1/*
2 * Copyright (C) 2013 Google Inc. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 *
8 * 1.  Redistributions of source code must retain the above copyright
9 *     notice, this list of conditions and the following disclaimer.
10 * 2.  Redistributions in binary form must reproduce the above copyright
11 *     notice, this list of conditions and the following disclaimer in the
12 *     documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
15 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
16 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
17 * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
18 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
19 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
20 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
21 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24 */
25
26#ifndef WebDiscardableMemory_h
27#define WebDiscardableMemory_h
28
29namespace blink {
30
31// A memory allocation that can be automatically discarded by the operating
32// system under memory pressure.
33//
34// Discardable usage is typically:
35//    WebDiscardableMemory* mem = allocateAndLockedDiscardableMemory(1024*1024);
36//    void* data = mem->data();
37//    memset(data, 3, 1024*1024);
38//    mem->unlock();
39//
40// Later, when you need it again:
41//    if (!mem->lock()) {
42//       ... handle the fact that the memory is gone...
43//       delete mem; // Make sure to destroy it. It is never going to come back.
44//       return;
45//    }
46//    ... use mem->data() as much as you want
47//    mem->unlock();
48//
49class WebDiscardableMemory {
50public:
51    // Must not be called while locked.
52    virtual ~WebDiscardableMemory() { }
53
54    // Locks the memory, prevent it from being discarded. Once locked. you may
55    // obtain a pointer to that memory using the data() method.
56    //
57    // lock() may return false, indicating that the underlying memory was
58    // discarded and that the lock failed. In this case, the
59    // WebDiscardableMemory is effectively dead.
60    //
61    // Nested calls to lock are not allowed.
62    virtual bool lock() = 0;
63
64    // Returns the current pointer for the discardable memory. This call is ONLY
65    // valid when the discardable memory object is locked.
66    virtual void* data() = 0;
67
68    // Unlock the memory so that it can be purged by the system. Must be called
69    // after every successful lock call.
70    virtual void unlock() = 0;
71};
72
73} // namespace blink
74
75#endif
76