sd_bus_process

systemd
sd_bus_process 3
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 message processing. 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 synchronously poll for I/O events before calling into `sd_bus_process()` again. For that either user the simple, synchronous 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 a 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()`.

## 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