Struct HoldTimer 

pub struct HoldTimer { /* private fields */ }

Times one actor turn.

This clock is no longer optional (0.12.0, W1)

Until 0.11.0 the field was #[cfg(feature = "metrics")] and elapsed() returned Duration::ZERO in a default build: the reading existed only to feed ActorMetrics::record_hold’s histogram, so a build that did not keep the histogram had no reason to read a clock.

The chunk loop changed what the reading is for. A chunk’s measured hold is now the input to the next chunk’s size (connection::next_chunk_size, named in prose because it is private — D-144), which means it is a control signal in every build and not an observation in some of them. Left gated, bulk_import would have sized its chunks off Duration::ZERO — a value that reads as “comfortably under budget” — and grown every chunk to the ceiling, in exactly the builds nobody was measuring.

So the clock is unconditional and only the histogram is still gated: record_hold remains a no-op without the feature. What that costs is one Instant::now() pair per actor turn — tens of nanoseconds against a turn measured in microseconds at best, and the same reasoning §5.1.5 uses to decide that a channel hop is free beside a chunk.

It stays a type rather than a bare Instant::now() in the loop because the ordering guarantee in crate::connection’s Turn is attached to it.

Implementations

impl HoldTimer

pub fn start() -> Self

pub fn elapsed(&self) -> Duration