From fba8d10dc59213d173d93d3a2fda10807b4e6a50 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Linus=20F=C3=A4rnstrand?= <faern@faern.net>
Date: Sat, 16 Nov 2019 15:05:15 +0100
Subject: [PATCH] Implement test without relying on std Mutex/Condvar

---
 core/src/parking_lot.rs | 51 ++++++++++++++++++-----------------------
 1 file changed, 22 insertions(+), 29 deletions(-)

diff --git a/core/src/parking_lot.rs b/core/src/parking_lot.rs
index fb7df0f5..15baa554 100644
--- a/core/src/parking_lot.rs
+++ b/core/src/parking_lot.rs
@@ -1396,8 +1396,8 @@ mod tests {
     use std::{
         ptr,
         sync::{
-            atomic::{AtomicIsize, AtomicPtr, Ordering},
-            Arc, Condvar, Mutex,
+            atomic::{AtomicIsize, AtomicPtr, AtomicUsize, Ordering},
+            Arc,
         },
         thread,
         time::Duration,
@@ -1488,8 +1488,7 @@ mod tests {
 
     struct SingleLatchTest {
         semaphore: AtomicIsize,
-        lock: Mutex<usize>,
-        condition: Condvar,
+        num_awake: AtomicUsize,
         /// Holds the pointer to the last *unprocessed* woken up thread.
         last_awoken: AtomicPtr<ThreadData>,
         /// Total number of threads participating in this test.
@@ -1501,8 +1500,7 @@ mod tests {
             Self {
                 // This implements a fair (FIFO) semaphore, and it starts out unavailable.
                 semaphore: AtomicIsize::new(0),
-                lock: Mutex::new(0),
-                condition: Condvar::new(),
+                num_awake: AtomicUsize::new(0),
                 last_awoken: AtomicPtr::new(ptr::null_mut()),
                 num_threads,
             }
@@ -1513,12 +1511,9 @@ mod tests {
             self.down();
 
             // Report back to the test verification code that this thread woke up
-            let mut num_awake = self.lock.lock().expect("Test thread poisoned a lock 1");
-            *num_awake += 1;
             let this_thread_ptr = super::with_thread_data(|t| t as *const _ as *mut _);
             self.last_awoken.store(this_thread_ptr, Ordering::SeqCst);
-            std::mem::drop(num_awake);
-            self.condition.notify_one();
+            self.num_awake.fetch_add(1, Ordering::SeqCst);
         }
 
         pub fn unpark_one(&self, single_unpark_index: usize) {
@@ -1532,21 +1527,17 @@ mod tests {
             });
             assert!(queue.len() <= self.num_threads - single_unpark_index);
 
-            // Lock before up() in order to guarantee we will reach condition.wait() below *before*
-            // the test thread reaches condition.notify_one()?
-            let mut num_awake = self.lock.lock().expect("Test thread poisoned a lock 3");
+            let num_awake_before_up = self.num_awake.load(Ordering::SeqCst);
 
             self.up();
 
             // Wait for a parked thread to wake up and update num_awake + last_awoken.
-            num_awake = self
-                .condition
-                .wait(num_awake)
-                .expect("Condvar::wait got poisoned lock 2");
-            assert_eq!(*num_awake, single_unpark_index + 1);
+            while self.num_awake.load(Ordering::SeqCst) != num_awake_before_up + 1 {
+                thread::yield_now();
+            }
 
-            let last_awoken = self.last_awoken.load(Ordering::SeqCst);
             // At this point the other thread should have set last_awoken inside the run() method
+            let last_awoken = self.last_awoken.load(Ordering::SeqCst);
             assert!(!last_awoken.is_null());
             if !queue.is_empty() && queue[0] != last_awoken {
                 panic!(
@@ -1559,7 +1550,7 @@ mod tests {
 
         pub fn finish(&self, num_single_unparks: usize) {
             // The amount of threads not unparked via unpark_one
-            let mut num_threads_left = self.num_threads - num_single_unparks;
+            let mut num_threads_left = self.num_threads.checked_sub(num_single_unparks).unwrap();
 
             // Wake remaining threads up with unpark_all. Has to be in a loop, because there might
             // still be threads that has not yet parked.
@@ -1570,24 +1561,26 @@ mod tests {
                 });
                 assert!(num_waiting_on_address <= num_threads_left);
 
-                let mut num_awake = self.lock.lock().expect("Test thread poisoned a lock 2");
-                let num_awake_before_unpark = *num_awake;
+                let num_awake_before_unpark = self.num_awake.load(Ordering::SeqCst);
 
                 let num_unparked =
                     unsafe { super::unpark_all(self.semaphore_addr(), DEFAULT_UNPARK_TOKEN) };
                 assert!(num_unparked >= num_waiting_on_address);
+                assert!(num_unparked <= num_threads_left);
 
-                // Wait for all unparked parked thread to wake up and update num_awake + last_awoken.
-                while *num_awake < num_awake_before_unpark + num_unparked {
-                    num_awake = self
-                        .condition
-                        .wait(num_awake)
-                        .expect("Condvar::wait got poisoned lock 1");
+                // Wait for all unparked threads to wake up and update num_awake + last_awoken.
+                while self.num_awake.load(Ordering::SeqCst)
+                    != num_awake_before_unpark + num_unparked
+                {
+                    thread::yield_now()
                 }
 
-                num_threads_left -= num_unparked;
+                num_threads_left = num_threads_left.checked_sub(num_unparked).unwrap();
             }
+            // By now, all threads should have been woken up
+            assert_eq!(self.num_awake.load(Ordering::SeqCst), self.num_threads);
 
+            // Make sure no thread is parked on our semaphore address
             let mut num_waiting_on_address = 0;
             for_each(self.semaphore_addr(), |_thread_data| {
                 num_waiting_on_address += 1;