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)