sigblock(3)

1SIGVEC(3)                  Linux Programmer's Manual                 SIGVEC(3)
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NAME

6       sigvec, sigblock, sigsetmask, siggetmask, sigmask - BSD signal API
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SYNOPSIS

9       #define _BSD_SOURCE
10       #include <signal.h>
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12       int sigvec(int sig, struct sigvec *vec, struct sigvec *ovec);
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14       int sigmask(int signum);
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16       int sigblock(int mask);
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18       int sigsetmask(int mask);
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20       int siggetmask(void);
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DESCRIPTION

23       These  functions are provided in glibc as a compatibility interface for
24       programs that make use of the historical BSD signal API.  This  API  is
25       obsolete:  new  applications  should  use  the POSIX signal API (sigac‐
26       tion(2), sigprocmask(2), etc.)
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28       The sigvec() function sets and/or gets the disposition  of  the  signal
29       sig  (like the POSIX sigaction(2)).  If vec is not NULL, it points to a
30       sigvec structure that defines the new disposition for sig.  If ovec  is
31       not  NULL,  it  points to a sigvec structure that is used to return the
32       previous disposition of sig.  To obtain the current disposition of  sig
33       without  changing  it, specify NULL for vec, and a non-NULL pointer for
34       ovec.
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36       The dispositions for SIGKILL and SIGSTOP cannot be changed.
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38       The sigvec structure has the following form:
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40       struct sigvec {
41           void (*sv_handler)();  /* Signal disposition */
42           int    sv_mask;        /* Signals to be blocked in handler */
43           int    sv_flags;       /* Flags */
44       };
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46       The sv_handler field specifies the disposition of the  signal,  and  is
47       either:  the  address  of a signal handler function; or SIG_DFL meaning
48       the default disposition applies for the signal; or SIG_IGN meaning that
49       the signal is ignored.
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51       If  sv_handler  specifies the address of a signal handler, then sv_mask
52       specifies a mask of signals that are to be blocked while the handler is
53       executing.  In addition, the signal for which the handler is invoked is
54       also blocked by default.  Attempts to  block  SIGKILL  or  SIGSTOP  are
55       silently ignored.
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57       If  sv_handler  specifies  the  address  of  a signal handler, then the
58       sv_flags field specifies flags controlling what happens when  the  han‐
59       dler  is  called.  This field may contain zero or more of the following
60       flags:
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62       SV_INTERRUPT
63              If the signal handler interrupts a blocking  system  call,  then
64              upon  return  from  the  handler  the  system  call  will not be
65              restarted: instead it will fail with the error EINTR.   If  this
66              flag  is  not  specified,  then  system  calls  are restarted by
67              default.
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69       SV_RESETHAND
70              Reset the disposition of the signal to the default before  call‐
71              ing the signal handler.  If this flag is not specified, then the
72              handler remains established until explicitly removed by a  later
73              call to sigvec() or until the process performs an execve(2).
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75       SV_ONSTACK
76              Handle  the  signal  on the alternate signal stack (historically
77              established under BSD using the  obsolete  sigstack()  function;
78              the POSIX replacement is sigaltstack()).
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80       The  sigmask()  function  constructs  and  returns  a "signal mask" for
81       signum.  For example, we can initialise the vec.sv_mask field given  to
82       sigvec() using code such as the following:
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84           vec.sv_mask = sigmask(SIGQUIT) | sigpause (SIGABRT);
85                       /* Block SIGQUIT and SIGABRT during
86                          handler execution */
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88       The  sigblock() function adds the signals in mask to the process's sig‐
89       nal mask (like POSIX sigprocmask(SIG_BLOCK)), and returns the process's
90       previous  signal  mask.   Attempts  to  block  SIGKILL  or  SIGSTOP are
91       silently ignored.
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93       The sigsetmask() function sets the process's signal mask to  the  value
94       given  in  mask  (like POSIX sigprocmask(SIG_SETMASK)), and returns the
95       process's previous signal mask.
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97       The siggetmask() function returns the process's  current  signal  mask.
98       This call is equivalent to sigblock(0).
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RETURN VALUE

101       The sigvec() function returns 0 on success; on error, it returns -1 and
102       sets errno to indicate the error.
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104       The sigblock() and sigsetmask() functions return  the  previous  signal
105       mask.
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107       The sigmask() function returns the signal mask for signum.
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ERRORS

110       See the ERRORS under sigaction(2) and sigprocmask(2).
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NOTES

113       On  4.3BSD,  the signal() function provided reliable semantics (as when
114       calling sigvec() with vec.sv_mask equal to 0).  On System  V,  signal()
115       provides  unreliable  semantics.   POSIX.1-2001 leaves these aspects of
116       signal() unspecified.  See signal(2) for further details.
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118       In order to wait for a signal, BSD and System V both provided  a  func‐
119       tion  named  sigpause(),  but this function has a different argument on
120       the two systems.  See sigpause(3) for details.
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CONFORMING TO

123       All of these functions were in 4.3BSD, except siggetmask(), whose  ori‐
124       gin  is  unclear.  These functions are obsolete: do not use them in new
125       programs.
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