make URLFile safe after fork() (#31309)

* make URLFile safe after fork()

* cache the pool manager in each instance

* type hints

tools/lib/url_file.py

@@ -6,6 +6,7 @@ from hashlib import sha256
 from urllib3 import PoolManager
 from urllib3.util import Timeout
 from tenacity import retry, wait_random_exponential, stop_after_attempt
+from typing import Optional
 
 from openpilot.common.file_helpers import atomic_write_in_dir
 from openpilot.system.hardware.hw import Paths
@@ -25,9 +26,12 @@ class URLFileException(Exception):
 
 
 class URLFile:
-  _tlocal = threading.local()
+  _pid: Optional[int] = None
+  _pool_manager: Optional[PoolManager] = None
+  _pool_manager_lock = threading.Lock()
 
   def __init__(self, url, debug=False, cache=None):
+    self._pool_manager = None
     self._url = url
     self._pos = 0
     self._length = None
@@ -41,11 +45,6 @@ class URLFile:
     if not self._force_download:
       os.makedirs(Paths.download_cache_root(), exist_ok=True)
 
-    try:
-      self._http_client = URLFile._tlocal.http_client
-    except AttributeError:
-      self._http_client = URLFile._tlocal.http_client = PoolManager()
-
   def __enter__(self):
     return self
 
@@ -55,10 +54,20 @@ class URLFile:
       self._local_file.close()
       self._local_file = None
 
+  def _http_client(self) -> PoolManager:
+    if self._pool_manager is None:
+      pid = os.getpid()
+      with URLFile._pool_manager_lock:
+        if URLFile._pid != pid or URLFile._pool_manager is None: # unsafe to share after fork
+          URLFile._pid = pid
+          URLFile._pool_manager = PoolManager(num_pools=10, maxsize=10)
+      self._pool_manager = URLFile._pool_manager
+    return self._pool_manager
+
   @retry(wait=wait_random_exponential(multiplier=1, max=5), stop=stop_after_attempt(3), reraise=True)
   def get_length_online(self):
     timeout = Timeout(connect=50.0, read=500.0)
-    response = self._http_client.request('HEAD', self._url, timeout=timeout, preload_content=False)
+    response = self._http_client().request('HEAD', self._url, timeout=timeout, preload_content=False)
     if not (200 <= response.status <= 299):
       return -1
     length = response.headers.get('content-length', 0)
@@ -131,7 +140,7 @@ class URLFile:
       t1 = time.time()
 
     timeout = Timeout(connect=50.0, read=500.0)
-    response = self._http_client.request('GET', self._url, timeout=timeout, preload_content=False, headers=headers)
+    response = self._http_client().request('GET', self._url, timeout=timeout, preload_content=False, headers=headers)
     ret = response.data
 
     if self._debug: