reference/generated/torchrl.modules.inference_server.PolicyClientModule

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PolicyClientModule

class torchrl.modules.inference_server.PolicyClientModule(*args, **kwargs)

TensorDict policy wrapper for remote inference-server clients.

PolicyClientModule makes a transport client look like a TorchRL policy: it accepts a TensorDictBase, submits it to an InferenceServer, and returns the TensorDict produced by the remote policy. It can be passed anywhere a TensorDict policy module is expected.

This class is the reference implementation of TorchRL’s service client contract: it duck-types the domain interface (a policy client IS a TensorDict policy, so consumer code cannot tell local from remote), it is cheap and picklable (it can be handed to spawned workers), and it carries no lifecycle rights – clients can call the service but never start or shut it down; only the owner that constructed the server can.

Note

Unlike a local TensorDictModule, the result crosses a transport boundary, so forward() returns a new TensorDict rather than writing the out_keys into the input TensorDict. Use the return value; do not rely on in-place updates of the input.

Parameters:

client (Callable or InferenceTransport) – actor-side inference client. If a transport is provided, transport.client() is called.

Keyword Arguments:

• in_keys (sequence of NestedKey, optional) – input keys advertised by the module. The full input TensorDict is still sent to the server.

• out_keys (sequence of NestedKey, optional) – output keys advertised by the module.

• max_inflight (int, optional) – maximum number of unresolved asynchronous requests submitted through this module; further submit() calls block until a slot frees up. A slot is freed when its request completes (including errors), not when result() is first called; a timed-out result() keeps the slot. Must be at least 1. None means unbounded.

Note

The caller’s active tensordict.nn.interaction_type() is automatically attached to every transport request, and the server executes the remote policy under that exploration context – exactly as a local policy would see it. In-process (plain callable) clients need no propagation since the caller’s context is already active.

Note

Version tracking is an instance of the generic service-stamped metadata pattern: a service may stamp every response with metadata describing the state it was served from (here: the behavior-policy version), and the data pipeline may enforce freshness constraints on that metadata. Bounded-staleness enforcement lives in the replay buffer through PolicyAgeFilter, which silently drops too-old elements on extend or sample instead of raising in the consumer.

Note

The default "policy_version" key is shared on purpose with the PolicyVersion transform and the collectors’ track_policy_version mechanism: they stamp the same concept (the behavior-policy version that produced the data), so consumers such as PolicyAgeFilter can read it without caring which component wrote it. Both counters are driven by the same weight-update cascade (update_policy_weights_), so they agree when wired through a weight-sync scheme. Keep a single authoritative writer per data stream – in a policy-server topology that is the server, which owns the weights; do not stack an independently-initialized PolicyVersion transform on top of server-stamped data.

Examples

>>> import torch
>>> import torch.nn as nn
>>> from tensordict import TensorDict
>>> from tensordict.nn import TensorDictModule
>>> from torchrl.modules.inference_server import (
...     InferenceServer,
...     PolicyClientModule,
...     ThreadingTransport,
... )
>>> policy = TensorDictModule(
...     nn.Linear(4, 2), in_keys=["observation"], out_keys=["action"]
... )
>>> transport = ThreadingTransport()
>>> server = InferenceServer(policy, transport).start()
>>> remote_policy = PolicyClientModule(
...     transport, in_keys=["observation"], out_keys=["action"]
... )
>>> td = remote_policy(TensorDict({"observation": torch.randn(4)}))
>>> "action" in td.keys()
True
>>> server.shutdown()

forward(tensordict: TensorDictBase) → TensorDictBase

Define the computation performed at every call.

Should be overridden by all subclasses.

Note

Although the recipe for forward pass needs to be defined within this function, one should call the Module instance afterwards instead of this since the former takes care of running the registered hooks while the latter silently ignores them.

submit(tensordict: TensorDictBase) → Future | _ImmediateFuture

Submit a TensorDict request and return a future-like object.

Parameters:

tensordict (TensorDictBase) – observation TensorDict to send to the remote policy.

Returns:

Future-like object whose result() method returns a TensorDict. When the wrapped client exposes submit this is the transport’s Future and submission errors raise synchronously; for a plain callable client the call runs eagerly and errors are deferred to result() on a reduced future that only implements done() and result().