# sd_event_add_signal

## NAME



           sd_event_add_signal, sd_event_source_get_signal,
           sd_event_signal_handler_t, SD_EVENT_SIGNAL_PROCMASK - Add a UNIX
           process signal event source to an event loop
    


## SYNOPSIS



           **#include <systemd/sd-event.h>**
    
           **typedef struct sd_event_source sd_event_source;**
    
           **SD_EVENT_SIGNAL_PROCMASK**
    
           **typedef int (*sd_event_signal_handler_t)(sd_event_source ***_s_**,**
                                                    **const struct signalfd_siginfo ***_si_**,**
                                                    **void ***_userdata_**);**
    
           **int sd_event_add_signal(sd_event ***_event_**, sd_event_source ****_source_**,**
                                   **int** _signal_**,**
                                   **sd_event_signal_handler_t** _handler_**,**
                                   **void ***_userdata_**);**
    
           **int sd_event_source_get_signal(sd_event_source ***_source_**);**
    


## DESCRIPTION



           **sd_event_add_signal()** adds a new UNIX process signal event source
           to an event loop. The event loop object is specified in the _event_
           parameter, and the event source object is returned in the _source_
           parameter. The _signal_ parameter specifies the numeric signal to be
           handled (see signal(7)).
    
           The _handler_ parameter is a function to call when the signal is
           received or **NULL**. The handler function will be passed the _userdata_
           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 signalfd(2) for further
           information. The handler may return negative to signal an error
           (see below), other return values are ignored. If _handler_ is **NULL** ,
           a default handler that calls sd_event_exit(3) will be used.
    
           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 sigprocmask(2) or pthread_sigmask(3)). For
           convenience, if the special flag **SD_EVENT_SIGNAL_PROCMASK** is ORed
           into the specified signal the signal will be automatically masked
           as necessary, for the calling thread. Note that this only works
           reliably if the signal is already masked in all other threads of
           the process, or if there are no other threads at the moment of
           invocation.
    
           By default, the event source is enabled permanently (**SD_EVENT_ON**),
           but this may be changed with sd_event_source_set_enabled(3). If
           the handler function returns a negative error code, it will either
           be disabled after the invocation, even if the **SD_EVENT_ON** mode was
           requested before, or it will cause the loop to terminate, see
           sd_event_source_set_exit_on_failure(3).
    
           To destroy an event source object use sd_event_source_unref(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
           sd_event_source_set_enabled(3) with **SD_EVENT_OFF**.
    
           If the second parameter of **sd_event_add_signal()** is **NULL** 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.
    
           If the _handler_ parameter to **sd_event_add_signal()** is **NULL** , and the
           event source fires, this will be considered a request to exit the
           event loop. In this case, the _userdata_ parameter, cast to an
           integer, is passed as the exit code parameter to sd_event_exit(3).
    
           **sd_event_source_get_signal()** returns the configured signal number
           of an event source created previously with **sd_event_add_signal()**.
           It takes the event source object as the _source_ parameter.
    


## RETURN VALUE



           On success, these functions return 0 or a positive integer. On
           failure, they return a negative errno-style error code.
    
       **Errors**
           Returned errors may indicate the following problems:
    
           **-ENOMEM**
               Not enough memory to allocate an object.
    
           **-EINVAL**
               An invalid argument has been passed.
    
           **-EBUSY**
               A handler is already installed for this signal or the signal
               was not blocked previously.
    
           **-ESTALE**
               The event loop is already terminated.
    
           **-ECHILD**
               The event loop has been created in a different process,
               library or module instance.
    
           **-EDOM**
               The passed event source is not a signal event source.
    


## NOTES



           Functions described here are available as a shared library, which
           can be compiled against and linked to with the
           **libsystemd pkg-config**(1) file.
    
           The code described here uses getenv(3), which is declared to be
           not multi-thread-safe. This means that the code calling the
           functions described here must not call setenv(3) from a parallel
           thread. It is recommended to only do calls to **setenv()** from an
           early phase of the program when no other threads have been
           started.
    


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