From 40df519be47f50069e50052e68d5e580f4c0436b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Markus=20M=C3=A4kel=C3=A4?= <markus.makela@mariadb.com>
Date: Thu, 21 Mar 2019 14:20:37 +0200
Subject: [PATCH] Never reactivate monitors

Reactivating monitors shouldn't be done as it's simpler to actually
destroy and create a new one. The performance of reactivation is
insignificant compared to the possible inconsistency problems it allows.
---
 server/core/config_runtime.cc   | 33 +++++++++++++--------------------
 server/core/internal/monitor.hh |  2 --
 server/core/monitor.cc          | 21 ---------------------
 3 files changed, 13 insertions(+), 43 deletions(-)

diff --git a/server/core/config_runtime.cc b/server/core/config_runtime.cc
index 9d5df5af9..ff34db31b 100644
--- a/server/core/config_runtime.cc
+++ b/server/core/config_runtime.cc
@@ -1234,14 +1234,9 @@ bool runtime_create_monitor(const char* name, const char* module, MXS_CONFIG_PAR
 
     if (MonitorManager::find_monitor(name) == NULL)
     {
-        Monitor* monitor = MonitorManager::reactivate_monitor(name, module);
         std::string reason;
 
-        if (monitor)
-        {
-            MXS_DEBUG("Repurposed monitor '%s'", name);
-        }
-        else if (config_is_valid_name(name, &reason))
+        if (config_is_valid_name(name, &reason))
         {
             MXS_CONFIG_PARAMETER final_params;
             bool ok;
@@ -1254,29 +1249,27 @@ bool runtime_create_monitor(const char* name, const char* module, MXS_CONFIG_PAR
                     final_params.set_multiple(*params);
                 }
 
-                if ((monitor = MonitorManager::create_monitor(name, module, &final_params)) == NULL)
+                Monitor* monitor = MonitorManager::create_monitor(name, module, &final_params);
+
+                if (!monitor)
                 {
                     config_runtime_error("Could not create monitor '%s' with module '%s'", name, module);
                 }
+                else if (!MonitorManager::monitor_serialize(monitor))
+                {
+                    config_runtime_error("Failed to serialize monitor '%s'", name);
+                }
+                else
+                {
+                    MXS_NOTICE("Created monitor '%s'", name);
+                    rval = true;
+                }
             }
         }
         else
         {
             config_runtime_error("%s", reason.c_str());
         }
-
-        if (monitor)
-        {
-            if (MonitorManager::monitor_serialize(monitor))
-            {
-                MXS_NOTICE("Created monitor '%s'", name);
-                rval = true;
-            }
-            else
-            {
-                config_runtime_error("Failed to serialize monitor '%s'", name);
-            }
-        }
     }
     else
     {
diff --git a/server/core/internal/monitor.hh b/server/core/internal/monitor.hh
index e6617c59a..d3783b4bc 100644
--- a/server/core/internal/monitor.hh
+++ b/server/core/internal/monitor.hh
@@ -132,8 +132,6 @@ public:
      */
     static mxs::Monitor* server_is_monitored(const SERVER* server);
 
-    static mxs::Monitor* reactivate_monitor(const char* name, const char* module);
-
     static void show_all_monitors(DCB* dcb);
     static void monitor_show(DCB* dcb, mxs::Monitor* monitor);
 
diff --git a/server/core/monitor.cc b/server/core/monitor.cc
index b9cbab8cf..ca4dac34e 100644
--- a/server/core/monitor.cc
+++ b/server/core/monitor.cc
@@ -680,27 +680,6 @@ Monitor* MonitorManager::find_monitor(const char* name)
     return rval;
 }
 
-/**
- * Find a destroyed monitor by name
- *
- * @param name The name of the monitor
- * @return  Pointer to the destroyed monitor or NULL if monitor is not found
- */
-Monitor* MonitorManager::reactivate_monitor(const char* name, const char* module)
-{
-    Monitor* rval = NULL;
-    this_unit.foreach_monitor([&rval, name, module](Monitor* monitor) {
-        if (strcmp(monitor->m_name, name) == 0 && (monitor->m_module == module))
-        {
-            mxb_assert(!monitor->m_active);
-            monitor->m_active = true;
-            rval = monitor;
-        }
-        return (rval == nullptr);
-    });
-    return rval;
-}
-
 /**
  * Return a resultset that has the current set of monitors in it
  *