Struct CpuLimiter 

pub struct CpuLimiter(/* private fields */);

A shared bound on concurrent CPU-heavy blocking jobs.

One CpuLimiter can be cloned and handed to many CogReaders and Tilers so the whole process (or a whole mosaic) shares a single CPU budget instead of each reader/tiler getting its own semaphore. Without this, a mosaic that opens N assets would allow N × available_parallelism decode jobs plus N independent warp pools, oversubscribing the machine and thrashing caches under load.

Cloning is cheap (an Arc bump); all clones draw permits from the same pool. Each default construction creates an independent pool sized to available parallelism, or four permits if that information is unavailable. Running blocking jobs retain their permits after request cancellation until they exit.

Deadlock-freedom invariant: a job must never hold one permit while awaiting a second from the same limiter. Acquire → spawn_blocking → drop must be flat, not nested. The tile pipeline upholds this by releasing a reader’s decode permit (inside its own spawn_blocking) before the warp/ render permit is acquired — see Tiler::run_tile_cpu.

Implementations

impl CpuLimiter

pub fn new(permits: usize) -> Self

Build an independent limiter allowing permits concurrent blocking jobs, clamped to 1..=tokio::sync::Semaphore::MAX_PERMITS.

pub fn available_permits(&self) -> usize

Current number of free permits (diagnostics/tests).

Trait Implementations

impl Clone for CpuLimiter

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 CpuLimiter

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

Formats the value using the given formatter.

impl Default for CpuLimiter

fn default() -> Self

Returns the “default value” for a type.