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Use rwlock rather than mutex for protecting THD_list

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modifications (insert/erase) are protected by write lock
iteration over list is protected by read lock.

This way, threads that iterate over the list (as in SHOW PROCESSLIST,
SHOW GLOBAL STATUS) do not block each other.
This commit is contained in:
Vladislav Vaintroub
2019-01-24 18:56:59 +01:00
committed by Sergey Vojtovich
parent 9824ec81aa
commit 8b4fcc434d
3 changed files with 17 additions and 15 deletions
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18
sql/sql_class.h
View File

@@ -6939,7 +6939,7 @@ private:
class THD_list
{
I_List<THD> threads;
mutable mysql_mutex_t mutex;
mutable mysql_rwlock_t lock;
public:
/**
@@ -6951,13 +6951,13 @@ public:
*/
void init()
{
mysql_mutex_init(key_Thread_map_mutex, &mutex, MY_MUTEX_INIT_FAST);
mysql_rwlock_init(key_rwlock_THD_list, &lock);
}
/** Destructor replacement. */
void destroy()
{
mysql_mutex_destroy(&mutex);
mysql_rwlock_destroy(&lock);
}
/**
@@ -6969,9 +6969,9 @@ public:
*/
void insert(THD *thd)
{
mysql_mutex_lock(&mutex);
mysql_rwlock_wrlock(&lock);
threads.append(thd);
mysql_mutex_unlock(&mutex);
mysql_rwlock_unlock(&lock);
}
/**
@@ -6984,9 +6984,9 @@ public:
void erase(THD *thd)
{
thd->assert_linked();
mysql_mutex_lock(&mutex);
mysql_rwlock_wrlock(&lock);
thd->unlink();
mysql_mutex_unlock(&mutex);
mysql_rwlock_unlock(&lock);
}
/**
@@ -7002,12 +7002,12 @@ public:
template <typename T> int iterate(my_bool (*action)(THD *thd, T *arg), T *arg= 0)
{
int res= 0;
mysql_mutex_lock(&mutex);
mysql_rwlock_rdlock(&lock);
I_List_iterator<THD> it(threads);
while (auto tmp= it++)
if ((res= action(tmp, arg)))
break;
mysql_mutex_unlock(&mutex);
mysql_rwlock_unlock(&lock);
return res;
}
};