Receiver::recv_timeout() returns instantly when duration overflows

[vandenoever]

When Receiver::recv_timeout receives certain large values, it returns immediately. This is probably due to an overflowing value. Instead, when there is overflow, it should fall back to Receiver::recv.

use std::sync::mpsc::Receiver;
use std::time::Duration;

let max = Duration::from_secs(u64::max_value());
receiver.recv_timeout(max);

Instant should probably not overflow like this:

let now = Instant::now();
let end_of_time = Instant::now() + Duration::from_secs(u64::max_value());
println!("{:?}", now);
println!("{:?}", end_of_time);
println!("did we pass end of time? {}", now > end_of_time);

[kennytm]

The Instance addition should panic on overflow (try u64::max_value()/2 instead of u64::max_value()). It seems there is some bug causing the panic not trigger.

[vandenoever]

u64::max_value()/2 panics. u64::max_value()/4 is fine.

[kennytm]

Oops.

rust/src/libstd/sys/unix/time.rs

Lines 43 to 45 in 97b01ab

	fn add_duration(&self, other: &Duration) -> Timespec {
	let secs = (self.t.tv_sec as i64).checked_add(other.as_secs() as i64);
	let mut secs = secs.expect("overflow when adding duration to time");

If only we used checked_cast (try_into)...

[vandenoever]

Why is it casting to i64?

[kennytm]

@vandenoever An Instant can represent time before the epoch, thus the number of seconds is a signed value. Arithmetic in Rust can only be performed between values of the same type, so the duration is cast to i64.

[vandenoever]

@kennytm I see. And the other cast self.t.tv_sec as i64 is not usually a cast because tv_sec is time_t which is (usually?) i64.