[Python 3]: replace time() with perf_counter() for better measure…

…ments of short duration. (openai#2385)

* Update record_episode_statistics.py

* Update stats_recorder.py

* Update async_vector_env.py

gym/vector/async_vector_env.py

@@ -349,10 +349,10 @@ def _poll(self, timeout=None):
         self._assert_is_running()
         if timeout is None:
             return True
-        end_time = time.time() + timeout
+        end_time = time.perf_counter() + timeout
         delta = None
         for pipe in self.parent_pipes:
-            delta = max(end_time - time.time(), 0)
+            delta = max(end_time - time.perf_counter(), 0)
             if pipe is None:
                 return False
             if pipe.closed or (not pipe.poll(delta)):

gym/wrappers/monitoring/stats_recorder.py

@@ -85,7 +85,7 @@ def before_reset(self):
 
         self.done = False
         if self.initial_reset_timestamp is None:
-            self.initial_reset_timestamp = time.time()
+            self.initial_reset_timestamp = time.perf_counter()
 
     def after_reset(self, observation):
         self.steps = 0
@@ -99,7 +99,7 @@ def save_complete(self):
         if self.steps is not None:
             self.episode_lengths.append(self.steps)
             self.episode_rewards.append(float(self.rewards))
-            self.timestamps.append(time.time())
+            self.timestamps.append(time.perf_counter())
 
     def close(self):
         self.flush()

gym/wrappers/record_episode_statistics.py

@@ -8,9 +8,7 @@ class RecordEpisodeStatistics(gym.Wrapper):
     def __init__(self, env, deque_size=100):
         super(RecordEpisodeStatistics, self).__init__(env)
         self.num_envs = getattr(env, "num_envs", 1)
-        self.t0 = (
-            time.time()
-        )  # TODO: use perf_counter when gym removes Python 2 support
+        self.t0 = time.perf_counter()
         self.episode_count = 0
         self.episode_returns = None
         self.episode_lengths = None
@@ -41,7 +39,7 @@ def step(self, action):
                 episode_info = {
                     "r": episode_return,
                     "l": episode_length,
-                    "t": round(time.time() - self.t0, 6),
+                    "t": round(time.perf_counter() - self.t0, 6),
                 }
                 infos[i]["episode"] = episode_info
                 self.return_queue.append(episode_return)