MXS-1848 Introduce a specific monitor type

Instead of using void there's now a MXS_SPECIFIC_MONITOR struct
from which monitor specific types can be derived. This change
does not bring about other benefits than a bit of clarity but
this is the first step in clearing up the monitor API.

include/maxscale/monitor.h

@@ -31,6 +31,14 @@ MXS_BEGIN_DECLS
 struct mxs_monitor;
 typedef struct mxs_monitor MXS_MONITOR;
 
+/**
+ * An opaque type from which types specific for a particular
+ * monitor can be derived.
+ */
+typedef struct mxs_specific_monitor
+{
+} MXS_SPECIFIC_MONITOR;
+
 /**
  * @verbatim
  * The "module object" structure for a backend monitor module
@@ -68,7 +76,8 @@ typedef struct mxs_monitor_object
      *
      * @return Pointer to the monitor specific data, stored in @c monitor->handle
      */
-    void *(*startMonitor)(MXS_MONITOR *monitor, const MXS_CONFIG_PARAMETER *params);
+    MXS_SPECIFIC_MONITOR *(*startMonitor)(MXS_MONITOR *monitor,
+                                          const MXS_CONFIG_PARAMETER *params);
 
     /**
      * @brief Stop the monitor
@@ -95,7 +104,7 @@ typedef struct mxs_monitor_object
  * The monitor API version number. Any change to the monitor module API
  * must change these versions using the rules defined in modinfo.h
  */
-#define MXS_MONITOR_VERSION {3, 1, 0}
+#define MXS_MONITOR_VERSION {4, 0, 0}
 
 /**
  * Specifies capabilities specific for monitor.
@@ -211,7 +220,7 @@ struct mxs_monitor
                                    */
     MXS_MONITOR_OBJECT *module;   /**< The "monitor object" */
     char *module_name;            /**< Name of the monitor module */
-    void *handle;                 /**< Handle returned from startMonitor */
+    MXS_SPECIFIC_MONITOR *handle; /**< Handle returned from startMonitor */
     size_t interval;              /**< The monitor interval */
     volatile bool server_pending_changes;
     /**< Are there any pending changes to a server?

server/modules/monitor/auroramon/auroramon.cc

@@ -25,14 +25,14 @@
 #include <maxscale/debug.h>
 #include <maxscale/mysql_utils.h>
 
-typedef struct aurora_monitor
+struct AURORA_MONITOR : public MXS_SPECIFIC_MONITOR
 {
     bool   shutdown;            /**< True if the monitor is stopped */
     THREAD thread;              /**< Monitor thread */
     char*  script;              /**< Launchable script */
     uint64_t   events;          /**< Enabled monitor events */
     MXS_MONITOR* monitor;
-} AURORA_MONITOR;
+};
 
 /**
  * @brief Update the status of a server
@@ -186,7 +186,7 @@ static void auroramon_free(AURORA_MONITOR *handle)
  * @param opt The configuration parameters for this monitor
  * @return Monitor handle
  */
-static void *
+static MXS_SPECIFIC_MONITOR *
 startMonitor(MXS_MONITOR *mon, const MXS_CONFIG_PARAMETER *params)
 {
     AURORA_MONITOR *handle = static_cast<AURORA_MONITOR*>(mon->handle);

server/modules/monitor/galeramon/galeramon.cc

@@ -30,7 +30,8 @@ static void monitorMain(void *);
 /** Log a warning when a bad 'wsrep_local_index' is found */
 static bool warn_erange_on_local_index = true;
 
-static void *startMonitor(MXS_MONITOR *, const MXS_CONFIG_PARAMETER *params);
+static MXS_SPECIFIC_MONITOR *startMonitor(MXS_MONITOR *,
+                                          const MXS_CONFIG_PARAMETER *params);
 static void stopMonitor(MXS_MONITOR *);
 static void diagnostics(DCB *, const MXS_MONITOR *);
 static json_t* diagnostics_json(const MXS_MONITOR *);
@@ -119,7 +120,7 @@ MXS_MODULE* MXS_CREATE_MODULE()
  *
  * @return A handle to use when interacting with the monitor
  */
-static void *
+static MXS_SPECIFIC_MONITOR *
 startMonitor(MXS_MONITOR *mon, const MXS_CONFIG_PARAMETER *params)
 {
     GALERA_MONITOR *handle = static_cast<GALERA_MONITOR*>(mon->handle);

server/modules/monitor/galeramon/galeramon.h

@@ -41,8 +41,6 @@
 #include <maxscale/config.h>
 #include <maxscale/hashtable.h>
 
-MXS_BEGIN_DECLS
-
 /**
  *  Galera Variables and server reference for each
  *  monitored node that could be part of cluster.
@@ -76,7 +74,7 @@ typedef struct galera_cluster_info
 /**
  * The handle for an instance of a Galera Monitor module
  */
-typedef struct
+struct GALERA_MONITOR : public MXS_SPECIFIC_MONITOR
 {
     THREAD thread; /**< Monitor thread */
     int shutdown; /**< Flag to shutdown the monitor thread */
@@ -96,8 +94,6 @@ typedef struct
     HASHTABLE *galera_nodes_info; /**< Contains Galera Cluster variables of all nodes */
     GALERA_CLUSTER_INFO cluster_info; /**< Contains Galera cluster info */
     MXS_MONITOR* monitor;
-} GALERA_MONITOR;
+};
-
-MXS_END_DECLS
 
