call_once(3) - NetBSD Manual Pages

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CALL_ONCE(3)            NetBSD 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 ini-
     tialize 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 11.99                   October 16, 2016                   NetBSD 11.99