Use guaranteed delta history for changes in current pool size

Author: vertexclique

src/task/blocking.rs

@@ -100,12 +100,12 @@ fn create_blocking_thread() {
         .spawn(move || {
             let wait_limit = Duration::from_millis(1000 + rand_sleep_ms);
 
-            CURRENT_POOL_SIZE.fetch_add(1, Ordering::Relaxed);
+            CURRENT_POOL_SIZE.fetch_add(1, Ordering::SeqCst);
             while let Ok(task) = POOL.receiver.recv_timeout(wait_limit) {
                 abort_on_panic(|| task.run());
                 calculate_dispatch_frequency();
             }
-            CURRENT_POOL_SIZE.fetch_sub(1, Ordering::Relaxed);
+            CURRENT_POOL_SIZE.fetch_sub(1, Ordering::SeqCst);
         })
         .expect("cannot start a dynamic thread driving blocking tasks");
 }