Merge commit 'ddf105b646' into sync-from-ra

crates/salsa/tests/parallel/race.rs

@@ -0,0 +1,37 @@
+use std::panic::AssertUnwindSafe;
+
+use crate::setup::{ParDatabase, ParDatabaseImpl};
+use salsa::{Cancelled, ParallelDatabase};
+
+/// Test where a read and a set are racing with one another.
+/// Should be atomic.
+#[test]
+fn in_par_get_set_race() {
+    let mut db = ParDatabaseImpl::default();
+
+    db.set_input('a', 100);
+    db.set_input('b', 10);
+    db.set_input('c', 1);
+
+    let thread1 = std::thread::spawn({
+        let db = db.snapshot();
+        move || Cancelled::catch(AssertUnwindSafe(|| db.sum("abc")))
+    });
+
+    let thread2 = std::thread::spawn(move || {
+        db.set_input('a', 1000);
+        db.sum("a")
+    });
+
+    // If the 1st thread runs first, you get 111, otherwise you get
+    // 1011; if they run concurrently and the 1st thread observes the
+    // cancellation, it'll unwind.
+    let result1 = thread1.join().unwrap();
+    if let Ok(value1) = result1 {
+        assert!(value1 == 111 || value1 == 1011, "illegal result {}", value1);
+    }
+
+    // thread2 can not observe a cancellation because it performs a
+    // database write before running any other queries.
+    assert_eq!(thread2.join().unwrap(), 1000);
+}