Rust - Instant now, elapsed Example

Instant now. How much time has passed between one part of a function and another part? With Instant now, we can capture the current time, and compute an elapsed duration of time.

By calling the elapsed() function, we can determine a duration of time that has passed. On Duration, we can use methods like as_millis() to get an integral number.

Example. This program uses Instant now twice, and then accesses methods on the Instant structs returned. The elapsed() method is most commonly used.

Part 1 Please make sure to add the "use" statement at the top of the program before calling Instant now in this way. We capture the current time.

Part 2 Just for this example program, we do some slow computations with a HashMap. This seems to require 4 ms in a release build.

Part 3 We can print the elapsed Duration with formatting codes in println, or we can access methods like as_millis() and get an integral number.

Part 4 The duration_since computes the elapsed time between 2 Instants. This can be used to time code. The original Instant could also be used.

use std::time::*; fn main() { // Part 1: call Instant now to capture current time. let t0 = Instant::now(); // Part 2: do some slow calculations (the effect is not important). let mut h = std::collections::HashMap::new(); for i in 0..100000 { h.insert(i, "?"); } // Part 3: print elapsed duration in a variety of ways. println!("ELAPSED: {:?}", t0.elapsed()); println!("{}", t0.elapsed().as_nanos()); println!("{}", t0.elapsed().as_millis()); println!("{}", t0.elapsed().as_micros()); println!("{}", t0.elapsed().as_secs()); // Part 4: get another Instant, and compute the duration since the previous instant. let t1 = Instant::now(); let result = t1.duration_since(t0); println!("DURATION SINCE: {:?}", result); println!("ELAPSED: {:?}", t0.elapsed()); }

ELAPSED: 3.0713ms 3208500 3 3863 0 DURATION SINCE: 4.3297ms ELAPSED: 4.4323ms

Summary. For timing code, or even external operations like network requests, Instant now is a good choice in Rust. With elapsed() and duration_since() we can compute the time that has passed.

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This page was last updated on Oct 21, 2024 (new).

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