GlueGen LibraryOnLoad Config: Generate `JNI_OnLoad(..)` for dynamic and `JNI_OnLoad_<LibraryBasename>(..)` for static libraries and `JVMUtil_GetJNIEnv(..)` to resolve the `JNIEnv*` as used by JavaCallback

4 files changed, 141 insertions, 5 deletions

diff --git a/doc/GlueGen_Mapping.md b/doc/GlueGen_Mapping.md
index 5503db3..ee23845 100644
--- a/doc/GlueGen_Mapping.md
+++ b/doc/GlueGen_Mapping.md
@@ -36,6 +36,8 @@ GlueGen also supports [producing an OO-Style API mapping](#oo-style-api-interfac
 GlueGen is capable to bind low-level APIs such as the Java Native Interface (JNI) and
 the AWT Native Interface (JAWT) back up to the Java programming language.
 
+Further, GlueGen supports generating `JNI_OnLoad(..)` for dynamic and `JNI_OnLoad_<LibraryBasename>(..)` for static libraries via [`LibraryOnLoad Bindingtest2`](#libraryonload-librarybasename-for-jni_onload-), which also provides `JVMUtil_GetJNIEnv(..)` to resolve the `JNIEnv*` as used by [Java callback methods](#java-callback-from-native-c-api-support).
+
 GlueGen utilizes [JCPP](https://jogamp.org/cgit/jcpp.git/about/), migrated C preprocessor written in Java.
 
 GlueGen is used for the [JogAmp](https://jogamp.org) projects
@@ -794,7 +796,20 @@ public interface Bindingtest2 {
 
 *TODO: Work in progress*
 
-#### Example
+## Misc Configurations
+
+### `LibraryOnLoad <LibraryBasename>` for `JNI_OnLoad*(..)` ...
+
+`LibraryOnLoad <LibraryBasename>` generates native JNI code `JNI_OnLoad(..)` used for dynamic libraries, 
+`JNI_OnLoad_<LibraryBasename>(..)` used for static libraries,
+`JVMUtil_GetJNIEnv(..)` and the instance of `JavaVM* <LibraryBasename>_jvmHandle`.
+
+The `JNI_OnLoad*(..)` methods set the `JavaVM* <LibraryBasename>_jvmHandle`, which in turn is utilized by 
+`JVMUtil_GetJNIEnv(..)` to attach a new thread to the `JavaVM*` generating a new `JNIEnv*`in daemon mode -
+or just to retrieve the thread's `JNIEnv*`, if already attached to the `JavaVM*`.
+
+The `LibraryBasename` parameter is used to generate the `JNI_OnLoad_<LibraryBasename>(..)` variant for statically linked libraries.
+`JNI_OnLoad(..)`, `JNI_OnLoad_<LibraryBasename>(..)` and `JVMUtil_GetJNIEnv(..)`
 
 ## Platform Header Files
 
diff --git a/src/java/com/jogamp/gluegen/CCodeUnit.java b/src/java/com/jogamp/gluegen/CCodeUnit.java
index df5c6e7..5c0db27 100644
--- a/src/java/com/jogamp/gluegen/CCodeUnit.java
+++ b/src/java/com/jogamp/gluegen/CCodeUnit.java
@@ -50,13 +50,16 @@ public class CCodeUnit extends CodeUnit {
         CodeGenUtils.emitAutogeneratedWarning(output, generator, "C-Unit: "+cUnitName+", "+filename);
     }
 
-    public void emitHeader(final String packageName, final String className, final List<String> customCode) {
+    public void emitHeader(final String libraryBasename, final String packageName, final String className, final List<String> customCode) {
         emitln("#include <jni.h>");
         emitln("#include <stdlib.h>");
         emitln("#include <string.h>");
         emitln("#include <assert.h>");
         emitln("#include <stddef.h>");
         emitln();
+        if( null != libraryBasename && libraryBasename.length() > 0 ) {
+            emitJNIOnLoadJNIEnvDecl(libraryBasename);
+        }
         emitln("static jobject JVMUtil_NewDirectByteBufferCopy(JNIEnv *env, jclass clazzBuffers, void * source_address, size_t capacity); /* forward decl. */");
         emitln();
 
@@ -71,6 +74,16 @@ public class CCodeUnit extends CodeUnit {
         }
     }
 
+    /** Emits {@link #getJNIOnLoadJNIEnvDecl(String)}. */
+    public void emitJNIOnLoadJNIEnvDecl(final String libraryBasename) {
+        emitln( getJNIOnLoadJNIEnvDecl(libraryBasename) );
+    }
+
+    /** Emits {@link #getJNIOnLoadJNIEnvCode(String)}. */
+    public void emitJNIOnLoadJNIEnvCode(final String libraryBasename) {
+        emitln( getJNIOnLoadJNIEnvCode(libraryBasename) );
+    }
+
     @Override
     public String toString() { return "CCodeUnit[unit "+cUnitName+", file "+filename+"]"; }
 
