[JAX] Replace uses of jax.devices("cpu") with jax.local_devices(backend="cpu").

An upcoming change to JAX will include non-local (addressable) CPU devices in jax.devices() when JAX is used multicontroller-style, where there are multiple Python processes.

This change preserves the current behavior by replacing uses of jax.devices("cpu"), which previously only returned local devices, with jax.local_devices("cpu"), which will return local devices both now and in the future.

This change is always be safe (i.e., it should always preserve the previous behavior) but it may sometimes be unnecessary if code is never used in a multicontroller setting.

PiperOrigin-RevId: 582544519

Author: hawkinsp

trax/layers/acceleration.py

@@ -208,7 +208,7 @@ def f(x):
 def _accelerate(f, n_devices):
   """Returns an accelerated version of ``f`` running on ``n_devices``."""
   if n_devices == 0:  # no accelerators - run on CPU
-    return fastmath.jit(f, device=jax.devices('cpu')[0])
+    return fastmath.jit(f, device=jax.local_devices(backend='cpu')[0])
 
   if n_devices == 1:
     return fastmath.jit(f)
@@ -248,7 +248,7 @@ def f(x):
 def on_cpu(x):
   """Puts ``x`` in CPU memory in JAX."""
   if fastmath.is_backend(fastmath.Backend.JAX):
-    return jax.device_put(x, jax.devices('cpu')[0])
+    return jax.device_put(x, jax.local_devices(backend='cpu')[0])
   else:
     return x