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mariadb/sql/table_cache.cc
Marko Mäkelä a2bd936c52 MDEV-33161 Function pointer signature mismatch in LF_HASH 
In cmake -DWITH_UBSAN=ON builds with clang but not with GCC,
-fsanitize=undefined will flag several runtime errors on
function pointer mismatch related to the lock-free hash table LF_HASH.

Let us use matching function signatures and remove function pointer
casts in order to avoid potential bugs due to undefined behaviour.

These errors could be caught at compilation time by
-Wcast-function-type-strict, which is available starting with clang-16,
but not available in any version of GCC as of now. The old GCC flag
-Wcast-function-type is enabled as part of -Wextra, but it specifically
does not catch these errors.

Reviewed by: Vladislav Vaintroub
2024-06-10 12:35:33 +03:00

1303 lines
36 KiB
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/* Copyright (c) 2000, 2012, Oracle and/or its affiliates.
Copyright (c) 2010, 2011 Monty Program Ab
Copyright (C) 2013 Sergey Vojtovich and MariaDB Foundation
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 */
/**
@file
Table definition cache and table cache implementation.
Table definition cache actions:
- add new TABLE_SHARE object to cache (tdc_acquire_share())
- acquire TABLE_SHARE object from cache (tdc_acquire_share())
- release TABLE_SHARE object to cache (tdc_release_share())
- purge unused TABLE_SHARE objects from cache (tdc_purge())
- remove TABLE_SHARE object from cache (tdc_remove_table())
- get number of TABLE_SHARE objects in cache (tdc_records())
Table cache actions:
- add new TABLE object to cache (tc_add_table())
- acquire TABLE object from cache (tc_acquire_table())
- release TABLE object to cache (tc_release_table())
- purge unused TABLE objects from cache (tc_purge())
- purge unused TABLE objects of a table from cache (tdc_remove_table())
- get number of TABLE objects in cache (tc_records())
Dependencies:
- close_cached_tables(): flush tables on shutdown
- alloc_table_share()
- free_table_share()
Table cache invariants:
- TABLE_SHARE::free_tables shall not contain objects with TABLE::in_use != 0
- TABLE_SHARE::free_tables shall not receive new objects if
TABLE_SHARE::tdc.flushed is true
*/
#include "mariadb.h"
#include "lf.h"
#include "table.h"
#include "sql_base.h"
/** Configuration. */
ulong tdc_size; /**< Table definition cache threshold for LRU eviction. */
ulong tc_size; /**< Table cache threshold for LRU eviction. */
uint32 tc_instances;
static std::atomic<uint32_t> tc_active_instances(1);
static std::atomic<bool> tc_contention_warning_reported;
/** Data collections. */
static LF_HASH tdc_hash; /**< Collection of TABLE_SHARE objects. */
/** Collection of unused TABLE_SHARE objects. */
static
I_P_List <TDC_element,
I_P_List_adapter<TDC_element, &TDC_element::next, &TDC_element::prev>,
I_P_List_null_counter,
I_P_List_fast_push_back<TDC_element> > unused_shares;
static bool tdc_inited;
/**
Protects unused shares list.
TDC_element::prev
TDC_element::next
unused_shares
*/
static mysql_mutex_t LOCK_unused_shares;
#ifdef HAVE_PSI_INTERFACE
static PSI_mutex_key key_LOCK_unused_shares, key_TABLE_SHARE_LOCK_table_share,
key_LOCK_table_cache;
static PSI_mutex_info all_tc_mutexes[]=
{
{ &key_LOCK_unused_shares, "LOCK_unused_shares", PSI_FLAG_GLOBAL },
{ &key_TABLE_SHARE_LOCK_table_share, "TABLE_SHARE::tdc.LOCK_table_share", 0 },
{ &key_LOCK_table_cache, "LOCK_table_cache", 0 }
};
static PSI_cond_key key_TABLE_SHARE_COND_release;
static PSI_cond_info all_tc_conds[]=
{
{ &key_TABLE_SHARE_COND_release, "TABLE_SHARE::tdc.COND_release", 0 }
};
#endif
static int fix_thd_pins(THD *thd)
{
return thd->tdc_hash_pins ? 0 :
(thd->tdc_hash_pins= lf_hash_get_pins(&tdc_hash)) == 0;
}
/*
Auxiliary routines for manipulating with per-share all/unused lists
and tc_count counter.
