[Core][Refactor][Diffusion] refactor request scheduler's admission wait policy (#5843)

Signed-off-by: Huang, Zeyu <11222265+fhfuih@users.noreply.github.com>
Co-authored-by: Hongsheng Liu <liuhongsheng4@huawei.com>

tests/diffusion/test_diffusion_engine.py

@@ -25,6 +25,7 @@ from vllm_omni.diffusion.request import OmniDiffusionRequest
 from vllm_omni.diffusion.sched.interface import (
     CachedRequestData,
     NewRequestData,
+    _AdmissionWaitDecision,
 )
 from vllm_omni.diffusion.sched.interface import (
     DiffusionSchedulerOutput as RealDiffusionSchedulerOutput,
@@ -75,6 +76,34 @@ class MockScheduler:
     def num_running_requests(self) -> int:
         return 0
 
+    def get_admission_wait_decision(
+        self,
+        *,
+        now: float,
+        dp_concurrent: bool = False,
+    ) -> _AdmissionWaitDecision:
+        del dp_concurrent
+        return _AdmissionWaitDecision(
+            should_wait=True,
+            deadline=now + 0.5,
+            stable_window_s=0.05,
+            max_batch=self.max_num_running_reqs,
+        )
+
+    def should_end_admission_wait(
+        self,
+        decision: _AdmissionWaitDecision,
+        *,
+        now: float,
+        stable_since: float,
+    ) -> bool:
+        waiting = self.num_waiting_requests()
+        return (
+            waiting >= decision.max_batch
+            or (waiting > 0 and now - stable_since >= decision.stable_window_s)
+            or (decision.deadline is not None and now >= decision.deadline)
+        )
+
     def schedule(self) -> DiffusionSchedulerOutput:
         if not self._waiting_queue:
             return DiffusionSchedulerOutput(step_id=self._step_id)
@@ -536,6 +565,11 @@ class TestRequestBatchAdmission:
         with pytest.raises(ValueError, match="request_batch_max_wait_ms"):
             OmniDiffusionConfig(model="test", request_batch_max_wait_ms=-1.0)
 
+    @pytest.mark.parametrize("bad_wait", [float("nan"), float("inf"), float("-inf")])
+    def test_config_rejects_nonfinite_request_batch_max_wait_ms(self, bad_wait: float) -> None:
+        with pytest.raises(ValueError, match="request_batch_max_wait_ms"):
+            OmniDiffusionConfig(model="test", request_batch_max_wait_ms=bad_wait)
+
     def test_config_normalizes_request_batch_max_wait_ms_to_float(self) -> None:
         config = OmniDiffusionConfig(model="test", request_batch_max_wait_ms=5)
 
@@ -603,7 +637,7 @@ class TestRequestBatchAdmission:
 
         start = time.monotonic()
         with engine._cv:
-            engine._wait_for_request_batch_admission_locked()
+            engine._wait_for_admission_if_needed_locked()
         waited_s = time.monotonic() - start
 
         # Stable-window exit (~50ms), not the full 1000ms deadline.