Auto merge of #12637 - asajeffrey:constellation-use-reentrant-logging-mutex, r=emilio

Replaced mutex in constellation logging by a reentrant mutex.

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The double-panic in #12553 may be caused by using a non-reentrant lock, which panics on reetry. This PR adds a reentrant lock type (slightly annoyingly, the implementation in std isn't exported) and uses it for logging. cc @jdm

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #12619.
- [X] These changes do not require tests because they are designed to remove a class of intermittents.

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tests/unit/util/lib.rs

@@ -8,4 +8,5 @@ extern crate util;
 
 mod opts;
 mod prefs;
+mod remutex;
 mod thread;

tests/unit/util/remutex.rs

@@ -0,0 +1,89 @@
+// Copyright 2015 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.
+
+// These tests came from https://github.com/rust-lang/rust/blob/master/src/libstd/sys/common/remutex.rs
+
+use std::cell::RefCell;
+use std::sync::Arc;
+use std::thread;
+use util::remutex::{ReentrantMutex, ReentrantMutexGuard};
+
+#[test]
+fn smoke() {
+    let m = ReentrantMutex::new(());
+    {
+        let a = m.lock().unwrap();
+        {
+            let b = m.lock().unwrap();
+            {
+                let c = m.lock().unwrap();
+                assert_eq!(*c, ());
+            }
+            assert_eq!(*b, ());
+        }
+        assert_eq!(*a, ());
+    }
+}
+
+#[test]
+fn is_mutex() {
+    let m = Arc::new(ReentrantMutex::new(RefCell::new(0)));
+    let m2 = m.clone();
+    let lock = m.lock().unwrap();
+    let child = thread::spawn(move || {
+        let lock = m2.lock().unwrap();
+        assert_eq!(*lock.borrow(), 4950);
+    });
+    for i in 0..100 {
+        let lock = m.lock().unwrap();
+        *lock.borrow_mut() += i;
+    }
+    drop(lock);
+    child.join().unwrap();
+}
+
+#[test]
+fn trylock_works() {
+    let m = Arc::new(ReentrantMutex::new(()));
+    let m2 = m.clone();
+    let _lock = m.try_lock().unwrap();
+    let _lock2 = m.try_lock().unwrap();
+    thread::spawn(move || {
+        let lock = m2.try_lock();
+        assert!(lock.is_err());
+    }).join().unwrap();
+    let _lock3 = m.try_lock().unwrap();
+}
+
+pub struct Answer<'a>(pub ReentrantMutexGuard<'a, RefCell<u32>>);
+impl<'a> Drop for Answer<'a> {
+    fn drop(&mut self) {
+        *self.0.borrow_mut() = 42;
+    }
+}
+
+#[test]
+fn poison_works() {
+    let m = Arc::new(ReentrantMutex::new(RefCell::new(0)));
+    let mc = m.clone();
+    let result = thread::spawn(move ||{
+        let lock = mc.lock().unwrap();
+        *lock.borrow_mut() = 1;
+        let lock2 = mc.lock().unwrap();
+        *lock.borrow_mut() = 2;
+        let _answer = Answer(lock2);
+        println!("Intentionally panicking.");
+        panic!("What the answer to my lifetimes dilemma is?");
+    }).join();
+    assert!(result.is_err());
+    let r = m.lock().err().unwrap().into_inner();
+    assert_eq!(*r.borrow(), 42);
+}
+