Create a null_mesh_context internal context manager to handle null contexts properly.

PiperOrigin-RevId: 700167406

jax/_src/mesh.py

@@ -455,17 +455,10 @@ class AbstractMesh:
     _raise_value_error("local_mesh")
 
   def __enter__(self):
-    mesh_context.stack.append(self)
-    mesh_context.mesh = self
-    jax_config.abstract_mesh_context_manager.set_local(
-        tuple(m for m in mesh_context.stack if m is not None))
-    return self
+    return push_mesh_context(self)
 
   def __exit__(self, exc_type, exc_value, traceback):
-    mesh_context.stack.pop()
-    mesh_context.mesh = mesh_context.stack[-1]
-    jax_config.abstract_mesh_context_manager.set_local(
-        tuple(m for m in mesh_context.stack if m is not None))
+    pop_mesh_context()
     return False
 
   @staticmethod
@@ -486,3 +479,26 @@ class MeshContext(threading.local):
     self.mesh = self.stack[-1]
 
 mesh_context = MeshContext()
+
+def push_mesh_context(val):
+  mesh_context.stack.append(val)
+  mesh_context.mesh = val
+  jax_config.abstract_mesh_context_manager.set_local(
+      tuple(m for m in mesh_context.stack if m is not None))
+  return val
+
+def pop_mesh_context():
+  mesh_context.stack.pop()
+  mesh_context.mesh = mesh_context.stack[-1]
+  jax_config.abstract_mesh_context_manager.set_local(
+      tuple(m for m in mesh_context.stack if m is not None))
+
+
+class null_mesh_context:
+
+  def __enter__(self):
+    return push_mesh_context(None)
+
+  def __exit__(self, *excinfo):
+    pop_mesh_context()
+    return False

jax/_src/pjit.py

@@ -16,7 +16,6 @@ from __future__ import annotations
 
 from collections import defaultdict
 from collections.abc import Callable, Sequence, Iterable
-import contextlib
 import dataclasses
 from functools import partial
 import inspect
@@ -696,7 +695,7 @@ def _infer_params_impl(
 
 def get_abstract_mesh(in_avals):
   if not config.sharding_in_types.value:
-    return contextlib.nullcontext()
+    return mesh_lib.null_mesh_context()
   m = None
   for a in in_avals:
     # TODO(yashkatariya): Remove this when mesh context can be set by the user.
@@ -709,7 +708,7 @@ def get_abstract_mesh(in_avals):
     m = a.sharding.mesh  # type: ignore
   # TODO(yashkatariya): Remove this when mesh context can be set by the user.
   if m is None:
-    return contextlib.nullcontext()
+    return mesh_lib.null_mesh_context()
   assert m is not None
   return m
 

jax/_src/stages.py

@@ -30,7 +30,6 @@ executable protocols described above.
 """
 from __future__ import annotations
 
-import contextlib
 import functools
 from collections.abc import Sequence
 from dataclasses import dataclass
@@ -44,6 +43,7 @@ from jax._src import source_info_util
 from jax._src import traceback_util
 from jax._src import tree_util
 from jax._src import util
+from jax._src import mesh as mesh_lib
 from jax._src.sharding_impls import UnspecifiedValue, AUTO
 from jax._src.layout import Layout
 from jax._src.interpreters import mlir
@@ -717,7 +717,7 @@ class Traced(Stage):
                "_args_flat", "_arg_names", "_num_consts"]
 
   def __init__(self, jaxpr: core.ClosedJaxpr, args_info, fun_name, out_tree,
-               lower_callable, abstract_mesh=contextlib.nullcontext(),
+               lower_callable, abstract_mesh=mesh_lib.null_mesh_context(),
                args_flat=None, arg_names=None, num_consts: int = 0):
     self.jaxpr = jaxpr
     self.args_info = args_info