fix: method ordering

src/mcp/server/lowlevel/server.py

@@ -459,30 +459,6 @@ class Server(Generic[LifespanResultT]):
 
         return decorator
 
-    async def _handle_message(
-        self,
-        message: RequestResponder[types.ClientRequest, types.ServerResult]
-        | types.ClientNotification
-        | Exception,
-        session: ServerSession,
-        lifespan_context: LifespanResultT,
-        raise_exceptions: bool = False,
-    ):
-        with warnings.catch_warnings(record=True) as w:
-            match message:
-                case (
-                    RequestResponder(request=types.ClientRequest(root=req)) as responder
-                ):
-                    with responder:
-                        await self._handle_request(
-                            message, req, session, lifespan_context, raise_exceptions
-                        )
-                case types.ClientNotification(root=notify):
-                    await self._handle_notification(notify)
-
-            for warning in w:
-                logger.info(f"Warning: {warning.category.__name__}: {warning.message}")
-
     async def run(
         self,
         read_stream: MemoryObjectReceiveStream[types.JSONRPCMessage | Exception],
@@ -512,6 +488,30 @@ class Server(Generic[LifespanResultT]):
                         raise_exceptions,
                     )
 
+    async def _handle_message(
+        self,
+        message: RequestResponder[types.ClientRequest, types.ServerResult]
+        | types.ClientNotification
+        | Exception,
+        session: ServerSession,
+        lifespan_context: LifespanResultT,
+        raise_exceptions: bool = False,
+    ):
+        with warnings.catch_warnings(record=True) as w:
+            match message:
+                case (
+                    RequestResponder(request=types.ClientRequest(root=req)) as responder
+                ):
+                    with responder:
+                        await self._handle_request(
+                            message, req, session, lifespan_context, raise_exceptions
+                        )
+                case types.ClientNotification(root=notify):
+                    await self._handle_notification(notify)
+
+            for warning in w:
+                logger.info(f"Warning: {warning.category.__name__}: {warning.message}")
+
     async def _handle_request(
         self,
         message: RequestResponder,

tests/issues/test_188_concurrency.py

@@ -0,0 +1,49 @@
+import anyio
+from pydantic import AnyUrl
+
+from mcp.server.fastmcp import FastMCP
+from mcp.shared.memory import (
+    create_connected_server_and_client_session as create_session,
+)
+
+_sleep_time_seconds = 0.01
+_resource_name = "slow://slow_resource"
+
+
+async def test_messages_are_executed_concurrently():
+    server = FastMCP("test")
+
+    @server.tool("sleep")
+    async def sleep_tool():
+        await anyio.sleep(_sleep_time_seconds)
+        return "done"
+
+    @server.resource(_resource_name)
+    async def slow_resource():
+        await anyio.sleep(_sleep_time_seconds)
+        return "slow"
+
+    async with create_session(server._mcp_server) as client_session:
+        start_time = anyio.current_time()
+        async with anyio.create_task_group() as tg:
+            for _ in range(10):
+                tg.start_soon(client_session.call_tool, "sleep")
+                tg.start_soon(client_session.read_resource, AnyUrl(_resource_name))
+
+        end_time = anyio.current_time()
+
+        duration = end_time - start_time
+        assert duration < 3 * _sleep_time_seconds
+        print(duration)
+
+
+def main():
+    anyio.run(test_messages_are_executed_concurrently)
+
+
+if __name__ == "__main__":
+    import logging
+
+    logging.basicConfig(level=logging.DEBUG)
+
+    main()