Use higher resolution time_ns() and avoid division by zero (#91)

* Use higher resolution time_ns and add max to avoid division by zero

* Add missing imports

* Update changelog

docs/misc/changelog.rst

@@ -15,6 +15,7 @@ New Features:
 
 Bug Fixes:
 ^^^^^^^^^^
+- Fixed division by zero error when computing FPS when a small number of time has elapsed in operating systems with low-precision timers.
 
 Deprecations:
 ^^^^^^^^^^^^^

sb3_contrib/ars/ars.py

@@ -1,4 +1,5 @@
 import copy
+import sys
 import time
 import warnings
 from functools import partial
@@ -242,8 +243,8 @@ class ARS(BaseAlgorithm):
         """
         Dump information to the logger.
         """
-        time_elapsed = time.time() - self.start_time
-        fps = int((self.num_timesteps - self._num_timesteps_at_start) / (time_elapsed + 1e-8))
+        time_elapsed = max((time.time_ns() - self.start_time) / 1e9, sys.float_info.epsilon)
+        fps = int((self.num_timesteps - self._num_timesteps_at_start) / time_elapsed)
         if len(self.ep_info_buffer) > 0 and len(self.ep_info_buffer[0]) > 0:
             self.logger.record("rollout/ep_rew_mean", safe_mean([ep_info["r"] for ep_info in self.ep_info_buffer]))
             self.logger.record("rollout/ep_len_mean", safe_mean([ep_info["l"] for ep_info in self.ep_info_buffer]))

sb3_contrib/ppo_mask/ppo_mask.py

@@ -1,3 +1,4 @@
+import sys
 import time
 from collections import deque
 from typing import Any, Dict, Optional, Tuple, Type, Union
@@ -242,7 +243,7 @@ class MaskablePPO(OnPolicyAlgorithm):
         :return:
         """
 
-        self.start_time = time.time()
+        self.start_time = time.time_ns()
         if self.ep_info_buffer is None or reset_num_timesteps:
             # Initialize buffers if they don't exist, or reinitialize if resetting counters
             self.ep_info_buffer = deque(maxlen=100)
@@ -566,13 +567,14 @@ class MaskablePPO(OnPolicyAlgorithm):
 
             # Display training infos
             if log_interval is not None and iteration % log_interval == 0:
-                fps = int((self.num_timesteps - self._num_timesteps_at_start) / (time.time() - self.start_time))
+                time_elapsed = max((time.time_ns() - self.start_time) / 1e9, sys.float_info.epsilon)
+                fps = int((self.num_timesteps - self._num_timesteps_at_start) / time_elapsed)
                 self.logger.record("time/iterations", iteration, exclude="tensorboard")
                 if len(self.ep_info_buffer) > 0 and len(self.ep_info_buffer[0]) > 0:
                     self.logger.record("rollout/ep_rew_mean", safe_mean([ep_info["r"] for ep_info in self.ep_info_buffer]))
                     self.logger.record("rollout/ep_len_mean", safe_mean([ep_info["l"] for ep_info in self.ep_info_buffer]))
                 self.logger.record("time/fps", fps)
-                self.logger.record("time/time_elapsed", int(time.time() - self.start_time), exclude="tensorboard")
+                self.logger.record("time/time_elapsed", int(time_elapsed), exclude="tensorboard")
                 self.logger.record("time/total_timesteps", self.num_timesteps, exclude="tensorboard")
                 self.logger.dump(step=self.num_timesteps)