> On Sep 22, 2017, at 6:18 PM, mandy chung <[email protected]> wrote:
>
> This patch proposes to replace the ClassLoader use of finalizer with phantom
> reference, specifically Cleaner, for unloading native libraries. It
> registers the class loader for cleanup only if it's not a builtin class
> loader which will never be unloaded.
>
> The spec for JNI_OnUnload [1] specifies that this function is called in an
> unknown context whereas the hotspot implementation uses the class loader
> being unloaded as the context, which I consider a bug. It should not load a
> class defined to that class loader. The proposed spec change for
> JNI_FindClass if called from JNI_OnUnload to use system class loader
> (consistent with no caller context case).
>
> Webrev:
> http://cr.openjdk.java.net/~mchung/jdk10/webrevs/8164512/webrev.00/
>
> CSR:
> https://bugs.openjdk.java.net/browse/JDK-8187882
>
> Please see the spec change an behavioral change in this CSR. A native
> library may fail to be reloaded if it is loaded immediately or soon after a
> class loader is GC'ed but the cleaner thread doesn't yet have the chance to
> handle the unloading of the native library. Likewise, there is no guarantee
> regarding the timing of finalization and a native library may fail to reload.
> It's believed that the compatibility risk should be low.
>
> I'm looking into adding a native jtreg test that will be added in the next
> revision.
>
> Mandy
> [1]
> http://docs.oracle.com/javase/9/docs/specs/jni/invocation.html#jni_onunload
Thanks for dealing with this.
==============================================================================
src/java.base/share/native/libjava/ClassLoader.c
415 Java_java_lang_ClassLoader_00024NativeLibrary_00024Unloader_unload
416 (JNIEnv *env, jobject this, jstring name, jboolean isBuiltin, jlong
address)
With this change, the "this" argument is no longer used.
Because of this, the native function could be a static member function
of the new Unloader class, or could (I think) still be a (now static)
member function of NativeLibrary. The latter would not require a name
change, only a signature change. But I don't really care which class
has the method.
==============================================================================
src/java.base/share/classes/java/lang/ClassLoader.java
2394 public void register() {
[...]
2406 // register the class loader for cleanup when unloaded
2407 if (loader != getBuiltinPlatformClassLoader() &&
2408 loader != getBuiltinAppClassLoader()) {
2409 CleanerFactory.cleaner()
2410 .register(loader, new Unloader(name, handle,
isBuiltin));
2411 }
Can anything before the cleanup registration throw? If so, do we leak
because we haven't registered the cleanup yet? And what if the
registration itself fails to complete?
==============================================================================
src/hotspot/share/prims/jni.cpp
405 // Special handling to make sure JNI_OnLoad are executed in the
correct class context.
s/are executed/is executed/
==============================================================================
