[Feature] Transform for partial steps

ghstack-source-id: 8110f09
Pull Request resolved: #2777

Author: Vincent Moens

.github/workflows/test-linux.yml

@@ -53,38 +53,6 @@ jobs:
         ## setup_env.sh
         bash .github/unittest/linux/scripts/run_all.sh
 
-  tests-cpu-oldget:
-    # Tests that TD_GET_DEFAULTS_TO_NONE=0 works fine as this will be the default for TD up to 0.7
-    strategy:
-      matrix:
-        python_version: ["3.12"]
-      fail-fast: false
-    uses: pytorch/test-infra/.github/workflows/linux_job_v2.yml@main
-    with:
-      runner: linux.12xlarge
-      repository: pytorch/rl
-      docker-image: "nvidia/cuda:12.2.0-devel-ubuntu22.04"
-      timeout: 90
-      script: |
-        if [[ "${{ github.ref }}" =~ release/* ]]; then
-          export RELEASE=1
-          export TORCH_VERSION=stable
-        else
-          export RELEASE=0
-          export TORCH_VERSION=nightly
-        fi
-        export TD_GET_DEFAULTS_TO_NONE=0
-
-        # Set env vars from matrix
-        export PYTHON_VERSION=${{ matrix.python_version }}
-        export CU_VERSION="cpu"
-
-        echo "PYTHON_VERSION: $PYTHON_VERSION"
-        echo "CU_VERSION: $CU_VERSION"
-
-        ## setup_env.sh
-        bash .github/unittest/linux/scripts/run_all.sh
-
   tests-gpu:
     strategy:
       matrix:

docs/source/reference/envs.rst

@@ -163,6 +163,81 @@ provides more information on how to design a custom environment from scratch.
     GymLikeEnv
     EnvMetaData
 
+Partial steps and partial resets
+--------------------------------
+
+TorchRL allows environments to reset some but not all the environments, or run a step in one but not all environments.
+If there is only one environment in the batch, then a partial reset / step is also allowed with the behavior detailed
+below.
+
+Batching environments and locking the batch
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. _ref_batch_locked:
+
+Before detailing what partial resets and partial steps do, we must distinguish cases where an environment has
+a batch size of its own (mostly stateful environments) or when the environment is just a mere module that, given an
+input of arbitrary size, batches the operations over all elements (mostly stateless environments).
+
+This is controlled via the :attr:`~torchrl.envs.batch_locked` attribute: a batch-locked environment requires all input
+tensordicts to have the same batch-size as the env's. Typical examples of these environments are
+:class:`~torchrl.envs.GymEnv` and related. Batch-unlocked envs are by contrast allowed to work with any input size.
+Notable examples are :class:`~torchrl.envs.BraxEnv` or :class:`~torchrl.envs.JumanjiEnv`.
+
+Executing partial steps in a batch-unlocked environment is straightforward: one just needs to mask the part of the
+tensordict that does not need to be executed, pass the other part to `step` and merge the results with the previous
+input.
+
+Batched environments (:class:`~torchrl.envs.ParallelEnv` and :class:`~torchrl.envs.SerialEnv`) can also deal with
+partial steps easily, they just pass the actions to the sub-environments that are required to be executed.
+
+In all other cases, TorchRL assumes that the environment handles the partial steps correctly.
+
+.. warning:: This means that custom environments may silently run the non-required steps as there is no way for torchrl
+    to control what happens within the `_step` method!
+
+Partial Steps
+~~~~~~~~~~~~~
+
+.. _ref_partial_steps:
+
+Partial steps are controlled via the temporary key `"_step"` which points to a boolean mask of the
+size of the tensordict that holds it. The classes armed to deal with this are:
+
+- Batched environments: :class:`~torchrl.envs.ParallelEnv` and :class:`~torchrl.envs.SerialEnv` will dispatch the
+  action to and only to the environments where `"_step"` is `True`;
+- Batch-unlocked environments;
+- Unbatched environments (i.e., environments without batch size). In these environments, the :meth:`~torchrl.envs.EnvBase.step`
+  method will first look for a `"_step"` entry and, if present, act accordingly.
+  If a :class:`~torchrl.envs.Transform` instance passes a `"_step"` entry to the tensordict, it is also captured by
+  :class:`~torchrl.envs.TransformedEnv`'s own `_step` method which will skip the `base_env.step` as well as any further
+  transformation.
+
+When dealing with partial steps, the strategy is always to use the step output and mask missing values with the previous
+content of the input tensordict, if present, or a `0`-valued tensor if the tensor cannot be found. This means that
+if the input tensordict does not contain all the previous observations, then the output tensordict will be 0-valued for
+all the non-stepped elements. Within batched environments, data collectors and rollouts utils, this is an issue that
+is not observed because these classes handle the passing of data properly.
+
+Partial steps are an essential feature of :meth:`~torchrl.envs.EnvBase.rollout` when `break_when_all_done` is `True`,
+as the environments with a `True` done state will need to be skipped during calls to `_step`.
+
+The :class:`~torchrl.envs.ConditionalSkip` transform allows you to programmatically ask for (partial) step skips.
+
+Partial Resets
+~~~~~~~~~~~~~~
+
+.. _ref_partial_resets:
+
+Partial resets work pretty much like partial steps, but with the `"_reset"` entry.
+
+The same restrictions of partial steps apply to partial resets.
+
+Likewise, partial resets are an essential feature of :meth:`~torchrl.envs.EnvBase.rollout` when `break_when_any_done` is `True`,
+as the environments with a `True` done state will need to be reset, but not others.
+
+See te following paragraph for a deep dive in partial resets within batched and vectorized environments.
+
 Vectorized envs
 ---------------
 
