Lockfile

[DllImport("Kernel32.dll")][return: MarshalAs(UnmanagedType.Bool)]
public static extern bool LockFile(IntPtr hFile,
   uint dwFileOffsetLow,
   uint dwFileOffsetHigh,
   uint nNumberOfBytesToLockLow,
   uint nNumberOfBytesToLockHigh
);

Microsoft documentation: Link