MDEV-32567 Remove thr_alarm from server codebase

This allows to simplify net_real_read() and net_real_write() a bit.

Removed some superfluous #ifdef/ifndef MYSQL_SERVER from net_serv.cc
The code always runs in server, either normal or embedded.
Dead code for switching socket between blocking and non-blocking modes,
is also removed.

Removed pthread_kill() with alarm signal that woke up main thread on
server shutdown. Used shutdown(2) on polling sockets instead, to the same
effect.

Removed yet another superstitious pthread_kill(), that ran on non-Windows
in terminate_slave_thread().

config.h.cmake

@@ -384,7 +384,6 @@
 #cmakedefine HAVE_GCC_C11_ATOMICS 1
 #cmakedefine HAVE_SOLARIS_ATOMIC 1
 #cmakedefine NO_FCNTL_NONBLOCK 1
-#cmakedefine NO_ALARM 1
 
 #cmakedefine _LARGE_FILES 1
 #cmakedefine _LARGEFILE_SOURCE 1

configure.cmake

@@ -836,7 +836,6 @@ CHECK_CXX_SOURCE_COMPILES("
   "
   HAVE_SOLARIS_STYLE_GETHOST)
 
-SET(NO_ALARM 1 CACHE BOOL  "No need to use alarm to implement timeout")
 
 # As a consequence of ALARMs no longer being used, thread
 # notification for KILL must close the socket to wake up

include/my_pthread.h

@@ -181,7 +181,6 @@ extern int my_pthread_create_detached;
 #define PTHREAD_CREATE_DETACHED &my_pthread_create_detached
 #define PTHREAD_SCOPE_SYSTEM  PTHREAD_SCOPE_GLOBAL
 #define PTHREAD_SCOPE_PROCESS PTHREAD_SCOPE_LOCAL
-#define USE_ALARM_THREAD
 #endif /* defined(PTHREAD_SCOPE_GLOBAL) && !defined(PTHREAD_SCOPE_SYSTEM) */
 
 #if defined(_BSDI_VERSION) && _BSDI_VERSION < 199910

include/thr_alarm.h

-/* Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.
-
-   This program is free software; you can redistribute it and/or modify
-   it under the terms of the GNU General Public License as published by
-   the Free Software Foundation; version 2 of the License.
-
-   This program is distributed in the hope that it will be useful,
-   but WITHOUT ANY WARRANTY; without even the implied warranty of
-   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-   GNU General Public License for more details.
-
-   You should have received a copy of the GNU General Public License
-   along with this program; if not, write to the Free Software
-   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335  USA */
-
-/* Prototypes when using thr_alarm library functions */
-
-#ifndef _thr_alarm_h
-#define _thr_alarm_h
-#ifdef	__cplusplus
-extern "C" {
-#endif
-
-#ifndef USE_ALARM_THREAD
-#define USE_ONE_SIGNAL_HAND		/* One must call process_alarm */
-#endif
-#ifdef HAVE_rts_threads
-#undef USE_ONE_SIGNAL_HAND
-#define USE_ALARM_THREAD
-#define THR_SERVER_ALARM SIGUSR1
-#else
-#define THR_SERVER_ALARM SIGALRM
-#endif
-
-typedef struct st_alarm_info
-{
-  time_t next_alarm_time;
-  uint active_alarms;
-  uint max_used_alarms;
-} ALARM_INFO;
-
-void thr_alarm_info(ALARM_INFO *info);
-extern my_bool my_disable_thr_alarm;
-
-#ifdef _WIN32
-#define DONT_USE_THR_ALARM
-#endif
-#if defined(DONT_USE_THR_ALARM)
-
-#define USE_ALARM_THREAD
-#undef USE_ONE_SIGNAL_HAND
-
-typedef my_bool thr_alarm_t;
-typedef my_bool ALARM;
-
-#define thr_alarm_init(A) (*(A))=0
-#define thr_alarm_in_use(A) (*(A) != 0)
-#define thr_end_alarm(A)
-#define thr_alarm(A,B,C) ((*(A)=1)-1)
-/* The following should maybe be (*(A)) */
-#define thr_got_alarm(A) 0
-#define init_thr_alarm(A)
-#define thr_alarm_kill(A)
-#define resize_thr_alarm(N)
-#define end_thr_alarm(A)
-
-#else
-#if defined(_WIN32)
-typedef struct st_thr_alarm_entry
-{
-  UINT_PTR crono;
-} thr_alarm_entry;
-
-#else /* System with posix threads */
-
-typedef int thr_alarm_entry;
-
-#define thr_got_alarm(thr_alarm) (**(thr_alarm))
-
-#endif /* _WIN32 */
-
-typedef thr_alarm_entry* thr_alarm_t;
-
-typedef struct st_alarm {
-  time_t expire_time;
-  thr_alarm_entry alarmed;		/* set when alarm is due */
-  pthread_t thread;
-  my_thread_id thread_id;
-  uint index_in_queue;
-  my_bool malloced;
-} ALARM;
-
-extern uint thr_client_alarm;
-extern pthread_t alarm_thread;
-
-#define thr_alarm_init(A) (*(A))=0
-#define thr_alarm_in_use(A) (*(A)!= 0)
-void init_thr_alarm(uint max_alarm);
-void resize_thr_alarm(uint max_alarms);
-my_bool thr_alarm(thr_alarm_t *alarmed, uint sec, ALARM *buff);
-void thr_alarm_kill(my_thread_id thread_id);
-void thr_end_alarm(thr_alarm_t *alarmed);
-void end_thr_alarm(my_bool free_structures);
-sig_handler process_alarm(int);
-#ifndef thr_got_alarm
-my_bool thr_got_alarm(thr_alarm_t *alrm);
-#endif
-
-
-#endif /* DONT_USE_THR_ALARM */
-
-#ifdef	__cplusplus
-}
-#endif /* __cplusplus */
-#endif /* _thr_alarm_h */

