Add more comments that explain example & usage

Change-Id: I4665cda50c2bbc8e0e323efb1baff653ace12579

taskflow/examples/create_parallel_volume.py

@@ -36,22 +36,59 @@ from taskflow.patterns import unordered_flow as uf
 from taskflow import task
 from taskflow.utils import reflection
 
+# INTRO: This examples shows how unordered_flow can be used to create a large
+# number of fake volumes in parallel (or serially, depending on a constant that
+# can be easily changed).
+
 
 @contextlib.contextmanager
-def show_time(name=''):
+def show_time(name):
     start = time.time()
     yield
     end = time.time()
     print(" -- %s took %0.3f seconds" % (name, end - start))
 
 
+# This affects how many volumes to create and how much time to *simulate*
+# passing for that volume to be created.
 MAX_CREATE_TIME = 3
 VOLUME_COUNT = 5
+
+# This will be used to determine if all the volumes are created in parallel
+# or whether the volumes are created serially (in an undefined ordered since
+# a unordered flow is used). Note that there is a disconnection between the
+# ordering and the concept of parallelism (since unordered items can still be
+# ran in a serial ordering). A typical use-case for offering both is to allow
+# for debugging using a serial approach, while when running at a larger scale
+# one would likely want to use the parallel approach.
+#
+# If you switch this flag from serial to parallel you can see the overall
+# time difference that this causes.
 SERIAL = False
+if SERIAL:
+    engine_conf = {
+        'engine': 'serial',
+    }
+else:
+    engine_conf = {
+        'engine': 'parallel',
+    }
 
 
 class VolumeCreator(task.Task):
     def __init__(self, volume_id):
+        # Note here that the volume name is composed of the name of the class
+        # along with the volume id that is being created, since a name of a
+        # task uniquely identifies that task in storage it is important that
+        # the name be relevant and identifiable if the task is recreated for
+        # subsequent resumption (if applicable).
+        #
+        # UUIDs are *not* used as they can not be tied back to a previous tasks
+        # state on resumption (since they are unique and will vary for each
+        # task that is created). A name based off the volume id that is to be
+        # created is more easily tied back to the original task so that the
+        # volume create can be resumed/revert, and is much easier to use for
+        # audit and tracking purposes.
         base_name = reflection.get_callable_name(self)
         super(VolumeCreator, self).__init__(name="%s-%s" % (base_name,
                                                             volume_id))
@@ -68,17 +105,13 @@ flow = uf.Flow("volume-maker")
 for i in range(0, VOLUME_COUNT):
     flow.add(VolumeCreator(volume_id="vol-%s" % (i)))
 
-if SERIAL:
-    engine_conf = {
-        'engine': 'serial',
-    }
-else:
-    engine_conf = {
-        'engine': 'parallel',
-    }
-
 
+# Show how much time the overall engine loading and running takes.
 with show_time(name=flow.name.title()):
     eng = engines.load(flow, engine_conf=engine_conf)
+    # This context manager automatically adds (and automatically removes) a
+    # helpful set of state transition notification printing helper utilities
+    # that show you exactly what transitions the engine is going through
+    # while running the various volume create tasks.
     with printing.PrintingListener(eng):
         eng.run()