MDEV-35574 remove obsolete pthread_exit calls

Threads can normally exit without a explicit pthread_exit call.

There seem to date to old glibc bugs, many around 2.2.5.

The semi related bug was https://bugs.mysql.com/bug.php?id=82886.

To improve safety in the signal handlers DBUG_* code was removed.

These where also needed to avoid some MSAN unresolved stack issues.

This is effectively a backport of 2719cc4925.

client/mysqlimport.c

@@ -631,7 +631,6 @@ error:
   pthread_cond_signal(&count_threshhold);
   pthread_mutex_unlock(&counter_mutex);
   mysql_thread_end();
-  pthread_exit(0);
   return 0;
 }
 

client/mysqltest.cc

@@ -991,7 +991,6 @@ end_thread:
   cn->mysql= 0;
   cn->query_done= 1;
   mysql_thread_end();
-  pthread_exit(0);
   DBUG_RETURN(0);
 }
 

mysys/thr_alarm.c

@@ -566,8 +566,7 @@ static void *alarm_handler(void *arg __attribute__((unused)))
   alarm_thread_running= 0;
   mysql_cond_signal(&COND_alarm);
   mysql_mutex_unlock(&LOCK_alarm);
-  pthread_exit(0);
+  return 0;
-  return 0;					/* Impossible */
 }
 #endif /* USE_ALARM_THREAD */
 #endif

mysys/thr_timer.c

@@ -330,8 +330,7 @@ static void *timer_handler(void *arg __attribute__((unused)))
   }
   mysql_mutex_unlock(&LOCK_timer);
   my_thread_end();
-  pthread_exit(0);
+  return 0;
-  return 0;					/* Impossible */
 }
 
 

plugin/feedback/sender_thread.cc

@@ -290,7 +290,6 @@ pthread_handler_t background_thread(void *arg __attribute__((unused)))
   }
 
   my_thread_end();
-  pthread_exit(0);
   return 0;
 }
 

sql/mysqld.cc

@@ -2948,7 +2948,6 @@ pthread_handler_t signal_hand(void *)
   sigset_t set;
   int sig;
   my_thread_init();				// Init new thread
-  DBUG_ENTER("signal_hand");
   signal_thread_in_use= 1;
 
   /*
@@ -3014,7 +3013,6 @@ pthread_handler_t signal_hand(void *)
       /* switch to the old log message processing */
       logger.set_handlers(global_system_variables.sql_log_slow ? LOG_FILE:LOG_NONE,
                           opt_log ? LOG_FILE:LOG_NONE);
-      DBUG_PRINT("info",("Got signal: %d  abort_loop: %d",sig,abort_loop));
 
       break_connect_loop();
       DBUG_ASSERT(abort_loop);
@@ -3050,12 +3048,9 @@ pthread_handler_t signal_hand(void *)
       break;					/* purecov: tested */
     }
   }
-  DBUG_PRINT("quit", ("signal_handler: calling my_thread_end()"));
   my_thread_end();
-  DBUG_LEAVE; // Must match DBUG_ENTER()
   signal_thread_in_use= 0;
-  pthread_exit(0); // Safety
+  return nullptr;
-  return(0);					/* purecov: deadcode */
 }
 
 static void check_data_home(const char *path)

storage/mroonga/vendor/groonga/src/groonga_benchmark.c

@@ -271,12 +271,7 @@ error_exit_in_thread(intptr_t code)
   CRITICAL_SECTION_ENTER(grntest_cs);
   grntest_stop_flag = 1;
   CRITICAL_SECTION_LEAVE(grntest_cs);
-#ifdef WIN32
+  return code;
-  _endthreadex(code);
-#else
-  pthread_exit((void *)code);
-#endif /* WIN32 */
-  return 0;
 }
 
 

tests/thread_test.c

@@ -70,7 +70,6 @@ end:
   thread_count--;
   pthread_cond_signal(&COND_thread_count); /* Tell main we are ready */
   pthread_mutex_unlock(&LOCK_thread_count);
-  pthread_exit(0);
   return 0;
 }
 

unittest/mysys/stack_allocation-t.c

@@ -91,7 +91,6 @@ pthread_handler_t thread_stack_check(void *arg __attribute__((unused)))
   test_stack_detection(1, STACK_ALLOC_SMALL_BLOCK_SIZE-1);
   test_stack_detection(2, STACK_ALLOC_SMALL_BLOCK_SIZE+1);
   my_thread_end();
-  pthread_exit(0);
   return 0;
 }
 

unittest/sql/my_apc-t.cc

@@ -108,7 +108,6 @@ void *test_apc_service_thread(void *ptr)
   apc_target.destroy();
   mysql_mutex_destroy(&target_mutex);
   my_thread_end();
-  pthread_exit(0);
   return NULL;
 }