src/bin/lttng-sessiond/notification-thread.h

   1 /*
   2  * Copyright (C) 2017 - Jérémie Galarneau <jeremie.galarneau@efficios.com>
   3  *
   4  * This program is free software; you can redistribute it and/or modify it
   5  * under the terms of the GNU General Public License, version 2 only, as
   6  * published by the Free Software Foundation.
   7  *
   8  * This program is distributed in the hope that it will be useful, but WITHOUT
   9  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  10  * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
  11  * more details.
  12  *
  13  * You should have received a copy of the GNU General Public License along with
  14  * this program; if not, write to the Free Software Foundation, Inc., 51
  15  * Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  16  */
  17
  18 #ifndef NOTIFICATION_THREAD_H
  19 #define NOTIFICATION_THREAD_H
  20
  21 #include <urcu/list.h>
  22 #include <urcu.h>
  23 #include <urcu/rculfhash.h>
  24 #include <lttng/trigger/trigger.h>
  25 #include <common/pipe.h>
  26 #include <common/compat/poll.h>
  27 #include <common/hashtable/hashtable.h>
  28 #include <pthread.h>
  29 #include <semaphore.h>
  30
  31 struct notification_thread_handle {
  32         /*
  33          * Queue of struct notification command.
  34          * event_pipe must be WRITE(2) to signal that a new command
  35          * has been enqueued.
  36          */
  37         struct {
  38                 struct lttng_pipe *event_pipe;
  39                 struct cds_list_head list;
  40                 pthread_mutex_t lock;
  41         } cmd_queue;
  42         /*
  43          * Read side of pipes used to receive channel status info collected
  44          * by the various consumer daemons.
  45          */
  46         struct {
  47                 int ust32_consumer;
  48                 int ust64_consumer;
  49                 int kernel_consumer;
  50         } channel_monitoring_pipes;
  51         /*
  52          * To inform the rotation thread we are ready.
  53          */
  54         sem_t *notification_thread_ready;
  55 };
  56
  57 /**
  58  * This thread maintains an internal state associating clients and triggers.
  59  *
  60  * In order to speed-up and simplify queries, hash tables providing the
  61  * following associations are maintained:
  62  *
  63  *   - client_socket_ht: associate a client's socket (fd) to its "struct client"
  64  *             This hash table owns the "struct client" which must thus be
  65  *             disposed-of on removal from the hash table.
  66  *
  67  *   - channel_triggers_ht:
  68  *             associates a channel key to a list of
  69  *             struct lttng_trigger_list_nodes. The triggers in this list are
  70  *             those that have conditions that apply to a particular channel.
  71  *             A channel entry is only created when a channel is added; the
  72  *             list of triggers applying to such a channel is built at that
  73  *             moment.
  74  *             This hash table owns the list, but not the triggers themselves.
  75  *
  76  *   - session_triggers_ht:
  77  *             associates a session name to a list of
  78  *             struct lttng_trigger_list_nodes. The triggers in this list are
  79  *             those that have conditions that apply to a particular session.
  80  *             A session entry is only created when a session is created; the
  81  *             list of triggers applying to this new session is built at that
  82  *             moment. This happens at the time of creation of a session_info.
  83  *             Likewise, the list is destroyed at the time of the session_info's
  84  *             destruction.
  85  *
  86  *   - channel_state_ht:
  87  *             associates a pair (channel key, channel domain) to its last
  88  *             sampled state received from the consumer daemon
  89  *             (struct channel_state).
  90  *             This previous sample is kept to implement edge-triggered
  91  *             conditions as we need to detect the state transitions.
  92  *             This hash table owns the channel state.
  93  *
  94  *   - notification_trigger_clients_ht:
  95  *             associates notification-emitting triggers to clients
  96  *             (struct notification_client_list) subscribed to those
  97  *             conditions.
  98  *             The condition's hash and match functions are used directly since
  99  *             all triggers in this hash table have the "notify" action.
 100  *             This hash table holds no ownership.
 101  *
 102  *   - channels_ht:
 103  *             associates a channel_key to a struct channel_info. The hash table
 104  *             holds the ownership of the struct channel_info.
 105  *
 106  *   - sessions_ht:
 107  *             associates a session_name (hash) to a struct session_info. The
 108  *             hash table holds no ownership of the struct session_info;
 109  *             the session_info structure is owned by the session's various
 110  *             channels through their struct channel_info (ref-counting is used).
 111  *
 112  *   - triggers_ht:
 113  *             associates a condition to a struct lttng_trigger_ht_element.
 114  *             The hash table holds the ownership of the
 115  *             lttng_trigger_ht_elements along with the triggers themselves.
