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Make allocate take a template type

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So we use the right alignment
This commit is contained in:
Andrew Noyes
2025-08-15 13:31:45 -04:00
parent 52f0eeee1f
commit 8e33b477eb
5 changed files with 117 additions and 63 deletions
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2
benchmarks/bench_arena_allocator.cpp
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@@ -16,7 +16,7 @@ int main() {
// Arena allocator benchmark
ArenaAllocator arena;
bench.run("ArenaAllocator", [&] {
void *ptr = arena.allocate(alloc_size);
void *ptr = arena.allocate_raw(alloc_size);
ankerl::nanobench::doNotOptimizeAway(ptr);
});
}

4
src/arena_allocator.cpp
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@@ -67,7 +67,7 @@ void ArenaAllocator::reset() {
void *ArenaAllocator::realloc(void *ptr, size_t old_size, size_t new_size,
size_t alignment) {
if (ptr == nullptr) {
return allocate(new_size, alignment);
return allocate_raw(new_size, alignment);
}
if (new_size == old_size) {
@@ -119,7 +119,7 @@ void *ArenaAllocator::realloc(void *ptr, size_t old_size, size_t new_size,
}
// Growing but can't extend in place - need to allocate new space and copy
void *new_ptr = allocate(new_size, alignment);
void *new_ptr = allocate_raw(new_size, alignment);
if (new_ptr && ptr) {
// Copy all the old data since we're growing
std::memcpy(new_ptr, ptr, old_size);

67
src/arena_allocator.hpp
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@@ -150,12 +150,14 @@ public:
ArenaAllocator &operator=(ArenaAllocator &&other) noexcept;
/**
* @brief Allocate memory with the specified size and alignment.
* @brief Allocate raw memory with the specified size and alignment.
*
* This is the core allocation method providing ~1ns allocation performance.
* It performs lazy initialization on first use and automatically grows
* the arena when needed using geometric growth (doubling block sizes).
*
* For type-safe allocation, prefer the allocate<T>() template method.
*
* @param size Number of bytes to allocate (0 returns nullptr)
* @param alignment Required alignment (default: alignof(std::max_align_t))
* @return Pointer to allocated memory, or nullptr if size is 0
@@ -168,10 +170,10 @@ public:
*
* ## Example:
* ```cpp
* void* ptr1 = arena.allocate(100); // Default alignment
* void* ptr2 = arena.allocate(64, 16); // 16-byte aligned
* void* ptr1 = arena.allocate_raw(100); // Default alignment
* void* ptr2 = arena.allocate_raw(64, 16); // 16-byte aligned
* MyStruct* ptr3 = static_cast<MyStruct*>(
* arena.allocate(sizeof(MyStruct), alignof(MyStruct)));
* arena.allocate_raw(sizeof(MyStruct), alignof(MyStruct)));
* ```
*
* ## Performance Note:
@@ -179,7 +181,8 @@ public:
* The allocation path is extremely hot and inlining eliminates function
* call overhead, allowing the ~1ns allocation performance.
*/
void *allocate(size_t size, size_t alignment = alignof(std::max_align_t)) {
void *allocate_raw(size_t size,
size_t alignment = alignof(std::max_align_t)) {
if (size == 0) {
return nullptr;
}
@@ -288,10 +291,60 @@ public:
"ArenaAllocator::construct requires trivially destructible types. "
"Objects constructed in the arena will not have their destructors "
"called.");
void *ptr = allocate(sizeof(T), alignof(T));
void *ptr = allocate_raw(sizeof(T), alignof(T));
return new (ptr) T(std::forward<Args>(args)...);
}
/**
* @brief Allocate space for an array of size T objects with proper alignment.
*
* This is a type-safe convenience method that combines sizing and alignment
* calculations for allocating arrays of type T. It's preferred over calling
* allocate_raw() directly as it prevents common errors with size calculations
* and alignment requirements.
*
* @tparam T The type of objects to allocate space for (must be trivially
* destructible)
* @param size Number of T objects to allocate space for
* @return Pointer to allocated memory suitable for constructing an array of T
* objects
* @throws std::bad_alloc if memory allocation fails
*
* ## Type Requirements:
* T must be trivially destructible (std::is_trivially_destructible_v<T>).
