Fix PPO input sharding to match pmap axis

brax/training/agents/ppo/train.py

@@ -753,16 +753,11 @@ def training_epoch_with_timing(
         {},
     )
 
-  devices = jax.local_devices()[:local_devices_to_use]
-  mesh = jax.sharding.Mesh(np.array(devices), ('_device_put_sharded',))
-  sharding = jax.NamedSharding(mesh, jax.P('_device_put_sharded'))
-
-  def _replicate(x):
-    if isinstance(x, jax.Array):
-      return jax.device_put(jnp.stack([x] * len(devices)), sharding)
-    return jax.device_put(np.stack([x] * len(devices)), sharding)
-
-  training_state = jax.tree_util.tree_map(_replicate, training_state)
+  training_state = pmap.bcast_local_devices(
+      training_state,
+      local_devices_to_use,
+      axis_name=_PMAP_AXIS_NAME,
+  )
 
   eval_env = _maybe_wrap_env(
       eval_env or environment,

brax/training/pmap.py

@@ -22,11 +22,13 @@
 import numpy as np
 
 
-def bcast_local_devices(value, local_devices_to_use=1):
+def bcast_local_devices(
+    value, local_devices_to_use=1, axis_name='_device_put_sharded'
+):
   """Broadcasts an object to all local devices."""
   devices = jax.local_devices()[:local_devices_to_use]
-  mesh = jax.sharding.Mesh(np.array(devices), ('_device_put_sharded',))
-  sharding = jax.NamedSharding(mesh, jax.P('_device_put_sharded'))
+  mesh = jax.sharding.Mesh(np.array(devices), (axis_name,))
+  sharding = jax.NamedSharding(mesh, jax.P(axis_name))
 
   def _replicate(x):
     if isinstance(x, jax.Array):

brax/training/pmap_test.py

@@ -0,0 +1,35 @@
+# Copyright 2026 The Brax Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Tests for pmap utilities."""
+
+from absl.testing import absltest
+from brax.training import pmap
+import jax
+import jax.numpy as jnp
+
+
+class PmapTest(absltest.TestCase):
+
+  def testBcastLocalDevicesUsesRequestedAxisName(self):
+    value = pmap.bcast_local_devices(
+        jnp.arange(4), local_devices_to_use=1, axis_name='i'
+    )
+
+    self.assertEqual(value.sharding.mesh.axis_names, ('i',))
+    self.assertEqual(value.sharding.spec, jax.P('i'))
+
+
+if __name__ == '__main__':
+  absltest.main()