Update Doc/library/functools.rst

Co-Authored-By: Tim Peters <[email protected]>

Author: pablogsal

Doc/library/functools.rst

@@ -586,7 +586,13 @@ The :mod:`functools` module defines the following functions:
                task_queue.put(node)
 
            # When the work for a node is done, workers put the node in
-           # 'finalized_tasks_queue' so we can get more nodes to work on
+           # 'finalized_tasks_queue' so we can get more nodes to work on.
+           # The definition of 'is_active()` guarantees that, at this point, at
+           # least one node has been placed on 'task_queue' that hasn't yet
+           # been passed to `done()`, so this blocking `get()` must (eventually)
+           # succeed.  After calling `done()`, we loop back to call `get_ready()`
+           # again, so put newly freed nodes on 'task_queue' as soon as
+           # logically possible.
            node = finalized_tasks_queue.get()
 
            topological_sorter.done(node)