1/*
2 * Copyright (C) 2014 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 are
6 * met:
7 *
8 *     * Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 *     * Redistributions in binary form must reproduce the above
11 * copyright notice, this list of conditions and the following disclaimer
12 * in the documentation and/or other materials provided with the
13 * distribution.
14 *     * Neither the name of Google Inc. nor the names of its
15 * contributors may be used to endorse or promote products derived from
16 * this software without specific prior written permission.
17 *
18 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
19 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
20 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
21 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
22 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
23 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
24 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
25 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
26 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
27 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
28 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
29 */
30
31#ifndef PurgeableVector_h
32#define PurgeableVector_h
33
34#include "platform/PlatformExport.h"
35#include "wtf/Forward.h"
36#include "wtf/Noncopyable.h"
37#include "wtf/Vector.h"
38
39namespace blink {
40
41class WebDiscardableMemory;
42
43// A simple vector implementation that supports purgeable memory. The vector is
44// already locked at construction and locking uses an internal counter which
45// means that N calls to lock() must be followed by N+1 calls to unlock() to
46// actually make the vector purgeable.
47class PLATFORM_EXPORT PurgeableVector {
48    WTF_MAKE_NONCOPYABLE(PurgeableVector);
49public:
50    enum PurgeableOption {
51        NotPurgeable,
52        Purgeable,
53    };
54
55    // Clients who know in advance that they will call unlock() should construct
56    // the instance with the Purgeable option so that the instance uses
57    // discardable memory from the start and unlock() doesn't cause a memcpy().
58    PurgeableVector(PurgeableOption = Purgeable);
59
60    ~PurgeableVector();
61
62    // WARNING: This causes a memcpy() if the instance was constructed with the
63    // Purgeable hint or had its internal vector moved to discardable memory
64    // after a call to unlock().
65    void adopt(Vector<char>& other);
66
67    void append(const char* data, size_t length);
68
69    void grow(size_t);
70
71    void clear();
72
73    // The instance must be locked before calling this.
74    char* data();
75
76    size_t size() const;
77
78    // Returns whether the memory is still resident.
79    bool lock();
80
81    // WARNING: Calling unlock() on an instance that wasn't created with the
82    // Purgeable option does an extra memcpy().
83    void unlock();
84
85    bool isLocked() const;
86
87    // Note that this method should be used carefully since it may not use
88    // exponential growth internally. This means that repeated/invalid uses of
89    // it can result in O(N^2) append(). If you don't exactly know what you are
90    // doing then you should probably not call this method.
91    void reserveCapacity(size_t capacity);
92
93private:
94    enum PurgeableAllocationStrategy {
95        UseExactCapacity,
96        UseExponentialGrowth,
97    };
98
99    // Copies data from the discardable buffer to the vector and clears the
100    // discardable buffer.
101    void moveDataFromDiscardableToVector();
102
103    void clearDiscardable();
104
105    bool reservePurgeableCapacity(size_t capacity, PurgeableAllocationStrategy);
106
107    size_t adjustPurgeableCapacity(size_t capacity) const;
108
109    // Vector used when the instance is constructed without the purgeability
110    // hint or when discardable memory allocation fails.
111    // Note that there can't be data both in |m_vector| and
112    // |m_discardable|, i.e. only one of them is used at a given time.
113    Vector<char> m_vector;
114    OwnPtr<WebDiscardableMemory> m_discardable;
115    size_t m_discardableCapacity;
116    size_t m_discardableSize;
117    bool m_isPurgeable;
118    int m_locksCount;
119};
120
121} // namespace blink
122
123#endif // PurgeableVector_h
124