mysql-test/suite/sys_vars/r/debug_no_thread_alarm_basic.result

-select @@global.debug_no_thread_alarm;
-@@global.debug_no_thread_alarm
-0
-select @@session.debug_no_thread_alarm;
-ERROR HY000: Variable 'debug_no_thread_alarm' is a GLOBAL variable
-show global variables like 'debug_no_thread_alarm';
-Variable_name	Value
-debug_no_thread_alarm	OFF
-show session variables like 'debug_no_thread_alarm';
-Variable_name	Value
-debug_no_thread_alarm	OFF
-select * from information_schema.global_variables where variable_name='debug_no_thread_alarm';
-VARIABLE_NAME	VARIABLE_VALUE
-DEBUG_NO_THREAD_ALARM	OFF
-select * from information_schema.session_variables where variable_name='debug_no_thread_alarm';
-VARIABLE_NAME	VARIABLE_VALUE
-DEBUG_NO_THREAD_ALARM	OFF
-set global debug_no_thread_alarm=1;
-ERROR HY000: Variable 'debug_no_thread_alarm' is a read only variable
-set session debug_no_thread_alarm=1;
-ERROR HY000: Variable 'debug_no_thread_alarm' is a read only variable

mysql-test/suite/sys_vars/r/sysvars_debug.result

@@ -46,21 +46,6 @@ ENUM_VALUE_LIST	OFF,ON
 READ_ONLY	YES
 COMMAND_LINE_ARGUMENT	OPTIONAL
 GLOBAL_VALUE_PATH	NULL
-VARIABLE_NAME	DEBUG_NO_THREAD_ALARM
-SESSION_VALUE	NULL
-GLOBAL_VALUE	OFF
-GLOBAL_VALUE_ORIGIN	COMPILE-TIME
-DEFAULT_VALUE	OFF
-VARIABLE_SCOPE	GLOBAL
-VARIABLE_TYPE	BOOLEAN
-VARIABLE_COMMENT	Disable system thread alarm calls. Disabling it may be useful in debugging or testing, never do it in production
-NUMERIC_MIN_VALUE	NULL
-NUMERIC_MAX_VALUE	NULL
-NUMERIC_BLOCK_SIZE	NULL
-ENUM_VALUE_LIST	OFF,ON
-READ_ONLY	YES
-COMMAND_LINE_ARGUMENT	OPTIONAL
-GLOBAL_VALUE_PATH	NULL
 VARIABLE_NAME	DEBUG_SYNC
 SESSION_VALUE	ON - current signals: ''
 GLOBAL_VALUE	NULL