Responsible for preserving invariants between those lists, counter
and TABLE::in_use member.
In fact those routines implement sort of implicit table cache as
part of table definition cache.
*/
struct Table_cache_instance
{
/**
Protects free_tables (TABLE::global_free_next and TABLE::global_free_prev),
records, Share_free_tables::List (TABLE::prev and TABLE::next),
TABLE::in_use.
*/
mysql_mutex_t LOCK_table_cache;
I_P_List <TABLE, I_P_List_adapter<TABLE, &TABLE::global_free_next,
&TABLE::global_free_prev>,
I_P_List_null_counter, I_P_List_fast_push_back<TABLE> >
free_tables;
ulong records;
uint mutex_waits;
uint mutex_nowaits;
/** Avoid false sharing between instances */
char pad[CPU_LEVEL1_DCACHE_LINESIZE];
Table_cache_instance(): records(0), mutex_waits(0), mutex_nowaits(0)
{
mysql_mutex_init(key_LOCK_table_cache, &LOCK_table_cache,
MY_MUTEX_INIT_FAST);
}
~Table_cache_instance()
{
mysql_mutex_destroy(&LOCK_table_cache);
DBUG_ASSERT(free_tables.is_empty());
DBUG_ASSERT(records == 0);
}
/**
Lock table cache mutex and check contention.
Instance is considered contested if more than 20% of mutex acquisiotions
can't be served immediately. Up to 100 000 probes may be performed to avoid
instance activation on short sporadic peaks. 100 000 is estimated maximum
number of queries one instance can serve in one second.
These numbers work well on a 2 socket / 20 core / 40 threads Intel Broadwell
system, that is expected number of instances is activated within reasonable
warmup time. It may have to be adjusted for other systems.
Only TABLE object acquistion is instrumented. We intentionally avoid this
overhead on TABLE object release. All other table cache mutex acquistions
are considered out of hot path and are not instrumented either.
*/
void lock_and_check_contention(uint32_t n_instances, uint32_t instance)
{
if (mysql_mutex_trylock(&LOCK_table_cache))
{
mysql_mutex_lock(&LOCK_table_cache);
if (++mutex_waits == 20000)
{
if (n_instances < tc_instances)
{
if (tc_active_instances.
compare_exchange_weak(n_instances, n_instances + 1,
std::memory_order_relaxed,
std::memory_order_relaxed))
{
sql_print_information("Detected table cache mutex contention at instance %d: "
"%d%% waits. Additional table cache instance "
"activated. Number of instances after "
"activation: %d.",
instance + 1,
mutex_waits * 100 / (mutex_nowaits + mutex_waits),
n_instances + 1);
}
}
else if (!tc_contention_warning_reported.exchange(true,
std::memory_order_relaxed))
{
sql_print_warning("Detected table cache mutex contention at instance %d: "
"%d%% waits. Additional table cache instance "
"cannot be activated: consider raising "
"table_open_cache_instances. Number of active "
"instances: %d.",
instance + 1,
mutex_waits * 100 / (mutex_nowaits + mutex_waits),
n_instances);
}
mutex_waits= 0;
mutex_nowaits= 0;
}
}
else if (++mutex_nowaits == 80000)
{
mutex_waits= 0;
mutex_nowaits= 0;
}
}
};
static Table_cache_instance *tc;
static void intern_close_table(TABLE *table)
{
delete table->triggers;
DBUG_ASSERT(table->file);
closefrm(table);
tdc_release_share(table->s);
my_free(table);
}
/**
Get number of TABLE objects (used and unused) in table cache.
*/
uint tc_records(void)
{
ulong total= 0;
for (uint32 i= 0; i < tc_instances; i++)
{
mysql_mutex_lock(&tc[i].LOCK_table_cache);
total+= tc[i].records;
mysql_mutex_unlock(&tc[i].LOCK_table_cache);
}
return total;
}
/**
Remove TABLE object from table cache.
