Add shutdown detection

The maxscale_is_shutting_down function is used to detect when MaxScale
should stop. This fixes a race condition in the code where the workers has
not yet been initialized but a termination signal has been received. It
also replaces the misuse of the service_should_stop variable with a proper
function.

include/maxscale/maxscale.h

@@ -43,4 +43,14 @@ time_t maxscale_started(void);
  */
 int maxscale_uptime(void);
 
+/**
+ * Is MaxScale shutting down
+ *
+ * This function can be used to detect whether the shutdown has been initiated. It does not tell
+ * whether the shutdown has been completed so thread-safety is still important.
+ *
+ * @return True if MaxScale is shutting down
+ */
+bool maxscale_is_shutting_down();
+
 MXS_END_DECLS

include/maxscale/service.h

@@ -146,9 +146,6 @@ typedef enum count_spec_t
 #define SERVICE_STATE_FAILED    3       /**< The service failed to start */
 #define SERVICE_STATE_STOPPED   4       /**< The service has been stopped */
 
-// Set to 1 when services should stop
-extern volatile sig_atomic_t service_should_stop;
-
 /**
  * Find a service
  *

server/core/gateway.cc

@@ -2037,6 +2037,13 @@ int main(int argc, char **argv)
         goto return_main;
     }
 
+    // Before we start the workers we need to check if a shutdown signal has been received
+    if (maxscale_is_shutting_down())
+    {
+        rc = MAXSCALE_SHUTDOWN;
+        goto return_main;
+    }
+
     if (!RoutingWorker::init())
     {
         MXS_ERROR("Failed to initialize routing workers.");
@@ -2044,6 +2051,16 @@ int main(int argc, char **argv)
         goto return_main;
     }
 
+    /**
+     * If a shutdown signal was received while we were initializing the workers, we need to exit.
+     * After this point, the shutdown will be driven by the workers.
+     */
+    if (maxscale_is_shutting_down())
+    {
+        rc = MAXSCALE_SHUTDOWN;
+        goto return_main;
+    }
+
     if (!config_load(cnf_file_path))
     {
         const char* fprerr =

server/core/misc.cc

@@ -36,15 +36,19 @@ int maxscale_uptime()
     return time(0) - started;
 }
 
+static sig_atomic_t n_shutdowns = 0;
+
+bool maxscale_is_shutting_down()
+{
+    return n_shutdowns != 0;
+}
+
 int maxscale_shutdown()
 {
-    static int n_shutdowns = 0;
-
-    int n = atomic_add(&n_shutdowns, 1);
+    int n = n_shutdowns++;
 
     if (n == 0)
     {
-        service_shutdown();
         mxs::RoutingWorker::shutdown_all();
     }
 

server/core/service.cc

@@ -481,7 +481,7 @@ int serviceStartAllPorts(Service* service)
 
     if (port)
     {
-        while (!service_should_stop && port)
+        while (!maxscale_is_shutting_down() && port)
         {
             listeners += serviceStartPort(service, port);
             port = port->next;
@@ -635,7 +635,7 @@ int service_launch_all()
             error = true;
         }
 
-        if (service_should_stop)
+        if (maxscale_is_shutting_down())
         {
             break;
         }
@@ -1520,13 +1520,6 @@ const char* serviceGetWeightingParameter(SERVICE *svc)
     return service->weightby;
 }
 
-volatile sig_atomic_t service_should_stop = 0;
-
-void service_shutdown()
-{
-    service_should_stop = 1;
-}
-
 void service_destroy_instances(void)
 {
     // The global list is modified by service_free so we need a copy of it

server/modules/authenticator/MySQLAuth/dbusers.cc

@@ -24,6 +24,7 @@
 #include <maxscale/alloc.h>
 #include <maxscale/dcb.h>
 #include <maxscale/log.h>
+#include <maxscale/maxscale.h>
 #include <maxscale/mysql_utils.h>
 #include <maxscale/paths.h>
 #include <maxscale/protocol/mysql.h>
@@ -923,7 +924,7 @@ static int get_users(SERV_LISTENER *listener, bool skip_local)
     int total_users = -1;
     bool no_active_servers = true;
 
-    for (server = service->dbref; !service_should_stop && server; server = server->next)
+    for (server = service->dbref; !maxscale_is_shutting_down() && server; server = server->next)
     {
         if (!SERVER_REF_IS_ACTIVE(server) || !server_is_active(server->server) ||
             (skip_local && server_is_mxs_service(server->server)))

server/modules/routing/avrorouter/avro_file.cc

@@ -34,6 +34,7 @@
 
 #include <maxscale/alloc.h>
 #include <maxscale/log.h>
+#include <maxscale/maxscale.h>
 #include <maxscale/pcre2.h>
 #include <maxscale/utils.h>
 
@@ -493,7 +494,7 @@ avro_binlog_end_t avro_read_all_events(Avro *router)
     std::string next_binlog;
     bool rotate_seen = false;
 
-    while (!service_should_stop)
+    while (!maxscale_is_shutting_down())
     {
         avro_binlog_end_t rc;
         REP_HEADER hdr;

server/modules/routing/avrorouter/avro_main.cc

@@ -24,6 +24,7 @@
 #include <ini.h>
 #include <sys/stat.h>
 #include <maxbase/atomic.h>
+#include <maxscale/maxscale.h>
 #include <maxbase/worker.hh>
 #include <maxscale/alloc.h>
 #include <maxscale/dcb.h>
@@ -328,7 +329,7 @@ static bool conversion_task_ctl(Avro *inst, bool start)
 {
     bool rval = false;
 
-    if (!service_should_stop)
+    if (!maxscale_is_shutting_down())
     {
         Worker* worker = static_cast<Worker*>(mxs_rworker_get(MXS_RWORKER_MAIN));
         std::unique_ptr<ConversionCtlTask> task(new (std::nothrow) ConversionCtlTask(inst, start));