streamWrapper::stream_lock — Advisory file locking
operation is one of the following:
LOCK_SHto acquire a shared lock (reader).
LOCK_EXto acquire an exclusive lock (writer).
LOCK_UNto release a lock (shared or exclusive).
LOCK_NBif you don't want flock() to block while locking. (not supported on Windows)
TRUE in caso di successo,
FALSE in caso di fallimento.
E_WARNING if call to this method fails (i.e. not implemented).