Function with_faer_par 

pub fn with_faer_par<R: Send>(
    token: Exec<'_>,
    f: impl FnOnce(Par<'_>) -> R + Send,
) -> R

Runs f with the parallelism faer should use for token.

A token that carries a team (minted by a threadteam::Team, or a child of one) and has more than one slot hands faer its own team as Par::Team: faer’s regions run on the reserved members as team sections, at the dispatch cost the floors were derived from. Any other token runs faer with Par::Seq on the calling thread and never enters a pool: only a team gives faer internal parallelism. Batch lanes still fork through threadteam before this point, so batch-level parallelism stays.

Examples

use std::num::NonZeroUsize;
let pool = threadteam::Pool::builder()
    .threads(2)
    .acquire_timeout(std::time::Duration::from_secs(10))
    .build()
    .unwrap();
// A token without a team runs faer sequentially.
let token = threadteam::Exec::new(&pool, 2).unwrap();
assert!(tcontract_exec::with_faer_par(token, |par| matches!(par, faer::Par::Seq)));
// A team token of two slots hands faer the team.
let team = pool.into_team(2).unwrap();
let token = team.exec(2);
assert!(tcontract_exec::with_faer_par(token, |par| matches!(par, faer::Par::Team(_))));
// One slot is sequential even on a team.
let one = team.exec(2).limit(NonZeroUsize::MIN);
assert!(tcontract_exec::with_faer_par(one, |par| matches!(par, faer::Par::Seq)));