mysql-test/suite/sys_vars/t/debug_no_thread_alarm_basic.test

-# bool readonly
-
-#
-# show values;
-#
-select @@global.debug_no_thread_alarm;
---error ER_INCORRECT_GLOBAL_LOCAL_VAR
-select @@session.debug_no_thread_alarm;
-show global variables like 'debug_no_thread_alarm';
-show session variables like 'debug_no_thread_alarm';
-select * from information_schema.global_variables where variable_name='debug_no_thread_alarm';
-select * from information_schema.session_variables where variable_name='debug_no_thread_alarm';
-
-#
-# show that it's read-only
-#
---error ER_INCORRECT_GLOBAL_LOCAL_VAR
-set global debug_no_thread_alarm=1;
---error ER_INCORRECT_GLOBAL_LOCAL_VAR
-set session debug_no_thread_alarm=1;
-

mysys/CMakeLists.txt

@@ -34,7 +34,7 @@ SET(MYSYS_SOURCES  array.c charset-def.c charset.c my_default.c
 				my_static.c my_symlink.c my_symlink2.c my_sync.c my_thr_init.c 
 				my_basename.c
 				my_write.c ptr_cmp.c queues.c stacktrace.c
-				string.c thr_alarm.c thr_lock.c thr_mutex.c
+				string.c thr_lock.c thr_mutex.c
 				thr_rwlock.c thr_timer.c
                                 tree.c typelib.c base64.c my_memmem.c
                                 my_getpagesize.c

mysys/my_init.c

@@ -468,7 +468,7 @@ PSI_mutex_key key_LOCK_localtime_r;
 
 PSI_mutex_key key_BITMAP_mutex, key_IO_CACHE_append_buffer_lock,
   key_IO_CACHE_SHARE_mutex, key_KEY_CACHE_cache_lock,
-  key_LOCK_alarm, key_LOCK_timer,
+  key_LOCK_timer,
   key_my_thread_var_mutex, key_THR_LOCK_charset, key_THR_LOCK_heap,
   key_THR_LOCK_lock, key_THR_LOCK_malloc,
   key_THR_LOCK_mutex, key_THR_LOCK_myisam, key_THR_LOCK_net,
@@ -487,7 +487,6 @@ static PSI_mutex_info all_mysys_mutexes[]=
   { &key_IO_CACHE_append_buffer_lock, "IO_CACHE::append_buffer_lock", 0},
   { &key_IO_CACHE_SHARE_mutex, "IO_CACHE::SHARE_mutex", 0},
   { &key_KEY_CACHE_cache_lock, "KEY_CACHE::cache_lock", 0},
-  { &key_LOCK_alarm, "LOCK_alarm", PSI_FLAG_GLOBAL},
   { &key_LOCK_timer, "LOCK_timer", PSI_FLAG_GLOBAL},
   { &key_my_thread_var_mutex, "my_thread_var::mutex", 0},
   { &key_THR_LOCK_charset, "THR_LOCK_charset", PSI_FLAG_GLOBAL},
@@ -504,13 +503,12 @@ static PSI_mutex_info all_mysys_mutexes[]=
   { &key_LOCK_uuid_generator, "LOCK_uuid_generator", PSI_FLAG_GLOBAL }
 };
 
-PSI_cond_key key_COND_alarm, key_COND_timer, key_IO_CACHE_SHARE_cond,
+PSI_cond_key key_COND_timer, key_IO_CACHE_SHARE_cond,
   key_IO_CACHE_SHARE_cond_writer, key_my_thread_var_suspend,
   key_THR_COND_threads, key_WT_RESOURCE_cond;
 
 static PSI_cond_info all_mysys_conds[]=
 {
-  { &key_COND_alarm, "COND_alarm", PSI_FLAG_GLOBAL},
   { &key_COND_timer, "COND_timer", PSI_FLAG_GLOBAL},
   { &key_IO_CACHE_SHARE_cond, "IO_CACHE_SHARE::cond", 0},
   { &key_IO_CACHE_SHARE_cond_writer, "IO_CACHE_SHARE::cond_writer", 0},
@@ -526,16 +524,10 @@ static PSI_rwlock_info all_mysys_rwlocks[]=
   { &key_SAFEHASH_mutex, "SAFE_HASH::mutex", 0}
 };
 
