tf::TaggedHead128 Struct Reference

tagged free-list head using a 128-bit (pointer, version) pair More...

#include <taskflow/utility/object_pool.hpp>

Public Types
using	pointer_type = uintptr_t
	block address representation
using	tag_type = uintptr_t
	ABA version counter representation.

Public Member Functions
	TaggedHead128 ()=default
	constructs a null, zero-tagged head
	TaggedHead128 (pointer_type p, tag_type t) noexcept
	constructs a head with an explicit block address and version counter
pointer_type	get_ptr () const noexcept
	returns the stored block address
tag_type	get_tag () const noexcept
	returns the ABA version counter

Public Attributes
pointer_type	ptr {0}
	block address (reinterpret-cast to/from ObjectBlock*)
tag_type	tag {0}
	ABA version counter; incremented on every push and pop.

Detailed Description

tagged free-list head using a 128-bit (pointer, version) pair

TaggedHead128 stores the free-list head pointer and an ABA version counter as two independent 64-bit words, yielding a 16-byte representation. std::atomic<TaggedHead128> requires a 128-bit compare-and-swap: CMPXCHG16B on x86-64 or CASP on ARMv8.1+. On platforms that lack a native 128-bit CAS (e.g. RISC-V, baseline ARMv8.0), the atomic falls back to a lock-based implementation — still correct, but no longer lock-free.

The full 64-bit version counter makes ABA wrap-around effectively impossible under any realistic workload.

// explicitly select the 128-bit head (this is also the default)
tf::ObjectPool<MyTask, 5, tf::TaggedHead128> pool;

See also

TaggedHead64 for an 8-byte alternative that is lock-free on all 64-bit platforms at the cost of a narrower version counter.

Constructor & Destructor Documentation

TaggedHead128()

tf::TaggedHead128::TaggedHead128 ( pointer_type p, tag_type t )

inlinenoexcept

constructs a head with an explicit block address and version counter

Parameters

p	block address as uintptr_t
t	ABA version counter

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The documentation for this struct was generated from the following file:

• taskflow/utility/object_pool.hpp