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xo-alloc2: refactor - explicit AllocHeader class

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This commit is contained in:
Roland Conybeare 2025-12-16 11:43:41 -05:00
commit 92fc2a4961
10 changed files with 251 additions and 37 deletions
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167
include/xo/alloc2/alloc/AllocHeader.hpp Normal file
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@ -0,0 +1,167 @@
/** @file AllocHeader.hpp
*
* @author Roland Conybeare, Dec 2025
**/
#pragma once
#include <type_traits>
#include <cstdint>
#include <cstddef>
namespace xo {
namespace mm {
struct AllocHeader {
using repr_type = std::uintptr_t;
using size_type = std::size_t;
explicit AllocHeader(repr_type x) : repr_{x} {}
#ifdef OBSOLETE
std::uint32_t tseq(const AllocHeaderConfig & cfg) const noexcept {
return cfg.tseq(repr_);
}
std::uint32_t age(const AllocHeaderConfig & cfg) const noexcept {
return cfg.age(repr_);
}
size_type size(const AllocHeaderConfig & cfg) const noexcept {
return cfg.size(repr_);
}
#endif
repr_type repr_;
};
static_assert(sizeof(AllocHeader) == sizeof(AllocHeader::repr_type));
static_assert(std::is_standard_layout_v<AllocHeader>);
/*
* Each allocation is preceded by a 64-bit header.
* Header is split into 3 configurable-width bit fields,
* labelled (from hi to lo bit order) {tseq, age, size}.
*
* 1. tseq. seq# identifying object types; needed for gc.
* 2. gen. age cohort; increases when alloc survives gc.
* 3. size. alloc size.
*
* Arena allocator only uses size.
* X1 collector uses {tseq, gen, size}
*
* alloc header
*
* TTTTTTTTTTTTGGGGGZZZZZZZZZZZZ
* < tseq ><gen>< size >
*
* masking
*
* ..432107654321076543210 bit
*
* > < .gen_bits
* 0..............01111111 gen_mask_unshifted
* 0..011111110..........0 gen_mask_shifted
* > < gen_shift
*/
struct AllocHeaderConfig {
using repr_type = AllocHeader;
AllocHeaderConfig() = default;
AllocHeaderConfig(std::uint8_t t, std::uint8_t a, std::uint8_t z) noexcept
: tseq_bits_{t}, age_bits_{a}, size_bits_{z} {}
std::uint64_t tseq_mask() const noexcept {
// e.g.
// FF FF FF 00 00 00 00 00
// with tseq_bits=24, age_bits=8, size_bits=32
//
return ((1ul << tseq_bits_) - 1) << (age_bits_ + size_bits_);
}
std::uint64_t age_mask() const noexcept {
// e.g.
// 00 00 00 FF 00 00 00 00
// with age_bits=8, size_bits=32
//
return ((1ul << age_bits_) - 1) << size_bits_;
}
std::uint64_t size_mask() const noexcept {
// e.g.
// 00 00 00 00 FF FF FF FF
// with size_bits=32
//
return ((1ul << size_bits_) - 1);
}
/** extract type id from alloc header @p hdr **/
std::uint32_t tseq(repr_type hdr) const noexcept {
// e.g.
// 0x302010
// for header
// 30 20 10 -- -- -- -- --
// with tseq_bits_ = 24, age_bits_ + size_bits_ = 40
//
return (hdr.repr_ & tseq_mask()) >> (age_bits_ + size_bits_);
}
/** extract age from alloc header @p hdr **/
std::uint32_t age(repr_type hdr) const noexcept {
// e.g.
// 0xa0
// for header
// -- -- -- a0 -- -- -- --
// with age_bits_ = 8, size_bits_ = 32
//
return (hdr.repr_ & age_mask()) >> size_bits_;
}
/** extract size from alloc header @p hdr **/
std::size_t size(repr_type hdr) const noexcept {
// e.g.
// 0x01020300
// for header
// -- -- -- -- 01 02 03 00
// with size_bits_ = 32
//
return (hdr.repr_ & size_mask());
}
/** true iff sentinel tseq, flagging a forwarding pointer **/
bool is_forwarding_tseq(repr_type hdr) const noexcept {
// e.g.
// 0xFFFFFF
// i.e. header
// FF FF FF -- -- -- -- --
// with tseq_bits_ = 24, age_bits + size_bits_ = 40
//
return (hdr.repr_ & tseq_mask()) == tseq_mask();
}
bool is_size_enabled() const noexcept { return size_bits_ > 0; }
/** number of bits for tseq **/
std::uint8_t tseq_bits_ = 24;
/** number of bits for age **/
std::uint8_t age_bits_ = 8;
/** number of bits for size **/
std::uint8_t size_bits_ = 32;
};
struct AllocInfo {
using size_type = AllocHeader::size_type;
AllocInfo(const AllocHeaderConfig * p_cfg, const AllocHeader * p_hdr)
: p_config_{p_cfg}, p_header_{p_hdr} {}
std::uint32_t tseq() const noexcept { return p_config_->tseq(*p_header_); }
std::uint32_t age() const noexcept { return p_config_->age (*p_header_); }
size_type size() const noexcept { return p_config_->size(*p_header_); }
const AllocHeaderConfig * p_config_ = nullptr;
const AllocHeader * p_header_ = nullptr;
};
}
}
/* end AllocHeader.hpp */