-#ifdef USE_ALARM_THREAD
-PSI_thread_key key_thread_alarm;
-#endif
 PSI_thread_key key_thread_timer;
 
 static PSI_thread_info all_mysys_threads[]=
 {
-#ifdef USE_ALARM_THREAD
-  { &key_thread_alarm, "alarm", PSI_FLAG_GLOBAL},
-#endif
   { &key_thread_timer, "statement_timer", PSI_FLAG_GLOBAL}
 };
 

mysys/my_pthread.c

@@ -20,7 +20,6 @@
 #include "mysys_priv.h"
 #include <signal.h>
 #include <m_string.h>
-#include <thr_alarm.h>
 #include <my_pthread.h>
 
 #if (defined(__BSD__) || defined(_BSDI_VERSION))
@@ -234,11 +233,7 @@ void *sigwait_thread(void *set_arg)
       sigaction(i, &sact, (struct sigaction*) 0);
     }
   }
-  /* Ensure that init_thr_alarm() is called */
-  DBUG_ASSERT(thr_client_alarm);
-  sigaddset(set, thr_client_alarm);
   pthread_sigmask(SIG_UNBLOCK,(sigset_t*) set,(sigset_t*) 0);
-  alarm_thread=pthread_self();			/* For thr_alarm */
 
   for (;;)
   {						/* Wait for signals */

mysys/mysys_priv.h

@@ -43,20 +43,17 @@ extern PSI_mutex_key key_LOCK_localtime_r;
 #endif /* !defined(HAVE_LOCALTIME_R) || !defined(HAVE_GMTIME_R) */
 
 extern PSI_mutex_key key_BITMAP_mutex, key_IO_CACHE_append_buffer_lock,
-  key_IO_CACHE_SHARE_mutex, key_KEY_CACHE_cache_lock, key_LOCK_alarm,
+  key_IO_CACHE_SHARE_mutex, key_KEY_CACHE_cache_lock,
   key_my_thread_var_mutex, key_THR_LOCK_charset, key_THR_LOCK_heap,
   key_THR_LOCK_lock, key_THR_LOCK_malloc,
   key_THR_LOCK_mutex, key_THR_LOCK_myisam, key_THR_LOCK_net,
   key_THR_LOCK_open, key_THR_LOCK_threads, key_LOCK_uuid_generator,
   key_TMPDIR_mutex, key_THR_LOCK_myisam_mmap, key_LOCK_timer;
 
-extern PSI_cond_key key_COND_alarm, key_COND_timer, key_IO_CACHE_SHARE_cond,
+extern PSI_cond_key key_COND_timer, key_IO_CACHE_SHARE_cond,
   key_IO_CACHE_SHARE_cond_writer, key_my_thread_var_suspend,
   key_THR_COND_threads;
 
-#ifdef USE_ALARM_THREAD
-extern PSI_thread_key key_thread_alarm;
-#endif /* USE_ALARM_THREAD */
 extern PSI_thread_key key_thread_timer;
 extern PSI_rwlock_key key_SAFEHASH_mutex;
 

sql/client_settings.h

@@ -20,7 +20,6 @@
 #error You have already included an client_settings.h and it should not be included twice
 #endif /* CLIENT_SETTINGS_INCLUDED */
 
-#include <thr_alarm.h>
 #include <sql_common.h>
 
 /*

sql/mysqld.cc

@@ -113,7 +113,6 @@
 #include <sys/prctl.h>
 #endif
 
-#include <thr_alarm.h>
 #include <ft_global.h>
 #include <errmsg.h>
 #include "sp_rcontext.h"
@@ -1670,10 +1669,11 @@ static void break_connect_loop()
     int UNINIT_VAR(error);
     DBUG_PRINT("info",("Waiting for select thread"));
 
-#ifndef DONT_USE_THR_ALARM
-    if (pthread_kill(select_thread, thr_client_alarm))
-      break;					// allready dead
-#endif
+    for(size_t i=0; i < listen_sockets.size(); i++)
+    {
+      int fd=mysql_socket_getfd(listen_sockets.at(i));
+      shutdown(fd, SHUT_RDWR);
+    }
     set_timespec(abstime, 2);
     for (uint tmp=0 ; tmp < 10 && select_thread_in_use; tmp++)
     {
@@ -1765,8 +1765,6 @@ static void close_connections(void)
   listen_sockets.free_memory();
   mysql_mutex_unlock(&LOCK_start_thread);
 
-  end_thr_alarm(0);			 // Abort old alarms.
-
   while (CONNECT::count)
     my_sleep(100);
 
