268 lines
9.3 KiB
Rust
268 lines
9.3 KiB
Rust
use std::marker::PhantomData;
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use crate::{utilities::OnceLock, Error};
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pub(crate) struct JobToken(PhantomData<()>);
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impl JobToken {
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fn new() -> Self {
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Self(PhantomData)
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}
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}
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impl Drop for JobToken {
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fn drop(&mut self) {
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match JobTokenServer::new() {
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JobTokenServer::Inherited(jobserver) => jobserver.release_token_raw(),
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JobTokenServer::InProcess(jobserver) => jobserver.release_token_raw(),
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}
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}
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}
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enum JobTokenServer {
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Inherited(inherited_jobserver::JobServer),
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InProcess(inprocess_jobserver::JobServer),
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}
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impl JobTokenServer {
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/// This function returns a static reference to the jobserver because
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/// - creating a jobserver from env is a bit fd-unsafe (e.g. the fd might
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/// be closed by other jobserver users in the process) and better do it
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/// at the start of the program.
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/// - in case a jobserver cannot be created from env (e.g. it's not
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/// present), we will create a global in-process only jobserver
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/// that has to be static so that it will be shared by all cc
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/// compilation.
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fn new() -> &'static Self {
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// TODO: Replace with a OnceLock once MSRV is 1.70
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static JOBSERVER: OnceLock<JobTokenServer> = OnceLock::new();
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JOBSERVER.get_or_init(|| {
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unsafe { inherited_jobserver::JobServer::from_env() }
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.map(Self::Inherited)
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.unwrap_or_else(|| Self::InProcess(inprocess_jobserver::JobServer::new()))
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})
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}
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}
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pub(crate) enum ActiveJobTokenServer {
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Inherited(inherited_jobserver::ActiveJobServer<'static>),
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InProcess(&'static inprocess_jobserver::JobServer),
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}
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impl ActiveJobTokenServer {
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pub(crate) fn new() -> Self {
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match JobTokenServer::new() {
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JobTokenServer::Inherited(inherited_jobserver) => {
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Self::Inherited(inherited_jobserver.enter_active())
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}
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JobTokenServer::InProcess(inprocess_jobserver) => Self::InProcess(inprocess_jobserver),
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}
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}
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pub(crate) async fn acquire(&mut self) -> Result<JobToken, Error> {
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match self {
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Self::Inherited(jobserver) => jobserver.acquire().await,
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Self::InProcess(jobserver) => Ok(jobserver.acquire().await),
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}
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}
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}
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mod inherited_jobserver {
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use super::JobToken;
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use crate::{parallel::async_executor::YieldOnce, Error, ErrorKind};
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use std::{
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io, mem,
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sync::{mpsc, Mutex, MutexGuard, PoisonError},
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};
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pub(super) struct JobServer {
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/// Implicit token for this process which is obtained and will be
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/// released in parent. Since `JobTokens` only give back what they got,
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/// there should be at most one global implicit token in the wild.
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///
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/// Since Rust does not execute any `Drop` for global variables,
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/// we can't just put it back to jobserver and then re-acquire it at
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/// the end of the process.
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///
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/// Use `Mutex` to avoid race between acquire and release.
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/// If an `AtomicBool` is used, then it's possible for:
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/// - `release_token_raw`: Tries to set `global_implicit_token` to true, but it is already
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/// set to `true`, continue to release it to jobserver
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/// - `acquire` takes the global implicit token, set `global_implicit_token` to false
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/// - `release_token_raw` now writes the token back into the jobserver, while
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/// `global_implicit_token` is `false`
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///
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/// If the program exits here, then cc effectively increases parallelism by one, which is
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/// incorrect, hence we use a `Mutex` here.
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global_implicit_token: Mutex<bool>,
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inner: jobserver::Client,
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}
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impl JobServer {
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pub(super) unsafe fn from_env() -> Option<Self> {
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jobserver::Client::from_env().map(|inner| Self {
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inner,
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global_implicit_token: Mutex::new(true),
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})
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}
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fn get_global_implicit_token(&self) -> MutexGuard<'_, bool> {
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self.global_implicit_token
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.lock()
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.unwrap_or_else(PoisonError::into_inner)
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}
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/// All tokens except for the global implicit token will be put back into the jobserver
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/// immediately and they cannot be cached, since Rust does not call `Drop::drop` on
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/// global variables.
