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 permanently.
35    Shutdown,
36    /// Stop all GC threads so that the VM can call `fork()`.
37    StopForFork,
38}
39
40impl WorkerGoals {
41    /// Set the `goal` as requested.  Return `true` if the requested state of the `goal` changed
42    /// from `false` to `true`.
43    pub fn set_request(&mut self, goal: WorkerGoal) -> bool {
44        if !self.requests[goal] {
45            self.requests[goal] = true;
46            true
47        } else {
48            false
49        }
50    }
51
52    /// Move the highest priority goal from the pending requests to the current request.  Return
53    /// that goal, or `None` if no goal has been requested.
54    pub fn poll_next_goal(&mut self) -> Option<WorkerGoal> {
55        for (goal, requested) in self.requests.iter_mut() {
56            if *requested {
57                *requested = false;
58                self.current = Some(goal);
59                probe!(mmtk, goal_set, goal);
60                return Some(goal);
61            }
62        }
63        None
64    }
65
66    /// Get the current goal if exists.
67    pub fn current(&self) -> Option<WorkerGoal> {
68        self.current
69    }
70
71    /// Called when the current goal is completed.  This will clear the current goal.
72    pub fn on_current_goal_completed(&mut self) {
73        probe!(mmtk, goal_complete);
74        self.current = None
75    }
76
77    /// Test if the given `goal` is requested.  Used for debug purpose, only.  The workers always
78    /// respond to the request of the highest priority first.
79    pub fn debug_is_requested(&self, goal: WorkerGoal) -> bool {
80        self.requests[goal]
81    }
82}
83
84#[cfg(test)]
85mod tests {
86    use super::{WorkerGoal, WorkerGoals};
87
88    #[test]
89    fn test_poll_none() {
90        let mut goals = WorkerGoals::default();
91        let next_goal = goals.poll_next_goal();
92
93        assert!(next_goal.is_none());
94        assert!(goals.current().is_none());
95    }
96
97    #[test]
98    fn test_poll_one() {
99        let mut goals = WorkerGoals::default();
100        goals.set_request(WorkerGoal::StopForFork);
101        let next_goal = goals.poll_next_goal();
102
103        assert!(matches!(next_goal, Some(WorkerGoal::StopForFork)));
104        assert!(matches!(goals.current(), Some(WorkerGoal::StopForFork)));
105    }
106
107    #[test]
108    fn test_goals_priority() {
109        let mut goals = WorkerGoals::default();
110        goals.set_request(WorkerGoal::StopForFork);
111        goals.set_request(WorkerGoal::Gc);
112
113        let next_goal = goals.poll_next_goal();
114
115        assert!(matches!(next_goal, Some(WorkerGoal::Gc)));
116        assert!(matches!(goals.current(), Some(WorkerGoal::Gc)));
117    }
118}
mmtk/scheduler/worker_goals.rs

mmtk/scheduler/
worker_goals.rs
