Added StackAllocator type.

source/mijin/memory/stack_allocator.hpp

@@ -0,0 +1,192 @@
+
+#pragma once
+
+#if !defined(MIJIN_MEMORY_STACK_ALLOCATOR_HPP_INCLUDED)
+#define MIJIN_MEMORY_STACK_ALLOCATOR_HPP_INCLUDED 1
+
+#include "../debug/assert.hpp"
+#include "../internal/common.hpp"
+#include "../util/align.hpp"
+#include "../util/traits.hpp"
+
+namespace mijin
+{
+template<typename TValue, typename TStackAllocator>
+struct StlStackAllocator
+{
+public:
+    using value_type = TValue;
+private:
+    TStackAllocator* base_;
+public:
+    explicit StlStackAllocator(TStackAllocator& base) MIJIN_NOEXCEPT : base_(&base) {}
+    template<typename TOtherValue>
+    StlStackAllocator(const StlStackAllocator<TOtherValue, TStackAllocator>& other) MIJIN_NOEXCEPT : base_(other.base) {}
+
+    template<typename TOtherValue>
+    StlStackAllocator& operator=(const StlStackAllocator<TOtherValue, TStackAllocator>& other) MIJIN_NOEXCEPT
+    {
+        base_ = other.base_;
+        return *this;
+    }
+
+    auto operator<=>(const StlStackAllocator&) const noexcept = default;
+
+    [[nodiscard]]
+    TValue* allocate(std::size_t count) const
+    {
+        return static_cast<TValue*>(base_->allocate(alignof(TValue), count * sizeof(TValue)));
+    }
+
+    void deallocate(TValue* /* ptr */, std::size_t /* count */) const MIJIN_NOEXCEPT {}
+};
+
+template<std::size_t chunkSize = 4096, template<typename> typename TBacking = MIJIN_DEFAULT_ALLOCATOR> requires (allocator_tmpl<TBacking>)
+class StackAllocator
+{
+public:
+    using backing_t = TBacking<void>;
+    static constexpr std::size_t ACTUAL_CHUNK_SIZE = chunkSize - sizeof(void*) - sizeof(std::size_t);
+
+    template<typename T>
+    using stl_allocator_t = StlStackAllocator<T, StackAllocator<chunkSize, TBacking>>;
+private:
+    struct Chunk
+    {
+        std::array<std::byte, ACTUAL_CHUNK_SIZE> data;
+        Chunk* next;
+        std::size_t allocated;
+    };
+    [[no_unique_address]] TBacking<Chunk> backing_;
+    Chunk* firstChunk_ = nullptr;
+public:
+    StackAllocator() MIJIN_NOEXCEPT_IF(std::is_nothrow_default_constructible_v<backing_t>) = default;
+    explicit StackAllocator(backing_t backing) MIJIN_NOEXCEPT_IF((std::is_nothrow_constructible_v<TBacking<Chunk>, backing_t&&>))
+        : backing_(std::move(backing)) {}
+    StackAllocator(const StackAllocator&) = delete;
+    StackAllocator(StackAllocator&& other) MIJIN_NOEXCEPT_IF(std::is_nothrow_move_constructible_v<TBacking<Chunk>>)
+        : firstChunk_(std::exchange(other.firstChunk_, nullptr)) {}
+    ~StackAllocator() noexcept
+    {
+        Chunk* chunk = firstChunk_;
+        while (chunk != nullptr)
+        {
+            Chunk* nextChunk = firstChunk_->next;
+            backing_.deallocate(chunk, 1);
+            chunk = nextChunk;
+        }
+    }
+    StackAllocator& operator=(const StackAllocator&) = delete;
+    StackAllocator& operator=(StackAllocator&& other) MIJIN_NOEXCEPT_IF(std::is_nothrow_move_assignable_v<TBacking<Chunk>>)
+    {
+        if (this != &other)
+        {
+            backing_ = std::move(other.backing_);
+            firstChunk_ = std::exchange(other.firstChunk_, nullptr);
+        }
+        return *this;
+    }
+
+    void* allocate(std::size_t alignment, std::size_t size)
+    {
+        // first check if this can ever fit
+        if (size > ACTUAL_CHUNK_SIZE)
+        {
+            return nullptr;
+        }
+
+        // then try to find space in the current chunks
+        for (Chunk* chunk = firstChunk_; chunk != nullptr; chunk = chunk->next)
+        {
+            const std::size_t remaining = ACTUAL_CHUNK_SIZE - chunk->allocated;
+            if (remaining < size)
+            {
+                continue;
+            }
+
+            std::byte* start = &chunk->data[chunk->allocated];
+            std::byte* pos = mijin::alignUp(start, alignment);
+
+            const std::ptrdiff_t alignmentBytes = pos - start;
+            const std::size_t combinedSize = size + alignmentBytes;
+
+            if (remaining < combinedSize)
+            {
+                continue;
+            }
+
+            chunk->allocated += combinedSize;
+            return pos;
+        }
+
+        // no free space in any chunk? allocate a new one
+        Chunk* newChunk = backing_.allocate(1);
+        if (newChunk == nullptr)
+        {
+            return nullptr;
+        }
+        initAndAddChunk(newChunk);
+
+        // now try with the new chunk
+        std::byte* start = newChunk->data.data();
+        std::byte* pos = mijin::alignUp(start, alignment);
+
+        const std::ptrdiff_t alignmentBytes = pos - start;
+        const std::size_t combinedSize = size + alignmentBytes;
+
+        // doesn't fit (due to alignment), time to give up
+        if (ACTUAL_CHUNK_SIZE < combinedSize)
+        {
+            return nullptr;
+        }
+
+        newChunk->allocated = combinedSize;
+        return pos;
+    }
+
+    void reset() noexcept
+    {
+        for (Chunk* chunk = firstChunk_; chunk != nullptr; chunk = chunk->next)
+        {
+            chunk->allocated = 0;
+        }
+    }
+
+    bool createChunks(std::size_t count)
+    {
+        if (count == 0)
+        {
+            return true;
+        }
+        Chunk* newChunks = backing_.allocate(count);
+        if (newChunks == nullptr)
+        {
+            return false;
+        }
+
+        // reverse so the chunks are chained from 0 to count (new chunks are inserted in front)
+        for (std::size_t pos = count; pos > 0; --pos)
+        {
+            initAndAddChunk(&newChunks[pos-1]);
+        }
+        return true;
+    }
+
+    template<typename T>
+    stl_allocator_t<T> makeStlAllocator() MIJIN_NOEXCEPT
+    {
+        return stl_allocator_t<T>(*this);
+    }
+private:
+    void initAndAddChunk(Chunk* newChunk) noexcept
+    {
+        ::new (newChunk) Chunk();
+
+        // put it in the front
+        newChunk->next = firstChunk_;
+        firstChunk_ = newChunk;
+    }
+};
+} // namespace mijin
+
+#endif // !defined(MIJIN_MEMORY_STACK_ALLOCATOR_HPP_INCLUDED)