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| 1 | +use std::sync::{Arc, Condvar, Mutex}; |
| 2 | + |
| 3 | +use rustc_session::Session; |
| 4 | + |
| 5 | +use jobserver::HelperThread; |
| 6 | + |
| 7 | +// FIXME don't panic when a worker thread panics |
| 8 | + |
| 9 | +pub(super) struct ConcurrencyLimiter { |
| 10 | + helper_thread: Option<HelperThread>, |
| 11 | + state: Arc<Mutex<state::ConcurrencyLimiterState>>, |
| 12 | + available_token_condvar: Arc<Condvar>, |
| 13 | +} |
| 14 | + |
| 15 | +impl ConcurrencyLimiter { |
| 16 | + pub(super) fn new(sess: &Session, pending_jobs: usize) -> Self { |
| 17 | + let state = Arc::new(Mutex::new(state::ConcurrencyLimiterState::new(pending_jobs))); |
| 18 | + let available_token_condvar = Arc::new(Condvar::new()); |
| 19 | + |
| 20 | + let state_helper = state.clone(); |
| 21 | + let available_token_condvar_helper = available_token_condvar.clone(); |
| 22 | + let helper_thread = sess |
| 23 | + .jobserver |
| 24 | + .clone() |
| 25 | + .into_helper_thread(move |token| { |
| 26 | + let mut state = state_helper.lock().unwrap(); |
| 27 | + state.add_new_token(token.unwrap()); |
| 28 | + available_token_condvar_helper.notify_one(); |
| 29 | + }) |
| 30 | + .unwrap(); |
| 31 | + ConcurrencyLimiter { |
| 32 | + helper_thread: Some(helper_thread), |
| 33 | + state, |
| 34 | + available_token_condvar: Arc::new(Condvar::new()), |
| 35 | + } |
| 36 | + } |
| 37 | + |
| 38 | + pub(super) fn acquire(&mut self) -> ConcurrencyLimiterToken { |
| 39 | + let mut state = self.state.lock().unwrap(); |
| 40 | + loop { |
| 41 | + state.assert_invariants(); |
| 42 | + |
| 43 | + if state.try_start_job() { |
| 44 | + return ConcurrencyLimiterToken { |
| 45 | + state: self.state.clone(), |
| 46 | + available_token_condvar: self.available_token_condvar.clone(), |
| 47 | + }; |
| 48 | + } |
| 49 | + |
| 50 | + self.helper_thread.as_mut().unwrap().request_token(); |
| 51 | + state = self.available_token_condvar.wait(state).unwrap(); |
| 52 | + } |
| 53 | + } |
| 54 | + |
| 55 | + pub(super) fn job_already_done(&mut self) { |
| 56 | + let mut state = self.state.lock().unwrap(); |
| 57 | + state.job_already_done(); |
| 58 | + } |
| 59 | +} |
| 60 | + |
| 61 | +impl Drop for ConcurrencyLimiter { |
| 62 | + fn drop(&mut self) { |
| 63 | + // |
| 64 | + self.helper_thread.take(); |
| 65 | + |
| 66 | + // Assert that all jobs have finished |
| 67 | + let state = Mutex::get_mut(Arc::get_mut(&mut self.state).unwrap()).unwrap(); |
| 68 | + state.assert_done(); |
| 69 | + } |
| 70 | +} |
| 71 | + |
| 72 | +#[derive(Debug)] |
| 73 | +pub(super) struct ConcurrencyLimiterToken { |
| 74 | + state: Arc<Mutex<state::ConcurrencyLimiterState>>, |
| 75 | + available_token_condvar: Arc<Condvar>, |
| 76 | +} |
| 77 | + |
| 78 | +impl Drop for ConcurrencyLimiterToken { |
| 79 | + fn drop(&mut self) { |
| 80 | + let mut state = self.state.lock().unwrap(); |
| 81 | + state.job_finished(); |
| 82 | + self.available_token_condvar.notify_one(); |
