third_party/WebKit/public/platform/WebDiscardableMemory.h

   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
  29 namespace 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 //
  49 class WebDiscardableMemory {
  50 public:
  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