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 124