Skip the flaky test_stateful_custom_logit_processor (#6251)

python/sglang/srt/sampling/custom_logit_processor.py

@@ -28,11 +28,26 @@ class CustomLogitProcessor(ABC):
         """Define the callable behavior."""
         raise NotImplementedError
 
-    def to_str(self) -> str:
+    @classmethod
+    def to_str(cls) -> str:
         """Serialize the callable function to a JSON-compatible string."""
-        return json.dumps({"callable": dill.dumps(self).hex()})
+        return json.dumps({"callable": dill.dumps(cls).hex()})
 
     @classmethod
     def from_str(cls, json_str: str):
         """Deserialize a callable function from a JSON string."""
-        return _cache_from_str(json_str)
+        return _cache_from_str(json_str)()
+
+
+class DisallowedTokensLogitsProcessor(CustomLogitProcessor):
+    def __call__(
+        self,
+        logits: torch.Tensor,
+        custom_param_list: Optional[List[Dict[str, Any]]] = None,
+    ) -> torch.Tensor:
+        disallowed_token_ids = custom_param_list[0]["token_ids"]
+        assert all(
+            disallowed_token_ids == c["token_ids"] for c in custom_param_list
+        ), f"{custom_param_list=}"
+        logits[..., disallowed_token_ids] = -float("inf")
+        return logits

test/srt/test_srt_endpoint.py

@@ -344,9 +344,7 @@ class TestSRTEndpoint(CustomTestCase):
         custom_json = base_json.copy()
         # Only set the custom logit processor if target_token_id is not None.
         if target_token_id is not None:
-            custom_json["custom_logit_processor"] = (
-                DeterministicLogitProcessor().to_str()
-            )
+            custom_json["custom_logit_processor"] = DeterministicLogitProcessor.to_str()
             custom_json["sampling_params"]["custom_params"] = custom_params
 
         custom_response = requests.post(
@@ -373,7 +371,6 @@ class TestSRTEndpoint(CustomTestCase):
         Should sample the first `delay` tokens normally, then output first_token_id and consecutive tokens after that.
         If first_token_id is None, the custom logit processor won't be passed in.
         """
-
         custom_params = {"token_id": first_token_id, "delay": 2}
 
         class DeterministicStatefulLogitProcessor(CustomLogitProcessor):
@@ -447,10 +444,22 @@ class TestSRTEndpoint(CustomTestCase):
         with ThreadPoolExecutor(len(target_token_ids)) as executor:
             list(executor.map(self.run_custom_logit_processor, target_token_ids))
 
+    @unittest.skip("Skip this test because this feature has a bug. See comments below.")
     def test_stateful_custom_logit_processor(self):
         """Test custom logit processor with a single request."""
+
+        """
+        NOTE: This feature has a race condition bug.
+        This line https://github.com/sgl-project/sglang/blob/ef8ec07b2ce4c70c2a33ec5acda4ce529bc3cda4/test/srt/test_srt_endpoint.py#L395-L396 can be accessed by two concurrent threads at the same time. The access order is not guaranteed.
+        In sglang, we use two python threads to overlap the GPU computation and CPU scheduling.
+        Thread 1 (the CPU scheduling thread) will update the `param_dict["__req__"].output_ids`.
+        Thread 2 (the GPU computation thread) will call `DeterministicStatefulLogitProcessor` because sampling is considered as GPU computation.
+        We can fix this by moving the call of DeterministicStatefulLogitProcessor to the CPU scheduling thread.
+        """
+
         self.run_stateful_custom_logit_processor(first_token_id=5)
 
+    @unittest.skip("Skip this test because this feature has a bug. See comments above.")
     def test_stateful_custom_logit_processor_batch_mixed(self):
         """Test a batch of requests mixed of requests with and without custom logit processor."""
         target_token_ids = list(range(32)) + [None] * 16