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comparison: layout/base/StackArena.h
layout/base/StackArena.h
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| 1 /* This Source Code Form is subject to the terms of the Mozilla Public | |
| 2 * License, v. 2.0. If a copy of the MPL was not distributed with this file, | |
| 3 * You can obtain one at http://mozilla.org/MPL/2.0/. */ | |
| 4 | |
| 5 #ifndef StackArena_h | |
| 6 #define StackArena_h | |
| 7 | |
| 8 #include "nsError.h" | |
| 9 #include "mozilla/Assertions.h" | |
| 10 #include "mozilla/MemoryReporting.h" | |
| 11 #include "mozilla/NullPtr.h" | |
| 12 | |
| 13 namespace mozilla { | |
| 14 | |
| 15 struct StackBlock; | |
| 16 struct StackMark; | |
| 17 class AutoStackArena; | |
| 18 | |
| 19 // Private helper class for AutoStackArena. | |
| 20 class StackArena { | |
| 21 private: | |
| 22 friend class AutoStackArena; | |
| 23 StackArena(); | |
| 24 ~StackArena(); | |
| 25 | |
| 26 nsresult Init() { return mBlocks ? NS_OK : NS_ERROR_OUT_OF_MEMORY; } | |
| 27 | |
| 28 // Memory management functions. | |
| 29 void* Allocate(size_t aSize); | |
| 30 void Push(); | |
| 31 void Pop(); | |
| 32 | |
| 33 size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const; | |
| 34 | |
| 35 // Our current position in memory. | |
| 36 size_t mPos; | |
| 37 | |
| 38 // A list of memory blocks. Usually there is only one | |
| 39 // but if we overrun our stack size we can get more memory. | |
| 40 StackBlock* mBlocks; | |
| 41 | |
| 42 // The current block. | |
| 43 StackBlock* mCurBlock; | |
| 44 | |
| 45 // Our stack of mark where push has been called. | |
| 46 StackMark* mMarks; | |
| 47 | |
| 48 // The current top of the mark list. | |
| 49 uint32_t mStackTop; | |
| 50 | |
| 51 // The size of the mark array. | |
| 52 uint32_t mMarkLength; | |
| 53 }; | |
| 54 | |
| 55 // Class for stack scoped arena memory allocations. | |
| 56 // | |
| 57 // Callers who wish to allocate memory whose lifetime corresponds to the | |
| 58 // lifetime of a stack-allocated object can use this class. First, | |
| 59 // declare an AutoStackArena object on the stack. Then all subsequent | |
| 60 // calls to Allocate will allocate memory from an arena pool that will | |
| 61 // be freed when that variable goes out of scope. Nesting is allowed. | |
| 62 // | |
| 63 // Individual allocations cannot exceed StackBlock::MAX_USABLE_SIZE | |
| 64 // bytes. | |
| 65 // | |
| 66 class MOZ_STACK_CLASS AutoStackArena { | |
| 67 public: | |
| 68 AutoStackArena() | |
| 69 : mOwnsStackArena(false) | |
| 70 { | |
| 71 if (!gStackArena) { | |
| 72 gStackArena = new StackArena(); | |
| 73 mOwnsStackArena = true; | |
| 74 gStackArena->Init(); | |
| 75 } | |
| 76 gStackArena->Push(); | |
| 77 } | |
| 78 | |
| 79 ~AutoStackArena() { | |
| 80 gStackArena->Pop(); | |
| 81 if (mOwnsStackArena) { | |
| 82 delete gStackArena; | |
| 83 gStackArena = nullptr; | |
| 84 } | |
| 85 } | |
| 86 | |
| 87 static void* Allocate(size_t aSize) { | |
| 88 return gStackArena->Allocate(aSize); | |
| 89 } | |
| 90 | |
| 91 private: | |
| 92 static StackArena* gStackArena; | |
| 93 bool mOwnsStackArena; | |
| 94 }; | |
| 95 | |
| 96 } // namespace mozilla | |
| 97 | |
| 98 #endif |
