sigvec.3: Fix small error in discussion of blocking of signals

[thirdparty/man-pages.git] / man3 / sigvec.3

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.TH SIGVEC 3 2012-09-06 "Linux" "Linux Programmer's Manual"
.SH NAME
sigvec, sigblock, sigsetmask, siggetmask, sigmask \- BSD signal API
.SH SYNOPSIS
.B #include <signal.h>
.sp
.BI "int sigvec(int " sig ", struct sigvec *" vec ", struct sigvec *" ovec );
.sp
.BI "int sigmask(int " signum );
.sp
.BI "int sigblock(int " mask );
.sp
.BI "int sigsetmask(int " mask );
.sp
.B int siggetmask(void);
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
All functions shown above:
_BSD_SOURCE
.SH DESCRIPTION
These functions are provided in glibc as a compatibility interface
for programs that make use of the historical BSD signal API.
This API is obsolete: new applications should use the POSIX signal API
.RB ( sigaction (2),
.BR sigprocmask (2),
etc.).

The
.BR sigvec ()
function sets and/or gets the disposition of the signal
.I sig
(like the POSIX
.BR sigaction (2)).
If
.I vec
is not NULL, it points to a
.I sigvec
structure that defines the new disposition for
.IR sig .
If
.I ovec
is not NULL, it points to a
.I sigvec
structure that is used to return the previous disposition of
.IR sig .
To obtain the current disposition of
.I sig
without changing it, specify NULL for
.IR vec ,
and a non-NULL pointer for
.IR ovec .

The dispositions for
.B SIGKILL
and
.B SIGSTOP
cannot be changed.

The
.I sigvec
structure has the following form:
.in +4n
.nf

struct sigvec {
    void (*sv_handler)();  /* Signal disposition */
    int    sv_mask;        /* Signals to be blocked in handler */
    int    sv_flags;       /* Flags */
};

.fi
.in
The
.I sv_handler
field specifies the disposition of the signal, and is either:
the address of a signal handler function; 
.BR SIG_DFL ,
meaning the default disposition applies for the signal; or
.BR SIG_IGN ,
meaning that the signal is ignored.

If
.I sv_handler
specifies the address of a signal handler, then
.I sv_mask
specifies a mask of signals that are to be blocked while
the handler is executing.
In addition, the signal for which the handler is invoked is
also blocked.
Attempts to block
.B SIGKILL
or
.B SIGSTOP
are silently ignored.

If
.I sv_handler
specifies the address of a signal handler, then the
.I sv_flags
field specifies flags controlling what happens when the handler is called.
This field may contain zero or more of the following flags:
.TP
.B SV_INTERRUPT
If the signal handler interrupts a blocking system call,
then upon return from the handler the system call will not be restarted:
instead it will fail with the error
.BR EINTR .
If this flag is not specified, then system calls are restarted
by default.
.TP
.B SV_RESETHAND
Reset the disposition of the signal to the default
before calling the signal handler.
If this flag is not specified, then the handler remains established
until explicitly removed by a later call to
.BR sigvec ()
or until the process performs an
.BR execve (2).
.TP
.B SV_ONSTACK
Handle the signal on the alternate signal stack
(historically established under BSD using the obsolete
.BR sigstack ()
function; the POSIX replacement is
.BR sigaltstack (2)).
.PP
The
.BR sigmask ()
function constructs and returns a "signal mask" for
.IR signum .
For example, we can initialize the
.I vec.sv_mask
field given to
.BR sigvec ()
using code such as the following:
.nf

    vec.sv_mask = sigmask(SIGQUIT) | sigpause(SIGABRT);
                /* Block SIGQUIT and SIGABRT during
                   handler execution */
.fi
.PP
The
.BR sigblock ()
function adds the signals in
.I mask
to the process's signal mask
(like POSIX
.IR sigprocmask(SIG_BLOCK) ),
and returns the process's previous signal mask.
Attempts to block
.B SIGKILL
or
.B SIGSTOP
are silently ignored.
.PP
The
.BR sigsetmask ()
function sets the process's signal mask to the value given in
.I mask
(like POSIX
.IR sigprocmask(SIG_SETMASK) ),
and returns the process's previous signal mask.
.PP
The
.BR siggetmask ()
function returns the process's current signal mask.
This call is equivalent to
.IR sigblock(0) .
.SH RETURN VALUE
The
.BR sigvec ()
function returns 0 on success; on error, it returns \-1 and sets
.I errno
to indicate the error.

The
.BR sigblock ()
and
.BR sigsetmask ()
functions return the previous signal mask.

The
.BR sigmask ()
function returns the signal mask for
.IR signum .
.SH ERRORS
See the ERRORS under
.BR sigaction (2)
and
.BR sigprocmask (2).
.SH "CONFORMING TO"
All of these functions were in
4.3BSD, except
.BR siggetmask (),
whose origin is unclear.
These functions are obsolete: do not use them in new programs.
.SH NOTES
On 4.3BSD, the
.BR signal ()
function provided reliable semantics (as when calling
.BR sigvec ()
with
.I vec.sv_mask
equal to 0).
On System V,
.BR signal ()
provides unreliable semantics.
POSIX.1-2001 leaves these aspects of
.BR signal ()
unspecified.
See
.BR signal (2)
for further details.

In order to wait for a signal,
BSD and System V both provided a function named
.BR sigpause (3),
but this function has a different argument on the two systems.
See
.BR sigpause (3)
for details.
.SH "SEE ALSO"
.BR kill (2),
.BR pause (2),
.BR sigaction (2),
.BR signal (2),
.BR sigprocmask (2),
.BR raise (3),
.BR sigpause (3),
.BR sigset (3),
.BR signal (7)