Fix for BUG#28030: test im_instance_conf fails with an assert.

The problem was a race condition on shutdown -- when IM got shutdown
request while a guarded mysqld is starting. In this case the Guardian
thread tried to stop the mysqld, but might fail if the mysqld hadn't
created pid-file so far. When this happened, the mysqld-monitor thread
didn't stop, so the assert in Thread_registry happened.

The fix is to make several attempts to stop mysqld if it is active.


server-tools/instance-manager/guardian.cc:
  Try to stop mysqld several times if it is still active.
server-tools/instance-manager/instance.cc:
  Make Instance::kill_mysqld() to return operation status.
server-tools/instance-manager/instance.h:
  Make Instance::kill_mysqld() to return operation status.
server-tools/instance-manager/thread_registry.cc:
  Log unregistered thread ids.

server-tools/instance-manager/guardian.cc

@@ -403,6 +403,8 @@ void Guardian::init()
 
 void Guardian::stop_instances()
 {
+  static const int NUM_STOP_ATTEMPTS = 100;
+
   Instance_map::Iterator instances_it(instance_map);
   Instance *instance;
 
@@ -438,7 +440,34 @@ void Guardian::stop_instances()
 
     /* Request mysqld to stop. */
 
-    instance->kill_mysqld(SIGTERM);
+    bool instance_stopped= FALSE;
+
+    for (int cur_attempt= 0; cur_attempt < NUM_STOP_ATTEMPTS; ++cur_attempt)
+    {
+      if (!instance->kill_mysqld(SIGTERM))
+      {
+        instance_stopped= TRUE;
+        break;
+      }
+
+      if (!instance->is_active())
+      {
+        instance_stopped= TRUE;
+        break;
+      }
+
+      /* Sleep for 0.3 sec and check again. */
+
+      my_sleep(300000);
+    }
+
+    /*
+      Abort if we failed to stop mysqld instance. That should not happen,
+      but if it happened, we don't know what to do and prefer to have clear
+      failure with coredump.
+    */
+
+    DBUG_ASSERT(instance_stopped);
 
     instance->unlock();
   }

server-tools/instance-manager/instance.cc

@@ -771,7 +771,7 @@ bool Instance::stop_mysqld()
     These operations should also be used in Guardian to manage instances.
 */
 
-void Instance::kill_mysqld(int signum)
+bool Instance::kill_mysqld(int signum)
 {
   pid_t mysqld_pid= options.load_pid();
 
@@ -780,7 +780,7 @@ void Instance::kill_mysqld(int signum)
     log_info("Instance '%s': no pid file to send a signal (%d).",
              (const char *) get_name()->str,
              (int) signum);
-    return;
+    return TRUE;
   }
 
   log_info("Instance '%s': sending %d to %d...",
@@ -792,7 +792,7 @@ void Instance::kill_mysqld(int signum)
   {
     log_info("Instance '%s': kill() failed.",
              (const char *) get_name()->str);
-    return;
+    return TRUE;
   }
 
   /* Kill suceeded */
@@ -804,6 +804,8 @@ void Instance::kill_mysqld(int signum)
     /* After sucessful hard kill the pidfile need to be removed */
     options.unlink_pidfile();
   }
+
+  return FALSE;
 }
 
 

server-tools/instance-manager/instance.h

@@ -104,7 +104,7 @@ public:
 
   bool start_mysqld();
   bool stop_mysqld();
-  void kill_mysqld(int signo);
+  bool kill_mysqld(int signo);
 
   void lock();
   void unlock();

server-tools/instance-manager/thread_registry.cc

@@ -64,8 +64,12 @@ Thread_registry::~Thread_registry()
   /* Check that no one uses the repository. */
   pthread_mutex_lock(&LOCK_thread_registry);
 
-  if (head.next != &head)
-    log_error("Not all threads died properly\n");
+  for (Thread_info *ti= head.next; ti != &head; ti= ti->next)
+  {
+    log_error("Thread_registry: unregistered thread: %lu.",
+              (unsigned long) ti->thread_id);
+  }
+
   /* All threads must unregister */
   DBUG_ASSERT(head.next == &head);