 #endif

server/modules/monitor/grmon/grmon.cc

@@ -30,7 +30,7 @@
 /**
  * The instance of a Group Replication Monitor
  */
-struct GRMon
+struct GRMon : public MXS_SPECIFIC_MONITOR
 {
     GRMon(const GRMon&);
     GRMon& operator&(const GRMon&);
@@ -99,7 +99,7 @@ void GRMon::stop()
  *
  * @return A handle to use when interacting with the monitor
  */
-static void *
+static MXS_SPECIFIC_MONITOR *
 startMonitor(MXS_MONITOR *mon, const MXS_CONFIG_PARAMETER *params)
 {
     return GRMon::create(mon, params);

server/modules/monitor/mariadbmon/mariadbmon.cc

@@ -912,7 +912,8 @@ bool MariaDBMonitor::check_sql_files()
  * @param params Configuration parameters
  * @return A pointer to MariaDBMonitor specific data. Should be stored in MXS_MONITOR's "handle"-field.
  */
-static void* startMonitor(MXS_MONITOR *monitor, const MXS_CONFIG_PARAMETER* params)
+static MXS_SPECIFIC_MONITOR* startMonitor(MXS_MONITOR *monitor,
+                                          const MXS_CONFIG_PARAMETER* params)
 {
     return MariaDBMonitor::start(monitor, params);
 }

server/modules/monitor/mariadbmon/mariadbmon.hh

@@ -35,7 +35,7 @@ typedef std::tr1::unordered_map<MXS_MONITORED_SERVER*, MariaDBServer*> ServerInf
 typedef std::vector<MariaDBServer*> ServerArray;
 
 // MariaDB Monitor instance data
-class MariaDBMonitor
+class MariaDBMonitor : public MXS_SPECIFIC_MONITOR
 {
 private:
     MariaDBMonitor(const MariaDBMonitor&);

server/modules/monitor/mmmon/mmmon.cc

@@ -38,7 +38,7 @@ MXS_MODULE info =
 };
 /*lint +e14 */
 
-static void *startMonitor(MXS_MONITOR *, const MXS_CONFIG_PARAMETER *);
+static MXS_SPECIFIC_MONITOR *startMonitor(MXS_MONITOR *, const MXS_CONFIG_PARAMETER *);
 static void stopMonitor(MXS_MONITOR *);
 static void diagnostics(DCB *, const MXS_MONITOR *);
 static json_t* diagnostics_json(const MXS_MONITOR *);
@@ -114,7 +114,7 @@ MXS_MODULE* MXS_CREATE_MODULE()
  * @param arg   The current handle - NULL if first start
  * @return A handle to use when interacting with the monitor
  */
-static void *
+static MXS_SPECIFIC_MONITOR *
 startMonitor(MXS_MONITOR *mon, const MXS_CONFIG_PARAMETER *params)
 {
     MM_MONITOR *handle = static_cast<MM_MONITOR*>(mon->handle);

server/modules/monitor/mmmon/mmmon.h

@@ -33,12 +33,10 @@
  * @file mmmon.h - The Multi-Master monitor
  */
 
-MXS_BEGIN_DECLS
-
 /**
  * The handle for an instance of a Multi-Master Monitor module
  */
-typedef struct
+struct MM_MONITOR : public MXS_SPECIFIC_MONITOR
 {
     THREAD thread; /**< Monitor thread */
     int shutdown; /**< Flag to shutdown the monitor thread */
@@ -49,8 +47,6 @@ typedef struct
     char* script; /*< Script to call when state changes occur on servers */
     uint64_t events; /*< enabled events */
     MXS_MONITOR* monitor;
-} MM_MONITOR;
+};
-
-MXS_END_DECLS
 
 #endif

server/modules/monitor/ndbclustermon/ndbclustermon.cc

@@ -30,7 +30,8 @@ static void monitorMain(void *);
 
 /*lint +e14 */
 
-static void *startMonitor(MXS_MONITOR *, const MXS_CONFIG_PARAMETER *params);
+static MXS_SPECIFIC_MONITOR *startMonitor(MXS_MONITOR *,
+                                          const MXS_CONFIG_PARAMETER *params);
 static void stopMonitor(MXS_MONITOR *);
 static void diagnostics(DCB *, const MXS_MONITOR *);
 static json_t* diagnostics_json(const MXS_MONITOR *);
@@ -105,7 +106,7 @@ MXS_MODULE* MXS_CREATE_MODULE()
  *
  * @return A handle to use when interacting with the monitor
  */
-static void *
+static MXS_SPECIFIC_MONITOR *
 startMonitor(MXS_MONITOR *mon, const MXS_CONFIG_PARAMETER *params)
 {
     NDBC_MONITOR *handle = static_cast<NDBC_MONITOR*>(mon->handle);

server/modules/monitor/ndbclustermon/ndbclustermon.h

@@ -18,7 +18,7 @@
 #include <maxscale/thread.h>
 
 // The handle for an instance of a NDB Cluster Monitor module
-typedef struct
+struct NDBC_MONITOR : public MXS_SPECIFIC_MONITOR
 {
     THREAD thread; /**< Monitor thread */
     SPINLOCK lock; /**< The monitor spinlock */
@@ -29,4 +29,4 @@ typedef struct
     MXS_MONITORED_SERVER *master; /**< Master server for MySQL Master/Slave replication */
     char* script; /*< Script to call when state changes occur on servers */
     MXS_MONITOR* monitor;
-} NDBC_MONITOR;
+};