flockfile(3)						     Library Functions Manual						      flockfile(3)

NAME

       flockfile, ftrylockfile, funlockfile - stdio locking functions

LIBRARY

       Standard C Library (libc.a)

SYNOPSIS

       #include <stdio.h> void flockfile(
	   FILE * file);

       int ftrylockfile(
	   FILE * file);

       void funlockfile(
	   FILE * file);

STANDARDS

       Interfaces documented on this reference page conform to industry standards as follows:

       flockfile, funlockfile:	POSIX.1c, XSH5.0

       ftrylockfile:  XSH5.0

       Refer to the standards(5) reference page for more information about industry standards and associated tags.

PARAMETERS

       Specifies the stream to be locked.

DESCRIPTION

       The  flockfile(),  ftrylockfile,  and funlockfile functions provide for explicit application-level locking of stdio (FILE*) objects.  These
       functions can be used by a thread to delineate a sequence of I/O statements that are to be executed as a unit.

       The flockfile() function locks a stdio stream so that a thread can have exclusive use of that stream for multiple I/O operations.  Use  the
       flockfile()  function  for  a  thread  that  wishes to ensure that the output of several printf() functions, for example, is not garbled by
       another thread also trying to use printf().

       The ftrylockfile() function is used by a thread to acquire ownership of a stdio (FILE*) object if the object is available.   The  ftrylock-
       file() function is a non-blocking version of flockfile().

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

       The behavior of the flockfile() and funlockfile() functions is unspecified if the file parameter does not point to a valid FILE	structure.
       The behavior of funlockfile() is also unspecified if a thread other than the current owner calls funlockfile().

       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.

RETURN VALUE

       None for flockfile() and funlockfile().	The ftrylockfile() function returns zero for success and non-zero to indicate that the lock cannot
       be acquired.

RELATED INFORMATION

       Functions: getc_unlocked(3), putc_unlocked(3) delim off

																      flockfile(3)