Move complete job tracker to a helper object (#1489)

This reduces visible implementation details, in case we want to change
this object in the future (e.g. using a `BTreeSet` or a sorted `Vec`).

downstairs/src/complete_jobs.rs

@@ -0,0 +1,55 @@
+use crate::JobId;
+
+/// Stores a flush operation and a set of complete jobs
+///
+/// The flush operation is not included in the list of complete jobs, but acts
+/// as a lower bound for dependencies; any job older than the flush is assumed
+/// to have completed.
+#[derive(Debug)]
+pub struct CompletedJobs {
+ last_flush: Option<JobId>,
+ completed: Vec<JobId>,
+}
+
+impl CompletedJobs {
+ pub fn new(last_flush: Option<JobId>) -> Self {
+ Self {
+ last_flush,
+ completed: vec![],
+ }
+ }
+
+ pub fn is_empty(&self) -> bool {
+ self.completed.is_empty()
+ }
+
+ /// Records a new complete job in the list
+ pub fn push(&mut self, id: JobId) {
+ self.completed.push(id);
+ }
+
+ /// Resets the data structure given a new barrier operation
+ pub fn reset(&mut self, id: JobId) {
+ self.last_flush = Some(id);
+ self.completed.clear();
+ }
+
+ /// Checks whether the given job is complete
+ ///
+ /// A job is complete if it precedes our last barrier operation or is listed
+ /// in the set of complete jobs.
+ pub fn is_complete(&self, id: JobId) -> bool {
+ // We deliberately reverse the `completed` list because new jobs are at
+ // the back and are more likely to be what we care about
+ self.last_flush.map(|b| id <= b).unwrap_or(false)
+ || self.completed.iter().rev().any(|j| *j == id)
+ }
+
+ pub fn completed(&self) -> &[JobId] {
+ &self.completed
+ }
+
+ pub fn last_flush(&self) -> Option<JobId> {
+ self.last_flush
+ }
+}