MXS-1847: Make server parameter updates atomic

The updates to server parameters are now performed in an atomic manner.

include/maxscale/server.h

@@ -311,6 +311,15 @@ void server_add_parameter(SERVER *server, const char *name, const char *value);
  */
 bool server_remove_parameter(SERVER *server, const char *name);
 
+/**
+ * @brief Update server parameter
+ *
+ * @param server Server to update
+ * @param name   Parameter to update
+ * @param value  New value of parameter
+ */
+void server_update_parameter(SERVER *server, const char *name, const char *value);
+
 /**
  * @brief Check if a server points to a local MaxScale service
  *

server/core/config_runtime.cc

@@ -385,14 +385,14 @@ bool runtime_alter_server(SERVER *server, const char *key, const char *value)
     }
     else
     {
-        if (!server_remove_parameter(server, key) && !value[0])
+        if (!value[0] && !server_remove_parameter(server, key))
         {
             // Not a valid parameter
         }
         else if (value[0])
         {
             valid = true;
-            server_add_parameter(server, key, value);
+            server_update_parameter(server, key, value);
 
             /**
              * It's likely that this parameter is used as a weighting parameter.

server/core/server.cc

@@ -848,6 +848,27 @@ server_update_credentials(SERVER *server, const char *user, const char *passwd)
     }
 }
 
+static SERVER_PARAM* allocate_parameter(const char* name, const char* value)
+{
+    char *my_name = MXS_STRDUP(name);
+    char *my_value = MXS_STRDUP(value);
+
+    SERVER_PARAM *param = (SERVER_PARAM *)MXS_MALLOC(sizeof(SERVER_PARAM));
+
+    if (!my_name || !my_value || !param)
+    {
+        MXS_FREE(my_name);
+        MXS_FREE(my_value);
+        MXS_FREE(param);
+        return NULL;
+    }
+
+    param->active = true;
+    param->name = my_name;
+    param->value = my_value;
+
+    return param;
+}
 
 /**
  * Add a server parameter to a server.
@@ -861,27 +882,15 @@ server_update_credentials(SERVER *server, const char *user, const char *passwd)
  */
 void server_add_parameter(SERVER *server, const char *name, const char *value)
 {
-    char *my_name = MXS_STRDUP(name);
+    SERVER_PARAM* param = allocate_parameter(name, value);
-    char *my_value = MXS_STRDUP(value);
 
-    SERVER_PARAM *param = (SERVER_PARAM *)MXS_MALLOC(sizeof(SERVER_PARAM));
+    if (param)
-
-    if (!my_name || !my_value || !param)
     {
-        MXS_FREE(my_name);
-        MXS_FREE(my_value);
-        MXS_FREE(param);
-        return;
-    }
-
-    param->active = true;
-    param->name = my_name;
-    param->value = my_value;
-
         spinlock_acquire(&server->lock);
         param->next = server->parameters;
         server->parameters = param;
         spinlock_release(&server->lock);
+    }
 }
 
 bool server_remove_parameter(SERVER *server, const char *name)
@@ -903,6 +912,32 @@ bool server_remove_parameter(SERVER *server, const char *name)
     return rval;
 }
 
+void server_update_parameter(SERVER *server, const char *name, const char *value)
+{
+    SERVER_PARAM* param = allocate_parameter(name, value);
+
+    if (param)
+    {
+        spinlock_acquire(&server->lock);
+
+        // Insert new value
+        param->next = server->parameters;
+        server->parameters = param;
+
+        // Mark old value, if found, as inactive
+        for (SERVER_PARAM *p = server->parameters->next; p; p = p->next)
+        {
+            if (strcmp(p->name, name) == 0 && p->active)
+            {
+                p->active = false;
+                break;
+            }
+        }
+
+        spinlock_release(&server->lock);
+    }
+}
+
 /**
  * Free a list of server parameters
  * @param tofree Parameter list to free