RFR: 8278131: runtime/cds/appcds/dynamicArchive/* tests failing in loom repo

[Ioi Lam]

On Wed, 15 Dec 2021 01:40:26 GMT, David Holmes <dholmes at openjdk.org> wrote:

> Sorry but this isn't making any sense to me. You can't GC a class until its classloader becomes unreachable - at which point the classloader and all its loaded classes become unreachable together. So you can't keep a class alive by storing a reference to it in a static field of a class loaded by the same classloader - it was already kept alive.
> 
> David

Hi David,


        URLClassLoader urlClassLoader =
            new URLClassLoader("HelloClassLoader", urls, null);
        Class c = Class.forName(className, true, urlClassLoader);
+       if (keepAlive) {
+           keptC = c;
+       }

The class `c` is defined by a custom class loader (`urlClassLoader`). Before this patch, when `urlClassLoader` and `c` fall out of scope, this class becomes eligible for garbage collection.

The class that runs the above code (`HelloUnload`) is loaded by the app class loader. By referencing `c` in a static field of `HelloUnload`, we make sure `c` is never unloaded.

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PR: https://git.openjdk.java.net/jdk/pull/6843