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Fixed-size pool allocator
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#include <iostream> | |
#include <memory> | |
#include <atomic> | |
#include <cassert> | |
struct Node { | |
uint8_t* const data; | |
size_t const length; | |
Node* next; | |
}; | |
constexpr auto kMaxBlockSize = size_t { 1024 }; | |
constexpr auto kActualBufferSize = kMaxBlockSize - sizeof(Node); | |
auto get_memory_head() -> std::atomic<Node*>& { | |
static std::atomic<Node*> head { }; | |
return head; | |
} | |
auto get_block_count() -> std::atomic<int64_t>& { | |
static std::atomic<int64_t> count { 0 }; | |
return count; | |
} | |
auto heap_allocate_block() -> Node* { | |
auto* node = static_cast<Node*>(std::malloc(kMaxBlockSize)); | |
std::cout << "Allocated block from heap\n"; | |
return new (static_cast<void*>(node)) Node { | |
reinterpret_cast<uint8_t*>(node + 1), | |
kActualBufferSize, | |
nullptr | |
}; | |
} | |
auto pop_block() -> Node* { | |
auto* next_node = get_memory_head().load(); | |
if (!next_node) { | |
return next_node; | |
} | |
while (!get_memory_head().compare_exchange_strong(next_node, | |
next_node->next)) | |
{ | |
next_node = get_memory_head().load(); | |
if (!next_node) { | |
return next_node; | |
} | |
} | |
get_block_count().fetch_sub(1); | |
return next_node; | |
} | |
auto allocate_block() -> uint8_t* { | |
auto* next_node = pop_block(); | |
if (!next_node) { | |
next_node = heap_allocate_block(); | |
} | |
else { | |
std::cerr << "Used block from pool\n"; | |
} | |
return next_node->data; | |
} | |
auto push_block(Node* node) { | |
node->next = get_memory_head().load(); | |
while (!get_memory_head().compare_exchange_strong(node->next, | |
node)) | |
; | |
get_block_count().fetch_add(1); | |
std::cerr << "Pushed block back to the pool\n"; | |
} | |
auto deallocate_block(uint8_t* data) { | |
auto* node = reinterpret_cast<Node*>(data - sizeof(Node)); | |
if (get_block_count().load() > 1) { | |
std::free(node); | |
std::cerr << "Destroyed block\n"; | |
return; | |
} | |
push_block(node); | |
} | |
using DataPtr = std::unique_ptr<uint8_t, decltype(deallocate_block)&>; | |
auto main() -> int { | |
auto p1 = DataPtr { allocate_block(), deallocate_block }; | |
auto p2 = DataPtr { allocate_block(), deallocate_block }; | |
DataPtr { allocate_block(), deallocate_block }; | |
DataPtr { allocate_block(), deallocate_block }; | |
(void)p1; | |
(void)p2; | |
return 0; | |
} |
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