Make SubprocVecEnv works with DummyVecEnv (#908)

* Make SubprocVecEnv works with DummyVecEnv (nested environments for synchronous sampling)

* SubprocVecEnv now supports running environments in series in each process

* Added docstring to the test definition

* Added additional test to check, whether SubprocVecEnv results with the same output when in_series parameter is enabled and not

* Added more test cases for in_series parameter

* Refactored worker function, added docstring for in_series parameter

* Remove check for TF presence in setup.py

baselines/common/vec_env/subproc_vec_env.py

@@ -4,33 +4,36 @@ import numpy as np
 from .vec_env import VecEnv, CloudpickleWrapper, clear_mpi_env_vars
 
 
-def worker(remote, parent_remote, env_fn_wrapper):
+def worker(remote, parent_remote, env_fn_wrappers):
+    def step_env(env, action):
+        ob, reward, done, info = env.step(action)
+        if done:
+            ob = env.reset()
+        return ob, reward, done, info
+
     parent_remote.close()
-    env = env_fn_wrapper.x()
+    envs = [env_fn_wrapper() for env_fn_wrapper in env_fn_wrappers.x]
     try:
         while True:
             cmd, data = remote.recv()
             if cmd == 'step':
-                ob, reward, done, info = env.step(data)
-                if done:
-                    ob = env.reset()
-                remote.send((ob, reward, done, info))
+                remote.send([step_env(env, action) for env, action in zip(envs, data)])
             elif cmd == 'reset':
-                ob = env.reset()
-                remote.send(ob)
+                remote.send([env.reset() for env in envs])
             elif cmd == 'render':
-                remote.send(env.render(mode='rgb_array'))
+                remote.send([env.render(mode='rgb_array') for env in envs])
             elif cmd == 'close':
                 remote.close()
                 break
             elif cmd == 'get_spaces_spec':
-                remote.send((env.observation_space, env.action_space, env.spec))
+                remote.send((envs[0].observation_space, envs[0].action_space, envs[0].spec))
             else:
                 raise NotImplementedError
     except KeyboardInterrupt:
         print('SubprocVecEnv worker: got KeyboardInterrupt')
     finally:
-        env.close()
+        for env in envs:
+            env.close()
 
 
 class SubprocVecEnv(VecEnv):
@@ -38,17 +41,23 @@ class SubprocVecEnv(VecEnv):
     VecEnv that runs multiple environments in parallel in subproceses and communicates with them via pipes.
     Recommended to use when num_envs > 1 and step() can be a bottleneck.
     """
-    def __init__(self, env_fns, spaces=None, context='spawn'):
+    def __init__(self, env_fns, spaces=None, context='spawn', in_series=1):
         """
         Arguments:
 
         env_fns: iterable of callables -  functions that create environments to run in subprocesses. Need to be cloud-pickleable
+        in_series: number of environments to run in series in a single process
+        (e.g. when len(env_fns) == 12 and in_series == 3, it will run 4 processes, each running 3 envs in series)
         """
         self.waiting = False
         self.closed = False
+        self.in_series = in_series
         nenvs = len(env_fns)
+        assert nenvs % in_series == 0, "Number of envs must be divisible by number of envs to run in series"
+        self.nremotes = nenvs // in_series
+        env_fns = np.array_split(env_fns, self.nremotes)
         ctx = mp.get_context(context)
-        self.remotes, self.work_remotes = zip(*[ctx.Pipe() for _ in range(nenvs)])
+        self.remotes, self.work_remotes = zip(*[ctx.Pipe() for _ in range(self.nremotes)])
         self.ps = [ctx.Process(target=worker, args=(work_remote, remote, CloudpickleWrapper(env_fn)))
                    for (work_remote, remote, env_fn) in zip(self.work_remotes, self.remotes, env_fns)]
         for p in self.ps:
@@ -61,10 +70,11 @@ class SubprocVecEnv(VecEnv):
         self.remotes[0].send(('get_spaces_spec', None))
         observation_space, action_space, self.spec = self.remotes[0].recv()
         self.viewer = None
-        VecEnv.__init__(self, len(env_fns), observation_space, action_space)
+        VecEnv.__init__(self, nenvs, observation_space, action_space)
 
