'\" t
.TH "SD_EVENT_ADD_SIGNAL" "3" "" "elogind 246.9.1" "sd_event_add_signal"
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.SH "NAME"
sd_event_add_signal, sd_event_source_get_signal, sd_event_signal_handler_t \- Add a UNIX process signal event source to an event loop
.SH "SYNOPSIS"
.sp
.ft B
.nf
#include <elogind/sd\-event\&.h>
.fi
.ft
.sp
.ft B
.nf
typedef struct sd_event_source sd_event_source;
.fi
.ft
.HP \w'typedef\ int\ (*sd_event_signal_handler_t)('u
.BI "typedef int (*sd_event_signal_handler_t)(sd_event_source\ *" "s" ", const\ struct\ signalfd_siginfo\ *" "si" ", void\ *" "userdata" ");"
.HP \w'int\ sd_event_add_signal('u
.BI "int sd_event_add_signal(sd_event\ *" "event" ", sd_event_source\ **" "source" ", int\ " "signal" ", sd_event_signal_handler_t\ " "handler" ", void\ *" "userdata" ");"
.HP \w'int\ sd_event_source_get_signal('u
.BI "int sd_event_source_get_signal(sd_event_source\ *" "source" ");"
.SH "DESCRIPTION"
.PP
\fBsd_event_add_signal()\fR
adds a new UNIX process signal event source to an event loop\&. The event loop object is specified in the
\fIevent\fR
parameter, and the event source object is returned in the
\fIsource\fR
parameter\&. The
\fIsignal\fR
parameter specifies the numeric signal to be handled (see
\fBsignal\fR(7))\&. The
\fIhandler\fR
parameter must reference a function to call when the signal is received or be
\fBNULL\fR\&. The handler function will be passed the
\fIuserdata\fR
pointer, which may be chosen freely by the caller\&. The handler also receives a pointer to a
signalfd_siginfo
structure containing information about the received signal\&. See
\fBsignalfd\fR(2)
for further information\&.
.PP
Only a single handler may be installed for a specific signal\&. The signal must be blocked in all threads before this function is called (using
\fBsigprocmask\fR(2)
or
\fBpthread_sigmask\fR(3))\&. If the handler is not specified (\fIhandler\fR
is
\fBNULL\fR), a default handler which causes the program to exit cleanly will be used\&.
.PP
By default, the event source is enabled permanently (\fBSD_EVENT_ON\fR), but this may be changed with
\fBsd_event_source_set_enabled\fR(3)\&. If the handler function returns a negative error code, it will be disabled after the invocation, even if the
\fBSD_EVENT_ON\fR
mode was requested before\&.
.PP
To destroy an event source object use
\fBsd_event_source_unref\fR(3), but note that the event source is only removed from the event loop when all references to the event source are dropped\&. To make sure an event source does not fire anymore, even if it is still referenced, disable the event source using
\fBsd_event_source_set_enabled\fR(3)
with
\fBSD_EVENT_OFF\fR\&.
.PP
If the second parameter of
\fBsd_event_add_signal()\fR
is
\fBNULL\fR
no reference to the event source object is returned\&. In this case the event source is considered "floating", and will be destroyed implicitly when the event loop itself is destroyed\&.
.PP
\fBsd_event_source_get_signal()\fR
returns the configured signal number of an event source created previously with
\fBsd_event_add_signal()\fR\&. It takes the event source object as the
\fIsource\fR
parameter\&.
.SH "RETURN VALUE"
.PP
On success, these functions return 0 or a positive integer\&. On failure, they return a negative errno\-style error code\&.
.SS "Errors"
.PP
Returned errors may indicate the following problems:
.PP
\fB\-ENOMEM\fR
.RS 4
Not enough memory to allocate an object\&.
.RE
.PP
\fB\-EINVAL\fR
.RS 4
An invalid argument has been passed\&.
.RE
.PP
\fB\-EBUSY\fR
.RS 4
A handler is already installed for this signal or the signal was not blocked previously\&.
.RE
.PP
\fB\-ESTALE\fR
.RS 4
The event loop is already terminated\&.
.RE
.PP
\fB\-ECHILD\fR
.RS 4
The event loop has been created in a different process\&.
.RE
.PP
\fB\-EDOM\fR
.RS 4
The passed event source is not a signal event source\&.
.RE
.SH "NOTES"
.PP
These APIs are implemented as a shared library, which can be compiled and linked to with the
\fBlibelogind\fR\ \&\fBpkg-config\fR(1)
file\&.
.SH "SEE ALSO"
.PP

\fBelogind\fR(8),

\fBsd-event\fR(3),
\fBsd_event_new\fR(3),
\fBsd_event_now\fR(3),
\fBsd_event_add_io\fR(3),
\fBsd_event_add_time\fR(3),
\fBsd_event_add_child\fR(3),
\fBsd_event_add_inotify\fR(3),
\fBsd_event_add_defer\fR(3),
\fBsd_event_source_set_enabled\fR(3),
\fBsd_event_source_set_description\fR(3),
\fBsd_event_source_set_userdata\fR(3),
\fBsd_event_source_set_floating\fR(3),
\fBsignal\fR(7),
\fBsignalfd\fR(2),
\fBsigprocmask\fR(2),
\fBpthread_sigmask\fR(3)