Hold cleanup handle in producer threads.

storage-proofs/porep/src/stacked/vanilla/create_label/multi.rs

@@ -260,9 +260,8 @@ fn create_layer_labels(
                 // This could fail, but we will ignore the error if so.
                 // It will be logged as a warning by `bind_core`.
                 debug!("binding core in producer thread {}", i);
-                if let Some(&core_index) = core_index {
-                    let _ = bind_core(core_index);
-                }
+                // When `_cleanup_handle` is dropped, the previous binding of thread will be restored.
+                let _cleanup_handle = core_index.map(|c| bind_core(*c));
 
                 create_label_runner(
                     parents_cache,