Launcher's ClassLoader is no longer parallel capable

[Rajin9601]

While debugging deadlock in our application, I found that spring-boot's LaunchedClassLoader is not registered as parallel capable class loader.

Even though LaunchedClassLoader register itself as parallel capable, ClassLoader only accepts registerAsParallelCapable if the super class is also parallel capable.

https://github.com/openjdk/jdk/blob/f174bbd3baf351ae9248b70454b3bc5a89acd7c6/src/java.base/share/classes/java/lang/ClassLoader.java#L270-L284

 static boolean register(Class<? extends ClassLoader> c) { synchronized (loaderTypes) { if (loaderTypes.contains(c.getSuperclass())) { // register the class loader as parallel capable // if and only if all of its super classes are. // Note: given current classloading sequence, if // the immediate super class is parallel capable, // all the super classes higher up must be too. loaderTypes.add(c); return true; } else { return false; } } 

Looking at this issue (#7333), it seems LaunchedClassLoader is parallel capable. So this PR registers LaunchedClassLoader's parent class, JarUrlClassLoader as parallel capable.

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[wilkinsona]

Thanks very much, @Rajin9601.

This looks like a regression in 3.2 to me where JarUrlClassLoader was introduced as the super-class of LaunchedURLClassLoader. In 3.2 with the classic loader or in 3.1, LaunchedURLClasssLoader extends URLClassLoader and will be parallel capable.

[wilkinsona]

Thanks very much, @Rajin9601 .