mirror of
https://github.com/42wim/matterbridge.git
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233 lines
8.6 KiB
C
233 lines
8.6 KiB
C
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/*
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* Copyright 2016 Google Inc.
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*
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* Use of this source code is governed by a BSD-style license that can be
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* found in the LICENSE file.
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*/
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#ifndef VARENAALLOC_H
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#define VARENAALLOC_H
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#include <cassert>
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#include <cstddef>
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#include <cstdint>
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#include <cstdlib>
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#include <cstring>
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#include <limits>
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#include <new>
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#include <type_traits>
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#include <utility>
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#include <vector>
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// SkArenaAlloc allocates object and destroys the allocated objects when destroyed. It's designed
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// to minimize the number of underlying block allocations. SkArenaAlloc allocates first out of an
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// (optional) user-provided block of memory, and when that's exhausted it allocates on the heap,
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// starting with an allocation of firstHeapAllocation bytes. If your data (plus a small overhead)
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// fits in the user-provided block, SkArenaAlloc never uses the heap, and if it fits in
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// firstHeapAllocation bytes, it'll use the heap only once. If 0 is specified for
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// firstHeapAllocation, then blockSize is used unless that too is 0, then 1024 is used.
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//
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// Examples:
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//
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// char block[mostCasesSize];
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// SkArenaAlloc arena(block, mostCasesSize);
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//
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// If mostCasesSize is too large for the stack, you can use the following pattern.
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//
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// std::unique_ptr<char[]> block{new char[mostCasesSize]};
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// SkArenaAlloc arena(block.get(), mostCasesSize, almostAllCasesSize);
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//
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// If the program only sometimes allocates memory, use the following pattern.
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//
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// SkArenaAlloc arena(nullptr, 0, almostAllCasesSize);
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//
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// The storage does not necessarily need to be on the stack. Embedding the storage in a class also
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// works.
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//
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// class Foo {
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// char storage[mostCasesSize];
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// SkArenaAlloc arena (storage, mostCasesSize);
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// };
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//
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// In addition, the system is optimized to handle POD data including arrays of PODs (where
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// POD is really data with no destructors). For POD data it has zero overhead per item, and a
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// typical per block overhead of 8 bytes. For non-POD objects there is a per item overhead of 4
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// bytes. For arrays of non-POD objects there is a per array overhead of typically 8 bytes. There
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// is an addition overhead when switching from POD data to non-POD data of typically 8 bytes.
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//
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// If additional blocks are needed they are increased exponentially. This strategy bounds the
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// recursion of the RunDtorsOnBlock to be limited to O(log size-of-memory). Block size grow using
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// the Fibonacci sequence which means that for 2^32 memory there are 48 allocations, and for 2^48
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// there are 71 allocations.
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class VArenaAlloc {
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public:
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VArenaAlloc(char* block, size_t blockSize, size_t firstHeapAllocation);
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explicit VArenaAlloc(size_t firstHeapAllocation)
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: VArenaAlloc(nullptr, 0, firstHeapAllocation)
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{}
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~VArenaAlloc();
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template <typename T, typename... Args>
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T* make(Args&&... args) {
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uint32_t size = ToU32(sizeof(T));
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uint32_t alignment = ToU32(alignof(T));
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char* objStart;
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if (std::is_trivially_destructible<T>::value) {
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objStart = this->allocObject(size, alignment);
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fCursor = objStart + size;
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} else {
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objStart = this->allocObjectWithFooter(size + sizeof(Footer), alignment);
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// Can never be UB because max value is alignof(T).
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uint32_t padding = ToU32(objStart - fCursor);
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// Advance to end of object to install footer.
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fCursor = objStart + size;
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FooterAction* releaser = [](char* objEnd) {
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char* objStart = objEnd - (sizeof(T) + sizeof(Footer));
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((T*)objStart)->~T();
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return objStart;
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};
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this->installFooter(releaser, padding);
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}
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// This must be last to make objects with nested use of this allocator work.
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return new(objStart) T(std::forward<Args>(args)...);
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}
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template <typename T>
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T* makeArrayDefault(size_t count) {
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uint32_t safeCount = ToU32(count);
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T* array = (T*)this->commonArrayAlloc<T>(safeCount);
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// If T is primitive then no initialization takes place.
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for (size_t i = 0; i < safeCount; i++) {
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new (&array[i]) T;
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}
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return array;
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}
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template <typename T>
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T* makeArray(size_t count) {
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uint32_t safeCount = ToU32(count);
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T* array = (T*)this->commonArrayAlloc<T>(safeCount);
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// If T is primitive then the memory is initialized. For example, an array of chars will
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// be zeroed.
