Standard C Library Functions                        flockfile(3C)



NAME
     flockfile, funlockfile, ftrylockfile - acquire  and  release
     stream lock

SYNOPSIS
     #include 

     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 calling 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, block-
     ing  other threads that might want to write to the same file
     between calls to fprintf(3C):





SunOS 5.11          Last change: 10 Sep 2003                    1






Standard C Library Functions                        flockfile(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] = getcunlocked(iop);
       }
       funlockfile(iop);


ATRIBUTES
     See attributes(5) for descriptions of the  following  attri-
     butes:



     
           ATRIBUTE TYPE               ATRIBUTE 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  IE  Std
     1003.1:2001.  See standards(5).












SunOS 5.11          Last change: 10 Sep 2003                    2