From 94f6a730bbc19316c237d4a30782c4e8204a84a2 Mon Sep 17 00:00:00 2001
From: "reed@google.com" <reed@google.com@2bbb7eff-a529-9590-31e7-b0007b416f81>
Date: Mon, 28 Mar 2011 03:47:18 +0000
Subject: [PATCH] add experimental Relay class

git-svn-id: http://skia.googlecode.com/svn/trunk@1010 2bbb7eff-a529-9590-31e7-b0007b416f81
---
 include/core/SkRelay.h | 50 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)
 create mode 100644 include/core/SkRelay.h

diff --git a/include/core/SkRelay.h b/include/core/SkRelay.h
new file mode 100644
index 0000000000..93614825cf
--- /dev/null
+++ b/include/core/SkRelay.h
@@ -0,0 +1,50 @@
+/*
+    Copyright 2010 Google Inc.
+
+    Licensed under the Apache License, Version 2.0 (the "License");
+    you may not use this file except in compliance with the License.
+    You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+    Unless required by applicable law or agreed to in writing, software
+    distributed under the License is distributed on an "AS IS" BASIS,
+    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+    See the License for the specific language governing permissions and
+    limitations under the License.
+ */
+
+#ifndef SkTRelay_DEFINED
+#define SkTRelay_DEFINED
+
+#include "SkRefCnt.h"
+
+/**
+ *  Similar to a weakptr in java, a Relay allows for a back-ptr to an
+ *  object to be "safe", without using a hard reference-count.
+ *
+ *  Typically, the target creates a Relay with a pointer to itself. Whenever it
+ *  wants to have another object maintain a safe-ptr to it, it gives them a
+ *  Relay, which they ref()/unref(). Through the Relay each external object can
+ *  retrieve a pointer to the Target. However, when the Target goes away, it
+ *  clears the Relay pointer to it (relay->set(NULL)) and then unref()s the
+ *  Relay. The other objects still have a ref on the Relay, but now when they
+ *  call get() the receive a NULL.
+ */
+template <template T> class SkTRelay : public SkRefCnt {
+public:
+    SkTRelay(T* ptr) : fPtr(ptr) {}
+
+    // consumers call this
+    T* get() const { return fPtr; }
+
+    // producer calls this
+    void set(T* ptr) { fPtr = ptr; }
+
+    void clear() { this->set(NULL); }
+
+private:
+    T* fPtr;
+};
+
+#endif