FLOCKFILE(3) OpenBSD Programmer's Manual FLOCKFILE(3)NAME
flockfile, ftrylockfile, funlockfile - application level locking of stdio
files
SYNOPSIS
#include <stdio.h>
void
flockfile(FILE *file);
int
ftrylockfile(FILE *file);
void
funlockfile(FILE *file);
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 is used by a thread to acquire ownership of a
FILE * object.
The ftrylockfile() function is used by a thread to acquire ownership of a
FILE * object if the object is available; ftrylockfile() is a non-
blocking version of flockfile().
The funlockfile() function is used to relinquish the ownership granted to
the thread. The behaviour is undefined if a thread other than the
current owner calls the funlockfile() function.
Logically, there is a lock count associated with each FILE * object.
This count is implicitly initialized to zero when the FILE * object is
created. The FILE * object is unlocked when the count is zero. When the
count is positive, a single thread owns the FILE * object. When the
flockfile() function is called, if the count is zero or if the count is
positive and the caller owns the FILE * object, the count is incremented.
Otherwise, the calling thread is suspended, waiting for the count to
return to zero. Each call to funlockfile() decrements the count. This
allows matching calls to flockfile() (or successful calls to
ftrylockfile()) and funlockfile() to be nested.
Library functions that reference FILE * behave as if they use flockfile()
and funlockfile() internally to obtain ownership of these FILE * objects.
RETURN VALUES
None for flockfile() and funlockfile(). The function ftrylockfile()
returns zero for success and non-zero to indicate that the lock cannot be
acquired.
ERRORS
None.
SEE ALSOgetc_unlocked(3), getchar_unlocked(3), pthreads(3), putc_unlocked(3),
putchar_unlocked(3)STANDARDSflockfile(), ftrylockfile() and funlockfile() conform to ISO/IEC 9945-1
ANSI/IEEE (``POSIX'') Std 1003.1c/D10.
OpenBSD 4.9 May 31, 2007 OpenBSD 4.9