     def step_async(self, actions):
         self._assert_not_closed()
+        actions = np.array_split(actions, self.nremotes)
         for remote, action in zip(self.remotes, actions):
             remote.send(('step', action))
         self.waiting = True
@@ -72,6 +82,7 @@ class SubprocVecEnv(VecEnv):
     def step_wait(self):
         self._assert_not_closed()
         results = [remote.recv() for remote in self.remotes]
+        results = _flatten_list(results)
         self.waiting = False
         obs, rews, dones, infos = zip(*results)
         return _flatten_obs(obs), np.stack(rews), np.stack(dones), infos
@@ -80,7 +91,9 @@ class SubprocVecEnv(VecEnv):
         self._assert_not_closed()
         for remote in self.remotes:
             remote.send(('reset', None))
-        return _flatten_obs([remote.recv() for remote in self.remotes])
+        obs = [remote.recv() for remote in self.remotes]
+        obs = _flatten_list(obs)
+        return _flatten_obs(obs)
 
     def close_extras(self):
         self.closed = True
@@ -97,6 +110,7 @@ class SubprocVecEnv(VecEnv):
         for pipe in self.remotes:
             pipe.send(('render', None))
         imgs = [pipe.recv() for pipe in self.remotes]
+        imgs = _flatten_list(imgs)
         return imgs
 
     def _assert_not_closed(self):
@@ -115,3 +129,10 @@ def _flatten_obs(obs):
         return {k: np.stack([o[k] for o in obs]) for k in keys}
     else:
         return np.stack(obs)
+
+def _flatten_list(l):
+    assert isinstance(l, (list, tuple))
+    assert len(l) > 0
+    assert all([len(l_) > 0 for l_ in l])
+
+    return [l__ for l_ in l for l__ in l_]

baselines/common/vec_env/test_vec_env.py

@@ -67,6 +67,50 @@ def test_vec_env(klass, dtype):  # pylint: disable=R0914
     assert_venvs_equal(env1, env2, num_steps=num_steps)
 
 
+@pytest.mark.parametrize('dtype', ('uint8', 'float32'))
+@pytest.mark.parametrize('num_envs_in_series', (3, 4, 6))
+def test_sync_sampling(dtype, num_envs_in_series):
+    """
+    Test that a SubprocVecEnv running with envs in series
+    outputs the same as DummyVecEnv.
+    """
+    num_envs = 12
+    num_steps = 100
+    shape = (3, 8)
+
+    def make_fn(seed):
+        """
+        Get an environment constructor with a seed.
+        """
+        return lambda: SimpleEnv(seed, shape, dtype)
+    fns = [make_fn(i) for i in range(num_envs)]
+    env1 = DummyVecEnv(fns)
+    env2 = SubprocVecEnv(fns, in_series=num_envs_in_series)
+    assert_venvs_equal(env1, env2, num_steps=num_steps)
+
+
+@pytest.mark.parametrize('dtype', ('uint8', 'float32'))
+@pytest.mark.parametrize('num_envs_in_series', (3, 4, 6))
+def test_sync_sampling_sanity(dtype, num_envs_in_series):
+    """
+    Test that a SubprocVecEnv running with envs in series
+    outputs the same as SubprocVecEnv without running in series.
+    """
+    num_envs = 12
+    num_steps = 100
+    shape = (3, 8)
+
+    def make_fn(seed):
+        """
+        Get an environment constructor with a seed.
+        """
+        return lambda: SimpleEnv(seed, shape, dtype)
+    fns = [make_fn(i) for i in range(num_envs)]
+    env1 = SubprocVecEnv(fns)
+    env2 = SubprocVecEnv(fns, in_series=num_envs_in_series)
+    assert_venvs_equal(env1, env2, num_steps=num_steps)
+
+
 class SimpleEnv(gym.Env):
     """
     An environment with a pre-determined observation space