Struct SyncStopper 

pub struct SyncStopper { /* private fields */ }

A cancellation primitive with Release/Acquire memory ordering.

Unlike Stopper, whose checks are Relaxed loads, SyncStopper guarantees that all writes before cancel() are visible to any clone that subsequently observes should_stop() == true.

Converts to StopToken via From/Into with zero overhead — the existing Arc is reused, not double-wrapped.

Performance

On x86-64 an Acquire load is an ordinary load, so a check costs what a Stopper’s does. On aarch64 it is ldar on targets without RCpc (Linux, Windows, Android, iOS) and ldapr with it (macOS): on a Neoverse-N1, a compute-bound loop checking every 64 bytes measured 3–10% slower than with a Relaxed check (code placement alone moved the same loop by similar amounts), and under 1% at a check per KiB or in memory-bound loops (benchmarks/stopper-ordering-2026-10-06.md). On ARMv6-M and ARMv7-M each check also executes a dmb. In a StopToken it is checked through the vtable.

Implementations

impl SyncStopper

pub fn new() -> Self

Create a new synchronized stopper.

pub fn cancelled() -> Self

Create a stopper that is already cancelled.

pub fn cancel(&self)

Cancel with a Release swap.

All memory writes before a cancel() are visible to any clone that observes should_stop() == true after it, even when several threads cancel.

pub fn is_cancelled(&self) -> bool

Check if cancelled with Acquire ordering.

If this returns true, all memory writes that happened before the corresponding cancel() call are guaranteed to be visible.

Trait Implementations

impl Clone for SyncStopper

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for SyncStopper

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for SyncStopper

fn default() -> Self

Returns the “default value” for a type.

impl From<SyncStopper> for StopToken

Reuses the SyncStopper’s Arc (no allocation); checks go through the vtable.

fn from(stopper: SyncStopper) -> Self

Converts to this type from the input type.

impl Stop for SyncStopper

fn check(&self) -> Result<(), StopReason>

Check if the operation should stop.

fn should_stop(&self) -> bool

Returns true if the operation should stop.

fn may_stop(&self) -> bool

Returns true if this stop can ever signal a stop.