java: new helper library for the Android port

src/java/Ref.hxx

@@ -0,0 +1,181 @@
+/*
+ * Copyright (C) 2010-2011 Max Kellermann <max@duempel.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef JAVA_REF_HXX
+#define JAVA_REF_HXX
+
+#include "Global.hxx"
+
+#include <jni.h>
+
+#include <assert.h>
+
+namespace Java {
+	/**
+	 * Hold a local reference on a JNI object.
+	 */
+	template<typename T>
+	class LocalRef {
+		JNIEnv *const env;
+		const T value;
+
+	public:
+		/**
+		 * The local reference is obtained by the caller.
+		 */
+		LocalRef(JNIEnv *_env, T _value):env(_env), value(_value) {
+			assert(env != nullptr);
+			assert(value != nullptr);
+		}
+
+		~LocalRef() {
+			env->DeleteLocalRef(value);
+		}
+
+		LocalRef(const LocalRef &other) = delete;
+		LocalRef &operator=(const LocalRef &other) = delete;
+
+		T Get() const {
+			return value;
+		}
+
+		operator T() const {
+			return value;
+		}
+	};
+
+	/**
+	 * Hold a global reference on a JNI object.
+	 */
+	template<typename T>
+	class GlobalRef {
+		T value;
+
+	public:
+		/**
+		 * Constructs an uninitialized object.  The method set() must be
+		 * called before it is destructed.
+		 */
+		GlobalRef() = default;
+
+		GlobalRef(JNIEnv *env, T _value):value(_value) {
+			assert(env != nullptr);
+			assert(value != nullptr);
+
+			value = (T)env->NewGlobalRef(value);
+		}
+
+		~GlobalRef() {
+			GetEnv()->DeleteGlobalRef(value);
+		}
+
+		GlobalRef(const GlobalRef &other) = delete;
+		GlobalRef &operator=(const GlobalRef &other) = delete;
+
+		/**
+		 * Sets the object, ignoring the previous value.  This is only
+		 * allowed once after the default constructor was used.
+		 */
+		void Set(JNIEnv *env, T _value) {
+			assert(_value != nullptr);
+
+			value = (T)env->NewGlobalRef(_value);
+		}
+
+		T Get() const {
+			return value;
+		}
+
+		operator T() const {
+			return value;
+		}
+	};
+
+	/**
+	 * Container for a global reference to a JNI object that gets
+	 * initialised and deinitialised explicitly.  Since there is no
+	 * implicit initialisation in the default constructor, this is a
+	 * trivial C++ class.  It should only be used for global variables
+	 * that are implicitly initialised with zeroes.
+	 */
+	template<typename T>
+	class TrivialRef {
+		T value;
+
+	public:
+		constexpr TrivialRef() {};
+
+		TrivialRef(const TrivialRef &other) = delete;
+		TrivialRef &operator=(const TrivialRef &other) = delete;
+
+		bool IsDefined() const {
+			return value != nullptr;
+		}
+
+		/**
+		 * Obtain a global reference on the specified object and store it.
+		 * This object must not be set already.
+		 */
+		void Set(JNIEnv *env, T _value) {
+			assert(value == nullptr);
+			assert(_value != nullptr);
+
+			value = (T)env->NewGlobalRef(_value);
+		}
+
+		/**
+		 * Release the global reference and clear this object.
+		 */
+		void Clear(JNIEnv *env) {
+			assert(value != nullptr);
+
+			env->DeleteGlobalRef(value);
+			value = nullptr;
+		}
+
+		/**
+		 * Release the global reference and clear this object.  It is
+		 * allowed to call this method without ever calling Set().
+		 */
+		void ClearOptional(JNIEnv *env) {
+			if (value != nullptr)
+				Clear(env);
+		}
+
+		T Get() const {
+			return value;
+		}
+
+		operator T() const {
+			return value;
+		}
+	};
+}
+
+#endif