MayaFlux::Memory::Seqlock Class Reference

Single-writer multiple-reader sequence lock for fixed-size data regions. More...

#include <SeqLock.hpp>

Collaboration diagram for MayaFlux::Memory::Seqlock:

Public Member Functions
void	begin_write () noexcept
	Begin a write: advances the counter to an odd value.
void	end_write () noexcept
	End a write: advances the counter back to an even value.
Seqlock &	operator= (const Seqlock &)=delete
Seqlock &	operator= (Seqlock &&)=delete
uint32_t	read_begin () const noexcept
	Begin a read: spin until the counter is even, return the snapshot.
bool	read_retry (uint32_t snapshot) const noexcept
	Check whether a write overlapped the read just completed.
	Seqlock () noexcept=default
	Seqlock (const Seqlock &)=delete
	Seqlock (Seqlock &&)=delete
uint32_t	sequence () const noexcept
	Return the raw sequence counter value.
	~Seqlock ()=default

Private Attributes
std::atomic< uint32_t >	m_seq { 0U }

Detailed Description

Single-writer multiple-reader sequence lock for fixed-size data regions.

Protects a data region that is written infrequently and read frequently. Readers never block writers; a reader that observes a write in progress simply retries. Writers are serialized externally (e.g. by the container's existing state machine or a higher-level mutex on the write path only).

Sequence counter convention: even — data is stable, safe to read odd — write in progress, readers must retry

Usage — writer side:

SeqlockWriteGuard guard(lock);
std::memcpy(dest, src, bytes);

Usage — reader side (unbounded):

uint32_t snap;
do {
    snap = lock.read_begin();
    // copy or sample the guarded data
} while (lock.read_retry(snap));

Usage — reader side (bounded, preferred in frame loops):

  auto result = seqlock_read(lock, max_attempts, [&]{ return read_data(); });
  if (!result) {
// stale read accepted or skip frame
}

Alignment to a cache line prevents false sharing when multiple Seqlock instances are stored in a contiguous array (e.g. one per texture layer).

Definition at line 44 of file SeqLock.hpp.

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

• SeqLock.hpp