[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: 582427762

Author: hawkinsp

chex/_src/asserts_test.py

@@ -1103,7 +1103,7 @@ def test_assert_tree_has_only_ndarrays(self):
       asserts.assert_tree_has_only_ndarrays({'a': jnp.zeros(101), 'b': [1, 2]})
 
   def test_assert_tree_is_on_host(self):
-    cpu = jax.devices('cpu')[0]
+    cpu = jax.local_devices(backend='cpu')[0]
 
     # Check Numpy arrays.
     for flag in (False, True):
@@ -1173,7 +1173,7 @@ def test_assert_tree_is_on_host(self):
 
   def test_assert_tree_is_on_device(self):
     # Check CPU platform.
-    cpu = jax.devices('cpu')[0]
+    cpu = jax.local_devices(backend='cpu')[0]
     to_cpu = lambda x: jax.device_put(x, cpu)
 
     cpu_tree = {'a': to_cpu(np.zeros(1)), 'b': to_cpu(np.ones(3))}
@@ -1262,7 +1262,7 @@ def _format(*devs):
       return re.escape(f'{devs}')
 
     # Check single-device case.
-    cpu = jax.devices('cpu')[0]
+    cpu = jax.local_devices(backend='cpu')[0]
     cpu_tree = jax.device_put_replicated(np_tree, (cpu,))
 
     asserts.assert_tree_is_sharded(cpu_tree, devices=(cpu,))