Clean up monitor initialization and destruction

Since monitors are now freed at MaxScale exit, the server data should be freed. Also,
gtid domain variables are now initialized with a common constant.

server/modules/monitor/mariadbmon/cluster_manipulation.cc

@@ -354,7 +354,7 @@ uint32_t MariaDBMonitor::do_rejoin(const ServerArray& joinable_servers, json_t**
  */
 bool MariaDBMonitor::cluster_can_be_joined()
 {
-    return (m_master != NULL && m_master->is_master() && m_master_gtid_domain >= 0);
+    return (m_master != NULL && m_master->is_master() && m_master_gtid_domain != GTID_DOMAIN_UNKNOWN);
 }
 
 /**
@@ -503,7 +503,7 @@ bool MariaDBMonitor::do_switchover(MariaDBServer** current_master, MariaDBServer
         demotion_target = *current_master;
     }
 
-    if (m_master_gtid_domain < 0)
+    if (m_master_gtid_domain == GTID_DOMAIN_UNKNOWN)
     {
         PRINT_MXS_JSON_ERROR(err_out, "Cluster gtid domain is unknown. Cannot switchover.");
         return false;
@@ -657,7 +657,7 @@ bool MariaDBMonitor::do_switchover(MariaDBServer** current_master, MariaDBServer
 bool MariaDBMonitor::do_failover(json_t** err_out)
 {
     // Topology has already been tested to be simple.
-    if (m_master_gtid_domain < 0)
+    if (m_master_gtid_domain == GTID_DOMAIN_UNKNOWN)
     {
         PRINT_MXS_JSON_ERROR(err_out, "Cluster gtid domain is unknown. Cannot failover.");
         return false;

server/modules/monitor/mariadbmon/mariadbmon.cc

@@ -56,31 +56,29 @@ const int PORT_UNKNOWN = 0;
 MariaDBMonitor::MariaDBMonitor(MXS_MONITOR* monitor_base)
     : m_monitor_base(monitor_base)
     , m_id(config_get_global_options()->id)
-    , m_master_gtid_domain(-1)
+    , m_master_gtid_domain(GTID_DOMAIN_UNKNOWN)
     , m_external_master_port(PORT_UNKNOWN)
     , m_warn_set_standalone_master(true)
 {}
 
 MariaDBMonitor::~MariaDBMonitor()
-{}
+{
+    clear_server_info();
+}
 
 /**
- * Initialize the server info hashtable.
+ * Reset and initialize server arrays and related data.
  */
-void MariaDBMonitor::init_server_info()
+void MariaDBMonitor::reset_server_info()
 {
     // If this monitor is being restarted, the server data needs to be freed.
-    for (auto iter = m_servers.begin(); iter != m_servers.end(); iter++)
+    clear_server_info();
-    {
+
-        delete *iter;
+    // Next, initialize the data.
-    }
-    m_servers.clear();
     for (auto mon_server = m_monitor_base->monitored_servers; mon_server; mon_server = mon_server->next)
     {
         m_servers.push_back(new MariaDBServer(mon_server));
     }
-
-    m_server_info.clear();
     for (auto iter = m_servers.begin(); iter != m_servers.end(); iter++)
     {
         auto mon_server = (*iter)->m_server_base;
@@ -90,6 +88,22 @@ void MariaDBMonitor::init_server_info()
     }
 }
 
+void MariaDBMonitor::clear_server_info()
+{
+    for (auto iter = m_servers.begin(); iter != m_servers.end(); iter++)
+    {
+        delete *iter;
+    }
+    // All MariaDBServer*:s are now invalid, as well as any dependant data.
+    m_servers.clear();
+    m_server_info.clear();
+    m_excluded_servers.clear();
+    m_master = NULL;
+    m_master_gtid_domain = GTID_DOMAIN_UNKNOWN;
+    m_external_master_host.clear();
+    m_external_master_port = PORT_UNKNOWN;
+}
+
 /**
  * Get monitor-specific server info for the monitored server.
  *
@@ -136,12 +150,10 @@ MariaDBMonitor* MariaDBMonitor::create(MXS_MONITOR *monitor)
 bool MariaDBMonitor::start(const MXS_CONFIG_PARAMETER* params)
 {
     bool error = false;
-
-    /* Always reset these values. The server dependent values must be reset as servers could have been
-     * added and removed. */
     m_keep_running = true;
-    m_master = NULL;
+    /* Reset all monitored state info. The server dependent values must be reset as servers could have been
-    init_server_info();
+     * added, removed and modified. */
+    reset_server_info();
 
     if (!load_config_params(params))
     {
@@ -477,7 +489,7 @@ void MariaDBMonitor::main_loop()
 void MariaDBMonitor::update_gtid_domain()
 {
     int64_t domain = m_master->m_gtid_domain_id;
-    if (m_master_gtid_domain >= 0 && domain != m_master_gtid_domain)
+    if (m_master_gtid_domain != GTID_DOMAIN_UNKNOWN && domain != m_master_gtid_domain)
     {
         MXS_NOTICE("Gtid domain id of master has changed: %" PRId64 " -> %" PRId64 ".",
                    m_master_gtid_domain, domain);

server/modules/monitor/mariadbmon/mariadbmon.hh

@@ -173,7 +173,8 @@ private:
     // Base methods
     MariaDBMonitor(MXS_MONITOR* monitor_base);
     ~MariaDBMonitor();
-    void init_server_info();
+    void reset_server_info();
+    void clear_server_info();
     bool load_config_params(const MXS_CONFIG_PARAMETER* params);
     bool set_replication_credentials(const MXS_CONFIG_PARAMETER* params);
     MariaDBServer* get_server_info(MXS_MONITORED_SERVER* db);

server/modules/monitor/mariadbmon/mariadbmon_common.cc

@@ -15,3 +15,5 @@
 
 /** Server id default value */
 const int64_t SERVER_ID_UNKNOWN = -1;
+/** Default gtid domain */
+const int64_t GTID_DOMAIN_UNKNOWN = -1;

server/modules/monitor/mariadbmon/mariadbmon_common.hh

@@ -33,3 +33,4 @@
     } while (false)
 
 extern const int64_t SERVER_ID_UNKNOWN;
+extern const int64_t GTID_DOMAIN_UNKNOWN;

server/modules/monitor/mariadbmon/mariadbserver.cc

@@ -49,7 +49,7 @@ MariaDBServer::MariaDBServer(MXS_MONITORED_SERVER* monitored_server)
     , m_n_slave_heartbeats(0)
     , m_heartbeat_period(0)
     , m_latest_event(0)
-    , m_gtid_domain_id(-1)
+    , m_gtid_domain_id(GTID_DOMAIN_UNKNOWN)
 {
     ss_dassert(monitored_server);
 }