Function measure 

pub fn measure(
    iterations: usize,
    operation: impl FnMut(),
) -> Result<Measurement, AlreadyMeasuring>

Measure a workload on this thread; nested scopes refuse before executing.

Setup, result formatting and other threads are excluded. Panics propagate, and an unwind guard disables accounting before returning control to the caller.

Errors

Returns AlreadyMeasuring when called from an active measurement.