refactor: Give the spec's attempts name to the counter that drives the delay

The exponent driver was _n and a second counter held the name attempts,
which is what Requirement 1.4.1 calls the exponent driver. A reviewer
reading self.attempts against the spec was reading the wrong field.

The second counter is gone. It had no reader outside tests, not even a
logger, and every test that used it recorded only normal failures --
where the two counters are equal by construction.

Author: jsonbailey

ldclient/impl/retry.py

@@ -140,9 +140,9 @@ class RetryState:
     Tracks how long a data source should wait before its next attempt.
 
     A failure moves the state on and decides the next wait, which
-    :attr:`next_delay` reports. The delay for attempt ``n`` is
-    ``min(min_delay * 2 ** (n - 1), max_delay)``, less a random jitter of up to
-    half of it, and never less than the operating cadence.
+    :attr:`next_delay` reports. The delay is
+    ``min(min_delay * 2 ** (attempts - 1), max_delay)``, less a random jitter
+    of up to half of it, and never less than the operating cadence.
 
     An unexpected failure moves the state to the extended regime, which raises
     both delay bounds. The bounds stay raised until the reset condition is met,
@@ -179,11 +179,10 @@ def __init__(
         self._reset_policy = reset_policy
         self._operating_cadence = operating_cadence
 
-        self._n = 0
+        self._attempts = 0
         self._extended = False
         self._min_delay = self._normal_initial_delay
         self._max_delay = max(self._normal_ceiling_delay, self._normal_initial_delay)
-        self._attempts = 0
         # Read before any outcome is recorded, this is the ordinary interval.
         self._next_delay = self._operating_cadence
 
@@ -204,7 +203,6 @@ def record_failure(self, kind: FailureKind) -> None:
         """
         # Only a time-based policy needs this: nothing runs while a stream is healthy.
         self._reset_if_due()
-        self._attempts += 1
         self._reset_policy.note_failure()
 
         if kind is FailureKind.UNEXPECTED and not self._extended:
@@ -215,11 +213,11 @@ def record_failure(self, kind: FailureKind) -> None:
             self._extended = True
             self._min_delay = self._extended_initial_delay
             self._max_delay = max(self._extended_ceiling_delay, self._min_delay)
-            self._n = 1
+            self._attempts = 1
         else:
-            self._n += 1
+            self._attempts += 1
 
-        exponent = min(max(self._n - 1, 0), _MAX_BACKOFF_EXPONENT)
+        exponent = min(max(self._attempts - 1, 0), _MAX_BACKOFF_EXPONENT)
         delay = min(self._min_delay * (2**exponent), self._max_delay)
         jitter = random.random() * delay / 2
 
@@ -243,7 +241,6 @@ def _reset_if_due(self) -> None:
         the delay bounds to the normal regime."""
         if not self._reset_policy.is_satisfied():
             return
-        self._n = 0
         self._attempts = 0
         self._extended = False
         self._min_delay = self._normal_initial_delay

ldclient/testing/impl/test_retry.py

@@ -454,7 +454,7 @@ def test_attempts_counts_every_failure(self):
         assert state._attempts == 5
 
     def test_a_reset_starts_the_attempt_count_over(self):
-        # A reset clears both counters, so the next failure is attempt 1.
+        # A reset clears the counter, so the next failure is attempt 1.
         with frozen_clock() as clock:
             state = for_streaming(1)
             state.record_failure(NORMAL)