83 lines
2.5 KiB
Rust
83 lines
2.5 KiB
Rust
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use thiserror::Error;
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#[derive(Debug, Clone, PartialEq, Eq)]
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pub struct ScreenLease {
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pub owner_id: String,
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pub fence: u32,
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}
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#[derive(Debug, Error, Clone, PartialEq, Eq)]
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#[error("computer is busy")]
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pub struct ComputerBusyError;
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pub fn screen_lease_id(run_id: &str, fence: u32) -> String {
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format!("{run_id}:{fence}")
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}
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pub fn parse_screen_lease_id(lease_id: &str) -> ScreenLease {
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match lease_id.rsplit_once(':') {
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Some((owner, fence)) if !owner.is_empty() => {
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if let Ok(fence) = fence.parse::<u32>() {
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return ScreenLease {
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owner_id: owner.to_string(),
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fence,
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};
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}
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}
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_ => {}
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}
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ScreenLease {
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owner_id: lease_id.to_string(),
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fence: 0,
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}
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}
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pub fn can_take_screen_lease(existing: Option<&str>, incoming: Option<&str>) -> bool {
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let Some(incoming) = incoming else {
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return false;
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};
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match existing {
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None => true,
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Some(existing) if existing == incoming => true,
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Some(existing) => parse_screen_lease_id(incoming).fence > parse_screen_lease_id(existing).fence,
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}
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}
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pub fn can_release_screen_lease(existing: Option<&str>, incoming: Option<&str>) -> bool {
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match (existing, incoming) {
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(_, None) | (None, _) => true,
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(Some(existing), Some(incoming)) if existing == incoming => true,
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(Some(existing), Some(incoming)) => {
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let current = parse_screen_lease_id(existing);
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let next = parse_screen_lease_id(incoming);
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next.owner_id == current.owner_id && next.fence >= current.fence
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}
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}
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}
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pub fn next_fence(current: u32) -> u32 {
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current.saturating_add(1)
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn newer_fence_takes_the_screen() {
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assert!(can_take_screen_lease(None, Some("run-a:1")));
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assert!(can_take_screen_lease(Some("run-a:1"), Some("run-a:1")));
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assert!(can_take_screen_lease(Some("run-a:1"), Some("run-b:2")));
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assert!(!can_take_screen_lease(Some("run-a:2"), Some("run-b:1")));
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assert!(!can_take_screen_lease(Some("run-a:1"), None));
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}
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#[test]
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fn release_requires_same_owner_and_non_decreasing_fence() {
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assert!(can_release_screen_lease(Some("run-a:1"), Some("run-a:1")));
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assert!(can_release_screen_lease(Some("run-a:1"), Some("run-a:2")));
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assert!(!can_release_screen_lease(Some("run-a:2"), Some("run-b:3")));
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assert!(!can_release_screen_lease(Some("run-a:2"), Some("run-a:1")));
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}
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}
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