Function tokio::time::pause

source ·
pub fn pause()
Available on crate features time and test-util only.
Expand description

Pauses time.

The current value of Instant::now() is saved and all subsequent calls to Instant::now() will return the saved value. The saved value can be changed by advance or by the time auto-advancing once the runtime has no work to do. This only affects the Instant type in Tokio, and the Instant in std continues to work as normal.

Pausing time requires the current_thread Tokio runtime. This is the default runtime used by #[tokio::test]. The runtime can be initialized with time in a paused state using the Builder::start_paused method.

For cases where time is immediately paused, it is better to pause the time using the main or test macro:

#[tokio::main(flavor = "current_thread", start_paused = true)]
async fn main() {
   println!("Hello world");


Panics if time is already frozen or if called from outside of a current_thread Tokio runtime.


If time is paused and the runtime has no work to do, the clock is auto-advanced to the next pending timer. This means that Sleep or other timer-backed primitives can cause the runtime to advance the current time when awaited.