Rollup merge of #55963 - stepancheg:mpsc-take-2, r=alexcrichton

Stress test for MPSC

`concurrent_recv_timeout_and_upgrade` reproduces a problem 100%
times on my MacBook with command:

```
./x.py test --stage 0 ./src/test/run-pass/mpsc_stress.rs
```

Thus it is commented out.

Other tests cases were useful for catching another test cases
which may arise during the fix.

This diff is a part of my previous rewrite attempt: #42883

CC #39364

Author: pietroalbini

src/test/run-pass/mpsc_stress.rs

@@ -0,0 +1,172 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags:--test
+// ignore-emscripten
+
+use std::sync::mpsc::channel;
+use std::sync::mpsc::TryRecvError;
+use std::sync::mpsc::RecvError;
+use std::sync::mpsc::RecvTimeoutError;
+use std::sync::Arc;
+use std::sync::atomic::AtomicUsize;
+use std::sync::atomic::Ordering;
+
+use std::thread;
+use std::time::Duration;
+
+
+/// Simple thread synchronization utility
+struct Barrier {
+    // Not using mutex/condvar for precision
+    shared: Arc<AtomicUsize>,
+    count: usize,
+}
+
+impl Barrier {
+    fn new(count: usize) -> Vec<Barrier> {
+        let shared = Arc::new(AtomicUsize::new(0));
+        (0..count).map(|_| Barrier { shared: shared.clone(), count: count }).collect()
+    }
+
+    fn new2() -> (Barrier, Barrier) {
+        let mut v = Barrier::new(2);
+        (v.pop().unwrap(), v.pop().unwrap())
+    }
+
+    /// Returns when `count` threads enter `wait`
+    fn wait(self) {
+        self.shared.fetch_add(1, Ordering::SeqCst);
+        while self.shared.load(Ordering::SeqCst) != self.count {
+        }
+    }
+}
+
+
+fn shared_close_sender_does_not_lose_messages_iter() {
+    let (tb, rb) = Barrier::new2();
+
+    let (tx, rx) = channel();
+    let _ = tx.clone(); // convert to shared
+
+    thread::spawn(move || {
+        tb.wait();
+        thread::sleep(Duration::from_micros(1));
+        tx.send(17).expect("send");
+        drop(tx);
+    });
+
+    let i = rx.into_iter();
+    rb.wait();
+    // Make sure it doesn't return disconnected before returning an element
+    assert_eq!(vec![17], i.collect::<Vec<_>>());
+}
+
+#[test]
+fn shared_close_sender_does_not_lose_messages() {
+    for _ in 0..10000 {
+        shared_close_sender_does_not_lose_messages_iter();
+    }
+}
+
+
+// https://github.com/rust-lang/rust/issues/39364
+fn concurrent_recv_timeout_and_upgrade_iter() {
+    // 1 us
+    let sleep = Duration::new(0, 1_000);
+
+    let (a, b) = Barrier::new2();
+    let (tx, rx) = channel();
+    let th = thread::spawn(move || {
+        a.wait();
+        loop {
+            match rx.recv_timeout(sleep) {
+                Ok(_) => {
+                    break;
+                },
+                Err(_) => {},
+            }
+        }
+    });
+    b.wait();
+    thread::sleep(sleep);
+    tx.clone().send(()).expect("send");
+    th.join().unwrap();
+}
+
+#[test]
+fn concurrent_recv_timeout_and_upgrade() {
+    // FIXME: fix and enable
+    if true { return }
+
+    // at the moment of writing this test fails like this:
+    // thread '<unnamed>' panicked at 'assertion failed: `(left == right)`
+    //  left: `4561387584`,
+    // right: `0`', libstd/sync/mpsc/shared.rs:253:13
+
+    for _ in 0..10000 {
+        concurrent_recv_timeout_and_upgrade_iter();
+    }
+}
+
+
+fn concurrent_writes_iter() {
+    const THREADS: usize = 4;
+    const PER_THR: usize = 100;
+
+    let mut bs = Barrier::new(THREADS + 1);
+    let (tx, rx) = channel();
+
+    let mut threads = Vec::new();
+    for j in 0..THREADS {
+        let tx = tx.clone();
+        let b = bs.pop().unwrap();
+        threads.push(thread::spawn(move || {
+            b.wait();
+            for i in 0..PER_THR {
+                tx.send(j * 1000 + i).expect("send");
+            }
+        }));
+    }
+
+    let b = bs.pop().unwrap();
+    b.wait();
+
+    let mut v: Vec<_> = rx.iter().take(THREADS * PER_THR).collect();
+    v.sort();
+
+    for j in 0..THREADS {
+        for i in 0..PER_THR {
+            assert_eq!(j * 1000 + i, v[j * PER_THR + i]);
+        }
+    }
+
+    for t in threads {
+        t.join().unwrap();
+    }
+
+    let one_us = Duration::new(0, 1000);
+
+    assert_eq!(TryRecvError::Empty, rx.try_recv().unwrap_err());
+    assert_eq!(RecvTimeoutError::Timeout, rx.recv_timeout(one_us).unwrap_err());
+
+    drop(tx);
+
+    assert_eq!(RecvError, rx.recv().unwrap_err());
+    assert_eq!(RecvTimeoutError::Disconnected, rx.recv_timeout(one_us).unwrap_err());
+    assert_eq!(TryRecvError::Disconnected, rx.try_recv().unwrap_err());
+}
+
+#[test]
+fn concurrent_writes() {
+    for _ in 0..100 {
+        concurrent_writes_iter();
+    }
+}