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SD_BUS_PROCESS(3) sd_bus_process SD_BUS_PROCESS(3)


sd_bus_process - Drive the connection


#include <elogind/sd-bus.h>

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


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, progress was made, but no message was processed, *ret is set to NULL.

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.


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.


Returned errors may indicate the following problems:


An invalid bus object was passed.


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


The bus connection has been terminated already.


The bus connection has been terminated just now.


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().


Functions described here are available as a shared library, which can be compiled against and linked to with the libelogind pkg-config(8) file.


sd_bus_process() was added in version 231.



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)

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