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Avoid taking LOCK_thread_count for thread_count protection

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Replaced wait on COND_thread_count with busy waiting with 1 millisecond
sleep.

Aim is to reduce usage of LOCK_thread_count and COND_thread_count.
This commit is contained in:
Sergey Vojtovich 2019-01-29 01:13:47 +04:00
parent 8553525931
commit 4b3656a44d
4 changed files with 7 additions and 34 deletions
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14
sql/mysqld.cc
View file

@ -689,10 +689,7 @@ static std::atomic<char*> shutdown_user;
pthread_key(THD*, THR_THD);
/*
LOCK_thread_count protects the following variables:
thread_count Number of threads with THD that servers queries.
*/
/** To be removed */
mysql_mutex_t LOCK_thread_count;
/*
@ -1794,13 +1791,9 @@ static void close_connections(void)
/* All threads has now been aborted */
DBUG_PRINT("quit", ("Waiting for threads to die (count=%u)",
uint32_t(thread_count)));
mysql_mutex_lock(&LOCK_thread_count);
while (thread_count)
{
mysql_cond_wait(&COND_thread_count, &LOCK_thread_count);
DBUG_PRINT("quit",("One thread died (count=%u)", uint32_t(thread_count)));
}
mysql_mutex_unlock(&LOCK_thread_count);
my_sleep(1000);
DBUG_PRINT("quit",("close_connections thread"));
DBUG_VOID_RETURN;
@ -4469,7 +4462,6 @@ static int init_thread_environment()
mysql_mutex_init(key_LOCK_global_system_variables,
&LOCK_global_system_variables, MY_MUTEX_INIT_FAST);
mysql_mutex_record_order(&LOCK_active_mi, &LOCK_global_system_variables);
mysql_mutex_record_order(&LOCK_status, &LOCK_thread_count);
mysql_prlock_init(key_rwlock_LOCK_system_variables_hash,
&LOCK_system_variables_hash);
mysql_mutex_init(key_LOCK_prepared_stmt_count,

7
sql/sql_class.cc
View file

@ -786,11 +786,6 @@ THD::THD(my_thread_id id, bool is_wsrep_applier, bool skip_global_sys_var_lock)
mysql_mutex_init(key_LOCK_wakeup_ready, &LOCK_wakeup_ready, MY_MUTEX_INIT_FAST);
mysql_mutex_init(key_LOCK_thd_kill, &LOCK_thd_kill, MY_MUTEX_INIT_FAST);
mysql_cond_init(key_COND_wakeup_ready, &COND_wakeup_ready, 0);
/*
LOCK_thread_count goes before LOCK_thd_data - the former is called around
'delete thd', the latter - in THD::~THD
*/
mysql_mutex_record_order(&LOCK_thread_count, &LOCK_thd_data);
/* Variables with default values */
proc_info="login";
@ -1640,8 +1635,6 @@ THD::~THD()
DBUG_ENTER("~THD()");
/* Make sure threads are not available via server_threads. */
assert_not_linked();
/* This takes a long time so we should not do this under LOCK_thread_count */
mysql_mutex_assert_not_owner(&LOCK_thread_count);
/*
In error cases, thd may not be current thd. We have to fix this so

11
sql/sql_class.h
View file

@ -2152,14 +2152,11 @@ struct THD_count
*/
~THD_count()
{
uint32_t t= thread_count--;
#ifndef DBUG_OFF
uint32_t t=
#endif
thread_count--;
DBUG_ASSERT(t > 0);
if (t == 1)
{
mysql_mutex_lock(&LOCK_thread_count);
mysql_cond_broadcast(&COND_thread_count);
mysql_mutex_unlock(&LOCK_thread_count);
}
}
};

9
sql/sql_parse.cc
View file

@ -1077,10 +1077,6 @@ void bootstrap(MYSQL_FILE *file)
thd->profiling.set_query_source(thd->query(), length);
#endif
/*
We don't need to obtain LOCK_thread_count here because in bootstrap
mode we have only one thread.
*/
thd->set_time();
Parser_state parser_state;
if (parser_state.init(thd, thd->query(), length))
@ -8994,9 +8990,6 @@ THD *find_thread_by_id(longlong id, bool query_id)
@param id Thread id or query id
@param kill_signal Should it kill the query or the connection
@param type Type of id: thread id or query id
@note
This is written such that we have a short lock on LOCK_thread_count
*/
uint
@ -9061,8 +9054,6 @@ kill_one_thread(THD *thd, longlong id, killed_state kill_signal, killed_type typ
@param only_kill_query Should it kill the query or the connection
@note
This is written such that we have a short lock on LOCK_thread_count
If we can't kill all threads because of security issues, no threads
are killed.
*/