Re: [Libvirt-cim] [PATCH] [RFC] Implement libvirt event callback management

18 Aug 2009

      Hi Hollis,

I applied your patch and the patches Richard submitted to do some 
testing. I noticed a few issues commented below...
...
+/* Delete all watches marked for deletion. */
+static void event_watch_free_deleted(void)
+{
+        struct watch *cur;
+        struct watch **link;
+
+        CU_DEBUG("%s", __func__);
+
+        pthread_mutex_lock(&watch_list_mutex);
+
+        cur = watch_list; 
+        link = &watch_list;
+        while (cur != NULL) {
+                struct watch *next = cur->next;
+
+                if (cur->deleted) {
+                        *link = next;
+
+                        cur->ff(cur->opaque);
I'm seeing a seg fault here because once we reach this point, cur is NULL.
...
+                        free(cur);
+                        watch_count--;
+                } else
+                        link = &cur->next;
+
+                cur = next;
+        }
+
+        pthread_mutex_unlock(&watch_list_mutex);
+}
+
...
+/* One thread to watch all fds for all events for all libvirt threads. */
+static void *event_thread(void *ptr)
+{
+        while (1) {
+                struct watch *cur;
+                struct pollfd *pollfds;
+                struct pollfd *pollfd;
+                int timeout;
+                int i;
+
+                pollfds = malloc(sizeof(struct pollfd) * watch_count);
+
+                /* fill in pollfds array from our watch list */
+                for (pollfd = &pollfds[0], cur = watch_list;
+                     cur != NULL;
+                     pollfd++, cur = cur->next) {
+                        pollfd->fd = cur->fd;
+                        pollfd->events = libvirt_to_poll_events(cur->events);
+                }
+
+                timeout = event_next_timeout();
+
+                poll(pollfds, watch_count, timeout);
+
+                /* invoke callbacks */
+                for (i = 0; i < watch_count; i++)
+                        for (cur = watch_list; cur != NULL; cur = cur->next)
+                                if (cur->fd == pollfds[i].fd
When I generate a event, poll never seems to catch it.  I tried forcing 
this by changing the timeout value to a minute.  And then generating the 
event.  I can see from the libvirt debug that the event has been generated:

15:00:34.232: debug : virEventRunOnce:567 : Poll got 1 event
15:00:34.239: debug : virEventDispatchHandles:450 : Dispatch n=2 f=8 w=3 
e=1 0x7f2a57d6e6b0

In the eventAddHandle() call, we have:

event.c(75): eventAddHandle
event.c(82): ++++++++++++++watch->id is 0
event.c(84): ++++++++++++++watch->fd is 11
event.c(86): ++++++++++++++watch->events is 1
event.c(88): ++++++++++++++watch->cb is 0x6b8f4c0, cb is 0x6b8f4c0
event.c(90): ++++++++++++++watch->opaque is 0x7fffdc014900

I haven't tracked down what is happening here.
...
+                                    && !cur->deleted) {
+                                        invoke_callback(cur, &pollfds[i]);
+                                        break;
+                                }
+
+                free(pollfds);
+
+                event_watch_free_deleted();
+                event_timer_free_deleted();
+        }
+
+        return NULL;
+}
+
+void init_events(void)
+{
+        static pthread_mutex_t thread_mutex = PTHREAD_MUTEX_INITIALIZER;
+
+        CU_DEBUG("%s", __func__);
+
+        pthread_mutex_lock(&thread_mutex);
+
+        if (!watch_thread_id) {
+                virEventRegisterImpl(eventAddHandle,
+                                     eventUpdateHandle,
+                                     eventRemoveHandle,
+                                     eventAddTimeout,
+                                     eventUpdateTimeout,
+                                     eventRemoveTimeout);
+
+                pthread_create(&watch_thread_id, NULL, event_thread, NULL);
+        }
+
+        pthread_mutex_unlock(&thread_mutex);
+}
-- 
Kaitlin Rupert
IBM Linux Technology Center
kaitlin@linux.vnet.ibm.com