Revert early HTTP port reservation (#17754, #19805) (#20468)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

python/sglang/srt/entrypoints/http_server.py

@@ -173,7 +173,7 @@ from sglang.srt.utils import (
     set_uvicorn_logging_configs,
 )
 from sglang.srt.utils.auth import AuthLevel, app_has_admin_force_endpoints, auth_level
-from sglang.utils import _prebind_listening_socket, get_exception_traceback
+from sglang.utils import get_exception_traceback
 from sglang.version import __version__
 
 logger = logging.getLogger(__name__)
@@ -1971,17 +1971,9 @@ def _setup_and_run_http_server(
 
     Called by launch_server after subprocesses have been launched.
     """
-    # Reserve the HTTP port before launching subprocesses to fail fast if port is unavailable.
-    # This prevents wasting time loading models only to discover port conflicts later.
-    reserved_socket = _prebind_listening_socket(server_args.host, server_args.port)
-    multi_tokenizer_args_shm = None
-
-    try:
     # Parse info got from the schedulers
     remote_instance_transfer_engine_info = (
-            parse_remote_instance_transfer_engine_info_from_scheduler_infos(
+        parse_remote_instance_transfer_engine_info_from_scheduler_infos(scheduler_infos)
-                scheduler_infos
-            )
     )
 
     # Set global states
@@ -2036,13 +2028,10 @@ def _setup_and_run_http_server(
             port_args, server_args, scheduler_infos[0]
         )
 
+    try:
         # Update logging configs
         set_uvicorn_logging_configs(server_args)
 
-        # Delay listen() until uvicorn startup to avoid accepting probe traffic
-        # while model/subprocess initialization is still in progress.
-        reserved_socket.listen(128)
-
         if server_args.ssl_certfile:
             logger.info(
                 f"SSL enabled: certfile={server_args.ssl_certfile}, "
@@ -2055,7 +2044,8 @@ def _setup_and_run_http_server(
                 # Use Config/Server API for access to the SSLContext.
                 config = uvicorn.Config(
                     app,
-                    fd=reserved_socket.fileno(),
+                    host=server_args.host,
+                    port=server_args.port,
                     root_path=server_args.fastapi_root_path,
                     log_level=server_args.log_level_http or server_args.log_level,
                     timeout_keep_alive=envs.SGLANG_TIMEOUT_KEEP_ALIVE.get(),
@@ -2091,7 +2081,8 @@ def _setup_and_run_http_server(
                 # Default case, one tokenizer process
                 uvicorn.run(
                     app,
-                    fd=reserved_socket.fileno(),
+                    host=server_args.host,
+                    port=server_args.port,
                     root_path=server_args.fastapi_root_path,
                     log_level=server_args.log_level_http or server_args.log_level,
                     timeout_keep_alive=envs.SGLANG_TIMEOUT_KEEP_ALIVE.get(),
@@ -2121,7 +2112,8 @@ def _setup_and_run_http_server(
 
             uvicorn.run(
                 "sglang.srt.entrypoints.http_server:app",
-                fd=reserved_socket.fileno(),
+                host=server_args.host,
+                port=server_args.port,
                 root_path=server_args.fastapi_root_path,
                 log_level=server_args.log_level_http or server_args.log_level,
                 timeout_keep_alive=envs.SGLANG_TIMEOUT_KEEP_ALIVE.get(),
@@ -2133,10 +2125,6 @@ def _setup_and_run_http_server(
                 ssl_keyfile_password=server_args.ssl_keyfile_password,
             )
     finally:
-        # Close the reserved socket after uvicorn exits or on any error
-        # This ensures the port is released even if initialization fails
-        reserved_socket.close()
-
         if server_args.tokenizer_worker_num > 1:
             if multi_tokenizer_args_shm is not None:
                 multi_tokenizer_args_shm.unlink()

python/sglang/utils.py

@@ -409,61 +409,6 @@ def reserve_port(host, start=30000, end=40000):
     raise RuntimeError("No free port available.")
 
 
-def _prebind_listening_socket(host: str, port: int) -> socket.socket:
-    """
-    Create and bind a server socket to reserve the port before model loading.
-
-    This prevents port conflicts that could occur if another process (e.g., a
-    subprocess spawned during model loading) binds to the same port before the
-    HTTP server starts. By binding early, we ensure the port is available and
-    reserved for the HTTP server. The socket is intentionally not put into
-    listening mode here to avoid accepting probe connections before uvicorn is
-    ready to serve requests.
-
-    Args:
-        host: The host address to bind to.
-        port: The port number to bind to.
-
-    Returns:
-        A bound socket object.
-
-    Raises:
-        RuntimeError: If the port is already in use or permission is denied.
-    """
-    import errno
-
-    from sglang.srt.utils.network import NetworkAddress
-
-    # Determine socket family based on address type
-    na = NetworkAddress(host or "0.0.0.0", port)
-    sock = socket.socket(family=na.family, type=socket.SOCK_STREAM)
-    # SO_REUSEADDR: Allows binding to a port in TIME_WAIT state
-    sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
-
-    try:
-        sock.bind(na.to_bind_tuple())
-        sock.set_inheritable(True)
-        logger.info(f"Successfully reserved port {port} on host '{na.host}'")
-    except OSError as e:
-        sock.close()
-        if e.errno == errno.EADDRINUSE:
-            raise RuntimeError(
-                f"Port {port} is already in use on host '{na.host}'. "
-                f"Please choose a different port with --port or stop the process using this port. "
-                f"You can find the process using: lsof -i :{port} or netstat -tlnp | grep {port}"
-            ) from e
-        elif e.errno == errno.EACCES:
-            raise RuntimeError(
-                f"Permission denied when trying to bind to port {port}. "
-                f"Ports below 1024 require root/sudo privileges. "
-                f"Consider using a port >= 1024 (e.g., --port 8000) or run with sudo."
-            ) from e
-        else:
-            raise RuntimeError(f"Failed to bind to {na}: {e}") from e
-
-    return sock
-
-
 def release_port(lock_socket):
     """
     Release the reserved port by closing the lock socket.