Re: [java-gnome-hackers] release candidate

[Andrew C. <an...@op...>]

On Tue, 2009-02-03 at 10:16 +0100, Mark Wielaard wrote:

> The problem is the definition of GetEnv which takes a (void **) as
> second argument, but you are pointing it to a (JNIEnv **). I am not sure
> why GetEnv is defined like that. It doesn't seem particular useful....

I'm sure the way we're using it was copy & pasted from some example in
the book somewhere.

>  But
> there is nothing you can do about that now since it is a standard
> interface definition.

That made me wonder if nonetheless we were doing it wrong.

>   union env_union
>   {
>     void **void_env;
>     JNIEnv **jni_env;
>   };
> 
>   e.jni_env = &env;
>   result = (*cachedJavaVM)->GetEnv (cachedJavaVM,
>                                     e.void_env,
>                                     JNI_VERSION_1_4);


The idea of using a union to hint the compiler is really interesting.
Thanks!

Instead of that, however, can we not just cast? I tried this:

=== modified file 'src/jni/bindings_java_util.c'
--- src/jni/bindings_java_util.c	2009-02-01 14:53:00 +0000
+++ src/jni/bindings_java_util.c	2009-02-04 06:54:56 +0000
@@ -50,11 +50,13 @@
 bindings_java_getEnv()
 {
 	JNIEnv* env = NULL;
+	void* ptr = NULL;
 	JavaVMAttachArgs args = { 0, };
 	static int i = 0; 
 	jint result;
 
-	result = (*cachedJavaVM)->GetEnv(cachedJavaVM, (void **) &env, JNI_VERSION_1_4);
+	result = (*cachedJavaVM)->GetEnv(cachedJavaVM, &ptr, JNI_VERSION_1_4);
+	env = (JNIEnv*) ptr;
 	if (env != NULL) {
 		return env;
 	}
@@ -64,7 +66,8 @@
 		args.version = JNI_VERSION_1_4;
 		args.name = g_strdup_printf("NativeThread%d", i++);
 
-		result = (*cachedJavaVM)->AttachCurrentThreadAsDaemon(cachedJavaVM, (void **) &env, &args);
+		result = (*cachedJavaVM)->AttachCurrentThreadAsDaemon(cachedJavaVM, &ptr, &args);
+		env = (JNIEnv*) ptr;
 		if ((result == JNI_OK) && (env != NULL)) {
 			g_free(args.name);




and the warnings have gone away for me. Any reason that isn't ok? This
sort of casting is, after all, how the entire java-gnome library works.

A bundle with this patch is attached. Give it a try?

AfC
Sydney

-- 
Andrew Frederick Cowie

Operational Dynamics is an operations and engineering consultancy
focusing on IT strategy, organizational architecture, systems
review, and effective procedures for change management: enabling
successful deployment of mission critical information technology in
enterprises, worldwide.

http://www.operationaldynamics.com/

Sydney   New York   Toronto   London