Small VM change #2: JVM_ entry point to extend the boot class path

[Karen Kinnear]

Mark,

Let's consider this a temporary J1 approach please. After J1 let's
have some discussions about alternative approaches please.

Question: in jvm.cpp and .hpp in the new
JVM_ExtendBootClassPath(JNIEnv *env, jclass cls, const char *path)
what is jclass cls used for?

also in that method, I suspect you too would like the 
ClassLoader::print_bootclasspath() to be conditional on 
TraceClassLoading - unless for the demo you want this to print always.

Other than that - just for the demo - go for it.

thanks,
Karen

Mark Reinhold wrote:
> As I hinted last week, the Jigsaw runtime needs the ability to extend the
> bootstrap class path after the VM has been initialized.
> 
> Why does it need this?  The java launcher knows only about the JDK "boot"
> module, but almost every application will need other JDK modules as well.
> To ensure compatibility, and to allow JDK packages to be split statically
> across multiple modules, the additional JDK modules must be loaded into
> the same module class loader as the boot module.
> 
> In theory it's possible for the java launcher to figure out what those
> modules are, but it's vastly easier to defer this to the Jigsaw runtime
> code.  So what I have working now is a modified BootLoader class which,
> upon initialization, adds the classes from all the other JDK modules
> required by the application to the boot class path.
> 
> (This isn't the only way to solve this problem, and indeed later on it
>  might be better to create a more intimate connection between the VM's
>  boot class loader and the Jigsaw runtime, but this will do for now.)
> 
> Patch attached, since this is a pretty simple change, though I can
> produce a webrev if preferred.  All I've really done is to expose the
> existing ClassLoader::update_class_path_entry_list procedure as the new
> JVM_ entry point JVM_ExtendBootClassPath.  I've copied the locking
> protocol from SystemDictionary::download_and_retry_class_load, which does
> a very similar thing, but I'm far from an expert on internal locking in
> HotSpot so please do point out anything I've gotten wrong here.
> 
> I've updated the Linux mapfiles but not those for Solaris.  I'm not doing
> Solaris (or Windows) builds at the moment, and if I forget to fix those
> mapfiles later then the problem will be glaringly obvious, so for the
> sake of expedience I'd like to make this change now and clean up the
> other builds later on.
> 
> Karen -- Okay to push?
> 
> Thanks,
> - Mark
> 
> 
> 
> ------------------------------------------------------------------------
> 
> diff -r 403a1b93874f make/linux/makefiles/mapfile-vers-debug
> --- a/make/linux/makefiles/mapfile-vers-debug	Thu May 14 14:48:35 2009 -0700
> +++ b/make/linux/makefiles/mapfile-vers-debug	Mon May 18 12:33:07 2009 -0700
> @@ -87,6 +87,7 @@
>                  JVM_DumpThreads;
>                  JVM_EnableCompiler;
>                  JVM_Exit;
> +                JVM_ExtendBootClassPath;
>                  JVM_FillInStackTrace;
>                  JVM_FindClassFromClass;
>                  JVM_FindClassFromClassLoader;
> diff -r 403a1b93874f make/linux/makefiles/mapfile-vers-product
> --- a/make/linux/makefiles/mapfile-vers-product	Thu May 14 14:48:35 2009 -0700
> +++ b/make/linux/makefiles/mapfile-vers-product	Mon May 18 12:33:07 2009 -0700
> @@ -87,6 +87,7 @@
>                  JVM_DumpThreads;
>                  JVM_EnableCompiler;
>                  JVM_Exit;
> +                JVM_ExtendBootClassPath;
>                  JVM_FillInStackTrace;
>                  JVM_FindClassFromClass;
>                  JVM_FindClassFromClassLoader;
> diff -r 403a1b93874f src/share/vm/classfile/classLoader.hpp
> --- a/src/share/vm/classfile/classLoader.hpp	Thu May 14 14:48:35 2009 -0700
> +++ b/src/share/vm/classfile/classLoader.hpp	Mon May 18 12:33:07 2009 -0700
> @@ -190,7 +190,7 @@
>    // to avoid confusing the zip library
>    static bool get_canonical_path(char* orig, char* out, int len);
>   public:
> -  // Used by the kernel jvm.
> +  // Used by the kernel jvm, and by Jigsaw via JVM_ExtendBootClassPath
>    static void update_class_path_entry_list(const char *path,
>                                             bool check_for_duplicates);
>    static void print_bootclasspath();
> diff -r 403a1b93874f src/share/vm/prims/jvm.cpp
> --- a/src/share/vm/prims/jvm.cpp	Thu May 14 14:48:35 2009 -0700
> +++ b/src/share/vm/prims/jvm.cpp	Mon May 18 12:33:07 2009 -0700
> @@ -851,6 +851,18 @@
>              (jclass) JNIHandles::make_local(env, Klass::cast(k)->java_mirror());
>  JVM_END
>  
> +JVM_ENTRY(void, JVM_ExtendBootClassPath(JNIEnv *env, jclass cls, const char *path))
> +  JVMWrapper2("JVM_ExtendBootClassPath(%s)", path)
> +  {
> +    // cf. SystemDictionary::download_and_retry_class_load
> +    HandleMark hm(THREAD);
> +    ResourceMark rm(THREAD);
> +    Handle loader_lock(THREAD, SystemDictionary::system_loader_lock());
> +    ObjectLocker ol(loader_lock, THREAD);
> +    ClassLoader::update_class_path_entry_list(path, true);
> +  }
> +  ClassLoader::print_bootclasspath();
> +JVM_END
>  
>  // Reflection support //////////////////////////////////////////////////////////////////////////////
>  
> diff -r 403a1b93874f src/share/vm/prims/jvm.h
> --- a/src/share/vm/prims/jvm.h	Thu May 14 14:48:35 2009 -0700
> +++ b/src/share/vm/prims/jvm.h	Mon May 18 12:33:07 2009 -0700
> @@ -438,6 +438,12 @@
>                        jobjectArray constants);
>  
>  /*
> + * Append a path to the boot class path
> + */
> +JNIEXPORT void JNICALL
> +JVM_ExtendBootClassPath(JNIEnv *env, jclass cls, const char *path);
> +
> +/*
>   * Reflection support functions
>   */
>