| 83 | + } |
| 84 | +} |
| 85 | + |
| 86 | +mod state { |
| 87 | + use jobserver::Acquired; |
| 88 | + |
| 89 | + #[derive(Debug)] |
| 90 | + pub(super) struct ConcurrencyLimiterState { |
| 91 | + pending_jobs: usize, |
| 92 | + active_jobs: usize, |
| 93 | + |
| 94 | + // None is used to represent the implicit token, Some to represent explicit tokens |
| 95 | + tokens: Vec<Option<Acquired>>, |
| 96 | + } |
| 97 | + |
| 98 | + impl ConcurrencyLimiterState { |
| 99 | + pub(super) fn new(pending_jobs: usize) -> Self { |
| 100 | + ConcurrencyLimiterState { pending_jobs, active_jobs: 0, tokens: vec![None] } |
| 101 | + } |
| 102 | + |
| 103 | + pub(super) fn assert_invariants(&self) { |
| 104 | + // There must be no excess active jobs |
| 105 | + assert!(self.active_jobs <= self.pending_jobs); |
| 106 | + |
| 107 | + // There may not be more active jobs than there are tokens |
| 108 | + assert!(self.active_jobs <= self.tokens.len()); |
| 109 | + } |
| 110 | + |
| 111 | + pub(super) fn assert_done(&self) { |
| 112 | + assert_eq!(self.pending_jobs, 0); |
| 113 | + assert_eq!(self.active_jobs, 0); |
| 114 | + } |
| 115 | + |
| 116 | + pub(super) fn add_new_token(&mut self, token: Acquired) { |
| 117 | + self.tokens.push(Some(token)); |
| 118 | + self.drop_excess_capacity(); |
| 119 | + } |
| 120 | + |
| 121 | + pub(super) fn try_start_job(&mut self) -> bool { |
| 122 | + if self.active_jobs < self.tokens.len() { |
| 123 | + // Using existing token |
| 124 | + self.job_started(); |
| 125 | + return true; |
| 126 | + } |
| 127 | + |
| 128 | + false |
| 129 | + } |
| 130 | + |
| 131 | + pub(super) fn job_started(&mut self) { |
| 132 | + self.assert_invariants(); |
| 133 | + self.active_jobs += 1; |
| 134 | + self.drop_excess_capacity(); |
| 135 | + self.assert_invariants(); |
| 136 | + } |
| 137 | + |
| 138 | + pub(super) fn job_finished(&mut self) { |
| 139 | + self.assert_invariants(); |
| 140 | + self.pending_jobs -= 1; |
| 141 | + self.active_jobs -= 1; |
| 142 | + self.assert_invariants(); |
| 143 | + self.drop_excess_capacity(); |
| 144 | + self.assert_invariants(); |
| 145 | + } |
| 146 | + |
| 147 | + pub(super) fn job_already_done(&mut self) { |
| 148 | + self.assert_invariants(); |
| 149 | + self.pending_jobs -= 1; |
| 150 | + self.assert_invariants(); |
| 151 | + self.drop_excess_capacity(); |
| 152 | + self.assert_invariants(); |
| 153 | + } |
| 154 | + |
| 155 | + fn drop_excess_capacity(&mut self) { |
| 156 | + self.assert_invariants(); |
| 157 | + |
| 158 | + // Drop all tokens that can never be used anymore |
| 159 | + self.tokens.truncate(std::cmp::max(self.pending_jobs, 1)); |
| 160 | + |
| 161 | + // Keep some excess tokens to satisfy requests faster |
| 162 | + const MAX_EXTRA_CAPACITY: usize = 2; |
| 163 | + self.tokens.truncate(std::cmp::max(self.active_jobs + MAX_EXTRA_CAPACITY, 1)); |
| 164 | + |
| 165 | + self.assert_invariants(); |
| 166 | + } |
| 167 | + } |
| 168 | +} |
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