From 10f9272e45ea97d1b8f8059c9d285049ff4b606d Mon Sep 17 00:00:00 2001
From: Christian Grothoff <christian@grothoff.org>
Date: Sun, 22 Aug 2021 00:12:18 +0200
Subject: -implement long polling support on reserve status (but not yet in C
 client library)

---
 src/exchangedb/plugin_exchangedb_postgres.c | 102 +++++++++++++++++++++++++---
 1 file changed, 91 insertions(+), 11 deletions(-)

(limited to 'src/exchangedb')

diff --git a/src/exchangedb/plugin_exchangedb_postgres.c b/src/exchangedb/plugin_exchangedb_postgres.c
index 1d05fb499..2d7ca0573 100644
--- a/src/exchangedb/plugin_exchangedb_postgres.c
+++ b/src/exchangedb/plugin_exchangedb_postgres.c
@@ -109,6 +109,39 @@ struct TALER_EXCHANGEDB_Session
 };
 
 
+/**
+ * Event registration record.
+ */
+struct TALER_EXCHANGEDB_EventHandler
+{
+  /**
+   * Underlying GNUnet event handler.
+   */
+  struct GNUNET_DB_EventHandler *geh;
+
+  /**
+   * Entry in the heap.
+   */
+  struct GNUNET_CONTAINER_HeapNode *hn;
+
+  /**
+   * Our timeout.
+   */
+  struct GNUNET_TIME_Absolute timeout;
+
+  /**
+   * Callback to invoke (on @e timeout).
+   */
+  GNUNET_DB_EventCallback cb;
+
+  /**
+   * Closure for @e cb.
+   */
+  void *cb_cls;
+
+};
+
+
 /**
  * Type of the "cls" argument given to each of the functions in
  * our API.
@@ -132,6 +165,12 @@ struct PostgresClosure
    */
   char *sql_dir;
 
+  /**
+   * Heap of `struct TALER_EXCHANGEDB_EventHandler`
+   * by timeout.
+   */
+  struct GNUNET_CONTAINER_Heap *event_heap;
+
   /**
    * After how long should idle reserves be closed?
    */
@@ -2832,18 +2871,41 @@ handle_events (void *cls)
     }
   };
   nfds_t nfds = (-1 == pg->pg_sock) ? 1 : 2;
+  struct TALER_EXCHANGEDB_EventHandler *r;
 
   GNUNET_assert (0 ==
                  pthread_mutex_lock (&pg->event_lock));
   while (0 != pg->listener_count)
   {
     int ret;
+    int timeout = -1; /* no timeout */
 
     GNUNET_assert (0 ==
                    pthread_mutex_unlock (&pg->event_lock));
+    while (1)
+    {
+      r = GNUNET_CONTAINER_heap_peek (pg->event_heap);
+      if (NULL == r)
+        break;
+      if (GNUNET_TIME_absolute_is_future (r->timeout))
+        break;
+      GNUNET_assert (r ==
+                     GNUNET_CONTAINER_heap_remove_root (pg->event_heap));
+      r->hn = NULL;
+      r->cb (r->cb_cls,
+             NULL,
+             0);
+    }
+    if (NULL != r)
+    {
+      struct GNUNET_TIME_Relative rem;
+
+      rem = GNUNET_TIME_absolute_get_remaining (r->timeout);
+      timeout = rem.rel_value_us / GNUNET_TIME_UNIT_MILLISECONDS.rel_value_us;
+    }
     ret = poll (pfds,
                 nfds,
-                -1 /* no timeout */);
+                timeout);
     if (-1 == ret)
       GNUNET_log_strerror (GNUNET_ERROR_TYPE_WARNING,
                            "poll");
@@ -2909,16 +2971,30 @@ pq_socket_cb (void *cls,
  * @param cb_cls closure for @a cb
  * @return handle useful to cancel the listener
  */
-static struct GNUNET_DB_EventHandler *
+static struct TALER_EXCHANGEDB_EventHandler *
 postgres_event_listen (void *cls,
-                       struct TALER_EXCHANGEDB_Session *session,
+                       struct GNUNET_TIME_Relative timeout,
                        const struct GNUNET_DB_EventHeaderP *es,
                        GNUNET_DB_EventCallback cb,
                        void *cb_cls)
 {
   struct PostgresClosure *pg = cls;
-  struct GNUNET_DB_EventHandler *eh;
+  struct TALER_EXCHANGEDB_EventHandler *eh;
+  struct TALER_EXCHANGEDB_Session *session;
 
+  session = postgres_get_session (pg);
+  eh = GNUNET_new (struct TALER_EXCHANGEDB_EventHandler);
+  eh->cb = cb;
+  eh->cb_cls = cb_cls;
+  eh->timeout = GNUNET_TIME_relative_to_absolute (timeout);
+  eh->geh = GNUNET_PQ_event_listen (session->conn,
+                                    es,
+                                    cb,
+                                    cb_cls);
+  GNUNET_assert (NULL != eh->geh);
+  eh->hn = GNUNET_CONTAINER_heap_insert (pg->event_heap,
+                                         eh,
+                                         eh->timeout.abs_value_us);
   GNUNET_assert (0 ==
                  pthread_mutex_lock (&pg->event_lock));
   pg->listener_count++;
@@ -2932,11 +3008,6 @@ postgres_event_listen (void *cls,
   }
   GNUNET_assert (0 ==
                  pthread_mutex_unlock (&pg->event_lock));
-  eh = GNUNET_PQ_event_listen (session->conn,
-                               es,
-                               cb,
-                               cb_cls);
-  GNUNET_assert (NULL != eh);
   return eh;
 }
 
@@ -2949,7 +3020,7 @@ postgres_event_listen (void *cls,
  */
 static void
 postgres_event_listen_cancel (void *cls,
-                              struct GNUNET_DB_EventHandler *eh)
+                              struct TALER_EXCHANGEDB_EventHandler *eh)
 {
   struct PostgresClosure *pg = cls;
 
@@ -2971,7 +3042,13 @@ postgres_event_listen_cancel (void *cls,
   }
   GNUNET_assert (0 ==
                  pthread_mutex_unlock (&pg->event_lock));
-  GNUNET_PQ_event_listen_cancel (eh);
+  if (NULL != eh->hn)
+  {
+    GNUNET_CONTAINER_heap_remove_node (eh->hn);
+    eh->hn = NULL;
+  }
+  GNUNET_PQ_event_listen_cancel (eh->geh);
+  GNUNET_free (eh);
 }
 
 
@@ -10917,6 +10994,8 @@ libtaler_plugin_exchangedb_postgres_init (void *cls)
 
   pg = GNUNET_new (struct PostgresClosure);
   pg->cfg = cfg;
+  pg->event_heap = GNUNET_CONTAINER_heap_create (
+    GNUNET_CONTAINER_HEAP_ORDER_MIN);
   pg->main_self = pthread_self (); /* loaded while single-threaded! */
   if (GNUNET_OK !=
       GNUNET_CONFIGURATION_get_value_filename (cfg,
@@ -11166,6 +11245,7 @@ libtaler_plugin_exchangedb_postgres_done (void *cls)
   GNUNET_break (0 ==
                 close (pg->event_fd));
   pthread_mutex_destroy (&pg->event_lock);
+  GNUNET_CONTAINER_heap_destroy (pg->event_heap);
   GNUNET_free (pg->sql_dir);
   GNUNET_free (pg->currency);
   GNUNET_free (pg);
-- 
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