[libvirt-users] event handler

[Michal Privoznik]

On 14.10.2013 10:57, Alexandr wrote:
> Michal Privoznik писал 2013-10-14 11:39:
>> On 14.10.2013 10:33, Alexandr wrote:
>>> Michal Privoznik писал 2013-10-14 08:48:
>>>> On 14.10.2013 02:42, Alexandr wrote:
>>>>> good day to all.
>>>>> i still have not solved my problem with event handling.
>>>>> currently i have following code
>>>>>
>>>>>
>>>>> void libvirt_eventloop_thr_func()
>>>>> {
>>>>>     while(true) //TODO: stop somehow on exit
>>>>>     {
>>>>>         if(virEventRunDefaultImpl() < 0)
>>>>>         {
>>>>>             virErrorPtr err = virGetLastError();
>>>>>             fprintf(stderr, "Failed to run event loop: %s\n", err &&
>>>>> err->message ? err->message : "Unknown error");
>>>>>         }
>>>>>     }
>>>>> }
>>>>>
>>>>>
>>>>>
>>>>> ...
>>>>>
>>>>>     virSetErrorFunc(NULL, libvirt_error_handler);
>>>>>     libvirt_connection = virConnectOpen("qemu:///system");
>>>>
>>>> Move this line ^^^ ...
>>>>
>>>>>     if (virEventRegisterDefaultImpl() < 0)
>>>>>     {
>>>>>         virErrorPtr err = virGetLastError();
>>>>>         fprintf(stderr, "Failed to register event implementation:
>>>>> %s\n",
>>>>> err && err->message ? err->message: "Unknown error");
>>>>>             return -1;
>>>>>     }
>>>>>     {
>>>>>         int callback =
>>>>> virConnectDomainEventRegisterAny(libvirt_connection, NULL,
>>>>> VIR_DOMAIN_EVENT_ID_LIFECYCLE,
>>>>> VIR_DOMAIN_EVENT_CALLBACK(domain_event_handler), NULL, NULL);
>>>>>         if(callback == -1)
>>>>>         {
>>>>>             std::cout<<"Error: failed to register domain event handle
>>>>> callback\n";
>>>>>             return -1;
>>>>>         }
>>>>>     }
>>>>>
>>>>>     boost::thread(boost::bind(&libvirt_eventloop_thr_func));
>>>>
>>>> ... over here. The virConnectOpen detects if there's an even loop
>>>> registered. And in your case you don't have any registered when
>>>> calling it.
>>>>
>>>> Michal
>>>
>>> thank you very match, it now working as expected, but one thing are
>>> missed from documentations, current api docs says what i do not need to
>>> call virInitialize(), but if i call virEventRegisterDefaultImpl()
>>> without calling virInitialize() programm crashing (i have not used
>>> virInitialize() in my programm, just virConnectOpen() as docs said).
>>> problem solved now.
>>
>> From virInitialize documentation [1]:
>>
>> "The only time it would be necessary to call virInitialize is if the
>> application did not invoke virConnectOpen as its first API call."
>>
>> Which is your case. But if you believe this can be written better,
>> propose a patch and I'll review it.
>>
>> Michal
>>
>> 1: http://libvirt.org/html/libvirt-libvirt.html#virInitialize
> 
> yes, i read this, but my first api call is virSetErrorFunc(), and this
> api call working fine without virInitialize(), this create a little
> confusion.

The fact that some functions *seem* to work well even without
virInitialize() called doesn't mean that you shouldn't call it. When I
started to write some programs involving libvirt I've looked into
virsh.c a lot and basically copied the main structure. virsh is
guaranteed to work and use the correct sequence of APIs. The other
option is to look at examples, e.g. event-test [2].

Michal

2:
http://libvirt.org/git/?p=libvirt.git;a=blob;f=examples/domain-events/events-c/event-test.c;h=52aa3d08d7326e422c12a8521717c3d55b2d8afd;hb=HEAD#l458