[RL] Add Pause and Resume Generation for Asynchronous RL Training (#28037)

Signed-off-by: SamitHuang <285365963@qq.com>
Signed-off-by: Samit <285365963@qq.com>
Signed-off-by: samithuang <285365963@qq.com>
Co-authored-by: 22quinn <33176974+22quinn@users.noreply.github.com>

vllm/entrypoints/openai/api_server.py

@@ -394,6 +394,84 @@ async def get_server_load_metrics(request: Request):
     return JSONResponse(content={"server_load": request.app.state.server_load_metrics})
 
 
+@router.post("/pause")
+async def pause_generation(
+    raw_request: Request,
+    wait_for_inflight_requests: bool = Query(False),
+    clear_cache: bool = Query(True),
+) -> JSONResponse:
+    """Pause generation requests to allow weight updates.
+
+    Args:
+        wait_for_inflight_requests: When ``True`` waits for in-flight
+            requests to finish before pausing. When ``False`` (default),
+            aborts any in-flight requests immediately.
+        clear_cache: Whether to clear KV/prefix caches after draining.
+    """
+
+    engine = engine_client(raw_request)
+
+    try:
+        await engine.pause_generation(
+            wait_for_inflight_requests=wait_for_inflight_requests,
+            clear_cache=clear_cache,
+        )
+        return JSONResponse(
+            content={"status": "paused"},
+            status_code=HTTPStatus.OK.value,
+        )
+
+    except ValueError as err:
+        return JSONResponse(
+            content={"error": str(err)},
+            status_code=HTTPStatus.BAD_REQUEST.value,
+        )
+    except Exception as err:  # pragma: no cover - defensive
+        logger.exception("Failed to pause generation")
+        return JSONResponse(
+            content={"error": f"Failed to pause generation: {err}"},
+            status_code=HTTPStatus.INTERNAL_SERVER_ERROR.value,
+        )
+
+
+@router.post("/resume")
+async def resume_generation(raw_request: Request) -> JSONResponse:
+    """Resume generation after a pause."""
+
+    engine = engine_client(raw_request)
+
+    try:
+        await engine.resume_generation()
+        return JSONResponse(
+            content={"status": "resumed"},
+            status_code=HTTPStatus.OK.value,
+        )
+    except Exception as err:  # pragma: no cover - defensive
+        logger.exception("Failed to resume generation")
+        return JSONResponse(
+            content={"error": f"Failed to resume generation: {err}"},
+            status_code=HTTPStatus.INTERNAL_SERVER_ERROR.value,
+        )
+
+
+@router.get("/is_paused")
+async def is_paused(raw_request: Request) -> JSONResponse:
+    """Return the current pause status."""
+
+    engine = engine_client(raw_request)
+
+    try:
+        paused = await engine.is_paused()
+    except Exception as err:  # pragma: no cover - defensive
+        logger.exception("Failed to fetch pause status")
+        return JSONResponse(
+            content={"error": f"Failed to fetch pause status: {err}"},
+            status_code=HTTPStatus.INTERNAL_SERVER_ERROR.value,
+        )
+
+    return JSONResponse(content={"is_paused": paused})
+
+
 @router.post(
     "/tokenize",
     dependencies=[Depends(validate_json_request)],