@@ -886,6 +961,7 @@ to be able to create this other composition:
     CenterCrop
     ClipTransform
     Compose
+    ConditionalSkip
     Crop
     DTypeCastTransform
     DeviceCastTransform

test/mocking_classes.py

@@ -635,7 +635,9 @@ def _step(
         while done.shape != tensordict.shape:
             done = done.any(-1)
         done = reward = done.unsqueeze(-1)
-        tensordict.set("reward", reward.to(torch.get_default_dtype()))
+        tensordict.set(
+            "reward", reward.to(self.reward_spec.dtype).expand(self.reward_spec.shape)
+        )
         tensordict.set("done", done)
         tensordict.set("terminated", done)
         return tensordict

test/test_env.py

@@ -4112,17 +4112,21 @@ def test_parallel_partial_steps(
                 use_buffers=use_buffers,
                 device=device,
             )
-            td = penv.reset()
-            psteps = torch.zeros(4, dtype=torch.bool)
-            psteps[[1, 3]] = True
-            td.set("_step", psteps)
-
-            td.set("action", penv.full_action_spec[penv.action_key].one())
-            td = penv.step(td)
-            assert (td[0].get("next") == 0).all()
-            assert (td[1].get("next") != 0).any()
-            assert (td[2].get("next") == 0).all()
-            assert (td[3].get("next") != 0).any()
+            try:
+                td = penv.reset()
+                psteps = torch.zeros(4, dtype=torch.bool)
+                psteps[[1, 3]] = True
+                td.set("_step", psteps)
+
+                td.set("action", penv.full_action_spec[penv.action_key].one())
+                td = penv.step(td)
+                assert_allclose_td(td[0].get("next"), td[0], intersection=True)
+                assert (td[1].get("next") != 0).any()
+                assert_allclose_td(td[2].get("next"), td[2], intersection=True)
+                assert (td[3].get("next") != 0).any()
+            finally:
+                penv.close()
+                del penv
 
     @pytest.mark.parametrize("use_buffers", [False, True])
     def test_parallel_partial_step_and_maybe_reset(
@@ -4135,17 +4139,21 @@ def test_parallel_partial_step_and_maybe_reset(
                 use_buffers=use_buffers,
                 device=device,
             )
-            td = penv.reset()
-            psteps = torch.zeros(4, dtype=torch.bool)
-            psteps[[1, 3]] = True
-            td.set("_step", psteps)
-
-            td.set("action", penv.full_action_spec[penv.action_key].one())
-            td, tdreset = penv.step_and_maybe_reset(td)
-            assert (td[0].get("next") == 0).all()
-            assert (td[1].get("next") != 0).any()
-            assert (td[2].get("next") == 0).all()
-            assert (td[3].get("next") != 0).any()
+            try:
+                td = penv.reset()
+                psteps = torch.zeros(4, dtype=torch.bool)
+                psteps[[1, 3]] = True
+                td.set("_step", psteps)
+
+                td.set("action", penv.full_action_spec[penv.action_key].one())
+                td, tdreset = penv.step_and_maybe_reset(td)
+                assert_allclose_td(td[0].get("next"), td[0], intersection=True)
+                assert (td[1].get("next") != 0).any()
+                assert_allclose_td(td[2].get("next"), td[2], intersection=True)
+                assert (td[3].get("next") != 0).any()
+            finally:
+                penv.close()
+                del penv
 
     @pytest.mark.parametrize("use_buffers", [False, True])
     def test_serial_partial_steps(self, use_buffers, device, env_device):
@@ -4156,17 +4164,21 @@ def test_serial_partial_steps(self, use_buffers, device, env_device):
                 use_buffers=use_buffers,
                 device=device,
             )
-            td = penv.reset()
-            psteps = torch.zeros(4, dtype=torch.bool)
-            psteps[[1, 3]] = True
-            td.set("_step", psteps)
-
-            td.set("action", penv.full_action_spec[penv.action_key].one())
-            td = penv.step(td)
-            assert (td[0].get("next") == 0).all()
-            assert (td[1].get("next") != 0).any()
-            assert (td[2].get("next") == 0).all()
-            assert (td[3].get("next") != 0).any()
+            try:
+                td = penv.reset()
+                psteps = torch.zeros(4, dtype=torch.bool)
+                psteps[[1, 3]] = True
+                td.set("_step", psteps)
+
+                td.set("action", penv.full_action_spec[penv.action_key].one())
+                td = penv.step(td)
+                assert_allclose_td(td[0].get("next"), td[0], intersection=True)
+                assert (td[1].get("next") != 0).any()
+                assert_allclose_td(td[2].get("next"), td[2], intersection=True)
+                assert (td[3].get("next") != 0).any()
+            finally:
+                penv.close()
+                del penv
 
     @pytest.mark.parametrize("use_buffers", [False, True])
     def test_serial_partial_step_and_maybe_reset(self, use_buffers, device, env_device):
@@ -4184,9 +4196,9 @@ def test_serial_partial_step_and_maybe_reset(self, use_buffers, device, env_devi
 
             td.set("action", penv.full_action_spec[penv.action_key].one())
             td = penv.step(td)
-            assert (td[0].get("next") == 0).all()
+            assert_allclose_td(td[0].get("next"), td[0], intersection=True)
             assert (td[1].get("next") != 0).any()
-            assert (td[2].get("next") == 0).all()
+            assert_allclose_td(td[2].get("next"), td[2], intersection=True)
             assert (td[3].get("next") != 0).any()