[Misc] fix unique_filepath (#25732)

Signed-off-by: zjy0516 <riverclouds.zhu@qq.com>
Co-authored-by: Luka Govedič <ProExpertProg@users.noreply.github.com>

vllm/utils/__init__.py

@@ -45,6 +45,7 @@ from concurrent.futures import ThreadPoolExecutor
 from concurrent.futures.process import ProcessPoolExecutor
 from dataclasses import dataclass, field
 from functools import cache, lru_cache, partial, wraps
+from pathlib import Path
 from types import MappingProxyType
 from typing import (TYPE_CHECKING, Any, Callable, Generic, Literal, NamedTuple,
                     Optional, TextIO, TypeVar, Union, cast, overload)
@@ -3536,3 +3537,23 @@ def set_env_var(key, value):
             del os.environ[key]
         else:
             os.environ[key] = old
+
+
+def unique_filepath(fn: Callable[[int], Path]) -> Path:
+    """
+    unique_filepath returns a unique path by trying
+    to include an integer in increasing order.
+
+    fn should be a callable that returns a path that
+    includes the passed int at a fixed location.
+
+    Note: This function has a TOCTOU race condition.
+    Caller should use atomic operations (e.g., open with 'x' mode)
+    when creating the file to ensure thread safety.
+    """
+    i = 0
+    while True:
+        p = fn(i)
+        if not p.exists():
+            return p
+        i += 1