*/
static void tc_remove_table(TABLE *table)
{
TDC_element *element= table->s->tdc;
mysql_mutex_lock(&element->LOCK_table_share);
/* Wait for MDL deadlock detector to complete traversing tdc.all_tables. */
while (element->all_tables_refs)
mysql_cond_wait(&element->COND_release, &element->LOCK_table_share);
element->all_tables.remove(table);
mysql_mutex_unlock(&element->LOCK_table_share);
intern_close_table(table);
}
static void tc_remove_all_unused_tables(TDC_element *element,
Share_free_tables::List *purge_tables)
{
for (uint32 i= 0; i < tc_instances; i++)
{
mysql_mutex_lock(&tc[i].LOCK_table_cache);
while (auto table= element->free_tables[i].list.pop_front())
{
tc[i].records--;
tc[i].free_tables.remove(table);
DBUG_ASSERT(element->all_tables_refs == 0);
element->all_tables.remove(table);
purge_tables->push_front(table);
}
mysql_mutex_unlock(&tc[i].LOCK_table_cache);
}
}
/**
Free all unused TABLE objects.
While locked:
- remove unused objects from TABLE_SHARE::tdc.free_tables and
TABLE_SHARE::tdc.all_tables
- decrement tc_count
While unlocked:
- free resources related to unused objects
@note This is called by 'handle_manager' when one wants to
periodicly flush all not used tables.
*/
static my_bool tc_purge_callback(void *_element, void *_purge_tables)
{
TDC_element *element= static_cast<TDC_element *>(_element);
Share_free_tables::List *purge_tables=
static_cast<Share_free_tables::List *>(_purge_tables);
mysql_mutex_lock(&element->LOCK_table_share);
tc_remove_all_unused_tables(element, purge_tables);
mysql_mutex_unlock(&element->LOCK_table_share);
return FALSE;
}
void tc_purge()
{
Share_free_tables::List purge_tables;
tdc_iterate(0, tc_purge_callback, &purge_tables);
while (auto table= purge_tables.pop_front())
intern_close_table(table);
}
/**
Add new TABLE object to table cache.
@pre TABLE object is used by caller.
Added object cannot be evicted or acquired.
While locked:
- add object to TABLE_SHARE::tdc.all_tables
- increment tc_count
- evict LRU object from table cache if we reached threshold
While unlocked:
- free evicted object
*/
void tc_add_table(THD *thd, TABLE *table)
{
uint32_t i=
thd->thread_id % tc_active_instances.load(std::memory_order_relaxed);
TABLE *LRU_table= 0;
TDC_element *element= table->s->tdc;
DBUG_ASSERT(table->in_use == thd);
table->instance= i;
mysql_mutex_lock(&element->LOCK_table_share);
/* Wait for MDL deadlock detector to complete traversing tdc.all_tables. */
while (element->all_tables_refs)
mysql_cond_wait(&element->COND_release, &element->LOCK_table_share);
element->all_tables.push_front(table);
mysql_mutex_unlock(&element->LOCK_table_share);
mysql_mutex_lock(&tc[i].LOCK_table_cache);
if (tc[i].records == tc_size)
{
if ((LRU_table= tc[i].free_tables.pop_front()))
{
LRU_table->s->tdc->free_tables[i].list.remove(LRU_table);
/* Needed if MDL deadlock detector chimes in before tc_remove_table() */
LRU_table->in_use= thd;
mysql_mutex_unlock(&tc[i].LOCK_table_cache);
/* Keep out of locked LOCK_table_cache */
tc_remove_table(LRU_table);
}
else
{
tc[i].records++;
mysql_mutex_unlock(&tc[i].LOCK_table_cache);
}
/* Keep out of locked LOCK_table_cache */
status_var_increment(thd->status_var.table_open_cache_overflows);
}
else
{
tc[i].records++;
mysql_mutex_unlock(&tc[i].LOCK_table_cache);
}
}
/**
Acquire TABLE object from table cache.
@pre share must be protected against removal.
Acquired object cannot be evicted or acquired again.
@return TABLE object, or NULL if no unused objects.
