contention patch

contention.diff

diff --git a/src/libstd/sys/unix/mutex.rs b/src/libstd/sys/unix/mutex.rs
index b43af8fdcaa..26c90cf6f31 100644
--- a/src/libstd/sys/unix/mutex.rs
+++ b/src/libstd/sys/unix/mutex.rs
@@ -1,6 +1,29 @@
 use crate::cell::UnsafeCell;
 use crate::mem::MaybeUninit;
 
+
+fn time_and_wrap(s: &str, f: impl FnOnce()) {
+    use crate::cell::Cell;
+    thread_local!(static SHOULD_CAPTURE: Cell<bool> = Cell::new(true););
+    SHOULD_CAPTURE.with(|capture| {
+        if capture.get() {
+            capture.set(false);
+            let start = crate::time::Instant::now();
+            f();
+            let elapsed = start.elapsed();
+            if elapsed.as_millis() > 300 {
+                use crate::io::Write;
+                let bt = crate::backtrace::Backtrace::force_capture();
+                let mut f = crate::fs::OpenOptions::new().create(true).append(true).open(&format!("/tmp/timings-{}", s)).unwrap();
+                let _ = f.write_all(format!("{} {:?}: {}", elapsed.as_nanos(), elapsed, bt).as_bytes());
+            }
+            capture.set(true);
+        } else {
+            f();
+        }
+    });
+}
+
 pub struct Mutex { inner: UnsafeCell<libc::pthread_mutex_t> }
 
 #[inline]
@@ -52,8 +75,10 @@ impl Mutex {
     }
     #[inline]
     pub unsafe fn lock(&self) {
-        let r = libc::pthread_mutex_lock(self.inner.get());
-        debug_assert_eq!(r, 0);
+        time_and_wrap("mutex", || {
+            let result = libc::pthread_mutex_lock(self.inner.get());
+            debug_assert_eq!(result, 0);
+        });
     }
     #[inline]
     pub unsafe fn unlock(&self) {
@@ -106,8 +131,10 @@ impl ReentrantMutex {
     }
 
     pub unsafe fn lock(&self) {
-        let result = libc::pthread_mutex_lock(self.inner.get());
-        debug_assert_eq!(result, 0);
+        time_and_wrap("reentrant", || {
+            let result = libc::pthread_mutex_lock(self.inner.get());
+            debug_assert_eq!(result, 0);
+        });
     }
 
     #[inline]