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

[mandy chung]

On 10/10/17 2:29 AM, Peter Levart wrote:
>
> 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?
>
The name parameter is the symbol name but not the library name. It's 
confusing and therefore I renamed NativeLibrary::find to 
NativeLibrary::findEntry.   I could rename the name parameter to 
entryName to make it clearer.

Mandy