[packagekit] [Q] How "GetDepends" connect with "get_depends"

[NZzi]

Richard Hughes wrote:
> On Tue, 2008-09-16 at 15:03 +0800, NZzi wrote:
>> i wonder how "pkcon get-updates package" implement,
>> so i browse packagekit code, but i know little
>> about dbus, so after a whole day, i still can not
>> understand how "GetDepends" connect with "get_depends".
>>
>> i browse from pk-console.c:
>>
>> } else if (strcmp (mode, "get-depends") == 0) {
>> 	...
>> 	ret = pk_console_get_depends (client, filters, value, &error);
>> }
>>
>> pk_console_get_depends()->pk_client_get_depends()->
>> ret = dbus_g_proxy_call (client->priv->proxy, "GetDepends", error,...)
> 
> Correct, the pkcon program is just a front-end to the libpackagekit
> library[4], which in turn is a front-end to the DBUS interface.
> 
>> i study some dbus docs, i konw dbus_g_proxy_call() call
>> "GetDepends" method through proxy object(client->priv->proxy),
>> but the "real" dependency-process function is get-depends() in
>> yumBackend.py. and i found it's backend_get_depends()(in
>> pk-backend-yum.c) invokd the get-depends().
>>
>> but i don't know how dbus_g_proxy_call (client->priv->proxy, 
>> "GetDepends"...)
>> invoke backend_get_depends()(in pk-backend-yum.c)
>>
>> can anyone give me some hints, thanks advance
> 
> No problem, thanks for taking the time to read the code. The actual
> process is actually pretty simple:
> 
> The dbus server pk-engine.c takes the request for a TID [1] (transaction
> ID) and creates a new PkTransaction object (and files it in a
> PkTransactionList object. When this object is called with GetDepends,
> (pk-transaction.c) takes the request[3], and saves all the parameters,
> checks permissions and that sort of thing.


your reply has not context, so i reply this mail, sorry.

i follow your words, and browse pk_transaction_run().
pk_transaction_set_running() will call corresponding
backend get_depends call, based on the "PK_ROLE_ENUM_GET_DEPENDS"
role.

i follow the call-chains, i found it's pk_transaction_get_depends()
set the "PK_ROLE_ENUM_GET_DEPENDS" roles.

but i don't know who called pk_transaction_get_depends()?

i compile packagekit, i found pk-interface-transaction.h, the
generated file has pk_transaction_get_depends and "GetDepends",
but i don't understand how packagekitd know that she should
call pk_transaction_get_depends() when received "GetDepends"
requests from dbus?

i read glib doc about "DBusGObjectInfo" and "DBusGMethodInfo",
but their explanation doesnt help about this.

BTW, i browse pk-engine.c, i still don't know where packagekitd
received dbus messages(requests),and process, and "goto"
pk-transaction.c?


> 
> When PkTransactionList detects that nothing else is running, the new
> PkTransaction is "run" which means that it takes control of the single
> PkBackend instance and the backend is run and waits for that transaction
> to finish.
> 
> Now, that explains how the daemon schedules requests (as the backend can
> only ever do one thing at a time) but doesn't explain how the yum code
> is actually run.
> 
> In the /etc/PackageKit/PackageKit.conf file you'll have a DefaultBackend
> option, which will point to yum. When the daemon starts up, it dlopens a
> shared object file for whichever the default backend is, in this case
> you can see the code in pk-backend-yum.c
> 
> This code maps a vtable (a table of functions) to the PkBackend
> instance, so that when the functions in PkBackend are called, these are
> mapped to the functions in pk-backend-yum.c
> 
> These functions are responsible for launching the yum executable
> yumBackend.py (using pk-backend-spawn.c, which in turn uses pk-spawn.c)
> and watches the standard out for replies, and then when it's done it
> kills the program. [2]
> 
> In the new dispatcher [5], it gets a little bit more complicated as the
> spawned executable is not closed down after every transaction, and
> instead can stay running in the backend for a few seconds. This makes
> using the GUI a lot snappier, as yum isn't being created and destroyed
> all the time.
> 
> Actually, when reading that back, it doesn't seem so simple anymore!
> 
> Feel free to ask about any of that stuff I've explained badly. I
> probably need to add something like this in the code anyway.
> 
> Richard.
> 
> [1] http://www.packagekit.org/gtk-doc/introduction-ideas-transactions.html
> [2] http://www.packagekit.org/gtk-doc/backend-spawn.html
> [3] http://www.packagekit.org/gtk-doc/Transaction.html
> [4] http://www.packagekit.org/gtk-doc/PkClient.html
> [5] http://article.gmane.org/gmane.comp.freedesktop.packagekit/3237
> 
> 
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