MDEV-31871: maria-install-db fails on MacOS

Follow-up to fix issue with access to probably not-initialized mutex/cond_var

Constructor of the class st_debug_sync_globals was changed to initialize
the data members dsp_hits, dsp_executed, dsp_max_active with zero.
Formerly, these data members were filled with zeroes by C-runtime since
the variable debug_sync_global was declared as static and according with C rules
the static variable initialized with zero bytes.

By the same reason, the data members
  debug_sync_global->ds_mutex
  debug_sync_global->ds_cond
were initialized by zeros before the patch for MDEV-31871. After this patch
the memory for the synch primitives debug_sync_global->ds_mutex
and debug_sync_global->ds_cond are initialized explicitly by calling
the functions mysql_mutex_init/mysql_cond_init so access to these synch
primitives should be done only after such initialization be completed.
Guarded access to these synch primitives has been added to the function
debug_sync_end_thread() that is called on clean up since that was single
problem place detected by MSAN. Theoretically problem places located in the
function debug_sync_execute were not protected with similar check since
it is not obvious that the variables debug_sync_global->ds_mutex
and debug_sync_global->ds_cond could be not initilialized for use cases where
the function debug_sync_execute() is called. It is required additional study
to conclude whether it does need or not.

Author: dmitryshulga

sql/debug_sync.cc

@@ -87,7 +87,9 @@ struct st_debug_sync_globals
   ulonglong             dsp_executed;           /* statistics */
   ulonglong             dsp_max_active;         /* statistics */
 
-  st_debug_sync_globals() : ds_signal_set(PSI_NOT_INSTRUMENTED, signal_key) {};
+  st_debug_sync_globals() :
+    ds_signal_set(PSI_NOT_INSTRUMENTED, signal_key),
+    dsp_hits (0), dsp_executed(0), dsp_max_active(0) {};
   ~st_debug_sync_globals()
   {
     clear_set();
@@ -422,12 +424,24 @@ void debug_sync_end_thread(THD *thd)
     }
 
     /* Statistics. */
-    mysql_mutex_lock(&debug_sync_global->ds_mutex);
+    /*
+      Protect access with debug_sync_global->ds_mutex only if
+      it had been initialized.
+    */
+    if (debug_sync_C_callback_ptr)
+      mysql_mutex_lock(&debug_sync_global->ds_mutex);
+
     debug_sync_global->dsp_hits+=           ds_control->dsp_hits;
     debug_sync_global->dsp_executed+=       ds_control->dsp_executed;
     if (debug_sync_global->dsp_max_active < ds_control->dsp_max_active)
       debug_sync_global->dsp_max_active=    ds_control->dsp_max_active;
-    mysql_mutex_unlock(&debug_sync_global->ds_mutex);
+
+    /*
+      Protect access with debug_sync_global->ds_mutex only if
+      it had been initialized.
+    */
+    if (debug_sync_C_callback_ptr)
+      mysql_mutex_unlock(&debug_sync_global->ds_mutex);
 
     my_free(ds_control);
     thd->debug_sync_control= NULL;

sql/sql_class.cc

@@ -1748,7 +1748,9 @@ THD::~THD()
     lf_hash_put_pins(tdc_hash_pins);
   if (xid_hash_pins)
     lf_hash_put_pins(xid_hash_pins);
+#if defined(ENABLED_DEBUG_SYNC)
   debug_sync_end_thread(this);
+#endif
   /* Ensure everything is freed */
   status_var.local_memory_used-= sizeof(THD);