add customizable thresholds for termination

impatient

@@ -14,6 +14,8 @@ parser.add_argument('-f', '--final', type=str, help='Expected final size/value a
 parser.add_argument('-i', '--interval', type=int, default=10, help='Interval in seconds between samples (default 10)')
 parser.add_argument('-w', '--window', type=int, default=100, help='Number of samples to keep for the sliding window (default 100)')
 parser.add_argument('-d', '--decay', type=float, default=1, help='Decay coefficient for older samples (default 1). Must be between 0 and 1 inclusive. The lower this is, the more responsive/swingy the estimate will be.')
+parser.add_argument('-V', '--termination-value-threshold', type=float, default=0.95, metavar='FRACTION', help='Fraction of the expected final value that must be reached in order to terminate (default 0.95). Reaching this threshold is necessary but not sufficient, see also -I')
+parser.add_argument('-I', '--termination-inactivity-threshold', type=int, default=10, metavar='COUNT', help='Number of consecutive unchanged samples that must be observed in order to terminate (default 10). Reaching this threshold is necessary but not sufficient, see also -V')
 tracker_types = parser.add_mutually_exclusive_group(required=True)
 tracker_types.add_argument('-p', '--path', type=str, help='Track total disk usage of a given path')
 tracker_types.add_argument('-c', '--command', type=str, help='Track value returned by a shell command; this should return a single number, optionally with a K/M/G/T suffix')
@@ -28,6 +30,12 @@ if args.window < 1:
 if args.decay < 0 or args.decay > 1:
     print('decay coefficient must be between 0 and 1', file=sys.stderr)
     exit(1)
+if args.termination_value_threshold < 0 or args.termination_value_threshold > 1:
+    print('termination value threshold must be between 0 and 1', file=sys.stderr)
+    exit(1)
+if args.termination_inactivity_threshold < 0:
+    print('termination inactivity threshold must be nonnegative', file=sys.stderr)
+    exit(1)
 
 def parse_value(v):
     suffix = v[-1].upper()
@@ -65,6 +73,9 @@ else:
 
 if args.final:
     final = parse_value(args.final)
+    if final <= 0:
+        print('final value must be positive', file=sys.stderr)
+        exit(1)
 else:
     final = None
 
@@ -109,6 +120,6 @@ while True:
             ), end='')
     sys.stdout.flush()
 
-    if final and current >= final and all(d == 0 for d in deltas[-10:]):
+    if final and current >= args.termination_value_threshold*final and all(d == 0 for d in deltas[-args.termination_inactivity_threshold:]):
         print()
         break