[Misc] Add type alias `ReqId` and `EngineId` for better readability (#19880)

Signed-off-by: Linkun Chen <github@lkchen.net>

vllm/distributed/kv_transfer/kv_connector/v1/nixl_connector.py

@@ -36,6 +36,8 @@ if TYPE_CHECKING:
     from vllm.v1.request import Request
 
 Transfer = tuple[int, float]  # (xfer_handle, start_time)
+EngineId = str
+ReqId = str
 GET_META_MSG = b"get_meta_msg"
 
 logger = init_logger(__name__)
@@ -75,7 +77,7 @@ class ReqMeta:
 class NixlConnectorMetadata(KVConnectorMetadata):
 
     def __init__(self):
-        self.requests: dict[str, ReqMeta] = {}
+        self.requests: dict[ReqId, ReqMeta] = {}
 
     def add_new_req(
         self,
@@ -96,16 +98,17 @@ class NixlConnector(KVConnectorBase_V1):
 
     def __init__(self, vllm_config: VllmConfig, role: KVConnectorRole):
         assert vllm_config.kv_transfer_config is not None
-        self.engine_id = vllm_config.kv_transfer_config.engine_id
+        assert vllm_config.kv_transfer_config.engine_id is not None
+        self.engine_id: EngineId = vllm_config.kv_transfer_config.engine_id
 
         if role == KVConnectorRole.SCHEDULER:
             self.connector_scheduler : Optional[NixlConnectorScheduler] = \
-                NixlConnectorScheduler(vllm_config, str(self.engine_id))
+                NixlConnectorScheduler(vllm_config, self.engine_id)
             self.connector_worker: Optional[NixlConnectorWorker] = None
         elif role == KVConnectorRole.WORKER:
             self.connector_scheduler = None
             self.connector_worker = NixlConnectorWorker(
-                vllm_config, str(self.engine_id))
+                vllm_config, self.engine_id)
 
     ############################################################
     # Scheduler Side Methods
@@ -179,7 +182,7 @@ class NixlConnectorScheduler:
     def __init__(self, vllm_config: VllmConfig, engine_id: str):
         self.vllm_config = vllm_config
         self.block_size = vllm_config.cache_config.block_size
-        self.engine_id = engine_id
+        self.engine_id: EngineId = engine_id
         self.side_channel_host = envs.VLLM_NIXL_SIDE_CHANNEL_HOST
         self.side_channel_port = (
             envs.VLLM_NIXL_SIDE_CHANNEL_PORT +
@@ -190,7 +193,7 @@ class NixlConnectorScheduler:
         # Requests that need to start recv.
         # New requests are added by update_state_after_alloc in
         # the scheduler. Used to make metadata passed to Worker.
-        self._reqs_need_recv: dict[str, tuple[Request, list[int]]] = {}
+        self._reqs_need_recv: dict[ReqId, tuple[Request, list[int]]] = {}
 
     def get_num_new_matched_tokens(
             self, request: "Request",
@@ -332,19 +335,19 @@ class NixlConnectorWorker:
         # Agent.
         self.nixl_wrapper = NixlWrapper(str(uuid.uuid4()), None)
         # Map of engine_id -> {rank0: agent_name0, rank1: agent_name1..}.
-        self._remote_agents: dict[str, dict[int, str]] = defaultdict(dict)
+        self._remote_agents: dict[EngineId, dict[int, str]] = defaultdict(dict)
 
         # NIXL handshake port.
         # NOTE(rob): Within a DP group, each DP rank gets its own
         # base port (which is sent in the KVTransferParams).
         # Each TP rank listens/queries on the base_port + tp_rank.
-        self.side_channel_port = (
+        self.side_channel_port: int = (
             envs.VLLM_NIXL_SIDE_CHANNEL_PORT +
             vllm_config.parallel_config.data_parallel_rank_local *
             vllm_config.parallel_config.tensor_parallel_size)
 
         # Metadata.
-        self.engine_id = engine_id
+        self.engine_id: EngineId = engine_id
         self.tp_rank = get_tensor_model_parallel_rank()
         self.world_size = get_tensor_model_parallel_world_size()
         self.tp_group = get_tp_group()
@@ -354,7 +357,7 @@ class NixlConnectorWorker:
 
         # Map of engine_id -> kv_caches_base_addr. For TP case, each local
         # rank will still only pull from a single remote TP worker.
-        self.kv_caches_base_addr: dict[str, list[int]] = {}
+        self.kv_caches_base_addr: dict[EngineId, list[int]] = {}
 
         # Number of NIXL regions. Currently one region per cache
         # (so 1 per layer for MLA, otherwise 2 per layer)
@@ -364,23 +367,23 @@ class NixlConnectorWorker:
         # nixl_prepped_dlist_handle.
         self.src_xfer_side_handle: int = 0
         # Map of engine_id -> nixl_prepped_dlist_handle (int)].
-        self.dst_xfer_side_handles: dict[str, int] = {}
+        self.dst_xfer_side_handles: dict[EngineId, int] = {}
 
         # Map of engine_id -> num_blocks. All ranks in the same deployment will
         # have the same number of blocks.
-        self.dst_num_blocks: dict[str, int] = {}
+        self.dst_num_blocks: dict[EngineId, int] = {}
         self._registered_descs: list[Any] = []
 
         # In progress transfers.
         # [req_id -> list[handle]]
-        self._recving_transfers = defaultdict[str, list[Transfer]](list)
+        self._recving_transfers = defaultdict[ReqId, list[Transfer]](list)
 
         # Complete transfer tracker. Used by the rank 0 to track finished
         # transactions on ranks 1 to N-1.
         # [req_id -> count]
-        self._done_recving_count: defaultdict[str,
+        self._done_recving_count: defaultdict[ReqId,
                                               int] = defaultdict(lambda: 0)
-        self._done_sending_count: defaultdict[str,
+        self._done_sending_count: defaultdict[ReqId,
                                               int] = defaultdict(lambda: 0)
 
         # Background thread for establishing new connections.
@@ -408,10 +411,10 @@ class NixlConnectorWorker:
         self._use_flashinfer = attn_backend == _Backend.FLASHINFER_VLLM_V1
         logger.debug("Detected attention backend %s", self.backend_name)
 
-        self._tp_size: dict[str, int] = {self.engine_id: self.world_size}
+        self._tp_size: dict[EngineId, int] = {self.engine_id: self.world_size}
         # With heterogeneous TP, P must wait for all assigned D TP workers to
         # finish reading before safely freeing the blocks.
-        self.consumer_notification_counts_by_req = defaultdict[str, int](int)
+        self.consumer_notification_counts_by_req = defaultdict[ReqId, int](int)
 
     @staticmethod
     def _nixl_handshake_listener(metadata: NixlAgentMetadata,