salsa 0.26.1

A generic framework for on-demand, incrementalized computation (experimental)
Documentation 
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#![allow(dead_code)]

use salsa::{Database, Storage};

use super::signal::Signal;
use super::sync::Arc;
use super::sync::atomic::{AtomicUsize, Ordering};

/// Various "knobs" and utilities used by tests to force
/// a certain behavior.
#[salsa::db]
pub(crate) trait KnobsDatabase: Database {
    /// Signal that we are entering stage `stage`.
    fn signal(&self, stage: usize);

    /// Wait until we reach stage `stage` (no-op if we have already reached that stage).
    fn wait_for(&self, stage: usize);
}

/// A database containing various "knobs" that can be used to customize how the queries
/// behave on one specific thread. Note that this state is
/// intentionally thread-local (apart from `signal`).
#[salsa::db]
pub(crate) struct Knobs {
    storage: salsa::Storage<Self>,

    /// A kind of flexible barrier used to coordinate execution across
    /// threads to ensure we reach various weird states.
    pub(crate) signal: Arc<Signal>,

    /// When this database is about to block, send this signal.
    signal_on_will_block: Arc<AtomicUsize>,

    /// When this database has set the cancellation flag, send this signal.
    signal_on_did_cancel: Arc<AtomicUsize>,
}

impl Knobs {
    pub fn signal_on_did_cancel(&self, stage: usize) {
        self.signal_on_did_cancel.store(stage, Ordering::Release);
    }

    pub fn signal_on_will_block(&self, stage: usize) {
        self.signal_on_will_block.store(stage, Ordering::Release);
    }
}

impl Clone for Knobs {
    #[track_caller]
    fn clone(&self) -> Self {
        // To avoid mistakes, check that when we clone, we haven't customized this behavior yet
        assert_eq!(self.signal_on_will_block.load(Ordering::Acquire), 0);
        assert_eq!(self.signal_on_did_cancel.load(Ordering::Acquire), 0);
        Self {
            storage: self.storage.clone(),
            signal: self.signal.clone(),
            signal_on_will_block: self.signal_on_will_block.clone(),
            signal_on_did_cancel: self.signal_on_did_cancel.clone(),
        }
    }
}

impl Default for Knobs {
    fn default() -> Self {
        let signal = <Arc<Signal>>::default();
        let signal_on_will_block = Arc::new(AtomicUsize::new(0));
        let signal_on_did_cancel = Arc::new(AtomicUsize::new(0));

        Self {
            storage: Storage::new(Some(Box::new({
                let signal = signal.clone();
                let signal_on_will_block = signal_on_will_block.clone();
                let signal_on_did_cancel = signal_on_did_cancel.clone();
                move |event| match event.kind {
                    salsa::EventKind::WillBlockOn { .. } => {
                        signal.signal(signal_on_will_block.load(Ordering::Acquire));
                    }
                    salsa::EventKind::DidSetCancellationFlag => {
                        signal.signal(signal_on_did_cancel.load(Ordering::Acquire));
                    }
                    _ => {}
                }
            }))),
            signal,
            signal_on_will_block,
            signal_on_did_cancel,
        }
    }
}

#[salsa::db]
impl salsa::Database for Knobs {}

#[salsa::db]
impl KnobsDatabase for Knobs {
    fn signal(&self, stage: usize) {
        self.signal.signal(stage);
    }

    fn wait_for(&self, stage: usize) {
        self.signal.wait_for(stage);
    }
}