5
include/xo/alloc2/arena/ArenaConfig.hpp
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@ -5,6 +5,7 @@
#pragma once
#include "alloc/AllocHeader.hpp"
#include "alloc/AllocatorError.hpp"
#include <string>
#include <cstdint>
@ -47,9 +48,13 @@ namespace xo {
* present in arena
**/
bool store_header_flag_ = false;
#ifdef OBSOLETE
/** number of bits to represent allocation size **/
std::uint64_t header_size_bits_ = 32;
std::uint64_t header_size_mask_ = (1ul << header_size_bits_) - 1;
#endif
/** configuration for per-alloc header **/
AllocHeaderConfig header_;
/** true to enable debug logging **/
bool debug_flag_ = false;

13
include/xo/alloc2/arena/DArena.hpp
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@ -10,17 +10,6 @@
namespace xo {
namespace mm {
/** **/
struct AllocHeader {
using repr_type = std::uint64_t;
explicit AllocHeader(repr_type x) : repr_{x} {}
repr_type repr_;
};
static_assert(sizeof(AllocHeader) == sizeof(AllocHeader::repr_type));
/** @class DArena
*
* @brief represent arena allocator state
@ -51,7 +40,7 @@ namespace xo {
/** @brief a contiguous memory range **/
using range_type = std::pair<value_type, value_type>;
/** @brief type for allocation header (if enabled) **/
using header_type = std::uint64_t;
using header_type = AllocHeader; //std::uint64_t;
///@}

9
include/xo/alloc2/gc/DX1Collector.hpp
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@ -8,6 +8,7 @@
#include "arena/ArenaConfig.hpp"
#include "arena/DArena.hpp"
#include "gc/generation.hpp"
#include "gc/object_age.hpp"
#include "gc/role.hpp"
#include <memory>
#include <array>
@ -40,6 +41,7 @@ namespace xo {
struct CollectorConfig {
using size_type = std::size_t;
#ifdef OBSOLETE // get from arena_config_.header_
/*
* alloc header
* TTTTTTTTTTTTGGGGGZZZZZZZZZZZZ
@ -63,6 +65,11 @@ namespace xo {
constexpr std::uint64_t tseq_shift() const;
constexpr std::uint64_t tseq_mask_unshifted() const;
constexpr std::uint64_t tseq_mask_shifted() const;
#endif
generation age2gen(object_age age) const noexcept {
return generation(age % n_survive_threshold_);
}
public:
// ----- Instance Variables -----
@ -175,7 +182,7 @@ namespace xo {
/** get allocation size from header **/
std::size_t header2size(header_type hdr) const noexcept;
/** get generation counter from alloc header **/
generation header2gen(header_type hdr) const noexcept;
object_age header2age(header_type hdr) const noexcept;
/** get tseq from alloc header **/
uint32_t header2tseq(header_type hdr) const noexcept;

32
include/xo/alloc2/gc/object_age.hpp Normal file
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@ -0,0 +1,32 @@
/** @file object_age.hpp
*
* @author Roland Conybeare, Dec 2025
**/
#pragma once
#include <cstdint>
namespace xo {
namespace mm {
/** hard maximum remembered object age **/
static constexpr uint32_t c_max_object_age = 127;
/** @class object_age
* @brief type-safe object age
*
* Object age measured in number of garbage collections survived.
**/
struct object_age {
using value_type = std::uint32_t;
explicit object_age(value_type x) : value_{x} {}
operator value_type() const { return value_; }
std::uint32_t value_;
};
}
}
/* end object_age.hpp */