@@ -1877,10 +1875,6 @@ extern "C" sig_handler print_signal_warning(int sig)
 #ifdef SIGNAL_HANDLER_RESET_ON_DELIVERY
   my_sigset(sig,print_signal_warning);		/* int. thread system calls */
 #endif
-#if !defined(_WIN32)
-  if (sig == SIGALRM)
-    alarm(2);					/* reschedule alarm */
-#endif
 }
 
 #ifdef _WIN32
@@ -2027,7 +2021,6 @@ static void clean_up(bool print_message)
   multi_keycache_free();
   sp_cache_end();
   free_status_vars();
-  end_thr_alarm(1);			/* Free allocated memory */
   end_thr_timer();
   my_free_open_file_info();
   if (defaults_argv)
@@ -3110,8 +3103,6 @@ void init_signals(void)
   struct sigaction sa;
   DBUG_ENTER("init_signals");
 
-  my_sigset(THR_SERVER_ALARM,print_signal_warning); // Should never be called!
-
   if (opt_stack_trace || (test_flags & TEST_CORE_ON_SIGNAL))
   {
     sa.sa_flags = SA_RESETHAND | SA_NODEFER;
@@ -3159,7 +3150,6 @@ void init_signals(void)
   sa.sa_flags = 0;
   sa.sa_handler = print_signal_warning;
   sigaction(SIGHUP, &sa, (struct sigaction*) 0);
-  sigaddset(&set,THR_SERVER_ALARM);
   if (test_flags & TEST_SIGINT)
   {
     /* Allow SIGINT to break mysqld. This is for debugging with --gdb */
@@ -3220,7 +3210,7 @@ pthread_handler_t kill_server_thread(void *arg __attribute__((unused)))
 #endif
 
 
-/** This threads handles all signals and alarms. */
+/** This threads handles all signals */
 /* ARGSUSED */
 pthread_handler_t signal_hand(void *arg __attribute__((unused)))
 {
@@ -3230,13 +3220,6 @@ pthread_handler_t signal_hand(void *arg __attribute__((unused)))
   DBUG_ENTER("signal_hand");
   signal_thread_in_use= 1;
 
-  /*
-    Setup alarm handler
-    This should actually be '+ max_number_of_slaves' instead of +10,
-    but the +10 should be quite safe.
-  */
-  init_thr_alarm(thread_scheduler->max_threads + extra_max_connections +
-		 global_system_variables.max_insert_delayed_threads + 10);
   if (test_flags & TEST_SIGINT)
   {
     /* Allow SIGINT to break mysqld. This is for debugging with --gdb */
@@ -3245,9 +3228,6 @@ pthread_handler_t signal_hand(void *arg __attribute__((unused)))
     (void) pthread_sigmask(SIG_UNBLOCK,&set,NULL);
   }
   (void) sigemptyset(&set);			// Setup up SIGINT for debug
-#ifdef USE_ONE_SIGNAL_HAND
-  (void) sigaddset(&set,THR_SERVER_ALARM);	// For alarms
-#endif
 #ifndef IGNORE_SIGHUP_SIGQUIT
   (void) sigaddset(&set,SIGQUIT);
   (void) sigaddset(&set,SIGHUP);
@@ -3311,7 +3291,7 @@ pthread_handler_t signal_hand(void *arg __attribute__((unused)))
                           error);
 #else
         my_sigset(sig, SIG_IGN);
-        break_connect_loop(); // MIT THREAD has a alarm thread
+        break_connect_loop(); 
 #endif
       }
       break;
@@ -3341,11 +3321,6 @@ pthread_handler_t signal_hand(void *arg __attribute__((unused)))
                             opt_log ? fixed_log_output_options : LOG_NONE);
       }
       break;
-#ifdef USE_ONE_SIGNAL_HAND
-    case THR_SERVER_ALARM:
-      process_alarm(sig);			// Trigger alarms.
-      break;
-#endif
     default:
 #ifdef EXTRA_DEBUG
       sql_print_warning("Got signal: %d  error: %d",sig,error); /* purecov: tested */
@@ -5854,7 +5829,7 @@ int mysqld_main(int argc, char **argv)
 #endif
 
