DBusWatch function, DBusTimeout functions Why these functions is needed ?

Wed Dec 28 09:21:29 UTC 2016

Hi Martin,

*>> They are just called once. Sockets must be monitored in order to let
dbus know when a new message arrives.*
I am only curios why *DBus *cannot monitor socket by itself. First time
when I faced with it it was surprise for me.

One additional point:
"*When you use dbus_connection_send()
<https://dbus.freedesktop.org/doc/api/html/group__DBusConnection.html#gae1cb64f4cf550949b23fd3a756b2f7d0>
or
one of its variants to send a message, the message is added to the outgoing
queue. It's actually written to the network later; either
in dbus_watch_handle()
<https://dbus.freedesktop.org/doc/api/html/group__DBusWatch.html#gac2acdb1794450ac01a43ec4c3e07ebf7>
invoked
by your main loop, or in dbus_connection_flush()
<https://dbus.freedesktop.org/doc/api/html/group__DBusConnection.html#ga10e68d9d2f41d655a4151ddeb807ff54>
which
blocks until it can write out the entire outgoing queue. The GLib/Qt add-on
libraries again handle the details here for you by setting up watch
functions.*"

For this I implemented calling *dbus_connection_flush()
<https://dbus.freedesktop.org/doc/api/html/group__DBusConnection.html#ga10e68d9d2f41d655a4151ddeb807ff54>
*on
event *POLLOUT*, but this event never appears. For me it is very strange
...
But all sent messages by  dbus_connection_send()
<https://dbus.freedesktop.org/doc/api/html/group__DBusConnection.html#gae1cb64f4cf550949b23fd3a756b2f7d0>
arrives
*successfully* (it even I have not received *POLLOUT *for making flush).

Do you know who ca *dbus_connection_flush()
<https://dbus.freedesktop.org/doc/api/html/group__DBusConnection.html#ga10e68d9d2f41d655a4151ddeb807ff54>
*in
this case ?

On 27 December 2016 at 21:02, Martin Häfner <martinhaefner at web.de> wrote:

> Hi Denis,
>
> the functions are called within this block in the dispatcher.cpp in order
> to register your callbacks:
>
> Private(DBusConnection* conn)
> {
> #ifdef USE_POLL
>    dbus_connection_set_watch_functions(conn, &add_watch, &remove_watch,
> &toggle_watch, this, nullptr);
>    dbus_connection_set_timeout_functions (conn, &add_timeout,
> &remove_timeout, &toggle_timeout, this, nullptr);
> #endif
> }
>
> They are just called once. Sockets must be monitored in order to let dbus
> know when a new message arrives. But dbus also has timeout handling - if
> messages do not arrive intime or the daemon is not able to send data on the
> socket in a certain time. This is why timeouts are needed. Note that in a
> simple dbus application there is mostly only one socket alive at a time
> (the bus connection).
>
> Regards,
> Martin
>
> 2016-12-26 10:59 GMT+01:00 Денис Котов <redradist at gmail.com>:
>
>> Hi Martin,
>>
>> Thanks for link, but I have not found where you use the
>> following functions:
>> dbus_connection_set_watch_functions
>> dbus_connection_set_timeout_functions
>>
>> ???
>>
>> From your explanation and this example https://lists.freedesk
>> top.org/archives/dbus/2007-October/008859.html I have understood that watch
>> - is a file descriptor that needed to be monitored ( for example in a new
>> client has connected to service ), but timeout what is the purpose of this
>> variable ?
>> Okay, let's imagine that libdbus asked to create the timer, but for what
>> purposes ? Should I handle file descriptor in that time or what ? And if I
>> would not handle something in that timeout what will happen ?
>>
>> On 25 December 2016 at 22:10, Martin Häfner <martinhaefner at web.de> wrote:
>>
>>> Hi Denis,
>>>
>>> DBusWatch and Timeout are dbus callouts to integrate the dbus library
>>> into external event loops. You can write simple dbus driven applications
>>> with a simple main loop just calling the dbus_connection_read_write_dispatch
>>> function in a simple main loop. If you develop real world applications
>>> you will probably have to integrate the dbus API into a third-party main
>>> loop, e.g. from QApplication when implementing a Qt base GUI application.
>>> For the Qt example, you will probably make a mapping from a DBusTimeout to
>>> a QTimer and from a DBusWatch to QSocketNotifier. So, whenever DBus tells
>>> you to create a watch you will create a QSocketNotifier, and whenever DBus
>>> calls the callout to create a Timeout you create a QTimer. I have written a
>>> template-based C++ wrapper on top of DBus which implements the two
>>> different possibilities, once in a simple poll loop: You can have a look
>>> into the example at https://github.com/martinhaefn
>>> er/simppl/blob/dbus2/src/dispatcher.cpp
>>>
>>> Regards,
>>> Martin
>>>
>>> 2016-12-24 19:02 GMT+01:00 Денис Котов <redradist at gmail.com>:
>>>
>>>> Hi All,
>>>>
>>>> Currently I have faced with understanding of watch and timeout
>>>> functions in libdbus.
>>>> I do not quit understand why they are needed.
>>>>
>>>> From description I understand they are needed to check state of socket.
>>>> If something changes then from libdbus I will receive this message and I
>>>> have either to read something or to write something to socket.
>>>>
>>>> It means that I should not create infinite while loop, but register
>>>> callbacks and when will be possibility I will write to out-queue or read to
>>>> in-queue, am I right ?
>>>>
>>>> And maybe some brief explanation what is DBusTimeout function ?
>>>>
>>>> --
>>>>
>>>> *Best RegardsDenis Kotov*
>>>>
>>>> _______________________________________________
>>>> dbus mailing list
>>>> dbus at lists.freedesktop.org
>>>> https://lists.freedesktop.org/mailman/listinfo/dbus
>>>>
>>>>
>>>
>>
>>
>> --
>>
>> *Best RegardsDenis Kotov*
>>
>
>

-- 

*Best RegardsDenis Kotov*
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