Merge rayon-rs#674

674: Make test 'iter_panic_fuse' deterministic r=cuviper a=Aaron1011

Fixes rayon-rs#667

'panic_fuse' will only stop other threads 'as soon as possible' -
if the other threads are fast enough, they might end up processing
the entire rest of the iterator.

This commit changes the test 'iter_panic_fuse' to properly take this
into account, by creating a custom threadpool with only 1 thread.
This makes the test deterministic - with only one thread, the panic
is guaranmteed to be observed when the next item is processed, causing
the desired early exit.

Co-authored-by: Aaron Hill <aa1ronham@gmail.com>
Co-authored-by: Josh Stone <cuviper@gmail.com>

Author: 3 people

src/iter/test.rs

@@ -447,53 +447,89 @@ fn check_cmp_gt_to_seq() {
 
 #[test]
 fn check_cmp_short_circuit() {
+    // We only use a single thread in order to make the short-circuit behavior deterministic.
+    let pool = ThreadPoolBuilder::new().num_threads(1).build().unwrap();
+
     let a = vec![0; 1024];
     let mut b = a.clone();
     b[42] = 1;
 
-    let counter = AtomicUsize::new(0);
-    let result = a
-        .par_iter()
-        .inspect(|_| {
-            counter.fetch_add(1, Ordering::SeqCst);
-        })
-        .cmp(&b);
-    assert!(result == ::std::cmp::Ordering::Less);
-    assert!(counter.load(Ordering::SeqCst) < a.len()); // should not have visited every single one
+    pool.install(|| {
+        let expected = ::std::cmp::Ordering::Less;
+        assert_eq!(a.par_iter().cmp(&b), expected);
+
+        for len in 1..10 {
+            let counter = AtomicUsize::new(0);
+            let result = a
+                .par_iter()
+                .with_max_len(len)
+                .inspect(|_| {
+                    counter.fetch_add(1, Ordering::SeqCst);
+                })
+                .cmp(&b);
+            assert_eq!(result, expected);
+            // should not have visited every single one
+            assert!(counter.into_inner() < a.len());
+        }
+    });
 }
 
 #[test]
 fn check_partial_cmp_short_circuit() {
+    // We only use a single thread to make the short-circuit behavior deterministic.
+    let pool = ThreadPoolBuilder::new().num_threads(1).build().unwrap();
+
     let a = vec![0; 1024];
     let mut b = a.clone();
     b[42] = 1;
 
-    let counter = AtomicUsize::new(0);
-    let result = a
-        .par_iter()
-        .inspect(|_| {
-            counter.fetch_add(1, Ordering::SeqCst);
-        })
-        .partial_cmp(&b);
-    assert!(result == Some(::std::cmp::Ordering::Less));
-    assert!(counter.load(Ordering::SeqCst) < a.len()); // should not have visited every single one
+    pool.install(|| {
+        let expected = Some(::std::cmp::Ordering::Less);
+        assert_eq!(a.par_iter().partial_cmp(&b), expected);
+
+        for len in 1..10 {
+            let counter = AtomicUsize::new(0);
+            let result = a
+                .par_iter()
+                .with_max_len(len)
+                .inspect(|_| {
+                    counter.fetch_add(1, Ordering::SeqCst);
+                })
+                .partial_cmp(&b);
+            assert_eq!(result, expected);
+            // should not have visited every single one
+            assert!(counter.into_inner() < a.len());
+        }
+    });
 }
 
 #[test]
 fn check_partial_cmp_nan_short_circuit() {
+    // We only use a single thread to make the short-circuit behavior deterministic.
+    let pool = ThreadPoolBuilder::new().num_threads(1).build().unwrap();
+
     let a = vec![0.0; 1024];
     let mut b = a.clone();
     b[42] = f64::NAN;
 
-    let counter = AtomicUsize::new(0);
-    let result = a
-        .par_iter()
-        .inspect(|_| {
-            counter.fetch_add(1, Ordering::SeqCst);
-        })
-        .partial_cmp(&b);
-    assert!(result == None);
-    assert!(counter.load(Ordering::SeqCst) < a.len()); // should not have visited every single one
+    pool.install(|| {
+        let expected = None;
+        assert_eq!(a.par_iter().partial_cmp(&b), expected);
+
+        for len in 1..10 {
+            let counter = AtomicUsize::new(0);
+            let result = a
+                .par_iter()
+                .with_max_len(len)
+                .inspect(|_| {
+                    counter.fetch_add(1, Ordering::SeqCst);
+                })
+                .partial_cmp(&b);
+            assert_eq!(result, expected);
+            // should not have visited every single one
+            assert!(counter.into_inner() < a.len());
+        }
+    });
 }
 
 #[test]

tests/iter_panic.rs

@@ -1,6 +1,7 @@
 extern crate rayon;
 
 use rayon::prelude::*;
+use rayon::ThreadPoolBuilder;
 use std::ops::Range;
 use std::panic::{self, UnwindSafe};
 use std::sync::atomic::{AtomicUsize, Ordering};
@@ -22,26 +23,32 @@ fn iter_panic() {
 
 #[test]
 fn iter_panic_fuse() {
-    fn count(iter: impl ParallelIterator + UnwindSafe) -> usize {
-        let count = AtomicUsize::new(0);
-        let result = panic::catch_unwind(|| {
-            iter.for_each(|_| {
-                count.fetch_add(1, Ordering::Relaxed);
+    // We only use a single thread in order to make the behavior
+    // of 'panic_fuse' deterministic
+    let pool = ThreadPoolBuilder::new().num_threads(1).build().unwrap();
+
+    pool.install(|| {
+        fn count(iter: impl ParallelIterator + UnwindSafe) -> usize {
+            let count = AtomicUsize::new(0);
+            let result = panic::catch_unwind(|| {
+                iter.for_each(|_| {
+                    count.fetch_add(1, Ordering::Relaxed);
+                });
             });
-        });
-        assert!(result.is_err());
-        count.into_inner()
-    }
-
-    // Without `panic_fuse()`, we'll reach every item except the panicking one.
-    let expected = ITER.len() - 1;
-    let iter = ITER.into_par_iter().with_max_len(1);
-    assert_eq!(count(iter.clone().inspect(check)), expected);
-
-    // With `panic_fuse()` anywhere in the chain, we'll reach fewer items.
-    assert!(count(iter.clone().inspect(check).panic_fuse()) < expected);
-    assert!(count(iter.clone().panic_fuse().inspect(check)) < expected);
-
-    // Try in reverse to be sure we hit the producer case.
-    assert!(count(iter.clone().panic_fuse().inspect(check).rev()) < expected);
+            assert!(result.is_err());
+            count.into_inner()
+        }
+
+        // Without `panic_fuse()`, we'll reach every item except the panicking one.
+        let expected = ITER.len() - 1;
+        let iter = ITER.into_par_iter().with_max_len(1);
+        assert_eq!(count(iter.clone().inspect(check)), expected);
+
+        // With `panic_fuse()` anywhere in the chain, we'll reach fewer items.
+        assert!(count(iter.clone().inspect(check).panic_fuse()) < expected);
+        assert!(count(iter.clone().panic_fuse().inspect(check)) < expected);
+
+        // Try in reverse to be sure we hit the producer case.
+        assert!(count(iter.clone().panic_fuse().inspect(check).rev()) < expected);
+    });
 }