third_party/WebKit/Source/platform/PurgeableVector.h

   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
  39 namespace blink {
  40
  41 class 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.
  47 class PLATFORM_EXPORT PurgeableVector {
  48     WTF_MAKE_NONCOPYABLE(PurgeableVector);
  49 public:
  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
  93 private:
  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