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+//
+// Copyright 2019 The ANGLE Project Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+//
+// PoolAlloc.h:
+// Defines the class interface for PoolAllocator.
+//
+
+#ifndef COMMON_POOLALLOC_H_
+#define COMMON_POOLALLOC_H_
+
+#if !defined(NDEBUG)
+# define ANGLE_POOL_ALLOC_GUARD_BLOCKS // define to enable guard block checking
+#endif
+
+//
+// This header defines an allocator that can be used to efficiently
+// allocate a large number of small requests for heap memory, with the
+// intention that they are not individually deallocated, but rather
+// collectively deallocated at one time.
+//
+// This simultaneously
+//
+// * Makes each individual allocation much more efficient; the
+// typical allocation is trivial.
+// * Completely avoids the cost of doing individual deallocation.
+// * Saves the trouble of tracking down and plugging a large class of leaks.
+//
+// Individual classes can use this allocator by supplying their own
+// new and delete methods.
+//
+
+#include "angleutils.h"
+#include "common/debug.h"
+
+namespace angle
+{
+class Allocation;
+class PageHeader;
+
+//
+// There are several stacks. One is to track the pushing and popping
+// of the user, and not yet implemented. The others are simply a
+// repositories of free pages or used pages.
+//
+// Page stacks are linked together with a simple header at the beginning
+// of each allocation obtained from the underlying OS. Multi-page allocations
+// are returned to the OS. Individual page allocations are kept for future
+// re-use.
+//
+// The "page size" used is not, nor must it match, the underlying OS
+// page size. But, having it be about that size or equal to a set of
+// pages is likely most optimal.
+//
+class PoolAllocator : angle::NonCopyable
+{
+ public:
+ static const int kDefaultAlignment = sizeof(void *);
+ //
+ // Create PoolAllocator. If alignment is set to 1 byte then fastAllocate()
+ // function can be used to make allocations with less overhead.
+ //
+ PoolAllocator(int growthIncrement = 8 * 1024, int allocationAlignment = kDefaultAlignment);
+
+ //
+ // Don't call the destructor just to free up the memory, call pop()
+ //
+ ~PoolAllocator();
+
+ //
+ // Initialize page size and alignment after construction
+ //
+ void initialize(int pageSize, int alignment);
+
+ //
+ // Call push() to establish a new place to pop memory to. Does not
+ // have to be called to get things started.
+ //
+ void push();
+
+ //
+ // Call pop() to free all memory allocated since the last call to push(),
+ // or if no last call to push, frees all memory since first allocation.
+ //
+ void pop();
+
+ //
+ // Call popAll() to free all memory allocated.
+ //
+ void popAll();
+
+ //
+ // Call allocate() to actually acquire memory. Returns 0 if no memory
+ // available, otherwise a properly aligned pointer to 'numBytes' of memory.
+ //
+ void *allocate(size_t numBytes);
+
+ //
+ // Call fastAllocate() for a faster allocate function that does minimal bookkeeping
+ // preCondition: Allocator must have been created w/ alignment of 1
+ ANGLE_INLINE uint8_t *fastAllocate(size_t numBytes)
+ {
+#if defined(ANGLE_DISABLE_POOL_ALLOC)
+ return reinterpret_cast<uint8_t *>(allocate(numBytes));
+#else
+ ASSERT(mAlignment == 1);
+ // No multi-page allocations
+ ASSERT(numBytes <= (mPageSize - mPageHeaderSkip));
+ //
+ // Do the allocation, most likely case inline first, for efficiency.
+ //
+ if (numBytes <= mPageSize - mCurrentPageOffset)
+ {
+ //
+ // Safe to allocate from mCurrentPageOffset.
+ //
+ uint8_t *memory = reinterpret_cast<uint8_t *>(mInUseList) + mCurrentPageOffset;
+ mCurrentPageOffset += numBytes;
+ return memory;
+ }
+ return allocateNewPage(numBytes);
+#endif
+ }
+
+ // There is no deallocate. The point of this class is that deallocation can be skipped by the
+ // user of it, as the model of use is to simultaneously deallocate everything at once by calling
+ // pop(), and to not have to solve memory leak problems.
+
+ // Catch unwanted allocations.
+ // TODO(jmadill): Remove this when we remove the global allocator.
+ void lock();
+ void unlock();
+
+ private:
+ size_t mAlignment; // all returned allocations will be aligned at
+ // this granularity, which will be a power of 2
+#if !defined(ANGLE_DISABLE_POOL_ALLOC)
+ struct AllocState
+ {
+ size_t offset;
+ PageHeader *page;
+ };
+ using AllocStack = std::vector<AllocState>;
+
+ // Slow path of allocation when we have to get a new page.
+ uint8_t *allocateNewPage(size_t numBytes);
+ // Track allocations if and only if we're using guard blocks
+ void *initializeAllocation(uint8_t *memory, size_t numBytes);
+
+ // Granularity of allocation from the OS
+ size_t mPageSize;
+ // Amount of memory to skip to make room for the page header (which is the size of the page
+ // header, or PageHeader in PoolAlloc.cpp)
+ size_t mPageHeaderSkip;
+ // Next offset in top of inUseList to allocate from. This offset is not necessarily aligned to
+ // anything. When an allocation is made, the data is aligned to mAlignment, and the header (if
+ // any) will align to pointer size by extension (since mAlignment is made aligned to at least
+ // pointer size).
+ size_t mCurrentPageOffset;
+ // List of popped memory
+ PageHeader *mFreeList;
+ // List of all memory currently being used. The head of this list is where allocations are
+ // currently being made from.
+ PageHeader *mInUseList;
+ // Stack of where to allocate from, to partition pool
+ AllocStack mStack;
+
+ int mNumCalls; // just an interesting statistic
+ size_t mTotalBytes; // just an interesting statistic
+
+#else // !defined(ANGLE_DISABLE_POOL_ALLOC)
+ std::vector<std::vector<void *>> mStack;
+#endif
+
+ bool mLocked;
+};
+
+} // namespace angle
+
+#endif // COMMON_POOLALLOC_H_