Move longpoll with changes to current active pool, selecting most suitable source for longpoll, or using any backup pool that has longpoll.

Actively stop longpoll if we already have longpoll running and have initiated a longpoll restart.
Make the longpoll activation notification warning level to make the switch visible.
Change lp_url to alloca to not lose malloced ram.

main.c

@@ -4868,6 +4868,25 @@ static void convert_to_work(json_t *val, bool rolltime)
 		applog(LOG_DEBUG, "Converted longpoll data to work");
 }
 
+/* If we want longpoll, enable it for the chosen default pool, or, if
+ * the pool does not support longpoll, find the first one that does
+ * and use its longpoll support */
+static struct pool *select_longpoll_pool(void)
+{
+	struct pool *cp = current_pool();
+	int i;
+
+	if (cp->hdr_path)
+		return cp;
+	for (i = 0; i < total_pools; i++) {
+		struct pool *pool = pools[i];
+
+		if (pool->hdr_path)
+			return pool;
+	}
+	return NULL;
+}
+
 static void *longpoll_thread(void *userdata)
 {
 	struct thr_info *mythr = userdata;
@@ -4875,7 +4894,7 @@ static void *longpoll_thread(void *userdata)
 	char *copy_start, *hdr_path, *lp_url = NULL;
 	bool need_slash = false;
 	int failures = 0;
-	struct pool *pool = current_pool();
+	struct pool *pool;
 
 	pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, NULL);
 	pthread_detach(pthread_self());
@@ -4887,8 +4906,9 @@ static void *longpoll_thread(void *userdata)
 	}
 
 	tq_pop(mythr->q, NULL);
+	pool = select_longpoll_pool();
 	if (!pool->hdr_path) {
-		applog(LOG_NOTICE, "No long-poll found on this server");
+		applog(LOG_WARNING, "No long-poll found on any pool server");
 		goto out;
 	}
 	hdr_path = pool->hdr_path;
@@ -4905,7 +4925,7 @@ static void *longpoll_thread(void *userdata)
 		if (pool->rpc_url[strlen(pool->rpc_url) - 1] != '/')
 			need_slash = true;
 
-		lp_url = malloc(strlen(pool->rpc_url) + strlen(copy_start) + 2);
+		lp_url = alloca(strlen(pool->rpc_url) + strlen(copy_start) + 2);
 		if (!lp_url)
 			goto out;
 
@@ -4913,7 +4933,7 @@ static void *longpoll_thread(void *userdata)
 	}
 
 	have_longpoll = true;
-	applog(LOG_NOTICE, "Long-polling activated for %s", lp_url);
+	applog(LOG_WARNING, "Long-polling activated for %s", lp_url);
 
 	while (1) {
 		struct timeval start, end;
@@ -4978,9 +4998,8 @@ static void start_longpoll(void)
 
 static void restart_longpoll(void)
 {
-	if (want_longpoll && have_longpoll)
-		return;
-	stop_longpoll();
+	if (have_longpoll)
+		stop_longpoll();
 	if (want_longpoll)
 		start_longpoll();
 }
@@ -5966,30 +5985,8 @@ retry_pools:
 		}
 	}
 
-	/* If we want longpoll, enable it for the chosen default pool, or, if
-	 * the pool does not support longpoll, find the first one that does
-	 * and use its longpoll support */
-	if (want_longpoll) {
-		if (currentpool->hdr_path)
-			start_longpoll();
-		else {
-			for (i = 0; i < total_pools; i++) {
-				struct pool *pool;
-
-				pool = pools[i];
-				if (pool->hdr_path) {
-					struct pool *temp = currentpool;
-
-					currentpool = pool;
-					start_longpoll();
-					/* Not real blocking, but good enough */
-					sleep(1);
-					currentpool = temp;
-					break;
-				}
-			}
-		}
-	}
+	if (want_longpoll)
+		start_longpoll();
 
 	gettimeofday(&total_tv_start, NULL);
 	gettimeofday(&total_tv_end, NULL);