[Misc][Utils] allow get_open_port to be called for multiple times (#5333)

tests/test_utils.py

 import asyncio
+import os
+import socket
 import sys
 from typing import (TYPE_CHECKING, Any, AsyncIterator, Awaitable, Protocol,
                     Tuple, TypeVar)
 
 import pytest
 
-from vllm.utils import deprecate_kwargs, merge_async_iterators
+from vllm.utils import deprecate_kwargs, get_open_port, merge_async_iterators
 
 from .utils import error_on_warning
 
@@ -116,3 +118,15 @@ def test_deprecate_kwargs_additional_message():
 
     with pytest.warns(DeprecationWarning, match="abcd"):
         dummy(old_arg=1)
+
+
+def test_get_open_port():
+    os.environ["VLLM_PORT"] = "5678"
+    # make sure we can get multiple ports, even if the env var is set
+    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s1:
+        s1.bind(("localhost", get_open_port()))
+        with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s2:
+            s2.bind(("localhost", get_open_port()))
+            with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s3:
+                s3.bind(("localhost", get_open_port()))
+    os.environ.pop("VLLM_PORT")

vllm/envs.py

@@ -99,6 +99,9 @@ environment_variables: Dict[str, Callable[[], Any]] = {
     lambda: os.getenv('VLLM_HOST_IP', "") or os.getenv("HOST_IP", ""),
 
     # used in distributed environment to manually set the communication port
+    # Note: if VLLM_PORT is set, and some code asks for multiple ports, the
+    # VLLM_PORT will be used as the first port, and the rest will be generated
+    # by incrementing the VLLM_PORT value.
     # '0' is used to make mypy happy
     'VLLM_PORT':
     lambda: int(os.getenv('VLLM_PORT', '0'))

vllm/utils.py

@@ -289,7 +289,15 @@ def get_distributed_init_method(ip: str, port: int) -> str:
 def get_open_port() -> int:
     port = envs.VLLM_PORT
     if port is not None:
+        while True:
+            try:
+                with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
+                    s.bind(("", port))
                     return port
+            except OSError:
+                port += 1  # Increment port number if already in use
+                logger.info("Port %d is already in use, trying port %d",
+                            port - 1, port)
     # try ipv4
     try:
         with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s: