fix: make server_backoff_time atomic

Signed-off-by: Wazir Ahmed <wazir@proxysql.com>

include/MySQL_HostGroups_Manager.h

@@ -212,7 +212,7 @@ class MySrvC {	// MySQL Server Container
 	// This is primarily used when `session_track_variables::ENFORCED` mode is active.
 	// If a server lacks the required capabilities in this mode, it is temporarily
 	// excluded from selection for a specified duration.
-	unsigned long long server_backoff_time;
+	std::atomic<unsigned long long> server_backoff_time;
 
 	MySrvConnList *ConnectionsUsed;
 	MySrvConnList *ConnectionsFree;

lib/MyHGC.cpp

@@ -18,6 +18,7 @@ MySrvC *MyHGC::get_random_MySrvC(char * gtid_uuid, uint64_t gtid_trxid, int max_
 	unsigned int TotalUsedConn=0;
 	unsigned int l=mysrvs->cnt();
 	static time_t last_hg_log = 0;
+	unsigned long long server_backoff_time;
 #ifdef TEST_AURORA
 	unsigned long long a1 = array_mysrvc_total/10000;
 	array_mysrvc_total += l;
@@ -39,8 +40,10 @@ MySrvC *MyHGC::get_random_MySrvC(char * gtid_uuid, uint64_t gtid_trxid, int max_
 			mysrvc=mysrvs->idx(j);
 			if (mysrvc->get_status() == MYSQL_SERVER_STATUS_ONLINE) { // consider this server only if ONLINE
 				// skip servers that are in backoff period
-				if (mysrvc->server_backoff_time > sess->thread->curtime)
+				server_backoff_time = mysrvc->server_backoff_time.load(std::memory_order_relaxed);
+				if (server_backoff_time > sess->thread->curtime) {
 					continue;
+				}
 
 				if (mysrvc->myhgc->num_online_servers.load(std::memory_order_relaxed) <= mysrvc->myhgc->attributes.max_num_online_servers) { // number of online servers in HG is within configured range
 					if (mysrvc->ConnectionsUsed->conns_length() < mysrvc->max_connections) { // consider this server only if didn't reach max_connections

lib/MySQL_Session.cpp

@@ -1,4 +1,5 @@
 #include "../deps/json/json.hpp"
+#include <atomic>
 using json = nlohmann::json;
 #define PROXYJSON
 
@@ -9764,8 +9765,9 @@ bool MySQL_Session::handle_session_track_capabilities() {
 	}
 
 	if (!server_support_session_track) {
-		// be_conn->parent->server_backoff_time = thread->curtime + (600 * 1000000); // 10 minutes
-		be_conn->parent->server_backoff_time = thread->curtime + (30 * 1000000); // 30 seconds
+		// set 30 seconds backoff time
+		be_conn->parent->server_backoff_time.store(thread->curtime + (30 * 1000000), std::memory_order_relaxed);
+
 		if (session_fast_forward) {
 			mybe->server_myds->destroy_MySQL_Connection_From_Pool(false);
 		} else {

lib/MySQL_Thread.cpp

@@ -1,4 +1,5 @@
 #include "../deps/json/json.hpp"
+#include <atomic>
 using json = nlohmann::json;
 #define PROXYJSON
 
@@ -6388,13 +6389,17 @@ MySQL_Connection * MySQL_Thread::get_MyConn_local(unsigned int _hid, MySQL_Sessi
 	if (sess->client_myds->myconn == NULL) return NULL;
 	if (sess->client_myds->myconn->userinfo == NULL) return NULL;
 	unsigned int i;
+	unsigned long long server_backoff_time;
 	std::vector<MySrvC *> parents; // this is a vector of srvers that needs to be excluded in case gtid_uuid is used
 	MySQL_Connection *c=NULL;
 	for (i=0; i<cached_connections->len; i++) {
 		c = (MySQL_Connection *) cached_connections->index(i);
+
 		// skip servers that are in backoff period
-		if (c->parent->server_backoff_time > curtime)
+		server_backoff_time = c->parent->server_backoff_time.load(std::memory_order_relaxed);
+		if (server_backoff_time > curtime) {
 			continue;
+		}
 
 		if (c->parent->myhgc->hid==_hid && sess->client_myds->myconn->match_tracked_options(c)) { // options are all identical
 			if (

lib/MySrvC.cpp

@@ -31,7 +31,7 @@ MySrvC::MySrvC(
 	bytes_recv=0;
 	max_connections_used=0;
 	queries_gtid_sync=0;
-	server_backoff_time = 0;
+	server_backoff_time.store(0);
 	time_last_detected_error=0;
 	connect_ERR_at_time_last_detected_error=0;
 	shunned_automatic=false;