Description

   The funlockfile function unlocks a stdio stream, causing the
   thread that had been holding the lock to relinquish exclusive use
   of the stream.

   File pointers passed are assumed to be valid; flockfile will
   perform locking even on invalid file pointers. Also, the
   funlockfile function will not fail if the calling thread does
   not own a lock on the file pointer passed.

   Matching flockfile and funlockfile calls can be nested. If the
   stream has been locked recursively, it will remain locked until
   the last matching funlockfile is called.

   All C RTL file-pointer I/O functions lock their file pointers as
   if calling flockfile and funlockfile.

   See also flockfile and ftrylockfile.