* This ensures consistency with the arena allocator's design where
* destructors are never called.
*
* ## Example:
* ```cpp
* // Allocate space for 100 integers
* int* numbers = arena.allocate<int>(100);
*
* // Allocate space for 50 POD structs
* MyPOD* objects = arena.allocate<MyPOD>(50);
*
* // Initialize some elements (no automatic construction)
* numbers[0] = 42;
* new (&objects[0]) MyPOD(arg1, arg2);
* ```
*
* ## Note:
* This method only allocates memory - it does not construct objects.
* Use placement new or other initialization methods as needed.
*/
template <typename T> T *allocate(size_t size) {
static_assert(
std::is_trivially_destructible_v<T>,
"ArenaAllocator::allocate requires trivially destructible types. "
"Objects allocated in the arena will not have their destructors "
"called.");
if (size == 0) {
return nullptr;
}
void *ptr = allocate_raw(sizeof(T) * size, alignof(T));
return static_cast<T *>(ptr);
}
/**
* @brief Reset the allocator to reuse the first block, freeing all others.
*
@@ -542,7 +595,7 @@ public:
T *allocate(size_type n) {
if (n == 0)
return nullptr;
return static_cast<T *>(arena_->allocate(n * sizeof(T), alignof(T)));
return static_cast<T *>(arena_->allocate_raw(n * sizeof(T), alignof(T)));
}
void deallocate(T *ptr, size_type n) noexcept {

4
src/commit_request.cpp
View File

@@ -45,7 +45,7 @@ std::string_view CommitRequest::store_string(std::string_view str) {
return {};
}
char *arena_str = static_cast<char *>(arena_.allocate(str.size()));
char *arena_str = arena_.allocate<char>(str.size());
std::memcpy(arena_str, str.data(), str.size());
return std::string_view(arena_str, str.size());
@@ -78,7 +78,7 @@ std::string_view CommitRequest::decode_base64(std::string_view base64_str) {
return {};
}
char *output = static_cast<char *>(arena_.allocate(output_len));
char *output = arena_.allocate<char>(output_len);
if (!output) {
return {};
}

103
tests/test_arena_allocator.cpp
View File

@@ -24,20 +24,20 @@ TEST_CASE("ArenaAllocator basic allocation") {
ArenaAllocator arena;
SUBCASE("allocate zero bytes returns nullptr") {
void *ptr = arena.allocate(0);
void *ptr = arena.allocate_raw(0);
CHECK(ptr == nullptr);
CHECK(arena.used_bytes() == 0);
}
SUBCASE("allocate single byte") {
void *ptr = arena.allocate(1);
void *ptr = arena.allocate_raw(1);
CHECK(ptr != nullptr);
CHECK(arena.used_bytes() >= 1);
}
SUBCASE("allocate multiple bytes") {
void *ptr1 = arena.allocate(100);
void *ptr2 = arena.allocate(200);
void *ptr1 = arena.allocate_raw(100);
void *ptr2 = arena.allocate_raw(200);
CHECK(ptr1 != nullptr);
CHECK(ptr2 != nullptr);
@@ -50,24 +50,24 @@ TEST_CASE("ArenaAllocator alignment") {
ArenaAllocator arena;
SUBCASE("default alignment") {
void *ptr = arena.allocate(1);
void *ptr = arena.allocate_raw(1);
CHECK(reinterpret_cast<uintptr_t>(ptr) % alignof(std::max_align_t) == 0);
}
SUBCASE("custom alignment") {
void *ptr8 = arena.allocate(1, 8);
void *ptr8 = arena.allocate_raw(1, 8);
CHECK(reinterpret_cast<uintptr_t>(ptr8) % 8 == 0);
void *ptr16 = arena.allocate(1, 16);
void *ptr16 = arena.allocate_raw(1, 16);
CHECK(reinterpret_cast<uintptr_t>(ptr16) % 16 == 0);
void *ptr32 = arena.allocate(1, 32);
void *ptr32 = arena.allocate_raw(1, 32);
