GlueGen JavaCallback: Revised: Static Java callback dispatcher, dropping native heap, support Struct UserParam ...

Implementation now generates a static Java callback dispatcher for each defined SetCallbackFunction, which gets invoked by the generated native static counterpart with all arguments required.

The static callback utilizes its own synchronization for thread-safety and fetches the required data set stored at SetCallbackFunction to dispatch the call to the users' CallbackFunction.
In case the callback has been removed already, the static callback simply bails out quietly.

The native code does not create, release or manage heap memory and therefore is considered safe.

+++

Further Struct Type UserParam are now supported including Heterogeneous UserParam mapping (read GlueGen_Mapping.*).

+++

Cleaned up code by extracting all JavaCallback emitter code into JavaCallbackEmitter class in one place,
leaving JavaMethodbindingEmitter and CMethodbindingEmitter mostly in their original stage (non-convoluted).

In this regard, I had to refactor a few function, i.e. moving CMethodbindingEmitter.getJNIMangledArg(..)
into JavaType.appendDescriptor(..) and JavaType.appendJNIDescriptor(..) while reusing the toJNIMethodDescriptor(..) conversion.

Test4JavaCallback covers and passes all cases.

Author: sgothel

README.md

@@ -31,7 +31,7 @@ GlueGen can produce native foreign function bindings to Java™ as well as
 [map native data structures](doc/GlueGen_Mapping.md#struct-mapping) to be fully accessible from Java™ including 
 potential calls to [embedded function pointer](doc/GlueGen_Mapping.md#struct-function-pointer-support).
 
-GlueGen supports [registering Java™ callback methods](doc/GlueGen_Mapping.md#java-callback-from-native-c-api-support)
+GlueGen supports [registering Java™ callback methods](doc/GlueGen_Mapping.md#java-callback)
 to receive asynchronous and off-thread native toolkit events,
 where a generated native callback function dispatches the events to Java™.
 

doc/GlueGen_Mapping.html

@@ -84,11 +84,6 @@ public void emitJNIOnLoadJNIEnvCode(final String libraryBasename) {
         emitln( getJNIOnLoadJNIEnvCode(libraryBasename) );
     }
 
-    /** Emits {@link #JavaCallbackGlueDataDecl}. */
-    public void emitJavaCallbackGlueDataDecl() {
-        emitln( JavaCallbackGlueDataDecl );
-    }
-
     @Override
     public String toString() { return "CCodeUnit[unit "+cUnitName+", file "+filename+"]"; }
 
@@ -113,16 +108,6 @@ public void emitJavaCallbackGlueDataDecl() {
         "    return jbyteBuffer;\n"+
         "}\n";
 
-    /** JavaCallback Glue Data typedef struct */
-    public static final String JavaCallbackGlueDataDecl =
-        "typedef struct {\n"+
-        "  jobject lockObj;\n"+
-        "  jobject cbFunc;\n"+
-        "  jmethodID cbMethodID;\n"+
-        "  jobject userParam;\n"+
-        "} T_JavaCallbackGlueData;\n"+
-        "\n";
-
     /**
      * Returns native JNI declarations for `JavaVM* {libraryBasename}_jvmHandle`
      * and `JVMUtil_GetJNIEnv(..)`.

doc/GlueGen_Mapping.md

@@ -114,6 +114,7 @@ public void addModifiers(final Iterator<EmissionModifier> mi)  {
    * Emit the function to the {@link #getUnit()}
    */
   public final void emit()  {
+    emitAdditionalCode();
     emitDocComment();
     //output.println("  // Emitter: " + getClass().getName());
     emitSignature();
@@ -139,6 +140,7 @@ public void setCommentEmitter(final CommentEmitter cEmitter)  {
    */
   public CommentEmitter getCommentEmitter() { return commentEmitter; }
 
+  protected void emitAdditionalCode() { }
   protected void emitDocComment() {
 
     if (commentEmitter != null)    {
@@ -154,32 +156,42 @@ protected void emitDocComment() {
     }
   }
 
-  protected void emitSignature()  {
+  protected final void emitSignature()  {
+    unit.emit(appendSignature(new StringBuilder()).toString());
+  }
 
-    unit.emit(getBaseIndentString()); // indent method
+  protected StringBuilder appendSignature(final StringBuilder buf)  {
+    buf.append(getBaseIndentString()); // indent method
 
-    final int numEmitted = emitModifiers();
+    final int numEmitted = appendModifiers(buf);
     if (numEmitted > 0)  {
-      unit.emit(" ");
+      buf.append(" ");
     }
 
-    emitReturnType();
-    unit.emit(" ");
+    appendReturnType(buf);
+    buf.append(" ");
 
-    emitName();
-    unit.emit("(");
+    appendName(buf);
+    buf.append("(");
 
-    emitArguments();
-    unit.emit(")");
+    appendArguments(buf);
+    buf.append(")");
+    return buf;
   }
 
-  protected int emitModifiers()  {
+  protected final int emitModifiers()  {
+      final StringBuilder buf = new StringBuilder();
+      final int n = appendModifiers(buf);
+      unit.emit(buf.toString());
+      return n;
+  }
+  protected int appendModifiers(final StringBuilder buf)  {
     int numEmitted = 0;
     for (final Iterator<EmissionModifier> it = getModifiers(); it.hasNext(); )   {
-      unit.emit(it.next().toString());
+      buf.append(it.next().toString());
       ++numEmitted;
       if (it.hasNext())  {
-        unit.emit(" ");
+        buf.append(" ");
       }
     }
     return numEmitted;
@@ -190,10 +202,23 @@ protected int emitModifiers()  {
   protected String getCommentStartString() { return "/* "; }
   protected String getCommentEndString() { return " */"; }
 
-  protected abstract void emitReturnType();
-  protected abstract void emitName();
+  protected final void emitReturnType() {
+      unit.emit(appendReturnType(new StringBuilder()).toString());
+  }
+  protected abstract StringBuilder appendReturnType(StringBuilder buf);
+  protected final void emitName() {
+      unit.emit(appendName(new StringBuilder()).toString());
+  }
+  protected abstract StringBuilder appendName(StringBuilder buf);
+  /** Returns the number of arguments emitted. */
+  protected final int emitArguments() {
+      final StringBuilder buf = new StringBuilder();
+      final int n = appendArguments(buf);
+      unit.emit(buf.toString());
+      return n;
+  }
   /** Returns the number of arguments emitted. */
-  protected abstract int emitArguments();
+  protected abstract int appendArguments(StringBuilder buf);
   protected abstract void emitBody();
 
   public static class EmissionModifier  {