 116  *
 117  * The thread reacts to the following internal events:
 118  *   1) creation of a tracing channel,
 119  *   2) destruction of a tracing channel,
 120  *   3) registration of a trigger,
 121  *   4) unregistration of a trigger,
 122  *   5) reception of a channel monitor sample from the consumer daemon.
 123  *
 124  * Events specific to notification-emitting triggers:
 125  *   6) connection of a notification client,
 126  *   7) disconnection of a notification client,
 127  *   8) subscription of a client to a conditions' notifications,
 128  *   9) unsubscription of a client from a conditions' notifications,
 129  *
 130  *
 131  * 1) Creation of a tracing channel
 132  *    - notification_trigger_clients_ht is traversed to identify
 133  *      triggers which apply to this new channel,
 134  *      - triggers identified are added to the channel_triggers_ht.
 135  *    - add channel to channels_ht
 136  *    - if it is the first channel of a session, a session_info is created and
 137  *      added to the sessions_ht. A list of the triggers associated with that
 138  *      session is built, and it is added to session_triggers_ht.
 139  *
 140  * 2) Destruction of a tracing channel
 141  *    - remove entry from channel_triggers_ht, releasing the list wrapper and
 142  *      elements,
 143  *    - remove entry from the channel_state_ht.
 144  *    - remove channel from channels_ht
 145  *    - if it was the last known channel of a session, the session_info
 146  *      structure is torndown, which in return destroys the list of triggers
 147  *      applying to that session.
 148  *
 149  * 3) Registration of a trigger
 150  *    - if the trigger's action is of type "notify",
 151  *      - traverse the list of conditions of every client to build a list of
 152  *        clients which have to be notified when this trigger's condition is met,
 153  *        - add list of clients (even if it is empty) to the
 154  *          notification_trigger_clients_ht,
 155  *    - add trigger to channel_triggers_ht (if applicable),
 156  *    - add trigger to session_triggers_ht (if applicable),
 157  *    - add trigger to triggers_ht
 158  *    - evaluate the trigger's condition right away to react if that condition
 159  *      is true from the beginning.
 160  *
 161  * 4) Unregistration of a trigger
 162  *    - if the trigger's action is of type "notify",
 163  *      - remove the trigger from the notification_trigger_clients_ht,
 164  *    - remove trigger from channel_triggers_ht (if applicable),
 165  *    - remove trigger from session_triggers_ht (if applicable),
 166  *    - remove trigger from triggers_ht
 167  *
 168  * 5) Reception of a channel monitor sample from the consumer daemon
 169  *    - evaluate the conditions associated with the triggers found in
 170  *      the channel_triggers_ht,
 171  *      - if a condition evaluates to "true" and the condition is of type
 172  *        "notify", query the notification_trigger_clients_ht and send
 173  *        a notification to the clients.
 174  *
 175  * 6) Connection of a client
 176  *    - add client socket to the client_socket_ht.
 177  *
 178  * 7) Disconnection of a client
 179  *    - remove client socket from the client_socket_ht,
 180  *    - traverse all conditions to which the client is subscribed and remove
 181  *      the client from the notification_trigger_clients_ht.
 182  *
 183  * 8) Subscription of a client to a condition's notifications
 184  *    - Add the condition to the client's list of subscribed conditions,
 185  *    - Look-up notification_trigger_clients_ht and add the client to
 186  *      list of clients.
 187  *    - Evaluate the condition for the client that subscribed if the trigger
 188  *      was already registered.
 189  *
 190  * 9) Unsubscription of a client to a condition's notifications
 191  *    - Remove the condition from the client's list of subscribed conditions,
 192  *    - Look-up notification_trigger_clients_ht and remove the client
 193  *      from the list of clients.
 194  */
 195 struct notification_thread_state {
 196         int notification_channel_socket;
 197         struct lttng_poll_event events;
 198         struct cds_lfht *client_socket_ht;
 199         struct cds_lfht *channel_triggers_ht;
 200         struct cds_lfht *session_triggers_ht;
 201         struct cds_lfht *channel_state_ht;
 202         struct cds_lfht *notification_trigger_clients_ht;
 203         struct cds_lfht *channels_ht;
 204         struct cds_lfht *sessions_ht;
 205         struct cds_lfht *triggers_ht;
 206 };
 207
 208 /* notification_thread_data takes ownership of the channel monitor pipes. */
 209 struct notification_thread_handle *notification_thread_handle_create(
 210                 struct lttng_pipe *ust32_channel_monitor_pipe,
 211                 struct lttng_pipe *ust64_channel_monitor_pipe,
 212                 struct lttng_pipe *kernel_channel_monitor_pipe,
 213                 sem_t *notification_thread_ready);
 214 void notification_thread_handle_destroy(
 215                 struct notification_thread_handle *handle);
 216
 217 void *thread_notification(void *data);
 218
 219 #endif /* NOTIFICATION_THREAD_H */