Two workers W1 and W2 working separately need two different tools, say drill and clamp to do some work (say precise drill). In order to do the job, each worker needs get both tools. However, due to the nature of work, W1 needs to get drill first and clamp second, while W2 needs to get clamp first and drill second. We obviously want to avoid a situation when W1 grabs drill and waits for clamp, while W2 grabs clamp and waits for drill