[core] allow callable in collective_rpc (#12151)

Signed-off-by: youkaichao <youkaichao@gmail.com>

tests/entrypoints/llm/test_collective_rpc.py

@@ -0,0 +1,36 @@
+import pytest
+
+from vllm import LLM
+
+from ...utils import fork_new_process_for_each_test
+
+
+@pytest.mark.parametrize("tp_size", [1, 2])
+@pytest.mark.parametrize("backend", ["mp", "ray"])
+@fork_new_process_for_each_test
+def test_collective_rpc(tp_size, backend):
+    if tp_size == 1 and backend == "ray":
+        pytest.skip("Skip duplicate test case")
+    if tp_size == 1:
+        backend = None
+
+    # intentionally define the method and class in the test function,
+    # to test if they can be serialized and sent to the workers
+    def echo_rank(self):
+        return self.rank
+
+    from vllm.worker.worker import Worker
+
+    class MyWorker(Worker):
+
+        def echo_rank(self):
+            return self.rank
+
+    llm = LLM(model="meta-llama/Llama-3.2-1B-Instruct",
+              enforce_eager=True,
+              load_format="dummy",
+              tensor_parallel_size=tp_size,
+              distributed_executor_backend=backend,
+              worker_cls=MyWorker)
+    for method in ["echo_rank", echo_rank]:
+        assert llm.collective_rpc(method) == list(range(tp_size))