Insert fake events under a lock

The thread-specific spinlock needs to be acquired before a fake event is
inserted from a non-polling thread. The usual situation is when a monitor
thread inserts a hangup event for a DCB.

Other, less common cases are when session timeouts have been enabled and
the DCB needs to be closed. Here it is better to insert a fake hangup
event instead of directly closing the DCB from an external thread.

server/core/poll.c

@@ -94,6 +94,7 @@ typedef struct fake_event
 static int *epoll_fd;    /*< The epoll file descriptor */
 static int next_epoll_fd = 0; /*< Which thread handles the next DCB */
 static fake_event_t **fake_events; /*< Thread-specific fake event queue */
+static SPINLOCK      *fake_event_lock;
 static int do_shutdown = 0;  /*< Flag the shutdown of the poll subsystem */
 static GWBITMASK poll_mask;
 #if MUTEX_EPOLL
@@ -235,11 +236,21 @@ poll_init()
         }
     }
 
-    if ((fake_events = MXS_CALLOC(sizeof(fake_event_t*), n_threads)) == NULL)
+    if ((fake_events = MXS_CALLOC(n_threads, sizeof(fake_event_t*))) == NULL)
     {
         exit(-1);
     }
 
+    if ((fake_event_lock = MXS_CALLOC(n_threads, sizeof(SPINLOCK))) == NULL)
+    {
+        exit(-1);
+    }
+
+    for (int i = 0; i < n_threads; i++)
+    {
+        spinlock_init(&fake_event_lock[i]);
+    }
+
     memset(&pollStats, 0, sizeof(pollStats));
     memset(&queueStats, 0, sizeof(queueStats));
     bitmask_init(&poll_mask);
@@ -719,17 +730,28 @@ poll_waitevents(void *arg)
             process_pollq(thread_id, &events[i]);
         }
 
-        /** Process fake events */
+        fake_event_t *event = NULL;
-        while (fake_events[thread_id])
-        {
-            fake_event_t *event = fake_events[thread_id];
-            fake_events[thread_id] = fake_events[thread_id]->next;
 
+        /** It is very likely that the queue is empty so to avoid hitting the
+         * spinlock every time we receive events, we only do a dirty read. Currently,
+         * only the monitors inject fake events from external threads. */
+        if (fake_events[thread_id])
+        {
+            spinlock_acquire(&fake_event_lock[thread_id]);
+            event = fake_events[thread_id];
+            fake_events[thread_id] = NULL;
+            spinlock_release(&fake_event_lock[thread_id]);
+        }
+
+        /** Process fake events */
+        while (event)
+        {
             struct epoll_event ev;
             event->dcb->dcb_fakequeue = event->data;
             ev.data.ptr = event->dcb;
             ev.events = event->event;
             process_pollq(thread_id, &ev);
+            event = event->next;
         }
 
         if (check_timeouts && hkheartbeat >= next_timeout_check)
@@ -1436,6 +1458,11 @@ static void poll_add_event_to_dcb(DCB*       dcb,
 
         int thr = dcb->owner;
 
+        /** It is possible that a housekeeper or a monitor thread inserts a fake
+         * event into the thread's event queue which is why the operation needs
+         * to be protected by a spinlock */
+        spinlock_acquire(&fake_event_lock[thr]);
+
         if (fake_events[thr])
         {
             fake_events[thr]->tail->next = event;
@@ -1445,6 +1472,8 @@ static void poll_add_event_to_dcb(DCB*       dcb,
         {
             fake_events[thr] = event;
         }
+
+        spinlock_release(&fake_event_lock[thr]);
     }
 }
 

server/core/session.c

@@ -42,6 +42,7 @@
 #include <maxscale/atomic.h>
 #include <maxscale/log_manager.h>
 #include <maxscale/housekeeper.h>
+#include <maxscale/poll.h>
 
 /* This list of all sessions */
 LIST_CONFIG SESSIONlist =
@@ -927,7 +928,7 @@ void process_idle_sessions()
                 if (all_session->service && all_session->client_dcb && all_session->client_dcb->state == DCB_STATE_POLLING &&
                     hkheartbeat - all_session->client_dcb->last_read > all_session->service->conn_idle_timeout * 10)
                 {
-                    dcb_close(all_session->client_dcb);
+                    poll_fake_hangup_event(all_session->client_dcb);
                 }
 
                 current = list_iterate(&SESSIONlist, current);