Fixes #2919: Access to GloMTH from 'refresh_variables' and it's destruction is now mutex protected

include/proxysql_glovars.hpp

@@ -92,6 +92,7 @@ class ProxySQL_GlobalVariables {
 #ifdef PROXYSQLCLICKHOUSE
 		bool clickhouse_server;
 #endif /* PROXYSQLCLICKHOUSE */
+		pthread_mutex_t ext_glomth_mutex;
 	} global;
 	struct mysql {
 		char *server_version;

lib/MySQL_Thread.cpp

@@ -4731,6 +4731,7 @@ void MySQL_Thread::process_all_sessions() {
 }
 
 void MySQL_Thread::refresh_variables() {
+	pthread_mutex_lock(&GloVars.global.ext_glomth_mutex);
 	if (GloMTH==NULL) {
 		return;
 	}
@@ -4910,6 +4911,7 @@ void MySQL_Thread::refresh_variables() {
 	mysql_thread___session_debug=(bool)GloMTH->get_variable_int((char *)"session_debug");
 #endif /* DEBUG */
 	GloMTH->wrunlock();
+	pthread_mutex_unlock(&GloVars.global.ext_glomth_mutex);
 }
 
 MySQL_Thread::MySQL_Thread() {

lib/ProxySQL_GloVars.cpp

@@ -100,6 +100,7 @@ ProxySQL_GlobalVariables::ProxySQL_GlobalVariables() :
 //	global.use_proxysql_mem=false;
 	pthread_mutex_init(&global.start_mutex,NULL);
 	pthread_mutex_init(&checksum_mutex,NULL);
+	pthread_mutex_init(&global.ext_glomth_mutex,NULL);
 	epoch_version = 0;
 	checksums_values.updates_cnt = 0;
 	checksums_values.dumped_at = 0;

src/main.cpp

@@ -1173,8 +1173,10 @@ void ProxySQL_Main_shutdown_all_modules() {
 	}
 	if (GloMTH) {
 		cpu_timer t;
+		pthread_mutex_lock(&GloVars.global.ext_glomth_mutex);
 		delete GloMTH;
 		GloMTH=NULL;
+		pthread_mutex_unlock(&GloVars.global.ext_glomth_mutex);
 #ifdef DEBUG
 		std::cerr << "GloMTH shutdown in ";
 #endif