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|
use std::sync::{Arc, Condvar, Mutex};
use rustc_session::Session;
use jobserver::HelperThread;
// FIXME don't panic when a worker thread panics
pub(super) struct ConcurrencyLimiter {
helper_thread: Option<HelperThread>,
state: Arc<Mutex<state::ConcurrencyLimiterState>>,
available_token_condvar: Arc<Condvar>,
}
impl ConcurrencyLimiter {
pub(super) fn new(sess: &Session, pending_jobs: usize) -> Self {
let state = Arc::new(Mutex::new(state::ConcurrencyLimiterState::new(pending_jobs)));
let available_token_condvar = Arc::new(Condvar::new());
let state_helper = state.clone();
let available_token_condvar_helper = available_token_condvar.clone();
let helper_thread = sess
.jobserver
.clone()
.into_helper_thread(move |token| {
let mut state = state_helper.lock().unwrap();
state.add_new_token(token.unwrap());
available_token_condvar_helper.notify_one();
})
.unwrap();
ConcurrencyLimiter {
helper_thread: Some(helper_thread),
state,
available_token_condvar: Arc::new(Condvar::new()),
}
}
pub(super) fn acquire(&mut self) -> ConcurrencyLimiterToken {
let mut state = self.state.lock().unwrap();
loop {
state.assert_invariants();
if state.try_start_job() {
return ConcurrencyLimiterToken {
state: self.state.clone(),
available_token_condvar: self.available_token_condvar.clone(),
};
}
self.helper_thread.as_mut().unwrap().request_token();
state = self.available_token_condvar.wait(state).unwrap();
}
}
pub(super) fn job_already_done(&mut self) {
let mut state = self.state.lock().unwrap();
state.job_already_done();
}
}
impl Drop for ConcurrencyLimiter {
fn drop(&mut self) {
//
self.helper_thread.take();
// Assert that all jobs have finished
let state = Mutex::get_mut(Arc::get_mut(&mut self.state).unwrap()).unwrap();
state.assert_done();
}
}
#[derive(Debug)]
pub(super) struct ConcurrencyLimiterToken {
state: Arc<Mutex<state::ConcurrencyLimiterState>>,
available_token_condvar: Arc<Condvar>,
}
impl Drop for ConcurrencyLimiterToken {
fn drop(&mut self) {
let mut state = self.state.lock().unwrap();
state.job_finished();
self.available_token_condvar.notify_one();
}
}
mod state {
use jobserver::Acquired;
#[derive(Debug)]
pub(super) struct ConcurrencyLimiterState {
pending_jobs: usize,
active_jobs: usize,
// None is used to represent the implicit token, Some to represent explicit tokens
tokens: Vec<Option<Acquired>>,
}
impl ConcurrencyLimiterState {
pub(super) fn new(pending_jobs: usize) -> Self {
ConcurrencyLimiterState { pending_jobs, active_jobs: 0, tokens: vec![None] }
}
pub(super) fn assert_invariants(&self) {
// There must be no excess active jobs
assert!(self.active_jobs <= self.pending_jobs);
// There may not be more active jobs than there are tokens
assert!(self.active_jobs <= self.tokens.len());
}
pub(super) fn assert_done(&self) {
assert_eq!(self.pending_jobs, 0);
assert_eq!(self.active_jobs, 0);
}
pub(super) fn add_new_token(&mut self, token: Acquired) {
self.tokens.push(Some(token));
self.drop_excess_capacity();
}
pub(super) fn try_start_job(&mut self) -> bool {
if self.active_jobs < self.tokens.len() {
// Using existing token
self.job_started();
return true;
}
false
}
pub(super) fn job_started(&mut self) {
self.assert_invariants();
self.active_jobs += 1;
self.drop_excess_capacity();
self.assert_invariants();
}
pub(super) fn job_finished(&mut self) {
self.assert_invariants();
self.pending_jobs -= 1;
self.active_jobs -= 1;
self.assert_invariants();
self.drop_excess_capacity();
self.assert_invariants();
}
pub(super) fn job_already_done(&mut self) {
self.assert_invariants();
self.pending_jobs -= 1;
self.assert_invariants();
self.drop_excess_capacity();
self.assert_invariants();
}
fn drop_excess_capacity(&mut self) {
self.assert_invariants();
// Drop all tokens that can never be used anymore
self.tokens.truncate(std::cmp::max(self.pending_jobs, 1));
// Keep some excess tokens to satisfy requests faster
const MAX_EXTRA_CAPACITY: usize = 2;
self.tokens.truncate(std::cmp::max(self.active_jobs + MAX_EXTRA_CAPACITY, 1));
self.assert_invariants();
}
}
}
|
