[utils] Improve file locking

* Implement non-blocking locks for windows
* Don't raise error when closing a closed file

yt_dlp/utils.py

@@ -2122,22 +2122,22 @@ if sys.platform == 'win32':
     whole_low = 0xffffffff
     whole_high = 0x7fffffff
 
-    def _lock_file(f, exclusive, block):  # todo: block unused on win32
+    def _lock_file(f, exclusive, block):
         overlapped = OVERLAPPED()
         overlapped.Offset = 0
         overlapped.OffsetHigh = 0
         overlapped.hEvent = 0
         f._lock_file_overlapped_p = ctypes.pointer(overlapped)
-        handle = msvcrt.get_osfhandle(f.fileno())
-        if not LockFileEx(handle, 0x2 if exclusive else 0x0, 0,
-                          whole_low, whole_high, f._lock_file_overlapped_p):
-            raise OSError('Locking file failed: %r' % ctypes.FormatError())
+
+        if not LockFileEx(msvcrt.get_osfhandle(f.fileno()),
+                          (0x2 if exclusive else 0x0) | (0x0 if block else 0x1),
+                          0, whole_low, whole_high, f._lock_file_overlapped_p):
+            raise BlockingIOError('Locking file failed: %r' % ctypes.FormatError())
 
     def _unlock_file(f):
         assert f._lock_file_overlapped_p
         handle = msvcrt.get_osfhandle(f.fileno())
-        if not UnlockFileEx(handle, 0,
-                            whole_low, whole_high, f._lock_file_overlapped_p):
+        if not UnlockFileEx(handle, 0, whole_low, whole_high, f._lock_file_overlapped_p):
             raise OSError('Unlocking file failed: %r' % ctypes.FormatError())
 
 else:
@@ -2175,6 +2175,8 @@ else:
 
 
 class locked_file(object):
+    _closed = False
+
     def __init__(self, filename, mode, block=True, encoding=None):
         assert mode in ['r', 'rb', 'a', 'ab', 'w', 'wb']
         self.f = io.open(filename, mode, encoding=encoding)
@@ -2192,9 +2194,11 @@ class locked_file(object):
 
     def __exit__(self, etype, value, traceback):
         try:
+            if not self._closed:
                 _unlock_file(self.f)
         finally:
             self.f.close()
+            self._closed = True
 
     def __iter__(self):
         return iter(self.f)