pthreads/pthread_once.3

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  33 .Dd April 4, 1996
  34 .Dt PTHREAD_ONCE 3
  35 .Os
  36 .Sh NAME
  37 .Nm pthread_once
  38 .Nd dynamic package initialization
  39 .Sh SYNOPSIS
  40 .Fd #include <pthread.h>
  41 .Pp
  42 pthread_once_t
  43 .Fa once_control
  44 = PTHREAD_ONCE_INIT;
  45 .Ft int
  46 .Fn pthread_once "pthread_once_t *once_control" "void (*init_routine)(void)"
  47 .Sh DESCRIPTION
  48 The first call to
  49 .Fn pthread_once
  50 by any thread in a process, with a given
  51 .Fa once_control ,
  52 will call the
  53 .Fn init_routine
  54 with no arguments.
  55 Subsequent calls to
  56 .Fn pthread_once
  57 with the same
  58 .Fa once_control
  59 will not call the
  60 .Fn init_routine .
  61 On return from
  62 .Fn pthread_once ,
  63 it is guaranteed that
  64 .Fn init_routine
  65 has completed.
  66 The
  67 .Fa once_control
  68 parameter is used to determine whether the associated initialization
  69 routine has been called.
  70 .Pp
  71 The function
  72 .Fn pthread_once
  73 is not a cancellation point.
  74 However, if
  75 .Fn init_routine
  76 is a cancellation point and is cancelled, the effect on
  77 .Fa once_control is as if
  78 .Fn pthread_once
  79 was never called.
  80 .Pp
  81 The constant
  82 .Fa PTHREAD_ONCE_INIT
  83 is defined by header
  84 .Aq Pa pthread.h .
  85 .Pp
  86 The behavior of
  87 .Fn pthread_once
  88 is undefined if
  89 .Fa once_control
  90 has automatic storage duration or is not initialized by
  91 .Fa PTHREAD_ONCE_INIT .
  92 .Sh RETURN VALUES
  93 If successful, the
  94 .Fn pthread_once
  95 function will return zero.
  96 Otherwise, an error number will be returned to indicate the error.
  97 .Sh ERRORS
  98 None.
  99 .Sh STANDARDS
 100 .Fn pthread_once
 101 conforms to
 102 .St -p1003.1-96 .