Get the JavaVM handle on Android targets

Alc/ALc.c

@@ -1166,6 +1166,70 @@ static void alc_initconfig(void)
 }
 #define DO_INITCONFIG() alcall_once(&alc_config_once, alc_initconfig)
 
+#ifdef __ANDROID__
+#include <jni.h>
+
+static JavaVM *gJavaVM;
+static pthread_key_t gJVMThreadKey;
+
+static void CleanupJNIEnv(void* UNUSED(ptr))
+{
+    JCALL0(gJavaVM,DetachCurrentThread)();
+}
+
+void *Android_GetJNIEnv(void)
+{
+    /* http://developer.android.com/guide/practices/jni.html
+     *
+     * All threads are Linux threads, scheduled by the kernel. They're usually
+     * started from managed code (using Thread.start), but they can also be
+     * created elsewhere and then attached to the JavaVM. For example, a thread
+     * started with pthread_create can be attached with the JNI
+     * AttachCurrentThread or AttachCurrentThreadAsDaemon functions. Until a
+     * thread is attached, it has no JNIEnv, and cannot make JNI calls.
+     * Attaching a natively-created thread causes a java.lang.Thread object to
+     * be constructed and added to the "main" ThreadGroup, making it visible to
+     * the debugger. Calling AttachCurrentThread on an already-attached thread
+     * is a no-op.
+     */
+    JNIEnv *env = pthread_getspecific(gJVMThreadKey);
+    if(!env)
+    {
+        int status = JCALL(gJavaVM,AttachCurrentThread)(&env, NULL);
+        if(status < 0)
+        {
+            ERR("Failed to attach current thread\n");
+            return NULL;
+        }
+        pthread_setspecific(gJVMThreadKey, env);
+    }
+    return env;
+}
+
+/* Automatically called by JNI. */
+JNIEXPORT jint JNICALL JNI_OnLoad(JavaVM *jvm, void* UNUSED(reserved))
+{
+    void *env;
+    int err;
+
+    gJavaVM = jvm;
+    if(JCALL(gJavaVM,GetEnv)(&env, JNI_VERSION_1_4) != JNI_OK)
+    {
+        ERR("Failed to get JNIEnv with JNI_VERSION_1_4\n");
+        return JNI_ERR;
+    }
+
+    /* Create gJVMThreadKey so we can keep track of the JNIEnv assigned to each
+     * thread. The JNIEnv *must* be detached before the thread is destroyed.
+     */
+    if((err=pthread_key_create(&gJVMThreadKey, CleanupJNIEnv)) != 0)
+        ERR("pthread_key_create failed: %d\n", err);
+    pthread_setspecific(gJVMThreadKey, env);
+    return JNI_VERSION_1_4;
+}
+
+#endif
+
 
 /************************************************
  * Library deinitialization

Alc/compat.h

@@ -46,4 +46,12 @@ void CloseLib(void *handle);
 void *GetSymbol(void *handle, const char *name);
 #endif
 
+#ifdef __ANDROID__
+#define JCALL(obj, func)  ((*(obj))->func((obj), EXTRACT_VCALL_ARGS
+#define JCALL0(obj, func)  ((*(obj))->func((obj) EXTRACT_VCALL_ARGS
+
+/** Returns a JNIEnv*. */
+void *Android_GetJNIEnv(void);
+#endif
+
 #endif /* AL_COMPAT_H */