sd_bus_process

systemd

sd_bus_process

Drive the connection

#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().

History

sd_bus_process() was added in version 221.