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for (size_t i = 0; i < safeCount; i++) {
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new (&array[i]) T();
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}
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return array;
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}
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// Only use makeBytesAlignedTo if none of the typed variants are impractical to use.
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void* makeBytesAlignedTo(size_t size, size_t align) {
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auto objStart = this->allocObject(ToU32(size), ToU32(align));
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fCursor = objStart + size;
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return objStart;
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}
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// Destroy all allocated objects, free any heap allocations.
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void reset();
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private:
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static void AssertRelease(bool cond) { if (!cond) { ::abort(); } }
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static uint32_t ToU32(size_t v) {
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return (uint32_t)v;
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}
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using Footer = int64_t;
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using FooterAction = char* (char*);
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static char* SkipPod(char* footerEnd);
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static void RunDtorsOnBlock(char* footerEnd);
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static char* NextBlock(char* footerEnd);
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void installFooter(FooterAction* releaser, uint32_t padding);
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void installUint32Footer(FooterAction* action, uint32_t value, uint32_t padding);
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void installPtrFooter(FooterAction* action, char* ptr, uint32_t padding);
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void ensureSpace(uint32_t size, uint32_t alignment);
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char* allocObject(uint32_t size, uint32_t alignment) {
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uintptr_t mask = alignment - 1;
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uintptr_t alignedOffset = (~reinterpret_cast<uintptr_t>(fCursor) + 1) & mask;
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uintptr_t totalSize = size + alignedOffset;
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AssertRelease(totalSize >= size);
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if (totalSize > static_cast<uintptr_t>(fEnd - fCursor)) {
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this->ensureSpace(size, alignment);
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alignedOffset = (~reinterpret_cast<uintptr_t>(fCursor) + 1) & mask;
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}
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return fCursor + alignedOffset;
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}
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char* allocObjectWithFooter(uint32_t sizeIncludingFooter, uint32_t alignment);
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template <typename T>
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char* commonArrayAlloc(uint32_t count) {
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char* objStart;
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AssertRelease(count <= std::numeric_limits<uint32_t>::max() / sizeof(T));
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uint32_t arraySize = ToU32(count * sizeof(T));
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uint32_t alignment = ToU32(alignof(T));
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if (std::is_trivially_destructible<T>::value) {
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objStart = this->allocObject(arraySize, alignment);
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fCursor = objStart + arraySize;
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} else {
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constexpr uint32_t overhead = sizeof(Footer) + sizeof(uint32_t);
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AssertRelease(arraySize <= std::numeric_limits<uint32_t>::max() - overhead);
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uint32_t totalSize = arraySize + overhead;
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objStart = this->allocObjectWithFooter(totalSize, alignment);
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// Can never be UB because max value is alignof(T).
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uint32_t padding = ToU32(objStart - fCursor);
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// Advance to end of array to install footer.?
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fCursor = objStart + arraySize;
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this->installUint32Footer(
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[](char* footerEnd) {
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char* objEnd = footerEnd - (sizeof(Footer) + sizeof(uint32_t));
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uint32_t count;
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memmove(&count, objEnd, sizeof(uint32_t));
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char* objStart = objEnd - count * sizeof(T);
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T* array = (T*) objStart;
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for (uint32_t i = 0; i < count; i++) {
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array[i].~T();
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}
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return objStart;
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},
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ToU32(count),
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padding);
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}
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return objStart;
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}
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char* fDtorCursor;
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char* fCursor;
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char* fEnd;
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char* const fFirstBlock;
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const uint32_t fFirstSize;
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const uint32_t fFirstHeapAllocationSize;
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// Use the Fibonacci sequence as the growth factor for block size. The size of the block
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// allocated is fFib0 * fFirstHeapAllocationSize. Using 2 ^ n * fFirstHeapAllocationSize
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// had too much slop for Android.
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uint32_t fFib0 {1}, fFib1 {1};
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};
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// Helper for defining allocators with inline/reserved storage.
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// For argument declarations, stick to the base type (SkArenaAlloc).
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template <size_t InlineStorageSize>
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class VSTArenaAlloc : public VArenaAlloc {
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public:
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explicit VSTArenaAlloc(size_t firstHeapAllocation = InlineStorageSize)
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: VArenaAlloc(fInlineStorage, InlineStorageSize, firstHeapAllocation) {}
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private:
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char fInlineStorage[InlineStorageSize];
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};
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#endif // VARENAALLOC_H
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