27
src/alloc2/DX1Collector.cpp
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@ -7,6 +7,7 @@
#include "arena/IAllocator_DArena.hpp"
#include "gc/DX1Collector.hpp"
#include "gc/generation.hpp"
#include "gc/object_age.hpp"
#include <xo/facet/obj.hpp>
#include <cassert>
#include <cstdint>
@ -23,6 +24,7 @@ namespace xo {
}
#endif
#ifdef OBSOLETE
constexpr std::uint64_t
CollectorConfig::gen_shift() const {
return arena_config_.header_size_bits_;
@ -37,6 +39,7 @@ namespace xo {
CollectorConfig::gen_mask_shifted() const {
return gen_mask_unshifted() << arena_config_.header_size_bits_;
}
#endif
#ifdef NOT_USING
constexpr std::uint64_t
@ -45,6 +48,7 @@ namespace xo {
}
#endif
#ifdef OBSOLETE
constexpr std::uint64_t
CollectorConfig::tseq_shift() const {
return gen_bits_ + arena_config_.header_size_bits_;
@ -59,6 +63,7 @@ namespace xo {
CollectorConfig::tseq_mask_shifted() const {
return tseq_mask_unshifted() << (gen_bits_ + arena_config_.header_size_bits_);
}
#endif
// ----- GCRunState -----
@ -84,7 +89,9 @@ namespace xo {
DX1Collector::DX1Collector(const CollectorConfig & cfg) : config_{cfg}
{
assert(config_.arena_config_.header_size_bits_ + config_.gen_bits_ + config_.tseq_bits_ <= 64);
assert(config_.arena_config_.header_.size_bits_ +
config_.arena_config_.header_.age_bits_ +
config_.arena_config_.header_.tseq_bits_ <= 64);
for (uint32_t igen = 0, ngen = cfg.n_generation_; igen < ngen; ++igen) {
space_storage_[0][igen] = DArena::map(cfg.arena_config_);
@ -177,25 +184,25 @@ namespace xo {
size_type
DX1Collector::header2size(header_type hdr) const noexcept
{
uint32_t z = (hdr & config_.arena_config_.header_size_mask_);
uint32_t z = config_.arena_config_.header_.size(hdr);
return z;
}
generation
DX1Collector::header2gen(header_type hdr) const noexcept
object_age
DX1Collector::header2age(header_type hdr) const noexcept
{
uint32_t g = (hdr & config_.gen_mask_shifted()) >> config_.gen_shift();
uint32_t age = config_.arena_config_.header_.age(hdr);
assert(g < c_max_generation);
assert(age < c_max_object_age);
return generation(g);
return object_age(age);
}
uint32_t
DX1Collector::header2tseq(header_type hdr) const noexcept
{
uint32_t tseq = (hdr & config_.tseq_mask_shifted()) >> config_.tseq_shift();
uint32_t tseq = config_.arena_config_.header_.tseq(hdr);
return tseq;
}
@ -203,8 +210,8 @@ namespace xo {
bool
DX1Collector::is_forwarding_header(header_type hdr) const noexcept
{
/** all 1 bits to flag forwarding pointer **/
return header2tseq(hdr) == config_.tseq_mask_shifted();
/** forwarding pointer encoded as sentinel tseq **/
return config_.arena_config_.header_.is_forwarding_tseq(hdr);
}
auto

4
src/alloc2/IAllocator_DArena.cpp
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@ -331,7 +331,7 @@ namespace xo {
if (store_header_flag)
{
if ((s.config_.header_size_mask_ & z0) == z0) [[likely]] {
if (s.config_.header_.is_size_enabled()) [[likely]] {
hz = sizeof(header);
} else {
/* req_z doesn't fit in configured header_size_mask bits */
@ -362,7 +362,7 @@ namespace xo {
/* and rembering for subsequent
* sub_alloc()
*/
s.last_header_ = (uint64_t *)s.free_;
s.last_header_ = (AllocHeader *)s.free_;
}
}

6
src/alloc2/ICollector_DX1Collector.cpp
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@ -118,7 +118,7 @@ namespace xo {
DArena::header_type alloc_hdr = *p_header;
/* recover allocation size */
std::size_t alloc_z = some_arena->config_.header_size_mask_ & alloc_hdr;
std::size_t alloc_z = some_arena->config_.header_.size(alloc_hdr);
/* need to be able to fit forwarding pointer
* in place of forwarded object.
@ -176,7 +176,9 @@ namespace xo {
// reversed: forwarding pointers are located in from-space and
// refer to to-space.
generation g = d.header2gen(alloc_hdr);
object_age age = d.header2age(alloc_hdr);
generation g = d.config_.age2gen(age);
assert(d.runstate_.is_running());

