freebsd-src/lib/libsys/sigwaitinfo.2

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.Dd April 21, 2022
.Dt SIGTIMEDWAIT 2
.Os
.Sh NAME
.Nm sigtimedwait , sigwaitinfo
.Nd "wait for queued signals (REALTIME)"
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In signal.h
.Ft int
.Fo sigtimedwait
.Fa "const sigset_t *restrict set" "siginfo_t *restrict info"
.Fa "const struct timespec *restrict timeout"
.Fc
.Ft int
.Fn sigwaitinfo "const sigset_t * restrict set" "siginfo_t * restrict info"
.Sh DESCRIPTION
The
.Fn sigtimedwait
system call is equivalent to
.Fn sigwaitinfo
except that if none of the signals specified by
.Fa set
are pending,
.Fn sigtimedwait
waits for the time interval specified in the
.Vt timespec
structure referenced by
.Fa timeout .
If the
.Vt timespec
structure pointed to by
.Fa timeout
is zero-valued and if none of the signals specified by
.Fa set
are pending, then
.Fn sigtimedwait
returns immediately with an error.
If
.Fa timeout
is the
.Dv NULL
pointer,
.Fn sigtimedwait
blocks indefinitely.
.Dv CLOCK_MONOTONIC
clock is used to measure the time interval specified by the
.Fa timeout
argument.
.Pp
The
.Fn sigwaitinfo
system call selects the pending signal from the set specified by
.Fa set .
Should any of multiple pending signals in the range
.Dv SIGRTMIN
to
.Dv SIGRTMAX
be selected, it shall be the lowest numbered one.
The
selection order between realtime and non-realtime signals, or
between multiple pending non-realtime signals, is unspecified.
If no signal in
.Fa set
is pending at the time of the call, the calling thread
is suspended until one or more signals in
.Fa set
become pending or until it is interrupted by an unblocked, caught signal.
.Pp
The
.Fn sigwaitinfo
system call is equivalent to the
.Fn sigwait
system call if the
.Fa info
argument is
.Dv NULL .
If the
.Fa info
argument is
.Pf non- Dv NULL ,
the
.Fn sigwaitinfo
function is equivalent to
.Fn sigwait ,
except that the selected signal number shall be stored in the
.Va si_signo
member, and the cause of the signal shall be stored in the
.Va si_code
member.
Besides this, the
.Fn sigwaitinfo
and
.Fn sigtimedwait
system calls may return
.Er EINTR
if interrupted by signal, which is not allowed for the
.Fn sigwait
function.
.Pp
If any value is queued to the selected signal, the first such queued
value is dequeued and, if the info argument is
.Pf non- Dv NULL ,
the value is stored in the
.Va si_value
member of
.Fa info .
The system resource used to queue the signal
is released and returned to the system for other use.
If no value is queued,
the content of the
.Va si_value
member is zero-valued.
If no further signals are
queued for the selected signal, the pending indication for that signal
is reset.
.Sh RETURN VALUES
Upon successful completion (that is, one of the signals specified by
.Fa set
is pending or is generated)
.Fn sigwaitinfo
and
.Fn sigtimedwait
return the selected signal number.
Otherwise, the functions return a value of \-1
and set the global variable
.Va errno
to indicate the error.
.Sh ERRORS
The
.Fn sigtimedwait
system call
will fail if:
.Bl -tag -width Er
.It Bq Er EAGAIN
No signal specified by set was generated within the specified timeout period.
.El
.Pp
The
.Fn sigtimedwait
and
.Fn sigwaitinfo
system calls fail if:
.Bl -tag -width Er
.It Bq Er EINTR
The wait was interrupted by an unblocked, caught signal.
.El
.Pp
The
.Fn sigtimedwait
system call may also fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa timeout
argument specified a
.Va tv_nsec
value less than zero or greater than or equal
to 1000 million.
Kernel only checks for this error if no signal is pending in set and it
is necessary to wait.
.El
.Sh SEE ALSO
.Xr sigaction 2 ,
.Xr sigpending 2 ,
.Xr sigqueue 2 ,
.Xr sigsuspend 2 ,
.Xr sigwait 2 ,
.Xr pause 3 ,
.Xr pthread_sigmask 3 ,
.Xr siginfo 3
.Sh STANDARDS
The
.Fn sigtimedwait
and
.Fn sigwaitinfo
system calls conform to
.St -p1003.1-96 .
POSIX
leaves the behavior of
.Fn sigtimedwait
with a
.Dv NULL
.Fa timeout
pointer unspecified.