[Bugfix] Add monkeypatch to prevent race condition from writing (#35420)

Signed-off-by: Lucas Kabela <lucaskabela@meta.com>

vllm/compilation/compiler_interface.py

@@ -184,6 +184,47 @@ def is_compile_cache_enabled(
     )
 
 
+def _patch_standalone_compile_atomic_save() -> None:
+    """Backport of pytorch/pytorch#162432 for torch < 2.10.0.
+
+    Patches CompiledArtifact.save() to use write_atomic for binary format,
+    preventing corrupt cache files when multiple processes compile
+    concurrently.
+    """
+    from torch._inductor.codecache import write_atomic
+    from torch._inductor.standalone_compile import CompiledArtifact as cls
+
+    if getattr(cls.save, "_vllm_patched", False):
+        return
+
+    original_save = cls.save
+
+    def _save(
+        self: Any, *, path: str, format: Literal["binary", "unpacked"] = "binary"
+    ) -> None:
+        if format != "binary":
+            return original_save(self, path=path, format=format)
+        from torch._dynamo.utils import dynamo_timed
+        from torch._inductor.codecache import torch_key
+        from torch.utils._appending_byte_serializer import BytesWriter
+
+        with dynamo_timed("CompiledArtifact.save"):
+            assert self._artifacts is not None
+            artifact_bytes, cache_info = self._artifacts
+            assert len(cache_info.aot_autograd_artifacts) == 1, cache_info
+            key = cache_info.aot_autograd_artifacts[0]
+            assert not os.path.isdir(path)
+            writer = BytesWriter()
+            writer.write_bytes(torch_key())
+            writer.write_str(key)
+            writer.write_bytes(artifact_bytes)
+            write_atomic(path, writer.to_bytes())
+
+    _save._vllm_patched = True  # type: ignore[attr-defined]
+    cls.save = _save  # type: ignore[assignment]
+    logger.debug("Patched %s.save for atomic writes (torch < 2.10)", cls.__name__)
+
+
 class InductorStandaloneAdaptor(CompilerInterface):
     """
     The adaptor for the Inductor compiler.
@@ -197,6 +238,8 @@ class InductorStandaloneAdaptor(CompilerInterface):
     name = "inductor_standalone"
 
     def __init__(self, save_format: Literal["binary", "unpacked"]) -> None:
+        if not is_torch_equal_or_newer("2.10.0"):
+            _patch_standalone_compile_atomic_save()
         self.save_format = save_format
 
     def compute_hash(self, vllm_config: VllmConfig) -> str: