funlockfile(3) [netbsd man page]

FLOCKFILE(3)						   BSD Library Functions Manual 					      FLOCKFILE(3)

NAME

     flockfile, ftrylockfile, funlockfile -- stdio stream 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

     The flockfile(), ftrylockfile(), and funlockfile() functions provide applications with explicit control of locking of stdio stream objects.
     They can be used by a thread to execute a sequence of I/O operations as a unit, without interference from another thread.

     Locks on stdio streams are recursive, and a lock count is maintained.  stdio streams are created unlocked, with a lock count of zero.  After
     successful acquisition of the lock, its count is incremented to one, indicating locked state of the stdio stream.	Each subsequent relock
     operation performed by the owner thread increments the lock count by one, and each subsequent unlock operation performed by the owner thread
     decrements the lock count by one, allowing matching lock and unlock operations to be nested.  After its lock count is decremented to zero,
     the stdio stream returns to unlocked state, and ownership of the stdio stream is relinquished.

     The flockfile() function acquires the ownership of file for the calling thread.  If file is already owned by another thread, the calling
     thread is suspended until the acquisition is possible (i.e., file is relinquished again and the calling thread is scheduled to acquire it).

     The ftrylockfile() function acquires the ownership of file for the calling thread only if file is available.

     The funlockfile() function relinquishes the ownership of file previously granted to the calling thread.  Only the current owner of file may
     funlockfile() it.

RETURN VALUES

     If successful, the ftrylockfile() function returns 0.  Otherwise, it returns non-zero to indicate that the lock cannot be acquired.

SEE ALSO

     flock(2), getc_unlocked(3), getchar_unlocked(3), lockf(3), putc_unlocked(3), putchar_unlocked(3)

STANDARDS

     The flockfile(), ftrylockfile() and funlockfile() functions conform to IEEE Std 1003.1-2001 (``POSIX.1'').

HISTORY

     The flockfile() function first appeared in FreeBSD 2.0.

BUGS

     The design of these interfaces does not allow for addressing the problem of priority inversion.

BSD
								 October 15, 2011							       BSD

flockfile(3C)						   Standard C Library Functions 					     flockfile(3C)

NAME

       flockfile, funlockfile, ftrylockfile - acquire and release stream lock

SYNOPSIS

       #include <stdio.h>

       void flockfile(FILE *stream);

       void funlockfile(FILE *stream);

       int ftrylockfile(FILE *stream);

DESCRIPTION

       The  flockfile() function acquires an internal lock of a stream stream. If the lock is already acquired by another thread, the thread call-
       ing flockfile() is suspended until it can acquire the lock.  In the case that the stream lock is available, flockfile() not  only  acquires
       the  lock,  but	keeps  track  of  the  number of times it is being called by the current thread.  This implies that the stream lock can be
       acquired more than once by the same thread.

       The funlockfile() function releases the lock being held by the current thread.  In the case of recursive locking,  this	function  must	be
       called  the  same  number  of  times flockfile() was called.  After the number of funlockfile() calls is equal to the number of flockfile()
       calls, the stream lock is available for other threads to acquire.

       The ftrylockfile() function acquires an internal lock of a stream stream, only if that object is available.  In essence ftrylockfile() is a
       non-blocking version of flockfile().

RETURN VALUES

       The ftrylockfile() function returns 0 on success and non-zero to indicate a lock cannot be acquired.

EXAMPLES

       Example 1: A sample program of flockfile().

       The  following  example	prints	everything out together, blocking other threads that might want to write to the same file between calls to
       fprintf(3C):

       FILE iop;
       flockfile(iop);
       fprintf(iop, "hello ");
       fprintf(iop, "world);
       fputc(iop, 'a');
       funlockfile(iop);

       An unlocked interface is available in case performance is an issue.  For example:

       flockfile(iop);
       while (!feof(iop)) {
	       *c++ = getc_unlocked(iop);
       }
       funlockfile(iop);

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       intro(3), __fsetlocking(3C), ferror(3C), fprintf(3C), getc(3C), putc(3C), stdio(3C), ungetc(3C), attributes(5), standards(5)

NOTES

       The interfaces on this page  are as specified in IEEE Std 1003.1:2001.  See standards(5).

SunOS 5.10							    10 Sep 2003 						     flockfile(3C)