Review Request JDK-8164512: Replace ClassLoader use of finalizer with phantom reference to unload native library

[Peter Levart]

On 10/09/2017 10:17 PM, mandy chung wrote:
> David, Peter, Alan
>
> The VM has a fast path to search the symbol from libjava.so first for 
> bootstrap loader.  That was the case I mostly concern about 
> performance and it's not impacted by this change.   Also I consulted 
> with Claes on the performance impact.   I took your suggestion and 
> made systemNativeLibraries and nativeLibraries volatile.
>
> Updated webrev:
> http://cr.openjdk.java.net/~mchung/jdk10/webrevs/8164512/webrev.04
>

Looks good now. Just one question (for a possible follow-up future 
optimization):

2674     private static long findNative(ClassLoader loader, String name) {
2675         Map<String, NativeLibrary> libs =
2676             loader != null ? loader.nativeLibraries() : 
systemNativeLibraries();
2677         if (libs.isEmpty())
2678             return 0;
2679
2680         // the native libraries map may be updated in another thread
2681         // when a native library is being loaded.  No symbol will be
2682         // searched from it yet.
2683         for (NativeLibrary lib : libs.values()) {
2684             long entry = lib.findEntry(name);
2685             if (entry != 0) return entry;
2686         }
2687         return 0;
2688     }

Now that (system)nativeLibraries is a Map, is it still necessary to 
iterate it and call lib.findEntry(name) on each NativeLibrary until the 
one that returns a non-zero entry or would it be semantically equivalent 
to 1st look-up the Map by the 'name' key to get the correct NativeLibrary?

Regards, Peter