CHECK(reinterpret_cast<uintptr_t>(ptr32) % 32 == 0);
}
SUBCASE("alignment with larger allocations") {
ArenaAllocator fresh_arena;
void *ptr = fresh_arena.allocate(100, 64);
void *ptr = fresh_arena.allocate_raw(100, 64);
CHECK(reinterpret_cast<uintptr_t>(ptr) % 64 == 0);
}
}
@@ -76,23 +76,23 @@ TEST_CASE("ArenaAllocator block management") {
ArenaAllocator arena(128);
SUBCASE("single block allocation") {
void *ptr = arena.allocate(64);
void *ptr = arena.allocate_raw(64);
CHECK(ptr != nullptr);
CHECK(arena.num_blocks() == 1);
CHECK(arena.used_bytes() == 64);
}
SUBCASE("multiple blocks when size exceeded") {
void *ptr1 = arena.allocate(100);
void *ptr1 = arena.allocate_raw(100);
CHECK(arena.num_blocks() == 1);
void *ptr2 = arena.allocate(50);
void *ptr2 = arena.allocate_raw(50);
CHECK(arena.num_blocks() == 2);
CHECK(ptr1 != ptr2);
}
SUBCASE("allocation larger than block size grows arena") {
void *ptr = arena.allocate(200);
void *ptr = arena.allocate_raw(200);
CHECK(ptr != nullptr);
CHECK(arena.num_blocks() == 1);
}
@@ -145,8 +145,8 @@ TEST_CASE("ArenaAllocator construct template") {
TEST_CASE("ArenaAllocator reset functionality") {
ArenaAllocator arena;
arena.allocate(100);
arena.allocate(200);
arena.allocate_raw(100);
arena.allocate_raw(200);
size_t used_before = arena.used_bytes();
CHECK(used_before > 0);
@@ -154,7 +154,7 @@ TEST_CASE("ArenaAllocator reset functionality") {
CHECK(arena.used_bytes() == 0);
CHECK(arena.num_blocks() >= 1);
void *ptr = arena.allocate(50);
void *ptr = arena.allocate_raw(50);
CHECK(ptr != nullptr);
CHECK(arena.used_bytes() == 50);
}
@@ -163,14 +163,15 @@ TEST_CASE("ArenaAllocator reset memory leak test") {
ArenaAllocator arena(32); // Smaller initial size
// Force multiple blocks
arena.allocate(30); // First block (32 bytes)
arena.allocate_raw(30); // First block (32 bytes)
CHECK(arena.num_blocks() == 1);
arena.allocate(30); // Should create second block (64 bytes due to doubling)
arena.allocate_raw(
30); // Should create second block (64 bytes due to doubling)
CHECK(arena.num_blocks() == 2);
arena.allocate(100); // Should create third block (128 bytes due to doubling,
// or larger for 100)
arena.allocate_raw(100); // Should create third block (128 bytes due to
// doubling, or larger for 100)
CHECK(arena.num_blocks() == 3);
size_t total_before = arena.total_allocated();
@@ -185,7 +186,7 @@ TEST_CASE("ArenaAllocator reset memory leak test") {
CHECK(arena.used_bytes() == 0);
// Should be able to use the first block again
void *ptr = arena.allocate(20);
void *ptr = arena.allocate_raw(20);
CHECK(ptr != nullptr);
CHECK(arena.used_bytes() == 20);
}
@@ -197,14 +198,14 @@ TEST_CASE("ArenaAllocator memory tracking") {
CHECK(arena.used_bytes() == 0);
CHECK(arena.available_in_current_block() == 0);
arena.allocate(100);
arena.allocate_raw(100);
CHECK(arena.used_bytes() >= 100);
CHECK(arena.available_in_current_block() <= 412);
arena.allocate(400);
arena.allocate_raw(400);
CHECK(arena.num_blocks() == 1);
arena.allocate(50);
arena.allocate_raw(50);
CHECK(arena.num_blocks() == 2);
CHECK(arena.total_allocated() >= 1024);
}
@@ -215,7 +216,7 @@ TEST_CASE("ArenaAllocator stress test") {
SUBCASE("many small allocations") {
