Home | History | Annotate | Download | only in platform 
      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 } // namespace blink
     44 
     45 namespace WebCore {
     46 
     47 // A simple vector implementation that supports purgeable memory. The vector is
     48 // already locked at construction and locking uses an internal counter which
     49 // means that N calls to lock() must be followed by N+1 calls to unlock() to
     50 // actually make the vector purgeable.
     51 class PLATFORM_EXPORT PurgeableVector {
     52     WTF_MAKE_NONCOPYABLE(PurgeableVector);
     53 public:
     54     enum PurgeableOption {
     55         NotPurgeable,
     56         Purgeable,
     57     };
     58 
     59     // Clients who know in advance that they will call unlock() should construct
     60     // the instance with the Purgeable option so that the instance uses
     61     // discardable memory from the start and unlock() doesn't cause a memcpy().
     62     PurgeableVector(PurgeableOption = Purgeable);
     63 
     64     ~PurgeableVector();
     65 
     66     // WARNING: This causes a memcpy() if the instance was constructed with the
     67     // Purgeable hint or had its internal vector moved to discardable memory
     68     // after a call to unlock().
     69     void adopt(Vector<char>& other);
     70 
     71     void append(const char* data, size_t length);
     72 
     73     void grow(size_t);
     74 
     75     void clear();
     76 
     77     // The instance must be locked before calling this.
     78     char* data();
     79 
     80     size_t size() const;
     81 
     82     // Returns whether the memory is still resident.
     83     bool lock();
     84 
     85     // WARNING: Calling unlock() on an instance that wasn't created with the
     86     // Purgeable option does an extra memcpy().
     87     void unlock();
     88 
     89     bool isLocked() const;
     90 
     91     // Note that this method should be used carefully since it may not use
     92     // exponential growth internally. This means that repeated/invalid uses of
     93     // it can result in O(N^2) append(). If you don't exactly know what you are
     94     // doing then you should probably not call this method.
     95     void reserveCapacity(size_t capacity);
     96 
     97 private:
     98     enum PurgeableAllocationStrategy {
     99         UseExactCapacity,
    100         UseExponentialGrowth,
    101     };
    102 
    103     // Copies data from the discardable buffer to the vector and clears the
    104     // discardable buffer.
    105     void moveDataFromDiscardableToVector();
    106 
    107     void clearDiscardable();
    108 
    109     bool reservePurgeableCapacity(size_t capacity, PurgeableAllocationStrategy);
    110 
    111     size_t adjustPurgeableCapacity(size_t capacity) const;
    112 
    113     // Vector used when the instance is constructed without the purgeability
    114     // hint or when discardable memory allocation fails.
    115     // Note that there can't be data both in |m_vector| and
    116     // |m_discardable|, i.e. only one of them is used at a given time.
    117     Vector<char> m_vector;
    118     OwnPtr<blink::WebDiscardableMemory> m_discardable;
    119     size_t m_discardableCapacity;
    120     size_t m_discardableSize;
    121     bool m_isPurgeable;
    122     int m_locksCount;
    123 };
    124 
    125 } // namespace WebCore
    126 
    127 #endif // PurgeableVector_h
    128