@@ -94,4 +107,98 @@ public class CCodeUnit extends CodeUnit {
         "    }\n"+
         "    return jbyteBuffer;\n"+
         "}\n";
+
+    /**
+     * Returns native JNI declarations for `JavaVM* {libraryBasename}_jvmHandle`
+     * and `JVMUtil_GetJNIEnv(..)`.
+     * <p>
+     * See {@link #getJNIOnLoadJNIEnvCode(String)} for details.
+     * </p>
+     * @param libraryBasename library basename to generate the `JNI_OnLoad_{libraryBasename}(..)` variant for statically linked libraries.
+     * @return the code
+     * @see #getJNIOnLoadJNIEnvCode(String)
+     */
+    public static final String getJNIOnLoadJNIEnvDecl(final String libraryBasename) {
+        return "extern JavaVM *"+libraryBasename+"_jvmHandle;\n"+
+               "JNIEnv* JVMUtil_GetJNIEnv();\n"+
+               "\n";
+    }
+    /**
+     * Returns native JNI code `JNI_OnLoad(..)` used for dynamic libraries,
+     * `JNI_OnLoad_{libraryBasename}(..)` used for static libraries,
+     * `JVMUtil_GetJNIEnv(..)` and the instance of `JavaVM* {libraryBasename}_jvmHandle`.
+     * <p>
+     * The `JNI_OnLoad*(..)` methods set the `JavaVM* {libraryBasename}_jvmHandle`,
+     * which in turn is utilized by `JVMUtil_GetJNIEnv(..)`
+     * to attach a new thread to the `JavaVM*` generating a new `JNIEnv*`in daemon mode -
+     * or just to retrieve the thread's `JNIEnv*`, if already attached to the `JavaVM*`.
+     * </p>
+     * @param libraryBasename library basename to generate the `JNI_OnLoad_{libraryBasename}(..)` variant for statically linked libraries.
+     * @return the code
+     * @see #getJNIOnLoadJNIEnvDecl(String)
+     */
+    public static final String getJNIOnLoadJNIEnvCode(final String libraryBasename) {
+        final String jvmHandleName = libraryBasename+"_jvmHandle";
+        final StringBuilder sb = new StringBuilder();
+        sb.append("JavaVM *").append(jvmHandleName).append(" = NULL;\n");
+        sb.append("JNIEXPORT jint JNICALL JNI_OnLoad(JavaVM *initVM, void *reserved) {\n");
+        sb.append("  (void)reserved;\n");
+        sb.append("  ").append(jvmHandleName).append(" = initVM;\n");
+        sb.append("  fprintf(stderr, \"ON_LOAD_0\\n\");\n");
+        sb.append("  return JNI_VERSION_1_8;\n");
+        sb.append("}\n");
+        sb.append("JNIEXPORT jint JNICALL JNI_OnLoad_").append(libraryBasename).append("(JavaVM *initVM, void *reserved) {\n");
+        sb.append("  (void)reserved;\n");
+        sb.append("  ").append(jvmHandleName).append(" = initVM;\n");
+        sb.append("  fprintf(stderr, \"ON_LOAD_1\\n\");\n");
+        sb.append("  return JNI_VERSION_1_8;\n");
+        sb.append("}\n");
+        sb.append("\n");
+        sb.append("JNIEXPORT void JNICALL JNI_OnUnload(JavaVM *vm, void *reserved) {\n");
+        sb.append("  (void)vm;\n");
+        sb.append("  (void)reserved;\n");
+        sb.append("  fprintf(stderr, \"ON_UNLOAD_0\\n\");\n");
+        sb.append("}\n");
+        sb.append("\n");
+        sb.append("JNIEXPORT void JNICALL JNI_OnUnload_").append(libraryBasename).append("(JavaVM *vm, void *reserved) {\n");
+        sb.append("  (void)vm;\n");
+        sb.append("  (void)reserved;\n");
+        sb.append("  fprintf(stderr, \"ON_UNLOAD_1\\n\");\n");
+        sb.append("}\n");
+        sb.append("\n");
+        sb.append("JNIEnv* JVMUtil_GetJNIEnv() {\n");
+        sb.append("    JNIEnv* curEnv = NULL;\n");
+        sb.append("    JNIEnv* newEnv = NULL;\n");
+        sb.append("    int envRes;\n");
+        sb.append("\n");
+        sb.append("    if(NULL==").append(jvmHandleName).append(") {\n");
+        sb.append("        fprintf(stderr, \"JVMUtil_GetJNIEnv(").append(libraryBasename).append("): No JavaVM handle registered.\");\n");
+        sb.append("        return NULL;\n");
+        sb.append("    }\n");
+        sb.append("\n");
+        sb.append("    // retrieve this thread's JNIEnv curEnv - or detect it's detached\n");
+        sb.append("    envRes = (*").append(jvmHandleName).append(")->GetEnv(").append(jvmHandleName).append(", (void **) &curEnv, JNI_VERSION_1_8) ;\n");
+        sb.append("    if( JNI_EDETACHED == envRes ) {\n");
+        sb.append("        // detached thread - attach to JVM as daemon, w/o need to be detached!\n");
+        sb.append("        envRes = (*").append(jvmHandleName).append(")->AttachCurrentThreadAsDaemon(").append(jvmHandleName).append(", (void**) &newEnv, NULL);\n");
+        sb.append("        if( JNI_OK != envRes ) {\n");
+        sb.append("            fprintf(stderr, \"JVMUtil_GetJNIEnv(").append(libraryBasename).append("): Can't attach thread: %d\\n\", envRes);\n");
+        sb.append("            return NULL;\n");
+        sb.append("        }\n");
+        sb.append("        curEnv = newEnv;\n");
+        sb.append("    } else if( JNI_OK != envRes ) {\n");
+        sb.append("        // oops ..\n");
+        sb.append("        fprintf(stderr, \"JVMUtil_GetJNIEnv(").append(libraryBasename).append("): Can't GetEnv: %d\\n\", envRes);\n");
+        sb.append("        return NULL;\n");
+        sb.append("    }\n");
+        sb.append("    if (curEnv==NULL) {\n");
+        sb.append("        fprintf(stderr, \"JVMUtil_GetJNIEnv(").append(libraryBasename).append("): env is NULL\\n\");\n");
+        sb.append("        return NULL;\n");
+        sb.append("    }\n");
+        sb.append("    return curEnv;\n");
+        sb.append("}\n");
+        sb.append("\n");
+        return sb.toString();
+    }
 }
+
diff --git a/src/java/com/jogamp/gluegen/JavaConfiguration.java b/src/java/com/jogamp/gluegen/JavaConfiguration.java
index 30ccbb2..3faddcd 100644
--- a/src/java/com/jogamp/gluegen/JavaConfiguration.java
+++ b/src/java/com/jogamp/gluegen/JavaConfiguration.java
@@ -62,6 +62,7 @@ import static com.jogamp.gluegen.JavaEmitter.EmissionStyle.*;
 
