SeqlockSnapshot.h File Reference

Single-writer / many-reader coherent snapshot of a POD value. More...

#include <atomic>
#include <climits>
#include <cstddef>
#include <cstdint>
#include <cstring>
#include <type_traits>
#include "OsAbstraction.h"
#include "OsUtility.h"

Go to the source code of this file.

Classes
class	hf::SnapshotReader< T >
class	hf::SnapshotWriter< T >
class	hf::SeqlockSnapshot< T >

Namespaces
namespace	hf

Detailed Description

Single-writer / many-reader coherent snapshot of a POD value.

Three types in one header:

• hf::SnapshotReader<T> — pure-virtual read-side ABC.
• hf::SnapshotWriter<T> — pure-virtual write-side ABC.
• hf::SeqlockSnapshot<T> — concrete impl deriving from both.

Algorithm

Writer: bumps seq_ to odd → memcpy T payload → bumps seq_ to even. Reader: snapshots seq_ → memcpy payload → re-reads seq_; retry while the start seq was odd or the two reads differ.

Thread-safety

• Single writer assumed (Publish not safe to call concurrently from multiple writers; protect externally if ever needed).
• Many readers — Read is wait-free in the absence of writes and bounded-retry under contention.
• Optional waiter: backed by a lazily-created FreeRTOS event group; WaitForChange is task-context only.

Allocation

No heap allocation. Inline T storage; event group created on first WaitForChange / ClearWaitEvent use.

Constraints

T must be trivially copyable.