1
2/*
3 * Copyright 2010 Google Inc.
4 *
5 * Use of this source code is governed by a BSD-style license that can be
6 * found in the LICENSE file.
7 */
8
9
10#ifndef SkTRelay_DEFINED
11#define SkTRelay_DEFINED
12
13#include "SkRefCnt.h"
14
15/**
16 *  Similar to a weakptr in java, a Relay allows for a back-ptr to an
17 *  object to be "safe", without using a hard reference-count.
18 *
19 *  Typically, the target creates a Relay with a pointer to itself. Whenever it
20 *  wants to have another object maintain a safe-ptr to it, it gives them a
21 *  Relay, which they ref()/unref(). Through the Relay each external object can
22 *  retrieve a pointer to the Target. However, when the Target goes away, it
23 *  clears the Relay pointer to it (relay->set(NULL)) and then unref()s the
24 *  Relay. The other objects still have a ref on the Relay, but now when they
25 *  call get() the receive a NULL.
26 */
27template <template T> class SkTRelay : public SkRefCnt {
28public:
29    SkTRelay(T* ptr) : fPtr(ptr) {}
30
31    // consumers call this
32    T* get() const { return fPtr; }
33
34    // producer calls this
35    void set(T* ptr) { fPtr = ptr; }
36
37    void clear() { this->set(NULL); }
38
39private:
40    T* fPtr;
41};
42
43#endif
44