mmtk/scheduler/
worker_goals.rs

1//! This module contain "goals" which are larger than work packets, and describes what workers are
2//! working towards on a high level.
3//!
4//! A "goal" is represented by a `WorkerGoal`.  All workers work towards a single goal at a time.
5//! The current goal influences the behavior of GC workers, especially the last parked worker.
6//! For example,
7//!
8//! -   When in the progress of GC, the last parker will try to open buckets or announce the GC
9//!     has finished.
10//! -   When stopping for fork, every waken worker should save its thread state (giving in the
11//!     `GCWorker` struct) and exit.
12//!
13//! The struct `WorkerGoals` keeps the set of goals requested by mutators, but GC workers will only
14//! respond to one request at a time, and will favor higher-priority goals.
15
16use enum_map::{Enum, EnumMap};
17
18/// This current and reqeusted goals.
19#[derive(Default, Debug)]
20pub(crate) struct WorkerGoals {
21    /// The current goal.
22    current: Option<WorkerGoal>,
23    /// Requests received from mutators.  `requests[goal]` is true if the `goal` is requested.
24    requests: EnumMap<WorkerGoal, bool>,
25}
26
27/// A goal, i.e. something that workers should work together to achieve.
28///
29/// Members of this `enum` should be listed from the highest priority to the lowest priority.
30#[derive(Debug, Enum, Clone, Copy)]
31pub(crate) enum WorkerGoal {
32    /// Do a garbage collection.
33    Gc,
34    /// Stop all GC threads so that the VM can call `fork()`.
35    StopForFork,
36}
37
38impl WorkerGoals {
39    /// Set the `goal` as requested.  Return `true` if the requested state of the `goal` changed
40    /// from `false` to `true`.
41    pub fn set_request(&mut self, goal: WorkerGoal) -> bool {
42        if !self.requests[goal] {
43            self.requests[goal] = true;
44            true
45        } else {
46            false
47        }
48    }
49
50    /// Move the highest priority goal from the pending requests to the current request.  Return
51    /// that goal, or `None` if no goal has been requested.
52    pub fn poll_next_goal(&mut self) -> Option<WorkerGoal> {
53        for (goal, requested) in self.requests.iter_mut() {
54            if *requested {
55                *requested = false;
56                self.current = Some(goal);
57                probe!(mmtk, goal_set, goal);
58                return Some(goal);
59            }
60        }
61        None
62    }
63
64    /// Get the current goal if exists.
65    pub fn current(&self) -> Option<WorkerGoal> {
66        self.current
67    }
68
69    /// Called when the current goal is completed.  This will clear the current goal.
70    pub fn on_current_goal_completed(&mut self) {
71        probe!(mmtk, goal_complete);
72        self.current = None
73    }
74
75    /// Test if the given `goal` is requested.  Used for debug purpose, only.  The workers always
76    /// respond to the request of the highest priority first.
77    pub fn debug_is_requested(&self, goal: WorkerGoal) -> bool {
78        self.requests[goal]
79    }
80}
81
82#[cfg(test)]
83mod tests {
84    use super::{WorkerGoal, WorkerGoals};
85
86    #[test]
87    fn test_poll_none() {
88        let mut goals = WorkerGoals::default();
89        let next_goal = goals.poll_next_goal();
90
91        assert!(next_goal.is_none());
92        assert!(goals.current().is_none());
93    }
94
95    #[test]
96    fn test_poll_one() {
97        let mut goals = WorkerGoals::default();
98        goals.set_request(WorkerGoal::StopForFork);
99        let next_goal = goals.poll_next_goal();
100
101        assert!(matches!(next_goal, Some(WorkerGoal::StopForFork)));
102        assert!(matches!(goals.current(), Some(WorkerGoal::StopForFork)));
103    }
104
105    #[test]
106    fn test_goals_priority() {
107        let mut goals = WorkerGoals::default();
108        goals.set_request(WorkerGoal::StopForFork);
109        goals.set_request(WorkerGoal::Gc);
110
111        let next_goal = goals.poll_next_goal();
112
113        assert!(matches!(next_goal, Some(WorkerGoal::Gc)));
114        assert!(matches!(goals.current(), Some(WorkerGoal::Gc)));
115    }
116}
mmtk/scheduler/worker_goals.rs

mmtk/scheduler/
worker_goals.rs
