rust/crates/salsa/tests/parallel/true_parallel.rs

use crate::setup::{Knobs, ParDatabase, ParDatabaseImpl, WithValue};
use salsa::ParallelDatabase;
use std::panic::{self, AssertUnwindSafe};

/// Test where two threads are executing sum. We show that they can
/// both be executing sum in parallel by having thread1 wait for
/// thread2 to send a signal before it leaves (similarly, thread2
/// waits for thread1 to send a signal before it enters).
#[test]
fn true_parallel_different_keys() {
    let mut db = ParDatabaseImpl::default();

    db.set_input('a', 100);
    db.set_input('b', 10);
    db.set_input('c', 1);

    // Thread 1 will signal stage 1 when it enters and wait for stage 2.
    let thread1 = std::thread::spawn({
        let db = db.snapshot();
        move || {
            let v = db
                .knobs()
                .sum_signal_on_entry
                .with_value(1, || db.knobs().sum_wait_for_on_exit.with_value(2, || db.sum("a")));
            v
        }
    });

    // Thread 2 will wait_for stage 1 when it enters and signal stage 2
    // when it leaves.
    let thread2 = std::thread::spawn({
        let db = db.snapshot();
        move || {
            let v = db
                .knobs()
                .sum_wait_for_on_entry
                .with_value(1, || db.knobs().sum_signal_on_exit.with_value(2, || db.sum("b")));
            v
        }
    });

    assert_eq!(thread1.join().unwrap(), 100);
    assert_eq!(thread2.join().unwrap(), 10);
}

/// Add a test that tries to trigger a conflict, where we fetch
/// `sum("abc")` from two threads simultaneously, and of them
/// therefore has to block.
#[test]
fn true_parallel_same_keys() {
    let mut db = ParDatabaseImpl::default();

    db.set_input('a', 100);
    db.set_input('b', 10);
    db.set_input('c', 1);

    // Thread 1 will wait_for a barrier in the start of `sum`
    let thread1 = std::thread::spawn({
        let db = db.snapshot();
        move || {
            let v = db
                .knobs()
                .sum_signal_on_entry
                .with_value(1, || db.knobs().sum_wait_for_on_entry.with_value(2, || db.sum("abc")));
            v
        }
    });

    // Thread 2 will wait until Thread 1 has entered sum and then --
    // once it has set itself to block -- signal Thread 1 to
    // continue. This way, we test out the mechanism of one thread
    // blocking on another.
    let thread2 = std::thread::spawn({
        let db = db.snapshot();
        move || {
            db.knobs().signal.wait_for(1);
            db.knobs().signal_on_will_block.set(2);
            db.sum("abc")
        }
    });

    assert_eq!(thread1.join().unwrap(), 111);
    assert_eq!(thread2.join().unwrap(), 111);
}

/// Add a test that tries to trigger a conflict, where we fetch `sum("a")`
/// from two threads simultaneously. After `thread2` begins blocking,
/// we force `thread1` to panic and should see that propagate to `thread2`.
#[test]
fn true_parallel_propagate_panic() {
    let mut db = ParDatabaseImpl::default();

    db.set_input('a', 1);

    // `thread1` will wait_for a barrier in the start of `sum`. Once it can
    // continue, it will panic.
    let thread1 = std::thread::spawn({
        let db = db.snapshot();
        move || {
            let v = db.knobs().sum_signal_on_entry.with_value(1, || {
                db.knobs()
                    .sum_wait_for_on_entry
                    .with_value(2, || db.knobs().sum_should_panic.with_value(true, || db.sum("a")))
            });
            v
        }
    });

    // `thread2` will wait until `thread1` has entered sum and then -- once it
    // has set itself to block -- signal `thread1` to continue.
    let thread2 = std::thread::spawn({
        let db = db.snapshot();
        move || {
            db.knobs().signal.wait_for(1);
            db.knobs().signal_on_will_block.set(2);
            db.sum("a")
        }
    });

    let result1 = panic::catch_unwind(AssertUnwindSafe(|| thread1.join().unwrap()));
    let result2 = panic::catch_unwind(AssertUnwindSafe(|| thread2.join().unwrap()));

    assert!(result1.is_err());
    assert!(result2.is_err());
}