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MDL_lock encapsulation: try_acquire_lock()

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Avoid accessing MDL_lock::m_rwlock from MDL_context::try_acquire_lock()
and MDL_context::acquire_lock(), code moved to
MDL_context::try_acquire_lock_impl() instead. It is an intermediate
change that reduce uses of MDL_lock::m_rwlock out of MDL_lock class.

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 2025-05-02 16:06:25 +04:00 committed by Sergei Golubchik
parent ebddd3ff14
commit 542ba51c4c
1 changed files with 21 additions and 30 deletions
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51
sql/mdl.cc
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@ -2071,25 +2071,7 @@ MDL_context::find_ticket(MDL_request *mdl_request,
bool bool
MDL_context::try_acquire_lock(MDL_request *mdl_request) MDL_context::try_acquire_lock(MDL_request *mdl_request)
{ {
MDL_ticket *ticket; return try_acquire_lock_impl(mdl_request, nullptr);
if (try_acquire_lock_impl(mdl_request, &ticket))
return TRUE;
if (! mdl_request->ticket)
{
/*
Our attempt to acquire lock without waiting has failed.
Let us release resources which were acquired in the process.
We can't get here if we allocated a new lock object so there
is no need to release it.
*/
DBUG_ASSERT(! ticket->m_lock->is_empty());
mysql_prlock_unlock(&ticket->m_lock->m_rwlock);
delete ticket;
}
return FALSE;
} }
@ -2188,8 +2170,21 @@ MDL_context::try_acquire_lock_impl(MDL_request *mdl_request,
mysql_mdl_set_status(ticket->m_psi, MDL_ticket::GRANTED); mysql_mdl_set_status(ticket->m_psi, MDL_ticket::GRANTED);
} }
else else if (out_ticket)
*out_ticket= ticket; *out_ticket= ticket;
else
{
/*
Our attempt to acquire lock without waiting has failed.
Let us release resources which were acquired in the process.
We can't get here if we allocated a new lock object so there
is no need to release it.
*/
DBUG_ASSERT(!ticket->m_lock->is_empty());
DBUG_PRINT("mdl", ("Nowait: %s", dbug_print_mdl(ticket)));
mysql_prlock_unlock(&ticket->m_lock->m_rwlock);
delete ticket;
}
return FALSE; return FALSE;
} }
@ -2325,7 +2320,7 @@ MDL_context::acquire_lock(MDL_request *mdl_request, double lock_wait_timeout)
mdl_lock_name, mdl_lock_name,
lock_wait_timeout)); lock_wait_timeout));
if (try_acquire_lock_impl(mdl_request, &ticket)) if (try_acquire_lock_impl(mdl_request, lock_wait_timeout ? &ticket : nullptr))
{ {
DBUG_PRINT("mdl", ("OOM: %s", mdl_lock_name)); DBUG_PRINT("mdl", ("OOM: %s", mdl_lock_name));
DBUG_RETURN(TRUE); DBUG_RETURN(TRUE);
@ -2343,27 +2338,22 @@ MDL_context::acquire_lock(MDL_request *mdl_request, double lock_wait_timeout)
DBUG_RETURN(FALSE); DBUG_RETURN(FALSE);
} }
#ifdef DBUG_TRACE
const char *ticket_msg= dbug_print_mdl(ticket);
#endif
/* /*
Our attempt to acquire lock without waiting has failed. Our attempt to acquire lock without waiting has failed.
As a result of this attempt we got MDL_ticket with m_lock As a result of this attempt we got MDL_ticket with m_lock
member pointing to the corresponding MDL_lock object which member pointing to the corresponding MDL_lock object which
has MDL_lock::m_rwlock write-locked. has MDL_lock::m_rwlock write-locked.
*/ */
lock= ticket->m_lock;
if (lock_wait_timeout == 0) if (lock_wait_timeout == 0)
{ {
DBUG_PRINT("mdl", ("Nowait: %s", ticket_msg));
mysql_prlock_unlock(&lock->m_rwlock);
delete ticket;
my_error(ER_LOCK_WAIT_TIMEOUT, MYF(0)); my_error(ER_LOCK_WAIT_TIMEOUT, MYF(0));
DBUG_RETURN(TRUE); DBUG_RETURN(TRUE);
} }
#ifdef DBUG_TRACE
const char *ticket_msg= dbug_print_mdl(ticket);
#endif
#ifdef WITH_WSREP #ifdef WITH_WSREP
if (WSREP(get_thd())) if (WSREP(get_thd()))
{ {
@ -2378,6 +2368,7 @@ MDL_context::acquire_lock(MDL_request *mdl_request, double lock_wait_timeout)
} }
#endif /* WITH_WSREP */ #endif /* WITH_WSREP */
lock= ticket->m_lock;
lock->m_waiting.add_ticket(ticket); lock->m_waiting.add_ticket(ticket);
/* /*