*/
TABLE *tc_acquire_table(THD *thd, TDC_element *element)
{
uint32_t n_instances= tc_active_instances.load(std::memory_order_relaxed);
uint32_t i= thd->thread_id % n_instances;
TABLE *table;
tc[i].lock_and_check_contention(n_instances, i);
table= element->free_tables[i].list.pop_front();
if (table)
{
DBUG_ASSERT(!table->in_use);
table->in_use= thd;
/* The ex-unused table must be fully functional. */
DBUG_ASSERT(table->db_stat && table->file);
/* The children must be detached from the table. */
DBUG_ASSERT(!table->file->extra(HA_EXTRA_IS_ATTACHED_CHILDREN));
tc[i].free_tables.remove(table);
}
mysql_mutex_unlock(&tc[i].LOCK_table_cache);
return table;
}
/**
Release TABLE object to table cache.
@pre object is used by caller.
Released object may be evicted or acquired again.
While locked:
- if object is marked for purge, decrement tc_count
- add object to TABLE_SHARE::tdc.free_tables
- evict LRU object from table cache if we reached threshold
While unlocked:
- mark object not in use by any thread
- free evicted/purged object
@note Another thread may mark share for purge any moment (even
after version check). It means to-be-purged object may go to
unused lists. This other thread is expected to call tc_purge(),
which is synchronized with us on TABLE_SHARE::tdc.LOCK_table_share.
@return
@retval true object purged
@retval false object released
*/
void tc_release_table(TABLE *table)
{
uint32 i= table->instance;
DBUG_ENTER("tc_release_table");
DBUG_ASSERT(table->in_use);
DBUG_ASSERT(table->file);
DBUG_ASSERT(!table->pos_in_locked_tables);
mysql_mutex_lock(&tc[i].LOCK_table_cache);
if (table->needs_reopen() || table->s->tdc->flushed ||
tc[i].records > tc_size)
{
tc[i].records--;
mysql_mutex_unlock(&tc[i].LOCK_table_cache);
tc_remove_table(table);
}
else
{
table->in_use= 0;
table->s->tdc->free_tables[i].list.push_front(table);
tc[i].free_tables.push_back(table);
mysql_mutex_unlock(&tc[i].LOCK_table_cache);
}
DBUG_VOID_RETURN;
}
static void tdc_assert_clean_share(TDC_element *element)
{
DBUG_ASSERT(element->share == 0);
DBUG_ASSERT(element->ref_count == 0);
DBUG_ASSERT(element->m_flush_tickets.is_empty());
DBUG_ASSERT(element->all_tables.is_empty());
#ifndef DBUG_OFF
for (uint32 i= 0; i < tc_instances; i++)
DBUG_ASSERT(element->free_tables[i].list.is_empty());
#endif
DBUG_ASSERT(element->all_tables_refs == 0);
DBUG_ASSERT(element->next == 0);
DBUG_ASSERT(element->prev == 0);
}
/**
Delete share from hash and free share object.
*/
static void tdc_delete_share_from_hash(TDC_element *element)
{
THD *thd= current_thd;
LF_PINS *pins;
TABLE_SHARE *share;
DBUG_ENTER("tdc_delete_share_from_hash");
mysql_mutex_assert_owner(&element->LOCK_table_share);
share= element->share;
DBUG_ASSERT(share);
element->share= 0;
PSI_CALL_release_table_share(share->m_psi);
share->m_psi= 0;
if (!element->m_flush_tickets.is_empty())
{
Wait_for_flush_list::Iterator it(element->m_flush_tickets);
Wait_for_flush *ticket;
while ((ticket= it++))
(void) ticket->get_ctx()->m_wait.set_status(MDL_wait::GRANTED);
do
{
mysql_cond_wait(&element->COND_release, &element->LOCK_table_share);
} while (!element->m_flush_tickets.is_empty());
}
mysql_mutex_unlock(&element->LOCK_table_share);
if (thd)
{
fix_thd_pins(thd);
pins= thd->tdc_hash_pins;
}
else
pins= lf_hash_get_pins(&tdc_hash);
DBUG_ASSERT(pins); // What can we do about it?
tdc_assert_clean_share(element);
lf_hash_delete(&tdc_hash, pins, element->m_key, element->m_key_length);
if (!thd)
lf_hash_put_pins(pins);
free_table_share(share);
DBUG_VOID_RETURN;
}
/**
Prepeare table share for use with table definition cache.
