flockfile(3) BSD Library Functions Manual flockfile(3)
NAME
flockfile, ftrylockfile, funlockfile -- stdio locking functions
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <stdio.h>
void
flockfile(FILE *file);
int
ftrylockfile(FILE *file);
void
funlockfile(FILE *file);
DESCRIPTION
These functions provide explicit application-level locking of stdio FILE
objects. They can be used to avoid output from multiple threads being
interspersed, input being dispersed among multiple readers, and to avoid
the overhead of locking the object for each operation.
The flockfile() function acquires an exclusive lock on the specified
object. If another thread has already locked the object, flockfile()
will block until the lock is released.
The ftrylockfile() function is a non-blocking version of flockfile(); if
the lock cannot be acquired immediately, ftrylockfile() returns non-zero
instead of blocking.
The funlockfile() function releases the lock on an object acquired by an
earlier call to flockfile() or ftrylockfile().
These functions behave as if there is a lock count associated with each
object. Each time flockfile() is called on the object, the count is
incremented, and each time funlockfile() is called on the object, the
count is decremented. The lock is only actually released when the count
reaches zero.
RETURN VALUES
The flockfile() and funlockfile() functions return no value.
The ftrylockfile() function returns zero if the object was successfully
locked, non-zero otherwise.
SEE ALSO
getc_unlocked(3), putc_unlocked(3)
STANDARDS
The flockfile(), ftrylockfile(), and funlockfile() functions conform to
IEEE Std 1003.1-2001 (``POSIX.1'').
BSD January 10, 2003 BSD
Mac OS X 10.8 - Generated Mon Aug 27 18:15:20 CDT 2012