std::vector<void *> ptrs;
for (int i = 0; i < 1000; ++i) {
void *ptr = arena.allocate(8);
void *ptr = arena.allocate_raw(8);
CHECK(ptr != nullptr);
ptrs.push_back(ptr);
}
@@ -227,8 +228,8 @@ TEST_CASE("ArenaAllocator stress test") {
SUBCASE("alternating small and large allocations") {
for (int i = 0; i < 50; ++i) {
void *small_ptr = arena.allocate(16);
void *large_ptr = arena.allocate(256);
void *small_ptr = arena.allocate_raw(16);
void *large_ptr = arena.allocate_raw(256);
CHECK(small_ptr != nullptr);
CHECK(large_ptr != nullptr);
CHECK(small_ptr != large_ptr);
@@ -238,7 +239,7 @@ TEST_CASE("ArenaAllocator stress test") {
TEST_CASE("ArenaAllocator move semantics") {
ArenaAllocator arena1(512);
arena1.allocate(100);
arena1.allocate_raw(100);
size_t used_bytes = arena1.used_bytes();
size_t num_blocks = arena1.num_blocks();
@@ -246,25 +247,25 @@ TEST_CASE("ArenaAllocator move semantics") {
CHECK(arena2.used_bytes() == used_bytes);
CHECK(arena2.num_blocks() == num_blocks);
void *ptr = arena2.allocate(50);
void *ptr = arena2.allocate_raw(50);
CHECK(ptr != nullptr);
}
TEST_CASE("ArenaAllocator edge cases") {
SUBCASE("very small block size") {
ArenaAllocator arena(16);
void *ptr = arena.allocate(8);
void *ptr = arena.allocate_raw(8);
CHECK(ptr != nullptr);
CHECK(arena.num_blocks() == 1);
}
SUBCASE("allocation exactly block size") {
ArenaAllocator arena(64);
void *ptr = arena.allocate(64);
void *ptr = arena.allocate_raw(64);
CHECK(ptr != nullptr);
CHECK(arena.num_blocks() == 1);
void *ptr2 = arena.allocate(1);
void *ptr2 = arena.allocate_raw(1);
CHECK(ptr2 != nullptr);
CHECK(arena.num_blocks() == 2);
}
@@ -272,7 +273,7 @@ TEST_CASE("ArenaAllocator edge cases") {
SUBCASE("multiple resets") {
ArenaAllocator arena;
for (int i = 0; i < 10; ++i) {
arena.allocate(100);
arena.allocate_raw(100);
arena.reset();
CHECK(arena.used_bytes() == 0);
}
@@ -308,19 +309,19 @@ TEST_CASE("ArenaAllocator geometric growth policy") {
ArenaAllocator arena(64);
SUBCASE("normal geometric growth doubles size") {
arena.allocate(60); // Fill first block
arena.allocate_raw(60); // Fill first block
size_t initial_total = arena.total_allocated();
arena.allocate(10); // Force new block
arena.allocate_raw(10); // Force new block
CHECK(arena.num_blocks() == 2);
CHECK(arena.total_allocated() == initial_total + 128); // 64 * 2 = 128
}
SUBCASE("large allocation creates appropriately sized block") {
arena.allocate(60); // Fill first block
arena.allocate_raw(60); // Fill first block
size_t initial_total = arena.total_allocated();
arena.allocate(200); // Force large block
arena.allocate_raw(200); // Force large block
CHECK(arena.num_blocks() == 2);
CHECK(arena.total_allocated() >= initial_total + 200); // At least 200 bytes
}
@@ -329,7 +330,7 @@ TEST_CASE("ArenaAllocator geometric growth policy") {
size_t allocation_size = 32;
for (int i = 0; i < 10; ++i) {
arena.allocate(allocation_size);
arena.allocate_raw(allocation_size);
}
// Should have grown logarithmically, not linearly
@@ -341,8 +342,8 @@ TEST_CASE("ArenaAllocator alignment edge cases") {
ArenaAllocator arena;
SUBCASE("unaligned then aligned allocation") {
void *ptr1 = arena.allocate(1, 1);
void *ptr2 = arena.allocate(8, 8);
