NAME

       pthread_sigmask, sigprocmask - examine and change blocked signals

SYNOPSIS

       #include <signal.h>

       int pthread_sigmask(int how, const sigset_t *restrict set,
              sigset_t *restrict oset);

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

DESCRIPTION

       The  pthread_sigmask()  function  shall  examine  or change (or both) the calling thread's
       signal mask, regardless of the number of threads in the process.  The  function  shall  be
       equivalent  to  sigprocmask(),  without the restriction that the call be made in a single-
       threaded process.

       In a single-threaded process, the sigprocmask() function shall examine or change (or both)
       the signal mask of the calling thread.

       If  the  argument  set  is not a null pointer, it points to a set of signals to be used to
       change the currently blocked set.

       The argument how indicates the way in which the set is changed, and the application  shall
       ensure it consists of one of the following values:

       SIG_BLOCK
              The  resulting set shall be the union of the current set and the signal set pointed
              to by set.

       SIG_SETMASK
              The resulting set shall be the signal set pointed to by set.

       SIG_UNBLOCK
              The resulting set shall be the intersection of the current set and  the  complement
              of the signal set pointed to by set.

       If  the  argument  oset  is  not  a null pointer, the previous mask shall be stored in the
       location pointed to by oset.  If set is a null pointer, the value of the argument  how  is
       not significant and the process' signal mask shall be unchanged; thus the call can be used
       to enquire about currently blocked signals.

       If there are any pending unblocked signals after the call to sigprocmask(), at  least  one
       of those signals shall be delivered before the call to sigprocmask() returns.

       It is not possible to block those signals which cannot be ignored.  This shall be enforced
       by the system without causing an error to be indicated.

       If any of the SIGFPE, SIGILL, SIGSEGV, or SIGBUS signals  are  generated  while  they  are
       blocked,  the result is undefined, unless the signal was generated by the kill() function,
       the sigqueue() function, or the raise() function.

       If sigprocmask() fails, the thread's signal mask shall not be changed.

       The use of the sigprocmask() function is unspecified in a multi-threaded process.

RETURN VALUE

       Upon successful completion pthread_sigmask() shall return 0; otherwise,  it  shall  return
       the corresponding error number.

       Upon successful completion, sigprocmask() shall return 0; otherwise, -1 shall be returned,
       errno shall be set to indicate the error, and the process' signal mask shall be unchanged.

ERRORS

       The pthread_sigmask()  and sigprocmask() functions shall fail if:

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

       The pthread_sigmask() function shall not return an error code of [EINTR].

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       None.

RATIONALE

       When a process' signal mask is changed in a signal-catching function that is installed  by
       sigaction(),  the  restoration  of  the  signal  mask  on  return from the signal-catching
       function overrides that change (see sigaction()).  If  the  signal-catching  function  was
       installed with signal(), it is unspecified whether this occurs.

       See kill() for a discussion of the requirement on delivery of signals.

FUTURE DIRECTIONS

       None.

SEE ALSO

       sigaction()  ,  sigaddset() , sigdelset() , sigemptyset() , sigfillset() , sigismember() ,
       sigpending()  ,  sigqueue()  ,   sigsuspend()   ,   the   Base   Definitions   volume   of
       IEEE Std 1003.1-2001, <signal.h>

COPYRIGHT

       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2003 Edition, Standard for Information Technology  --  Portable  Operating  System
       Interface  (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by
       the Institute of Electrical and Electronics Engineers, Inc and  The  Open  Group.  In  the
       event  of  any  discrepancy  between this version and the original IEEE and The Open Group
       Standard, the original IEEE and The Open Group  Standard  is  the  referee  document.  The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .