Add AutoJObject and AutoGlobalJObject

base/android/scoped_java_global_reference.h

+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_ANDROID_SCOPED_JAVA_GLOBAL_REFERENCE_H_
+#define BASE_ANDROID_SCOPED_JAVA_GLOBAL_REFERENCE_H_
+
+#include <jni.h>
+#include <stddef.h>
+
+#include "base/android/scoped_java_reference.h"
+#include "base/basictypes.h"
+
+namespace base {
+namespace android {
+
+// Holds a global reference to a Java object. The global reference is scoped
+// to the lifetime of this object. Note that since a JNI Env is only suitable
+// for use on a single thread, objects of this class must be created, used and
+// destroyed on the same thread.
+template<typename T>
+class ScopedJavaGlobalReference {
+ public:
+  // Holds a NULL reference.
+  ScopedJavaGlobalReference()
+      : env_(NULL),
+        obj_(NULL) {
+  }
+  // Takes a new global reference to the Java object held by obj.
+  explicit ScopedJavaGlobalReference(const ScopedJavaReference<T>& obj)
+      : env_(obj.env()),
+        obj_(static_cast<T>(obj.env()->NewGlobalRef(obj.obj()))) {
+  }
+  ~ScopedJavaGlobalReference() {
+    Reset();
+  }
+
+  void Reset() {
+    if (env_ && obj_)
+      env_->DeleteGlobalRef(obj_);
+    env_ = NULL;
+    obj_ = NULL;
+  }
+  void Reset(const ScopedJavaGlobalReference& other) {
+    Reset();
+    env_ = other.env_;
+    obj_ = other.env_ ? static_cast<T>(other.env_->NewGlobalRef(other.obj_)) :
+        NULL;
+  }
+
+  T obj() const { return obj_; }
+
+ private:
+  JNIEnv* env_;
+  T obj_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedJavaGlobalReference);
+};
+
+}  // namespace android
+}  // namespace base
+
+#endif  // BASE_ANDROID_SCOPED_JAVA_GLOBAL_REFERENCE_H_