   /*
-    init signals & alarm
+    init signals
     After this we can't quit by a simple unireg_abort
   */
   start_signal_handler();				// Creates pidfile

sql/slave.cc

@@ -36,7 +36,6 @@
 #include "rpl_filter.h"
 #include "repl_failsafe.h"
 #include "transaction.h"
-#include <thr_alarm.h>
 #include <my_dir.h>
 #include <sql_common.h>
 #include <errmsg.h>
@@ -1075,24 +1074,11 @@ terminate_slave_thread(THD *thd,
 
     mysql_mutex_lock(&thd->LOCK_thd_kill);
     mysql_mutex_lock(&thd->LOCK_thd_data);
-#ifndef DONT_USE_THR_ALARM
-    /*
-      Error codes from pthread_kill are:
-      EINVAL: invalid signal number (can't happen)
-      ESRCH: thread already killed (can happen, should be ignored)
-    */
-    int err __attribute__((unused))= pthread_kill(thd->real_id, thr_client_alarm);
-    DBUG_ASSERT(err != EINVAL);
-#endif
     thd->awake_no_mutex(NOT_KILLED);
 
     mysql_mutex_unlock(&thd->LOCK_thd_kill);
     mysql_mutex_unlock(&thd->LOCK_thd_data);
 
-    /*
-      There is a small chance that slave thread might miss the first
-      alarm. To protect againts it, resend the signal until it reacts
-    */
     struct timespec abstime;
     set_timespec(abstime,2);
     error= mysql_cond_timedwait(term_cond, term_lock, &abstime);

sql/sql_class.cc

@@ -48,7 +48,6 @@
 #include "sql_audit.h"
 #include <m_ctype.h>
 #include <sys/stat.h>
-#include <thr_alarm.h>
 #include <mysys_err.h>
 #include <limits.h>
 
@@ -1903,9 +1902,6 @@ void THD::awake_no_mutex(killed_state state_to_set)
     }
 #endif
 
-    /* Mark the target thread's alarm request expired, and signal alarm. */
-    thr_alarm_kill(thread_id);
-
     /* Send an event to the scheduler that a thread should be killed. */
     if (!slave_thread)
       MYSQL_CALLBACK(scheduler, post_kill_notification, (this));

sql/sql_test.cc

@@ -26,7 +26,6 @@
 #include "keycaches.h"
 #include "my_json_writer.h"
 #include <hash.h>
-#include <thr_alarm.h>
 #include "sql_connect.h"
 #include "thread_cache.h"
 #if defined(HAVE_MALLINFO) && defined(HAVE_MALLOC_H)
@@ -611,17 +610,6 @@ Open streams:  %10lu\n",
 	 my_file_opened,
 	 my_stream_opened);
 
-#ifndef DONT_USE_THR_ALARM
-  ALARM_INFO alarm_info;
-  thr_alarm_info(&alarm_info);
-  printf("\nAlarm status:\n\
-Active alarms:   %u\n\
-Max used alarms: %u\n\
-Next alarm time: %lu\n",
-	 alarm_info.active_alarms,
-	 alarm_info.max_used_alarms,
-	(ulong)alarm_info.next_alarm_time);
-#endif
   display_table_locks();
 #if defined(HAVE_MALLINFO2)
   struct mallinfo2 info = mallinfo2();

sql/sys_vars.cc

@@ -38,7 +38,6 @@
 #include "my_sys.h"
 
 #include "events.h"
-#include <thr_alarm.h>
 #include "slave.h"
 #include "rpl_mi.h"
 #include "rpl_filter.h"
@@ -1735,10 +1734,6 @@ Sys_max_binlog_size(
 
 static bool fix_max_connections(sys_var *self, THD *thd, enum_var_type type)
 {
-#ifndef EMBEDDED_LIBRARY
-  resize_thr_alarm(max_connections + extra_max_connections +
-                   global_system_variables.max_insert_delayed_threads + 10);
-#endif
   return false;
 }
 
@@ -6753,13 +6748,6 @@ static Sys_var_enum Sys_histogram_type(
        SESSION_VAR(histogram_type), CMD_LINE(REQUIRED_ARG),
        histogram_types, DEFAULT(2));
 
-static Sys_var_mybool Sys_no_thread_alarm(
-       "debug_no_thread_alarm",
-       "Disable system thread alarm calls. Disabling it may be useful "
-       "in debugging or testing, never do it in production",
-       READ_ONLY GLOBAL_VAR(my_disable_thr_alarm), CMD_LINE(OPT_ARG),
-       DEFAULT(FALSE));
-
 static Sys_var_mybool Sys_query_cache_strip_comments(
        "query_cache_strip_comments",
        "Strip all comments from a query before storing it "