X-Git-Url: http://git.efficios.com/?p=lttng-tools.git;a=blobdiff_plain;f=src%2Fbin%2Flttng-sessiond%2Fnotification-thread.h;h=a9c771104d48118a1a61ce65008f8df9b76c3439;hp=c401b410becb8df1ff4c927ffba8e01341cbc710;hb=74df9916833ae6a69520c1a49ddce44ba3eea078;hpb=5332364f00f5ed785ec35bc93a790c976a5ca454

diff --git a/src/bin/lttng-sessiond/notification-thread.h b/src/bin/lttng-sessiond/notification-thread.h
index c401b410b..a9c771104 100644
--- a/src/bin/lttng-sessiond/notification-thread.h
+++ b/src/bin/lttng-sessiond/notification-thread.h
@@ -49,6 +49,116 @@ struct notification_thread_handle {
 	} channel_monitoring_pipes;
 };
 
+/**
+ * This thread maintains an internal state associating clients and triggers.
+ *
+ * In order to speed-up and simplify queries, hash tables providing the
+ * following associations are maintained:
+ *
+ *   - client_socket_ht: associate a client's socket (fd) to its "struct client"
+ *             This hash table owns the "struct client" which must thus be
+ *             disposed-of on removal from the hash table.
+ *
+ *   - channel_triggers_ht:
+ *             associates a channel key to a list of
+ *             struct lttng_trigger_list_nodes. The triggers in this list are
+ *             those that have conditions that apply to this channel.
+ *             A channel entry is only created when a channel is added; the
+ *             list of triggers applying to such a channel is built at that
+ *             moment.
+ *             This hash table owns the list, but not the triggers themselves.
+ *
+ *   - channel_state_ht:
+ *             associates a pair (channel key, channel domain) to its last
+ *             sampled state received from the consumer daemon
+ *             (struct channel_state).
+ *             This previous sample is kept to implement edge-triggered
+ *             conditions as we need to detect the state transitions.
+ *             This hash table owns the channel state.
+ *
+ *   - notification_trigger_clients_ht:
+ *             associates notification-emitting triggers to clients
+ *             (struct notification_client_list) subscribed to those
+ *             conditions.
+ *             The condition's hash and match functions are used directly since
+ *             all triggers in this hash table have the "notify" action.
+ *             This hash table holds no ownership.
+ *
+ *   - channels_ht:
+ *             associates a channel_key to a struct channel_info. The hash table
+ *             holds the ownership of the struct channel_info.
+ *
+ *   - triggers_ht:
+ *             associated a condition to a struct lttng_trigger_ht_element.
+ *             The hash table holds the ownership of the
+ *             lttng_trigger_ht_elements along with the triggers themselves.
+ *
+ * The thread reacts to the following internal events:
+ *   1) creation of a tracing channel,
+ *   2) destruction of a tracing channel,
+ *   3) registration of a trigger,
+ *   4) unregistration of a trigger,
+ *   5) reception of a channel monitor sample from the consumer daemon.
+ *
+ * Events specific to notification-emitting triggers:
+ *   6) connection of a notification client,
+ *   7) disconnection of a notification client,
+ *   8) subscription of a client to a conditions' notifications,
+ *   9) unsubscription of a client from a conditions' notifications,
+ *
+ *
+ * 1) Creation of a tracing channel
+ *    - notification_trigger_clients_ht is traversed to identify
+ *      triggers which apply to this new channel,
+ *    - triggers identified are added to the channel_triggers_ht.
+ *    - add channel to channels_ht
+ *
+ * 2) Destruction of a tracing channel
+ *    - remove entry from channel_triggers_ht, releasing the list wrapper and
+ *      elements,
+ *    - remove entry from the channel_state_ht.
+ *    - remove channel from channels_ht
+ *
+ * 3) Registration of a trigger
+ *    - if the trigger's action is of type "notify",
+ *      - traverse the list of conditions of every client to build a list of
+ *        clients which have to be notified when this trigger's condition is met,
+ *        - add list of clients (even if it is empty) to the
+ *          notification_trigger_clients_ht,
+ *    - add trigger to channel_triggers_ht (if applicable),
+ *    - add trigger to triggers_ht
+ *
+ * 4) Unregistration of a trigger
+ *    - if the trigger's action is of type "notify",
+ *      - remove the trigger from the notification_trigger_clients_ht,
+ *    - remove trigger from channel_triggers_ht (if applicable),
+ *    - remove trigger from triggers_ht
+ *
+ * 5) Reception of a channel monitor sample from the consumer daemon
+ *    - evaluate the conditions associated with the triggers found in
+ *      the channel_triggers_ht,
+ *      - if a condition evaluates to "true" and the condition is of type
+ *        "notify", query the notification_trigger_clients_ht and send
+ *        a notification to the clients.
+ *
+ * 6) Connection of a client
+ *    - add client socket to the client_socket_ht.
+ *
+ * 7) Disconnection of a client
+ *    - remove client socket from the client_socket_ht,
+ *    - traverse all conditions to which the client is subscribed and remove
+ *      the client from the notification_trigger_clients_ht.
+ *
+ * 8) Subscription of a client to a condition's notifications
+ *    - Add the condition to the client's list of subscribed conditions,
+ *    - Look-up notification_trigger_clients_ht and add the client to
+ *      list of clients.
+ *
+ * 9) Unsubscription of a client to a condition's notifications
+ *    - Remove the condition from the client's list of subscribed conditions,
+ *    - Look-up notification_trigger_clients_ht and remove the client
+ *      from the list of clients.
+ */
 struct notification_thread_state {
 	int notification_channel_socket;
 	struct lttng_poll_event events;