June 2018 Update

Task/Use-another-language-to-call-a-function/Scala/use-another-language-to-call-a-function-1.scala

@@ -0,0 +1,12 @@
+/* Query.scala */
+object Query {
+  def call(data: Array[Byte], length: Array[Int]): Boolean = {
+    val message = "Here am I"
+    val mb = message.getBytes("utf-8")
+    if (length(0) >= mb.length) {
+      length(0) = mb.length
+      System.arraycopy(mb, 0, data, 0, mb.length)
+      true
+    } else false
+  }
+}

Task/Use-another-language-to-call-a-function/Scala/use-another-language-to-call-a-function-2.scala

@@ -0,0 +1,105 @@
+/* query-jni.c */
+#include <stdio.h>
+#include <stdlib.h>
+#include <jni.h>
+
+static JavaVM *jvm = NULL;
+static JNIEnv *jenv = NULL;
+
+static void die(const char *message) {
+    fprintf(stderr, "%s\n", message);
+    exit(1);
+}
+
+static void oom(void) {
+    die("Query: out of memory");
+}
+
+static void except(void) {
+    if ((*jenv)->ExceptionCheck(jenv))
+	die("Query: unexpected Java exception");
+}
+
+static void do_at_exit(void) {
+    (*jvm)->DestroyJavaVM(jvm);
+}
+
+static void require_jvm(void) {
+    JavaVMInitArgs args;
+
+    if (jvm)
+	return;
+
+    args.version = JNI_VERSION_1_4;
+    args.nOptions = 0;
+    args.options = NULL;
+    args.ignoreUnrecognized = JNI_FALSE;
+    if (JNI_CreateJavaVM(&jvm, (void **)&jenv, &args) != JNI_OK)
+	die("Query: can't create Java VM");
+    atexit(do_at_exit);
+}
+
+int Query(char *data, size_t *length) {
+    jclass cQuery;
+    jmethodID mcall;
+    jintArray jlength;
+    jint jlength0;
+    jbyteArray jdata;
+    jboolean result;
+
+    jlength0 = (jint)length[0];
+    if ((size_t)jlength0 != length[0])
+	die("Query: length is too large for Scala array");
+
+    require_jvm();
+
+    /* Create a local frame for references to Scala objects. */
+    if ((*jenv)->PushLocalFrame(jenv, 16))
+	oom();
+
+    /* Look for class Query, static boolean call(byte[], int[]) */
+    cQuery = (*jenv)->FindClass(jenv, "Query");
+    if (cQuery == NULL)
+	die("Query: can't find Query.class");
+    mcall = (*jenv)->GetStaticMethodID(jenv, cQuery, "call", "([B[I)Z");
+    if (mcall == NULL)
+	die("Query: missing call() method");
+
+    /*
+     * Make arguments to Query.call().  We can't pass data[] and
+     * length[] to Scala, so we make new Scala arrays jdata[] and
+     * jlength[].
+     */
+    jdata = (*jenv)->NewByteArray(jenv, (jsize)jlength0);
+    if (jdata == NULL)
+	oom();
+    jlength = (*jenv)->NewIntArray(jenv, 1);
+    if (jlength == NULL)
+	oom();
+
+    /* Set jlength[0] = length[0]. */
+    (*jenv)->SetIntArrayRegion(jenv, jlength, 0, 1, &jlength0);
+    except();
+
+    /*
+     * Call our Scala method.
+     */
+    result = (*jenv)->CallStaticBooleanMethod
+	(jenv, cQuery, mcall, jdata, jlength);
+    except();
+
+    /*
+     * Set length[0] = jlength[0].
+     * Copy length[0] bytes from jdata[] to data[].
+     */
+    (*jenv)->GetIntArrayRegion(jenv, jlength, 0, 1, &jlength0);
+    except();
+    length[0] = (size_t)jlength0;
+    (*jenv)->GetByteArrayRegion
+	(jenv, jdata, 0, (jsize)jlength0, (jbyte *)data);
+
+    /* Drop our local frame and its references. */
+    (*jenv)->PopLocalFrame(jenv, NULL);
+
+    return (int)result;
+}

Task/Use-another-language-to-call-a-function/Scala/use-another-language-to-call-a-function-3.scala

@@ -0,0 +1,22 @@
+# Makefile
+
+# Edit these lines to match your JDK.
+JAVA_HOME = /Library/Java/Home
+CPPFLAGS = -I$(JAVA_HOME)/include
+LIBS = -framework JavaVM
+JAVAC = $(JAVA_HOME)/bin/javac
+CC = cc
+
+all: calljava Query.class
+
+calljava: main.o query-jni.o
+	$(CC) -o calljava main.o query-jni.o $(LIBS)
+
+.SUFFIXES: .c .class .java .o
+.c.o:
+	$(CC) $(CPPFLAGS) -c $<
+.java.class:
+	$(JAVAC) $<
+
+clean:
+	rm -f calljava main.o query-jni.o Query.class