std: sleep_until on Motor and VEX

[joboet]

This PR:

• Forwards the public sleep_until to the private sleep_until on Motor OS
• Adds a sleep_until implementation on VEX that yields until the deadline has passed

CC @lasiotus
CC @lewisfm @tropicaaal @Gavin-Niederman @max-niederman

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[lasiotus]

This PR:

• Forwards the public sleep_until to the private sleep_until on Motor OS

Thanks!

[lewisfm]

Regarding the changes to the VEX sleep impl, they are causing a segfault via null pointer dereference inside vexTaskSleep's internals when I run this program:

use vex_sdk_jumptable as _;
fn main() {
    sleep(Duration::from_secs(1));
}

It seems like vexTaskSleep is only valid to call from inside a VEXos task, which is a cooperative thread that is created by calling vexTaskAdd, polled by calling vexTasksRun, and yielded from by calling vexTaskSleep. (Some system processes like flushing I/O are implemented as tasks.)

I assume vexTaskSleep is trying to look up some field on the current task but finding it's a null pointer since there's no current task.

[tropicaaal]

Can concur with Lewis - vexTaskSleep is exposed via the SDK for completeness reasons and can only be used within a cooperative task spawned via vexTaskAdd or similar. The scheduler API in the SDK exposed to user code is considered to be incomplete, so the vexos modules in std avoid using it as e.g. an implementation for thread entirely aside from vexTasksRun which is required to be called to tick some important OS-spawned tasks responsible for I/O.

[joboet]

Ah, alright, thanks for your responses! I've changed it back to the vexTasksRun-based version and added a specialised sleep_until instead.

[Mark-Simulacrum]

@bors r+

[rust-bors]

📌 Commit dee0e39 has been approved by Mark-Simulacrum

It is now in the queue for this repository.