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Don't block the event loop on non-async functions #1909

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Don't block the event loop on non-async functions #1909

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18 changes: 6 additions & 12 deletions src/mcp/server/fastmcp/utilities/func_metadata.py
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Original file line number Diff line number Diff line change
@@ -1,19 +1,15 @@
import functools
import inspect
import json
from collections.abc import Awaitable, Callable, Sequence
from itertools import chain
from types import GenericAlias
from typing import Annotated, Any, cast, get_args, get_origin, get_type_hints

import anyio
import anyio.to_thread
import pydantic_core
from pydantic import (
BaseModel,
ConfigDict,
Field,
RootModel,
WithJsonSchema,
create_model,
)
from pydantic import BaseModel, ConfigDict, Field, RootModel, WithJsonSchema, create_model
from pydantic.fields import FieldInfo
from pydantic.json_schema import GenerateJsonSchema, JsonSchemaWarningKind
from typing_extensions import is_typeddict
Expand Down Expand Up @@ -60,9 +56,7 @@ def model_dump_one_level(self) -> dict[str, Any]:
kwargs[output_name] = value
return kwargs

model_config = ConfigDict(
arbitrary_types_allowed=True,
)
model_config = ConfigDict(arbitrary_types_allowed=True)


class FuncMetadata(BaseModel):
Expand Down Expand Up @@ -92,7 +86,7 @@ async def call_fn_with_arg_validation(
if fn_is_async:
return await fn(**arguments_parsed_dict)
else:
return fn(**arguments_parsed_dict)
return await anyio.to_thread.run_sync(functools.partial(fn, **arguments_parsed_dict))

def convert_result(self, result: Any) -> Any:
"""Convert the result of a function call to the appropriate format for
Expand Down