Add a set_mesh API to jax.sharding. set_mesh sets the sharding and never unsets it i.e. this is just __enter__ of a ctx manager without __exit__

PiperOrigin-RevId: 736261724

Author: yashk2810

jax/_src/mesh.py

@@ -587,9 +587,3 @@ def set_concrete_mesh(mesh: Mesh | None):
 
 def get_concrete_mesh():
   return jax_config.device_context.value
-
-
-@contextlib.contextmanager
-def use_mesh(mesh: Mesh):
-  with set_abstract_mesh(mesh.abstract_mesh), set_concrete_mesh(mesh):
-    yield

jax/_src/pjit.py

@@ -690,7 +690,7 @@ def _infer_params(
     fun: Callable, ji: PjitInfo, args: tuple[Any, ...], kwargs: dict[str, Any]
   ) -> tuple[PjitParams, list[Any]]:
   if ji.use_resource_env:
-    with mesh_lib.use_mesh(mesh_lib.thread_resources.env.physical_mesh):
+    with sharding_impls.use_mesh(mesh_lib.thread_resources.env.physical_mesh):
       return _infer_params_internal(fun, ji, args, kwargs)
   return _infer_params_internal(fun, ji, args, kwargs)
 

jax/_src/sharding_impls.py

@@ -15,6 +15,7 @@
 from __future__ import annotations
 
 import collections
+import contextlib
 from collections.abc import Mapping, Sequence
 import dataclasses
 import functools
@@ -1410,3 +1411,28 @@ def make_mesh(axis_shapes: Sequence[int], axis_names: Sequence[str],
       allow_split_physical_axes=allow_split_physical_axes)
   axis_types = _get_axis_types(auto_axes, explicit_axes, manual_axes)
   return mesh_lib.Mesh(mesh_devices, axis_names, axis_types=axis_types)
+
+
+@contextlib.contextmanager
+def use_mesh(mesh: mesh_lib.Mesh):
+  if not isinstance(mesh, mesh_lib.Mesh):
+    raise ValueError(
+        f"Expected mesh of type `jax.sharding.Mesh`. Got {type(mesh)}")
+
+  # TODO(yashkatariya): Enable this.
+  # if not core.trace_state_clean():
+  #   raise ValueError('`use_mesh` can only be used outside of `jax.jit`')
+
+  with (mesh_lib.set_abstract_mesh(mesh.abstract_mesh),
+        mesh_lib.set_concrete_mesh(mesh)):
+    yield
+
+def set_mesh(mesh: mesh_lib.Mesh) -> None:
+  if not isinstance(mesh, mesh_lib.Mesh):
+    raise ValueError(
+        f"Expected mesh of type `jax.sharding.Mesh`. Got {type(mesh)}")
+  if not core.trace_state_clean():
+    raise ValueError('`set_mesh` can only be used outside of `jax.jit`.')
+
+  config.abstract_mesh_context_manager.set_local(mesh.abstract_mesh)
+  config.device_context.set_local(mesh)

jax/_src/test_util.py

@@ -1576,7 +1576,7 @@ def with_user_mesh(sizes, names, axis_types=None):
   def decorator(fn):
     def mesh_fn(*args, **kwargs):
       mesh = create_mesh(sizes, names, axis_types=axis_types)
-      with mesh_lib.use_mesh(mesh):
+      with jax.sharding.use_mesh(mesh):
         return fn(*args, **kwargs, mesh=mesh)
     return mesh_fn
   return decorator

jax/sharding.py

@@ -22,6 +22,8 @@
     PmapSharding as PmapSharding,
     GSPMDSharding as GSPMDSharding,
     PositionalSharding as PositionalSharding,
+    use_mesh as use_mesh,
+    set_mesh as set_mesh,
 )
 from jax._src.partition_spec import (
     PartitionSpec as PartitionSpec,
@@ -30,7 +32,6 @@
 from jax._src.mesh import (
     AbstractMesh as AbstractMesh,
     AxisTypes as AxisTypes,
-    use_mesh as use_mesh
 )
 
 _deprecations = {

tests/pjit_test.py

@@ -5943,7 +5943,7 @@ def f(x, x2):
       a = z @ x2
       return a
 
-    with mesh_lib.use_mesh(mesh):
+    with jax.sharding.use_mesh(mesh):
       out = f(arr, arr.T)
       self.assertEqual(out.sharding, NamedSharding(mesh, P('x',)))
       lowered_text = f.lower(arr, arr.T).as_text()
@@ -5952,7 +5952,7 @@ def f(x, x2):
     mesh2 = jtu.create_mesh((2, 2), ('x', 'y'),
                             axis_types={mesh_lib.AxisTypes.Explicit: 'x',
                                         mesh_lib.AxisTypes.Auto: 'y'})
-    with mesh_lib.use_mesh(mesh2):
+    with jax.sharding.use_mesh(mesh2):
       arr = jax.device_put(arr, NamedSharding(mesh2, P('x', 'y')))
       arr2 = jax.device_put(np_inp.T, NamedSharding(mesh2, P('y', None)))
       out = f(arr, arr2)
@@ -5966,7 +5966,7 @@ def f(x, x2):
     mesh3 = jtu.create_mesh((2, 2), ('x', 'y'),
                             axis_types={mesh_lib.AxisTypes.Explicit: 'y',
                                         mesh_lib.AxisTypes.Auto: 'x'})
-    with mesh_lib.use_mesh(mesh3):
+    with jax.sharding.use_mesh(mesh3):
       arr = jax.device_put(arr, NamedSharding(mesh3, P('x', 'y')))
       arr2 = jax.device_put(np_inp.T, NamedSharding(mesh3, P(None, 'x')))
       out = f(arr, arr2)
@@ -6143,7 +6143,7 @@ def test_inputs_different_context(self, mesh):
     arr = jax.device_put(np_inp, s)
 
     auto_mesh = jax.make_mesh((2,), 'x', auto_axes='x')
-    with mesh_lib.use_mesh(auto_mesh):
+    with jax.sharding.use_mesh(auto_mesh):
       arr2 = jnp.ones(8)
     self.assertDictEqual(arr2.sharding.mesh.axis_types,
                          {AxisTypes.Auto: ('x',)})
@@ -7083,6 +7083,19 @@ def f(x):
     out = f(np.arange(8))
     self.assertEqual(out.sharding, NamedSharding(mesh, P('x')))
 
+  def test_set_mesh(self):
+    mesh = jtu.create_mesh((2,), ('x',), axis_types={AxisTypes.Explicit: 'x'})
+    prev_mesh = config.device_context.value
+    prev_abstract_mesh = config.abstract_mesh_context_manager.value
+    try:
+      jax.sharding.set_mesh(mesh)
+
+      out = reshard(np.arange(8), P('x'))
+      self.assertEqual(out.sharding, NamedSharding(mesh, P('x')))
+    finally:
+      config.device_context.set_local(prev_mesh)
+      config.abstract_mesh_context_manager.set_local(prev_abstract_mesh)
+
 
 @jtu.pytest_mark_if_available('multiaccelerator')
 class PJitErrorTest(jtu.JaxTestCase):