*/
static void lf_alloc_constructor(uchar *arg)
{
TDC_element *element= (TDC_element*) (arg + LF_HASH_OVERHEAD);
DBUG_ENTER("lf_alloc_constructor");
mysql_mutex_init(key_TABLE_SHARE_LOCK_table_share,
&element->LOCK_table_share, MY_MUTEX_INIT_FAST);
mysql_cond_init(key_TABLE_SHARE_COND_release, &element->COND_release, 0);
element->m_flush_tickets.empty();
element->all_tables.empty();
for (uint32 i= 0; i < tc_instances; i++)
element->free_tables[i].list.empty();
element->all_tables_refs= 0;
element->share= 0;
element->ref_count= 0;
element->next= 0;
element->prev= 0;
DBUG_VOID_RETURN;
}
/**
Release table definition cache specific resources of table share.
*/
static void lf_alloc_destructor(uchar *arg)
{
TDC_element *element= (TDC_element*) (arg + LF_HASH_OVERHEAD);
DBUG_ENTER("lf_alloc_destructor");
tdc_assert_clean_share(element);
mysql_cond_destroy(&element->COND_release);
mysql_mutex_destroy(&element->LOCK_table_share);
DBUG_VOID_RETURN;
}
static void tdc_hash_initializer(LF_HASH *,
void *_element, const void *_key)
{
TDC_element *element= static_cast<TDC_element *>(_element);
const LEX_STRING *key= static_cast<const LEX_STRING *>(_key);
memcpy(element->m_key, key->str, key->length);
element->m_key_length= (uint)key->length;
tdc_assert_clean_share(element);
}
static uchar *tdc_hash_key(const unsigned char *_element, size_t *length,
my_bool)
{
const TDC_element *element= (const TDC_element *) _element;
*length= element->m_key_length;
return (uchar*) element->m_key;
}
/**
Initialize table definition cache.
*/
bool tdc_init(void)
{
DBUG_ENTER("tdc_init");
#ifdef HAVE_PSI_INTERFACE
mysql_mutex_register("sql", all_tc_mutexes, array_elements(all_tc_mutexes));
mysql_cond_register("sql", all_tc_conds, array_elements(all_tc_conds));
#endif
/* Extra instance is allocated to avoid false sharing */
if (!(tc= new Table_cache_instance[tc_instances + 1]))
DBUG_RETURN(true);
tdc_inited= true;
mysql_mutex_init(key_LOCK_unused_shares, &LOCK_unused_shares,
MY_MUTEX_INIT_FAST);
lf_hash_init(&tdc_hash, sizeof(TDC_element) +
sizeof(Share_free_tables) * (tc_instances - 1),
LF_HASH_UNIQUE, 0, 0,
(my_hash_get_key) tdc_hash_key,
&my_charset_bin);
tdc_hash.alloc.constructor= lf_alloc_constructor;
tdc_hash.alloc.destructor= lf_alloc_destructor;
tdc_hash.initializer= (lf_hash_initializer) tdc_hash_initializer;
DBUG_RETURN(false);
}
/**
Notify table definition cache that process of shutting down server
has started so it has to keep number of TABLE and TABLE_SHARE objects
minimal in order to reduce number of references to pluggable engines.
*/
void tdc_start_shutdown(void)
{
DBUG_ENTER("tdc_start_shutdown");
if (tdc_inited)
{
/*
Ensure that TABLE and TABLE_SHARE objects which are created for
tables that are open during process of plugins' shutdown are
immediately released. This keeps number of references to engine
plugins minimal and allows shutdown to proceed smoothly.
*/
tdc_size= 0;
tc_size= 0;
/* Free all cached but unused TABLEs and TABLE_SHAREs. */
purge_tables();
}
DBUG_VOID_RETURN;
}
/**
Deinitialize table definition cache.
*/
void tdc_deinit(void)
{
DBUG_ENTER("tdc_deinit");
if (tdc_inited)
{
tdc_inited= false;
lf_hash_destroy(&tdc_hash);
mysql_mutex_destroy(&LOCK_unused_shares);
delete [] tc;
}
DBUG_VOID_RETURN;
}
/**
Get number of cached table definitions.
