PTHREAD_ONCE(3P)                     SysV                     PTHREAD_ONCE(3P)



NAME
     pthread_once - Calls an initialization routine Threads Library
     (libpthreads.a)

SYNOPSIS
     #include <pthread.h>

     static pthread_once_t      once_block= pthread_once_init;

     int pthread_once (once_block, init_routine)
     pthread_once_t *once_block;
     void(*init_routine)();

DESCRIPTION
     The pthread_once function determines whether or not init_routine has been
     called by a previous pthread_once call; if init_routine has not been
     called, pthread_once calls it.

     The pthread_once function does not return to any calling thread until the
     init_routine has been completed.  You should declare a single once_block
     for each initialization routine.

     The arguments specify the following names:

     once_block
               Specifies a name to use for the routine that is used to check
               whether the initialization routine has already been executed.

     init_routine
               Specifies the name of the initialization routine.

     Undefined behavior results if once_block is not initialized or is not
     declared as static.

NOTES
     This interface is based on draft 4 of the IEEE P1003.4a standard, and
     will be changed to conform to the final version.

DIAGNOSTICS
     Upon successful completion, a value of 0 (zero) is returned. Otherwise,
     -1 is returned and errno is set to indicate the error.

ERRORS
     If the pthread_once function fails, errno may be set to one of the
     following values:

     [EINVAL]  The value specified by the once_block or init_routine argument
               is invalid.

SEE ALSO
     pthread_mutex_init(3P), pthread_cond_init(3P)