9
utest/Collector.test.cpp
View file

@ -25,6 +25,7 @@ namespace xo {
using xo::mm::CollectorConfig;
using xo::mm::DX1Collector;
using xo::mm::ArenaConfig;
using xo::mm::AllocHeaderConfig;
using xo::mm::generation;
using xo::mm::c_max_generation;
using xo::facet::with_facet;
@ -53,7 +54,7 @@ namespace xo {
ArenaConfig arena_cfg = { .name_ = "_test_unused",
.size_ = 4*1024*1024,
.store_header_flag_ = true,
.header_size_mask_ = 0x0000ffff, };
.header_ = AllocHeaderConfig(0, 0, 16), };
CollectorConfig cfg = { .arena_config_ = arena_cfg,
.n_generation_ = 2,
.gc_trigger_v_ = {{64*1024, 1024*1024, 0, 0,
@ -97,7 +98,7 @@ namespace xo {
ArenaConfig arena_cfg = { .name_ = "_test_unused",
.size_ = 4*1024*1024,
.store_header_flag_ = true,
.header_size_mask_ = 0x0000ffff, };
.header_ = AllocHeaderConfig(0, 0, 16), };
CollectorConfig cfg = { .arena_config_ = arena_cfg,
.n_generation_ = 2,
.gc_trigger_v_ = {{64*1024, 1024*1024, 0, 0,
@ -119,7 +120,7 @@ namespace xo {
ArenaConfig arena_cfg = { .name_ = "_test_unused",
.size_ = 4*1024*1024,
.store_header_flag_ = true,
.header_size_mask_ = 0x0000ffff, };
.header_ = AllocHeaderConfig(0, 0, 16), };
CollectorConfig cfg = { .arena_config_ = arena_cfg,
.n_generation_ = 2,
.gc_trigger_v_ = {{64*1024, 1024*1024, 0, 0,
@ -141,7 +142,7 @@ namespace xo {
ArenaConfig arena_cfg = { .name_ = "_test_unused",
.size_ = 4*1024*1024,
.store_header_flag_ = true,
.header_size_mask_ = 0x0000ffff, };
.header_ = AllocHeaderConfig(0, 0, 16), };
/* collector with one generation collapses to a non-generational copying collector */
CollectorConfig cfg = { .arena_config_ = arena_cfg,

16
utest/arena.test.cpp
View file

@ -20,7 +20,9 @@ namespace xo {
using xo::mm::IAllocator_Xfer;
using xo::mm::AllocatorError;
using xo::mm::DArena;
using xo::mm::AllocHeaderConfig;
using xo::mm::ArenaConfig;
using xo::mm::AllocHeader;
using xo::mm::padding;
using xo::mm::error;
using xo::facet::obj;
@ -176,14 +178,14 @@ namespace xo {
TEST_CASE("allocator-alloc-2", "[alloc2][Allocator]")
{
using header_type = AAllocator::header_type;
using header_type = AllocHeader;
/* typed allocator a1o, with object header */
ArenaConfig cfg { .name_ = "testarena",
.size_ = 64*1024,
.store_header_flag_ = true,
/* up to 4GB */
.header_size_mask_ = 0xffffffff,
.header_ = AllocHeaderConfig(0, 0, 32),
.debug_flag_ = false,
};
DArena arena = DArena::map(cfg);
@ -202,7 +204,8 @@ namespace xo {
header_type* header = (header_type*)(m0 - sizeof(header_type));
REQUIRE(a1o.contains(header));
REQUIRE(((*header) & cfg.header_size_mask_) == padding::with_padding(z0));
REQUIRE(cfg.header_.size(*header) == padding::with_padding(z0));
//REQUIRE(((*header) & cfg.header_size_mask_) == padding::with_padding(z0));
REQUIRE(a1o.last_error().error_ == error::none);
REQUIRE(a1o.last_error().error_seq_ == 0);
REQUIRE(a1o.allocated() >= z0);
@ -214,7 +217,7 @@ namespace xo {
TEST_CASE("allocator-alloc-3", "[alloc2][Allocator]")
{
using header_type = AAllocator::header_type;
using header_type = AllocHeader;
/* typed allocator a1o, with object header + guard bytes */
ArenaConfig cfg { .name_ = "testarena",
@ -223,7 +226,7 @@ namespace xo {
.guard_byte_ = 0xfd,
.store_header_flag_ = true,
/* up to 4GB */
.header_size_mask_ = 0xffffffff,
.header_ = AllocHeaderConfig(0, 0, 32),
.debug_flag_ = false,
};
DArena arena = DArena::map(cfg);
@ -254,7 +257,8 @@ namespace xo {
REQUIRE(a1o.contains(guard0));
REQUIRE(a1o.contains(header));
REQUIRE(((*header) & cfg.header_size_mask_) == padding::with_padding(z0));
REQUIRE(cfg.header_.size(*header) == padding::with_padding(z0));
//REQUIRE(((*header) & cfg.header_size_mask_) == padding::with_padding(z0));
REQUIRE(a1o.last_error().error_ == error::none);
REQUIRE(a1o.last_error().error_seq_ == 0);