ftrylockfile(3) [osf1 man page]

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)

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)