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 WebKit { 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 WebKit 74 75 #endif 76
