Merge #184

184: Miri has gained some more features r=matklad a=RalfJung

Barriers, concurrency, and spinloops should all work now.

Co-authored-by: Ralf Jung <post@ralfj.de>

src/imp_std.rs

@@ -281,7 +281,6 @@ mod tests {
     }
 
     #[test]
-    #[cfg(not(miri))]
     fn stampede_once() {
         static O: OnceCell<()> = OnceCell::new();
         static mut RUN: bool = false;

tests/it.rs

@@ -331,11 +331,10 @@ mod sync {
     }
 
     #[test]
-    #[cfg_attr(miri, ignore)] // miri doesn't support Barrier
     fn get_or_init_stress() {
         use std::sync::Barrier;
-        let n_threads = 1_000;
-        let n_cells = 1_000;
+        let n_threads = if cfg!(miri) { 30 } else { 1_000 };
+        let n_cells = if cfg!(miri) { 30 } else { 1_000 };
         let cells: Vec<_> = std::iter::repeat_with(|| (Barrier::new(n_threads), OnceCell::new()))
             .take(n_cells)
             .collect();
@@ -577,9 +576,8 @@ mod sync {
     }
 
     #[test]
-    #[cfg_attr(miri, ignore)] // FIXME: deadlocks, likely caused by https://github.com/rust-lang/miri/issues/1388
     fn once_cell_does_not_leak_partially_constructed_boxes() {
-        let n_tries = 100;
+        let n_tries = if cfg!(miri) { 10 } else { 100 };
         let n_readers = 10;
         let n_writers = 3;
         const MSG: &str = "Hello, World";
@@ -604,7 +602,6 @@ mod sync {
     }
 
     #[test]
-    #[cfg_attr(miri, ignore)] // miri doesn't support Barrier
     fn get_does_not_block() {
         use std::sync::Barrier;