comments on the area allocator

v1
Brett 2023-12-18 19:51:55 -05:00
parent 19743d2be0
commit 825e2c71a4
1 changed files with 79 additions and 27 deletions

View File

@ -20,6 +20,7 @@
#include <utility> #include <utility>
#include <cstring> #include <cstring>
#include <array> #include <array>
#include <optional>
#if defined(__clang__) || defined(__llvm__) || defined(__GNUC__) || defined(__GNUG__) #if defined(__clang__) || defined(__llvm__) || defined(__GNUC__) || defined(__GNUG__)
@ -518,12 +519,29 @@ namespace blt
typedef void* void_pointer; typedef void* void_pointer;
typedef const void* const_void_pointer; typedef const void* const_void_pointer;
private: private:
/**
* Stores a view to a region of memory that has been deallocated
* This is a non-owning reference to the memory block
*
* pointer p is the pointer to the beginning of the block of memory
* size_t n is the number of elements that this block can hold
*/
struct pointer_view struct pointer_view
{ {
pointer p; pointer p;
size_t n; size_t n;
}; };
/**
* Stores the actual data for allocated blocks. Since we would like to be able to allocate an arbitrary number of items
* we need a way of storing that data. The block storage holds an owning pointer to a region of memory with used elements
* Only up to used has to have their destructors called, which should be handled by the deallocate function
* it is UB to not deallocate memory allocated by this allocator
*
* an internal vector is used to store the regions of memory which have been deallocated. the allocate function will search for
* free blocks with sufficient size in order to maximize memory usage. In the future more advanced methods should be used
* for both faster access to deallocated blocks of sufficient size and to ensure coherent memory.
*/
struct block_storage struct block_storage
{ {
pointer data; pointer data;
@ -532,48 +550,79 @@ namespace blt
std::vector<pointer_view> unallocated_blocks; std::vector<pointer_view> unallocated_blocks;
}; };
/**
* Stores an index to a pointer_view along with the amount of memory leftover after the allocation
* it also stores the block being allocated to in question. The new inserted leftover should start at old_ptr + size
*/
struct block_view
{
block_storage* blk;
size_t index;
size_t leftover;
block_view(block_storage* blk, size_t index, size_t leftover): blk(blk), index(index), leftover(leftover)
{}
};
/**
* Allocate a new block of memory and push it to the back of blocks.
*/
inline void allocate_block() inline void allocate_block()
{ {
BLT_INFO("Allocating a new block of size %d", BLOCK_SIZE); //BLT_INFO("Allocating a new block of size %d", BLOCK_SIZE);
auto* blk = new block_storage(); auto* blk = new block_storage();
blk->data = static_cast<pointer>(malloc(sizeof(T) * BLOCK_SIZE)); blk->data = static_cast<pointer>(malloc(sizeof(T) * BLOCK_SIZE));
blocks.push_back(blk); blocks.push_back(blk);
} }
inline pointer find_available_block(size_t n) /**
* Searches for a free block inside the block storage with sufficient space and returns an optional view to it
* The optional will be empty if no open block can be found.
*/
inline std::optional<block_view> search_for_block(block_storage* blk, size_t n)
{ {
for (auto* blk : blocks)
{
size_t index = -1ull;
size_t leftover = 0;
for (auto kv : blt::enumerate(blk->unallocated_blocks)) for (auto kv : blt::enumerate(blk->unallocated_blocks))
{ {
if (kv.second.n >= n) if (kv.second.n >= n)
{ return block_view{blk, kv.first, kv.second.n - n};
index = kv.first;
leftover = kv.second.n - n;
break;
} }
} return {};
if (index != -1ull)
{
pointer_view ptr = blk->unallocated_blocks[index];
std::iter_swap(blk->unallocated_blocks.begin() + index, blk->unallocated_blocks.end() - 1);
blk->unallocated_blocks.pop_back();
// BLT_INFO("Found block! %d, Unallocated leftover %d", index, leftover);
if (leftover > 0)
blk->unallocated_blocks.push_back({ptr.p + n, leftover});
return ptr.p;
}
}
return nullptr;
} }
/**
* removes the block of memory from the unallocated_blocks storage in the underlying block, inserting a new unallocated block if
* there was any leftover. Returns a pointer to the beginning of the new block.
*/
inline pointer swap_pop_resize_if(const block_view& view, size_t n)
{
pointer_view ptr = view.blk->unallocated_blocks[view.index];
std::iter_swap(view.blk->unallocated_blocks.begin() + view.index, view.blk->unallocated_blocks.end() - 1);
view.blk->unallocated_blocks.pop_back();
if (view.leftover > 0)
view.blk->unallocated_blocks.push_back({ptr.p + n, view.leftover});
return ptr.p;
}
/**
* Finds the next available unallocated block of memory, or empty if there is none which meet size requirements
*/
inline std::optional<pointer> find_available_block(size_t n)
{
for (auto* blk : blocks)
{
if (auto view = search_for_block(blk, n))
return swap_pop_resize_if(view.value(), n);
}
return {};
}
/**
* returns a pointer to a block of memory along with an offset into that pointer that the requested block can be found at
*/
inline std::pair<pointer, size_t> getBlock(size_t n) inline std::pair<pointer, size_t> getBlock(size_t n)
{ {
auto* blk = find_available_block(n); if (auto blk = find_available_block(n))
if (blk != nullptr) return {blk.value(), 0};
return {blk, 0};
if (blocks.back()->used + n > BLOCK_SIZE) if (blocks.back()->used + n > BLOCK_SIZE)
allocate_block(); allocate_block();
@ -583,6 +632,9 @@ namespace blt
return ptr; return ptr;
} }
/**
* Calls the constructor on elements if they require construction, otherwise constructor will not be called and this function is useless
*/
inline void allocate_in_block(pointer begin, size_t n) inline void allocate_in_block(pointer begin, size_t n)
{ {
if constexpr (std::is_default_constructible_v<T> && !std::is_trivially_default_constructible_v<T>) if constexpr (std::is_default_constructible_v<T> && !std::is_trivially_default_constructible_v<T>)