@return Number of cached table definitions
*/
ulong tdc_records(void)
{
return lf_hash_size(&tdc_hash);
}
void tdc_purge(bool all)
{
DBUG_ENTER("tdc_purge");
while (all || tdc_records() > tdc_size)
{
TDC_element *element;
mysql_mutex_lock(&LOCK_unused_shares);
if (!(element= unused_shares.pop_front()))
{
mysql_mutex_unlock(&LOCK_unused_shares);
break;
}
/* Concurrent thread may start using share again, reset prev and next. */
element->prev= 0;
element->next= 0;
mysql_mutex_lock(&element->LOCK_table_share);
if (element->ref_count)
{
mysql_mutex_unlock(&element->LOCK_table_share);
mysql_mutex_unlock(&LOCK_unused_shares);
continue;
}
mysql_mutex_unlock(&LOCK_unused_shares);
tdc_delete_share_from_hash(element);
}
DBUG_VOID_RETURN;
}
/**
Lock table share.
Find table share with given db.table_name in table definition cache. Return
locked table share if found.
Locked table share means:
- table share is protected against removal from table definition cache
- no other thread can acquire/release table share
Caller is expected to unlock table share with tdc_unlock_share().
@retval 0 Share not found
@retval MY_ERRPTR OOM
@retval ptr Pointer to locked table share
*/
TDC_element *tdc_lock_share(THD *thd, const char *db, const char *table_name)
{
TDC_element *element;
char key[MAX_DBKEY_LENGTH];
DBUG_ENTER("tdc_lock_share");
if (unlikely(fix_thd_pins(thd)))
DBUG_RETURN((TDC_element*) MY_ERRPTR);
element= (TDC_element *) lf_hash_search(&tdc_hash, thd->tdc_hash_pins,
(uchar*) key,
tdc_create_key(key, db, table_name));
if (element)
{
mysql_mutex_lock(&element->LOCK_table_share);
if (unlikely(!element->share || element->share->error))
{
mysql_mutex_unlock(&element->LOCK_table_share);
element= 0;
}
lf_hash_search_unpin(thd->tdc_hash_pins);
}
DBUG_RETURN(element);
}
/**
Unlock share locked by tdc_lock_share().
*/
void tdc_unlock_share(TDC_element *element)
{
DBUG_ENTER("tdc_unlock_share");
mysql_mutex_unlock(&element->LOCK_table_share);
DBUG_VOID_RETURN;
}
int tdc_share_is_cached(THD *thd, const char *db, const char *table_name)
{
char key[MAX_DBKEY_LENGTH];
if (unlikely(fix_thd_pins(thd)))
return -1;
if (lf_hash_search(&tdc_hash, thd->tdc_hash_pins, (uchar*) key,
tdc_create_key(key, db, table_name)))
{
lf_hash_search_unpin(thd->tdc_hash_pins);
return 1;
}
return 0;
}
/*
Get TABLE_SHARE for a table.
tdc_acquire_share()
thd Thread handle
tl Table that should be opened
flags operation: what to open table or view
out_table TABLE for the requested table
IMPLEMENTATION
Get a table definition from the table definition cache.
If it doesn't exist, create a new from the table definition file.
RETURN
0 Error
# Share for table
*/
TABLE_SHARE *tdc_acquire_share(THD *thd, TABLE_LIST *tl, uint flags,
TABLE **out_table)
{
TABLE_SHARE *share;
TDC_element *element;
const char *key;
uint key_length= get_table_def_key(tl, &key);
my_hash_value_type hash_value= tl->mdl_request.key.tc_hash_value();
bool was_unused;
DBUG_ENTER("tdc_acquire_share");
if (fix_thd_pins(thd))
DBUG_RETURN(0);
retry:
while (!(element= (TDC_element*) lf_hash_search_using_hash_value(&tdc_hash,
thd->tdc_hash_pins, hash_value, (uchar*) key, key_length)))
{
LEX_STRING tmp= { const_cast<char*>(key), key_length };
int res= lf_hash_insert(&tdc_hash, thd->tdc_hash_pins, (uchar*) &tmp);
if (res == -1)
DBUG_RETURN(0);
else if (res == 1)
continue;
element= (TDC_element*) lf_hash_search_using_hash_value(&tdc_hash,
