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MDL_lock encapsulation: MDL_lock::get_lock_owner()

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Avoid accessing MDL_lock::m_rwlock from MDL_map::get_lock_owner(),
code moved to MDL_lock::get_lock_owner() instead.

get_lock_owner() doesn't have to check BACKUP namespace since it is
used by user level locks only.

This is part of broader cleanup, which aims to make large part of
MDL_lock members private. It is needed to simplify further work on
MDEV-19749 - MDL scalability regression after backup locks.
This commit is contained in:
Sergey Vojtovich 2025-04-30 20:03:27 +04:00 committed by Sergei Golubchik
parent f0ee3948b6
commit 8d0ccd911f
1 changed files with 31 additions and 41 deletions
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72
sql/mdl.cc
View File

@ -584,7 +584,7 @@ public:
If m_wrlock prefers readers (actually ignoring pending writers is
enough) ctxA and ctxB will continue and no deadlock will occur.
*/
mysql_prlock_t m_rwlock;
mutable mysql_prlock_t m_rwlock;
bool is_empty() const
{
@ -601,8 +601,6 @@ public:
bool can_grant_lock(enum_mdl_type type, MDL_context *requstor_ctx,
bool ignore_lock_priority) const;
inline unsigned long get_lock_owner() const;
void reschedule_waiters();
void remove_ticket(LF_PINS *pins, Ticket_list MDL_lock::*queue,
@ -686,6 +684,29 @@ public:
lock->m_strategy= &m_object_lock_strategy;
}
/**
Return thread id of the thread to which the first ticket was
granted.
Intended for user level locks. They make use of SNW lock only,
thus there can be only one granted ticket.
We can skip check for m_strategy here, because m_granted
must be empty for such locks anyway.
*/
unsigned long get_lock_owner() const
{
unsigned long res= 0;
DBUG_ASSERT(key.mdl_namespace() == MDL_key::USER_LOCK);
mysql_prlock_rdlock(&m_rwlock);
DBUG_ASSERT(m_strategy || is_empty());
if (!m_granted.is_empty())
res= m_granted.begin()->get_ctx()->get_thread_id();
mysql_prlock_unlock(&m_rwlock);
return res;
}
const MDL_lock_strategy *m_strategy;
private:
static const MDL_backup_lock m_backup_lock_strategy;
@ -893,31 +914,15 @@ retry:
unsigned long
MDL_map::get_lock_owner(LF_PINS *pins, const MDL_key *mdl_key)
{
unsigned long res= 0;
if (mdl_key->mdl_namespace() == MDL_key::BACKUP)
DBUG_ASSERT(mdl_key->mdl_namespace() == MDL_key::USER_LOCK);
if (MDL_lock *lock= (MDL_lock*) lf_hash_search(&m_locks, pins, mdl_key->ptr(),
mdl_key->length()))
{
mysql_prlock_rdlock(&m_backup_lock->m_rwlock);
res= m_backup_lock->get_lock_owner();
mysql_prlock_unlock(&m_backup_lock->m_rwlock);
unsigned long res= lock->get_lock_owner();
lf_hash_search_unpin(pins);
return res;
}
else
{
MDL_lock *lock= (MDL_lock*) lf_hash_search(&m_locks, pins, mdl_key->ptr(),
mdl_key->length());
if (lock)
{
/*
We can skip check for m_strategy here, becase m_granted
must be empty for such locks anyway.
*/
mysql_prlock_rdlock(&lock->m_rwlock);
res= lock->get_lock_owner();
mysql_prlock_unlock(&lock->m_rwlock);
lf_hash_search_unpin(pins);
}
}
return res;
return 0;
}
@ -1811,21 +1816,6 @@ MDL_lock::can_grant_lock(enum_mdl_type type_arg,
}
/**
Return thread id of the thread to which the first ticket was
granted.
*/
inline unsigned long
MDL_lock::get_lock_owner() const
{
if (m_granted.is_empty())
return 0;
return m_granted.begin()->get_ctx()->get_thread_id();
}
/** Remove a ticket from waiting or pending queue and wakeup up waiters. */
void MDL_lock::remove_ticket(LF_PINS *pins, Ticket_list MDL_lock::*list,