Trait WatermarkHandler 

pub trait WatermarkHandler: Send + Sync {
    // Required methods
    fn on_warn(&self, event: WatermarkEvent);
    fn on_critical(&self, event: WatermarkEvent);
    fn on_oom(&self, event: WatermarkEvent);
}

Callback handler invoked on threshold crossings and on OOM.

Implementations must be cheap — they run on the allocation hot path. Set a flag, write to a non-blocking channel, or increment a metric; avoid blocking I/O.

Panic safety

Handler methods MUST NOT panic. If on_warn / on_critical panics after the inner allocator has already issued a block, Watermark unwinds out of allocate without returning the block to the caller — the slot is carved on the inner allocator and the allocated counter has been incremented, but the caller never receives the pointer and so can never free it. The block is leaked for the lifetime of the inner allocator. If on_oom panics, the caller’s AllocError is replaced by the panic; no block was issued and the counters are unchanged, so this case is consistent but noisier.

If your handler can fail (e.g. it writes to a possibly-full channel), absorb the failure inside the handler — set a flag, log, silently drop the event — rather than letting it escape. Treat handler-level panics as a fatal bug in your monitoring code.

Required Methods

fn on_warn(&self, event: WatermarkEvent)

Called once per crossing of the warn_pct threshold (rising edge).

fn on_critical(&self, event: WatermarkEvent)

Called once per crossing of the critical_pct threshold (rising edge).

fn on_oom(&self, event: WatermarkEvent)

Called when an allocation returns AllocError.

Dyn Compatibility

This trait is dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors

impl WatermarkHandler for LogHandler

Available on crate feature std only.

impl WatermarkHandler for NullHandler

impl<F> WatermarkHandler for FnHandler<F>

where F: Fn(WatermarkEvent) + Send + Sync,