SD_BUS_PROCESS(3)

NAME
sd_bus_process - Drive the connection

SYNOPSIS

#include <systemd/sd-bus.h>

int sd_bus_process(sd_bus *bus, sd_bus_message **ret);

DESCRIPTION

sd_bus_process() drives the connection between the client and the message bus. That is, it handles connecting, authentication, and processing of messages. When invoked, pending I/O work is executed, and queued incoming messages are dispatched to registered callbacks. Each time it is invoked a single operation is executed. It returns zero when no operations were pending and positive if a message was processed. When zero is returned the caller should poll for I/O events before calling into sd_bus_process() again. For that either use the simple, blocking sd_bus_wait(3) call, or hook up the bus connection object to an external or manual event loop using sd_bus_get_fd(3).

sd_bus_process() processes at most one incoming message per call. If the parameter ret is not NULL and the call processed a message, *ret is set to this message. The caller owns a reference to this message and should call sd_bus_message_unref(3) when the message is no longer needed. If ret is not NULL and progress was made, but no message was processed, *ret is set to NULL. Note that only messages not already handled by the various types of registered message handlers (i.e. by filters registered via sd_bus_add_filter(3), object handlers registered via sd_bus_add_object(3), matches registered via sd_bus_add_match(3), and related) will be returned through this parameter. Also note that if such a message handler returns a zero return value (as opposed to some value > 0) an incoming message will not be considered handled, and be passed to other suitable handlers (until one returns > > 0), or returned by sd_bus_process() (in case none returns > 0).

If the bus object is connected to an sd-event(3) event loop (with sd_bus_attach_event(3)), it is not necessary to call sd_bus_process() directly as it is invoked automatically when necessary.

RETURN VALUE

If progress was made, a positive integer is returned. If no progress was made, 0 is returned. If an error occurs, a negative errno-style error code is returned.

  Errors

Returned errors may indicate the following problems:

-EINVAL
    An invalid bus object was passed.

-ECHILD
    The bus connection was allocated in a parent process and is being reused in a child process after fork().

-ENOTCONN
    The bus connection has been terminated already.

-ECONNRESET
    The bus connection has been terminated just now.

-EBUSY
    This function is already being called, i.e. sd_bus_process() has been called from a callback function that itself was called by sd_bus_process().

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.

HISTORY

sd_bus_process() was added in version 221.

SEE ALSO

systemd(1), sd-bus(3), sd_bus_wait(3), sd_bus_get_fd(3), sd_bus_message_unref(3), sd-event(3), sd_bus_attach_event(3)