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 5.11							    10 Sep 2003 						     flockfile(3C)