thd->tdc_hash_pins, hash_value, (uchar*) key, key_length);
/* It's safe to unpin the pins here, because an empty element was inserted
above, "empty" means at least element->share = 0. Some other thread can't
delete it while element->share == 0. And element->share is also protected
with element->LOCK_table_share mutex. */
lf_hash_search_unpin(thd->tdc_hash_pins);
DBUG_ASSERT(element);
if (!(share= alloc_table_share(tl->db.str, tl->table_name.str, key, key_length)))
{
lf_hash_delete(&tdc_hash, thd->tdc_hash_pins, key, key_length);
DBUG_RETURN(0);
}
/* note that tdc_acquire_share() *always* uses discovery */
open_table_def(thd, share, flags | GTS_USE_DISCOVERY);
if (checked_unlikely(share->error))
{
free_table_share(share);
lf_hash_delete(&tdc_hash, thd->tdc_hash_pins, key, key_length);
DBUG_RETURN(0);
}
mysql_mutex_lock(&element->LOCK_table_share);
element->share= share;
share->tdc= element;
element->ref_count++;
element->flushed= false;
mysql_mutex_unlock(&element->LOCK_table_share);
tdc_purge(false);
if (out_table)
{
status_var_increment(thd->status_var.table_open_cache_misses);
*out_table= 0;
}
share->m_psi= PSI_CALL_get_table_share(false, share);
goto end;
}
/* cannot force discovery of a cached share */
DBUG_ASSERT(!(flags & GTS_FORCE_DISCOVERY));
if (out_table && (flags & GTS_TABLE))
{
if ((*out_table= tc_acquire_table(thd, element)))
{
lf_hash_search_unpin(thd->tdc_hash_pins);
DBUG_ASSERT(!(flags & GTS_NOLOCK));
DBUG_ASSERT(element->share);
DBUG_ASSERT(!element->share->error);
DBUG_ASSERT(!element->share->is_view);
status_var_increment(thd->status_var.table_open_cache_hits);
DBUG_RETURN(element->share);
}
status_var_increment(thd->status_var.table_open_cache_misses);
}
mysql_mutex_lock(&element->LOCK_table_share);
if (!(share= element->share))
{
mysql_mutex_unlock(&element->LOCK_table_share);
lf_hash_search_unpin(thd->tdc_hash_pins);
goto retry;
}
lf_hash_search_unpin(thd->tdc_hash_pins);
/*
We found an existing table definition. Return it if we didn't get
an error when reading the table definition from file.
*/
if (unlikely(share->error))
{
open_table_error(share, share->error, share->open_errno);
goto err;
}
if (share->is_view && !(flags & GTS_VIEW))
{
open_table_error(share, OPEN_FRM_NOT_A_TABLE, ENOENT);
goto err;
}
if (!share->is_view && !(flags & GTS_TABLE))
{
open_table_error(share, OPEN_FRM_NOT_A_VIEW, ENOENT);
goto err;
}
was_unused= !element->ref_count;
element->ref_count++;
mysql_mutex_unlock(&element->LOCK_table_share);
if (was_unused)
{
mysql_mutex_lock(&LOCK_unused_shares);
if (element->prev)
{
/*
Share was not used before and it was in the old_unused_share list
Unlink share from this list
*/
DBUG_PRINT("info", ("Unlinking from not used list"));
unused_shares.remove(element);
element->next= 0;
element->prev= 0;
}
mysql_mutex_unlock(&LOCK_unused_shares);
}
end:
DBUG_PRINT("exit", ("share: %p ref_count: %u",
share, share->tdc->ref_count));
if (flags & GTS_NOLOCK)
{
tdc_release_share(share);
/*
if GTS_NOLOCK is requested, the returned share pointer cannot be used,
the share it points to may go away any moment.
But perhaps the caller is only interested to know whether a share or
table existed?
Let's return an invalid pointer here to catch dereferencing attempts.
*/
share= UNUSABLE_TABLE_SHARE;
}
DBUG_RETURN(share);
err:
mysql_mutex_unlock(&element->LOCK_table_share);
DBUG_RETURN(0);
}
/**
Release table share acquired by tdc_acquire_share().