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pub(super) fn release_token_raw(&self) {
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let mut global_implicit_token = self.get_global_implicit_token();
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if *global_implicit_token {
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// There's already a global implicit token, so this token must
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// be released back into jobserver.
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//
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// `release_raw` should not block
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let _ = self.inner.release_raw();
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} else {
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*global_implicit_token = true;
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}
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}
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pub(super) fn enter_active(&self) -> ActiveJobServer<'_> {
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ActiveJobServer {
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jobserver: self,
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helper_thread: None,
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}
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}
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}
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struct HelperThread {
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inner: jobserver::HelperThread,
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/// When rx is dropped, all the token stored within it will be dropped.
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rx: mpsc::Receiver<io::Result<jobserver::Acquired>>,
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}
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impl HelperThread {
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fn new(jobserver: &JobServer) -> Result<Self, Error> {
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let (tx, rx) = mpsc::channel();
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Ok(Self {
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rx,
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inner: jobserver.inner.clone().into_helper_thread(move |res| {
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let _ = tx.send(res);
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})?,
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})
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}
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}
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pub(crate) struct ActiveJobServer<'a> {
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jobserver: &'a JobServer,
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helper_thread: Option<HelperThread>,
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}
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impl ActiveJobServer<'_> {
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pub(super) async fn acquire(&mut self) -> Result<JobToken, Error> {
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let mut has_requested_token = false;
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loop {
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// Fast path
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if mem::replace(&mut *self.jobserver.get_global_implicit_token(), false) {
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break Ok(JobToken::new());
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}
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match self.jobserver.inner.try_acquire() {
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Ok(Some(acquired)) => {
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acquired.drop_without_releasing();
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break Ok(JobToken::new());
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}
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Ok(None) => YieldOnce::default().await,
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Err(err) if err.kind() == io::ErrorKind::Unsupported => {
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// Fallback to creating a help thread with blocking acquire
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let helper_thread = if let Some(thread) = self.helper_thread.as_ref() {
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thread
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} else {
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self.helper_thread
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.insert(HelperThread::new(self.jobserver)?)
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};
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match helper_thread.rx.try_recv() {
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Ok(res) => {
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let acquired = res?;
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acquired.drop_without_releasing();
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break Ok(JobToken::new());
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}
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Err(mpsc::TryRecvError::Disconnected) => break Err(Error::new(
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ErrorKind::JobserverHelpThreadError,
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"jobserver help thread has returned before ActiveJobServer is dropped",
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)),
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Err(mpsc::TryRecvError::Empty) => {
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if !has_requested_token {
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helper_thread.inner.request_token();
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has_requested_token = true;
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}
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YieldOnce::default().await
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}
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}
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}
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Err(err) => break Err(err.into()),
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}
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}
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}
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}
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}
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mod inprocess_jobserver {
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use super::JobToken;
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use crate::parallel::async_executor::YieldOnce;
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use std::{
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env::var,
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sync::atomic::{
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AtomicU32,
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Ordering::{AcqRel, Acquire},
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},
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};
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pub(crate) struct JobServer(AtomicU32);
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impl JobServer {
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#[allow(clippy::disallowed_methods)]
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pub(super) fn new() -> Self {
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// Use `NUM_JOBS` if set (it's configured by Cargo) and otherwise
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// just fall back to the number of cores on the local machine, or a reasonable
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// default if that cannot be determined.
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let parallelism = var("NUM_JOBS")
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.ok()
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.and_then(|j| j.parse::<u32>().ok())
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.or_else(|| Some(std::thread::available_parallelism().ok()?.get() as u32))
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.unwrap_or(4);
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Self(AtomicU32::new(parallelism))
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}
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pub(super) async fn acquire(&self) -> JobToken {
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loop {
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let res = self
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.0
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.fetch_update(AcqRel, Acquire, |tokens| tokens.checked_sub(1));
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if res.is_ok() {
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break JobToken::new();
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}
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YieldOnce::default().await
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}
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}
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pub(super) fn release_token_raw(&self) {
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self.0.fetch_add(1, AcqRel);
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}
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}
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}
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