sigprocmask(S)                 6 January 1993                 sigprocmask(S)


 Name

    sigprocmask - change and/or examine blocked signals.

 Syntax


    cc  . . .  -lc


    #include  <signal.h>

    int sigprocmask (how, set, oset)
    int how;
    sigset_t *set, *oset;


 Description

    The routine sigprocmask changes and/or examines the calling process' sig-
    nal mask.  A process' signal mask lists the signals that are blocked;
    that is, if a signal in the signal mask is generated, it is not delivered
    to the process until the signal is unblocked by being removed from the
    mask.

    The signal mask of a process is initialized to that of its parent by
    fork(S).  The mask is changed by the sigprocmask, sigaction(S), and
    sigsuspend(S) routines.  The contents of a mask are manipulated by the
    sigset(S) routines.

    The argument, how, dictates how the current signal mask is changed.  As
    defined in the header file, <signal.h>, the following options are allow-
    able:


    __________________________________________________
    Name           Description
    __________________________________________________
    SIG_BLOCK      The resulting set is the union of
                   the current set and the set to
                   which the argument set points (sig-
                   nals in set are added to the exist-
                   ing set).

    SIG_UNBLOCK    The resulting set is the intersec-
                   tion of the current set and the
                   complement of the set to which the
                   argument set points (signals in set
                   are removed from the existing set).

    SIG_SETMASK    The resulting set is the set to
                   which the argument set points.


    If the argument set is not NULL, it points to the signal set that will be
    used to change the current signal mask, depending on the value of the
    argument how.  If the argument set is NULL, the value of how is imma-
    terial and the process's signal mask remains unchanged by the routine.
    In this latter case, the routine can be used to enquire about currently
    blocked signals.

    If the argument oset is not NULL, the previous mask is stored in the
    object to which the argument oset points.

    If any pending unblocked signals exist after the call to this routine, at
    least one of those signals is delivered before the sigprocmask routine
    returns.

    Generation of the SIGFPE, SIGILL, or SIGSEGV signals while they are
    blocked yields an undefined result unless the signal was generated by a
    call to the raise(S) or kill(S) routines.

    Un-ignorable signals, described in signal(S) or sigaction, cannot be
    blocked.  The system automatically enforces this restriction without
    indicating an error.

 Return value

    Upon successful completion, a value of zero is returned.  If sigprocmask
    fails, a value of -1 is returned and errno is set to indicate the error.
    In the latter case, the process's signal mask is not changed.

 Diagnostics

    If the following condition occurs, the sigprocmask function returns -1
    and sets errno to the corresponding value:

    [EINVAL]  The value of the how argument is not equal to one of the
              defined values.


 See also

    sigaction(S), signal(S), sigpending(S), sigset(S), sigsetjmp(S)
    sigsetv(S), sigsuspend(S),

 Standards conformance

    sigprocmask conforms with:
    IEEE POSIX Std 1003.1-1990 System Application Program Interface (API) [C
    Language] (ISO/IEC 9945-1);
    X/Open Portability Guide, Issue 3, 1989;
    and NIST FIPS 151-1.