 public class JavaConfiguration {
     private int nestedReads;
+    private String libraryOnLoadName;
     private String packageName;
     private String implPackageName;
     private String className;
@@ -284,6 +285,11 @@ public class JavaConfiguration {
 
   public void setOutputRootDir(final String s) { outputRootDir=s; }
 
+    /** Returns the library basename used to {@link CCodeUnit#emitJNIOnLoadJNIEnvCode(String)}. */
+    public String libraryOnLoadName() {
+        return libraryOnLoadName;
+    }
+
     /** Returns the package name parsed from the configuration file. */
     public String packageName() {
         return packageName;
@@ -1310,8 +1316,10 @@ public class JavaConfiguration {
 
   protected void dispatch(final String cmd, final StringTokenizer tok, final File file, final String filename, final int lineNo) throws IOException {
     //System.err.println("read cmd = [" + cmd + "]");
-    if (cmd.equalsIgnoreCase("Package")) {
-      packageName = readString("package", tok, filename, lineNo);
+    if (cmd.equalsIgnoreCase("LibraryOnLoad")) {
+      libraryOnLoadName = readString("LibraryOnLoad", tok, filename, lineNo);
+    } else if (cmd.equalsIgnoreCase("Package")) {
+      packageName = readString("Package", tok, filename, lineNo);
     } else if (cmd.equalsIgnoreCase("GlueGenRuntimePackage")) {
       gluegenRuntimePackage = readString("GlueGenRuntimePackage", tok, filename, lineNo);
     } else if (cmd.equalsIgnoreCase("ImplPackage")) {
diff --git a/src/java/com/jogamp/gluegen/JavaEmitter.java b/src/java/com/jogamp/gluegen/JavaEmitter.java
index 3a86239..939ce92 100644
--- a/src/java/com/jogamp/gluegen/JavaEmitter.java
+++ b/src/java/com/jogamp/gluegen/JavaEmitter.java
@@ -2980,7 +2980,10 @@ public class JavaEmitter implements GlueEmitter {
       }
 
       if (cfg.emitImpl()) {
-        cUnit().emitHeader(getImplPackageName(), cfg.implClassName(), cfg.customCCode());
+        if( !cfg.getJavaCallbackList().isEmpty() && null == cfg.libraryOnLoadName() ) {
+            LOG.log(WARNING, "JavaCallback used, but no 'LibraryOnLoad' basename specified for JNI_OnLoad(..). Exactly one native code-unit for the library must specify with 'LibraryOnLoad' basename");
+        }
+        cUnit().emitHeader(cfg.libraryOnLoadName(), getImplPackageName(), cfg.implClassName(), cfg.customCCode());
       }
     } catch (final Exception e) {
       throw new RuntimeException(
@@ -3004,6 +3007,9 @@ public class JavaEmitter implements GlueEmitter {
       javaImplUnit.emitTailCode();
       javaImplUnit().emitln("} // end of class " + cfg.implClassName());
     }
+    if (cfg.emitImpl() && null != cfg.libraryOnLoadName() ) {
+      cUnit.emitJNIOnLoadJNIEnvCode(cfg.libraryOnLoadName());
+    }
   }
 
   private JavaType javaType(final Class<?> c) {