void *ptr1 = arena.allocate_raw(1, 1);
void *ptr2 = arena.allocate_raw(8, 8);
CHECK(ptr1 != nullptr);
CHECK(ptr2 != nullptr);
@@ -351,7 +352,7 @@ TEST_CASE("ArenaAllocator alignment edge cases") {
SUBCASE("large alignment requirements") {
ArenaAllocator fresh_arena;
void *ptr = fresh_arena.allocate(1, 128);
void *ptr = fresh_arena.allocate_raw(1, 128);
CHECK(ptr != nullptr);
CHECK(reinterpret_cast<uintptr_t>(ptr) % 128 == 0);
}
@@ -364,7 +365,7 @@ TEST_CASE("ArenaAllocator realloc functionality") {
// realloc with new_size == 0 returns nullptr and reclaims memory if it's
// the last allocation
ArenaAllocator fresh_arena(256);
void *ptr = fresh_arena.allocate(100);
void *ptr = fresh_arena.allocate_raw(100);
size_t used_before = fresh_arena.used_bytes();
CHECK(used_before == 100);
@@ -374,8 +375,8 @@ TEST_CASE("ArenaAllocator realloc functionality") {
// Test case where it's NOT the last allocation - memory cannot be reclaimed
ArenaAllocator arena2(256);
void *ptr1 = arena2.allocate(50);
void *ptr2 = arena2.allocate(50);
void *ptr1 = arena2.allocate_raw(50);
void *ptr2 = arena2.allocate_raw(50);
size_t used_before2 = arena2.used_bytes();
CHECK(used_before2 >= 100); // At least 100 bytes due to potential alignment
@@ -397,7 +398,7 @@ TEST_CASE("ArenaAllocator realloc functionality") {
SUBCASE("in-place extension - growing") {
ArenaAllocator fresh_arena(1024);
void *ptr = fresh_arena.allocate(100);
void *ptr = fresh_arena.allocate_raw(100);
CHECK(ptr != nullptr);
// Fill the allocation with test data
@@ -418,7 +419,7 @@ TEST_CASE("ArenaAllocator realloc functionality") {
SUBCASE("in-place shrinking") {
ArenaAllocator fresh_arena(1024);
void *ptr = fresh_arena.allocate(200);
void *ptr = fresh_arena.allocate_raw(200);
std::memset(ptr, 0xCD, 200);
// Should shrink in place
@@ -437,11 +438,11 @@ TEST_CASE("ArenaAllocator realloc functionality") {
ArenaAllocator fresh_arena(256); // Larger block to avoid edge cases
// Allocate first chunk
void *ptr1 = fresh_arena.allocate(60);
void *ptr1 = fresh_arena.allocate_raw(60);
std::memset(ptr1, 0x11, 60);
// Allocate second chunk (this prevents in-place extension of ptr1)
void *ptr2 = fresh_arena.allocate(30);
void *ptr2 = fresh_arena.allocate_raw(30);
std::memset(ptr2, 0x22, 30);
// Try to reallocate ptr1 - should copy since ptr2 is now the last
@@ -472,7 +473,7 @@ TEST_CASE("ArenaAllocator realloc functionality") {
ArenaAllocator fresh_arena(100);
// Allocate almost all space
void *ptr = fresh_arena.allocate(90);
void *ptr = fresh_arena.allocate_raw(90);
std::memset(ptr, 0x33, 90);
// Try to extend beyond block size - should copy to new block
@@ -491,7 +492,7 @@ TEST_CASE("ArenaAllocator realloc functionality") {
ArenaAllocator fresh_arena(1024);
// Allocate with specific alignment
void *ptr = fresh_arena.allocate(50, 16);
void *ptr = fresh_arena.allocate_raw(50, 16);
CHECK(reinterpret_cast<uintptr_t>(ptr) % 16 == 0);
std::memset(ptr, 0x44, 50);
@@ -509,7 +510,7 @@ TEST_CASE("ArenaAllocator realloc functionality") {
SUBCASE("realloc stress test") {
ArenaAllocator fresh_arena(512);
void *ptr = fresh_arena.allocate(50);
void *ptr = fresh_arena.allocate_raw(50);
size_t current_size = 50;
// Fill with pattern