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CALL_ONCE(3)               Library Functions Manual               CALL_ONCE(3)

NAME
     call_once - calls function exactly once

LIBRARY
     POSIX Threads Library (libpthread, -lpthread)

SYNOPSIS
     #include <threads.h>

     void
     call_once(once_flag *flag, void (*func)(void));

     #define ONCE_FLAG_INIT /* implementation specified */

DESCRIPTION
     The call_once function uses the flag parameter to ensure that func is
     called exactly once, even if called from several threads.

     The ONCE_FLAG_INIT definition expands to a value that can be used to
     initialize an object of type once_flag.

     This portable interface is implemented on top of the pthread_once(3)
     functionality.

RETURN VALUES
     None.

EXAMPLES
     The following calls call_once from two threads using the portable thrd(3)
     interface.

           #include <stdio.h>
           #include <threads.h>

           static once_flag oflag = ONCE_FLAG_INIT;

           void
           called_once(void)
           {
                   printf("called once0);
           }

           int
           tfun(void *ptr)
           {
                   call_once(&oflag, called_once);
           }

           int
           main(int argc, char **argv)
           {
                   thrd_t th1, th2;

                   thrd_create(&th1, tfun, NULL);
                   thrd_create(&th2, tfun, NULL);

                   thrd_join(th1, NULL);
                   thrd_join(th2, NULL);

                   return 0;
           }

SEE ALSO
     pthread_once(3), threads(3)

STANDARDS
     The call_once function conforms to ISO/IEC 9899:2011 ("ISO C11").

HISTORY
     This interface first appeared in NetBSD 9.

AUTHORS
     Kamil Rytarowski <kamil@NetBSD.org>

NetBSD 10.99                   October 16, 2016                   NetBSD 10.99