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.

[bulach, 2011/08/05 12:03:02]

perhaps we can also add a comment saying that this isn't thread-friendly as the
jnienv can't cross thread boundaries / must be only used / destroyed in the
thread that created it?

[steveblock, 2011/08/08 11:28:32]

Done.

+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. The global
+  // reference is deleted when this object goes out of scope.

[bulach, 2011/08/05 12:03:02]

the second sentence seems a bit redundant with the class comment on 17.

[steveblock, 2011/08/08 11:28:32]

Done.

+  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;
+  }

[bulach, 2011/08/05 12:03:02]

I'm not sure if we have a pattern for \n, but I'd add one here to separate the
methods above.

[steveblock, 2011/08/08 11:28:32]

Done.

+  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_