Merge pull request #1246 from Heap-Hop/opt_condvar

Update condvar in concurrency-with-threads

src/advance/concurrency-with-threads/sync1.md

@@ -451,18 +451,17 @@ fn main() {
     let ccond = cond.clone();
 
     let hdl = spawn(move || {
-        let mut m = { *cflag.lock().unwrap() };
+        let mut lock = cflag.lock().unwrap();
         let mut counter = 0;
 
         while counter < 3 {
-            while !m {
-                m = *ccond.wait(cflag.lock().unwrap()).unwrap();
-            }
-
-            {
-                m = false;
-                *cflag.lock().unwrap() = false;
+            while !*lock {
+                // wait方法会接收一个MutexGuard<'a, T>，且它会自动地暂时释放这个锁，使其他线程可以拿到锁并进行数据更新。
+                // 同时当前线程在此处会被阻塞，直到被其他地方notify后，它会将原本的MutexGuard<'a, T>还给我们，即重新获取到了锁，同时唤醒了此线程。
+                lock = ccond.wait(lock).unwrap();
             }
+            
+            *lock = false;
 
             counter += 1;
             println!("inner counter: {}", counter);