add experimental Relay class
git-svn-id: http://skia.googlecode.com/svn/trunk@1010 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/include/core/SkRelay.h b/include/core/SkRelay.h
new file mode 100644
index 0000000..9361482
--- /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