java: mraa jni library now dynamically links to libmraa

libmraajava.so was statically linking to mraa object files causing
duplicate mraa platform instances if a UPM Java module was also loaded.

JNI functionality has been moved into src/java/mraajni.c. JVM object is
now set when JVM is loaded; see updates to src/java/mraajava.i.
This was necessary as the JVM object cannot be directly referenced from
mraa as it will not be available when building C/C++ examples.

Signed-off-by: Henry Bruce <henry.bruce@intel.com>
Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>

src/java/CMakeLists.txt

@@ -1,11 +1,3 @@
-FIND_PACKAGE (JNI REQUIRED)
-
-include_directories (
-  ${JAVA_INCLUDE_PATH}
-  ${JAVA_INCLUDE_PATH2}
-  ${CMAKE_CURRENT_SOURCE_DIR}/..
-)
-
 # SWIG treats SWIG_FLAGS as a list and not a string so semicolon seperation is required
 set_source_files_properties (mraajava.i PROPERTIES SWIG_FLAGS ";-package;mraa;-I${CMAKE_BINARY_DIR}/src")
 set_source_files_properties (mraajava.i PROPERTIES CPLUSPLUS ON)
@@ -25,8 +17,8 @@ else ()
   set (JAR $ENV{JAVA_HOME_NATIVE}/bin/jar)
 endif ()
 
-swig_add_module (mraajava java mraajava.i ${mraa_LIB_SRCS})
-swig_link_libraries (mraajava ${JAVA_LIBRARIES} ${mraa_LIBS})
+swig_add_module (mraajava java mraajava.i)
+swig_link_libraries (mraajava ${JAVA_LIBRARIES} mraa)
 
 add_custom_command (TARGET mraajava
   POST_BUILD

src/java/mraajava.i

@@ -65,11 +65,11 @@ class Spi;
 %include ../mraa.i
 
 %wrapper %{
-    JavaVM *globVM;
+    #include "java/mraajni.h"
 
     jint JNI_OnLoad(JavaVM *vm, void *reserved) {
         /* initialize mraa */
-        globVM = vm;
+        mraa_java_set_jvm(vm);
         mraa_init();
         return JNI_VERSION_1_6;
     }

src/java/mraajni.c

@@ -0,0 +1,103 @@
+/*
+ * Author: Henry Bruce <henry.bruce@intel.com>
+ * Copyright (c) 2016 Intel Corporation.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#include <pthread.h>
+#include "java/mraajni.h"
+
+static pthread_key_t env_key;
+static pthread_once_t env_key_init = PTHREAD_ONCE_INIT;
+static jmethodID runGlobal;
+static JavaVM* globVM = NULL;
+
+
+void
+mraa_java_set_jvm(JavaVM* vm)
+{
+    globVM = vm;
+}
+
+static void
+mraa_java_make_env_key(void)
+{
+    if (globVM != NULL) {
+        JNIEnv *jenv;
+        (*globVM)->GetEnv(globVM, (void **)&jenv, JNI_VERSION_1_8);
+        jclass rcls = (*jenv)->FindClass(jenv, "java/lang/Runnable");
+        jmethodID runm = (*jenv)->GetMethodID(jenv, rcls, "run", "()V");
+        runGlobal = (jmethodID)(*jenv)->NewGlobalRef(jenv, (jobject)runm);
+        pthread_key_create(&env_key, NULL);
+    }
+}
+
+void
+mraa_java_isr_callback(void* data)
+{
+    JNIEnv *jenv = (JNIEnv *) pthread_getspecific(env_key);
+    (*jenv)->CallVoidMethod(jenv, (jobject)data, runGlobal);
+}
+
+mraa_result_t
+mraa_java_attach_thread()
+{
+    if (globVM != NULL) {
+        JNIEnv *jenv;
+        jint err = (*globVM)->AttachCurrentThreadAsDaemon(globVM, (void **)&jenv, NULL);
+        if (err == JNI_OK) {
+            pthread_once(&env_key_init, mraa_java_make_env_key);
+            pthread_setspecific(env_key, jenv);
+            return MRAA_SUCCESS;
+        }
+    }
+    return MRAA_ERROR_UNSPECIFIED;
+}
+
+void
+mraa_java_detach_thread()
+{
+    if (globVM != NULL)
+        (*globVM)->DetachCurrentThread(globVM);
+}
+
+void*
+mraa_java_create_global_ref(void* args)
+{
+    if (globVM != NULL) {
+        JNIEnv *jenv;
+        (*globVM)->GetEnv(globVM, (void **)&jenv, JNI_VERSION_1_8);
+        jobject grunnable = (*jenv)->NewGlobalRef(jenv, (jobject) args);
+        return (void *)grunnable;
+    } else
+        return NULL;
+}
+
+void
+mraa_java_delete_global_ref(void *ref)
+{
+    if (globVM != NULL) {
+        JNIEnv *jenv;
+        (*globVM)->GetEnv(globVM, (void **)&jenv, JNI_VERSION_1_8);
+        (*jenv)->DeleteGlobalRef(jenv, (jobject)ref);
+    }
+}
+