to fix problems that occur only in NB code.

What I propose is that a more fine grained locking mechanism is used. Look to the JDK for inspiration. This will solve such deadlock issues. I don't think it is necessary to actually claim that it is now fully multi-thread safe by calling registerAsParallelCapable()|[https://docs.oracle.com/javase/7/docs/api/java/lang/ClassLoader.html#registerAsParallelCapable()]. This can be left for a later exercise. First step is to remove the lock on the classloader as a whole.

NETBEANS-58 contains a simple minimal example which can be used as a measure of success. Once an NB application can use the pattern in the example without freezing then we have accomplished the goal.
 
(I'm personally not confident with fiddling with the NB classloaders. Scares the sh.. out of me because I know it is the heart of the platform. So won't come up with a PR. Sorry.)







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