*/
void tdc_release_share(TABLE_SHARE *share)
{
DBUG_ENTER("tdc_release_share");
mysql_mutex_lock(&share->tdc->LOCK_table_share);
DBUG_PRINT("enter",
("share: %p table: %s.%s ref_count: %u",
share, share->db.str, share->table_name.str,
share->tdc->ref_count));
DBUG_ASSERT(share->tdc->ref_count);
if (share->tdc->ref_count > 1)
{
share->tdc->ref_count--;
if (!share->is_view)
mysql_cond_broadcast(&share->tdc->COND_release);
mysql_mutex_unlock(&share->tdc->LOCK_table_share);
DBUG_VOID_RETURN;
}
mysql_mutex_unlock(&share->tdc->LOCK_table_share);
mysql_mutex_lock(&LOCK_unused_shares);
mysql_mutex_lock(&share->tdc->LOCK_table_share);
if (--share->tdc->ref_count)
{
if (!share->is_view)
mysql_cond_broadcast(&share->tdc->COND_release);
mysql_mutex_unlock(&share->tdc->LOCK_table_share);
mysql_mutex_unlock(&LOCK_unused_shares);
DBUG_VOID_RETURN;
}
if (share->tdc->flushed || tdc_records() > tdc_size)
{
mysql_mutex_unlock(&LOCK_unused_shares);
tdc_delete_share_from_hash(share->tdc);
DBUG_VOID_RETURN;
}
/* Link share last in used_table_share list */
DBUG_PRINT("info", ("moving share to unused list"));
DBUG_ASSERT(share->tdc->next == 0);
unused_shares.push_back(share->tdc);
mysql_mutex_unlock(&share->tdc->LOCK_table_share);
mysql_mutex_unlock(&LOCK_unused_shares);
DBUG_VOID_RETURN;
}
void tdc_remove_referenced_share(THD *thd, TABLE_SHARE *share)
{
DBUG_ASSERT(thd->mdl_context.is_lock_owner(MDL_key::TABLE, share->db.str,
share->table_name.str,
MDL_EXCLUSIVE));
share->tdc->flush_unused(false);
mysql_mutex_lock(&share->tdc->LOCK_table_share);
share->tdc->wait_for_refs(1);
DBUG_ASSERT(share->tdc->all_tables.is_empty());
share->tdc->ref_count--;
tdc_delete_share_from_hash(share->tdc);
}
/**
Removes all TABLE instances and corresponding TABLE_SHARE
@param thd Thread context
@param db Name of database
@param table_name Name of table
@note It assumes that table instances are already not used by any
(other) thread (this should be achieved by using meta-data locks).
*/
void tdc_remove_table(THD *thd, const char *db, const char *table_name)
{
TDC_element *element;
DBUG_ENTER("tdc_remove_table");
DBUG_PRINT("enter", ("name: %s", table_name));
DBUG_ASSERT(thd->mdl_context.is_lock_owner(MDL_key::TABLE, db, table_name,
MDL_EXCLUSIVE));
mysql_mutex_lock(&LOCK_unused_shares);
if (!(element= tdc_lock_share(thd, db, table_name)))
{
mysql_mutex_unlock(&LOCK_unused_shares);
DBUG_VOID_RETURN;
}
DBUG_ASSERT(element != MY_ERRPTR); // What can we do about it?
if (!element->ref_count)
{
if (element->prev)
{
unused_shares.remove(element);
element->prev= 0;
element->next= 0;
}
mysql_mutex_unlock(&LOCK_unused_shares);
tdc_delete_share_from_hash(element);
DBUG_VOID_RETURN;
}
mysql_mutex_unlock(&LOCK_unused_shares);
element->ref_count++;
mysql_mutex_unlock(&element->LOCK_table_share);
/* We have to relock the mutex to avoid code duplication. Sigh. */
tdc_remove_referenced_share(thd, element->share);
DBUG_VOID_RETURN;
}
/**
Check if table's share is being removed from the table definition
cache and, if yes, wait until the flush is complete.
@param thd Thread context.
@param table_list Table which share should be checked.
@param timeout Timeout for waiting.
@param deadlock_weight Weight of this wait for deadlock detector.
@retval 0 Success. Share is up to date or has been flushed.
@retval 1 Error (OOM, was killed, the wait resulted
in a deadlock or timeout). Reported.
*/
int tdc_wait_for_old_version(THD *thd, const char *db, const char *table_name,
ulong wait_timeout, uint deadlock_weight)
{
TDC_element *element;
if (!(element= tdc_lock_share(thd, db, table_name)))
return FALSE;
else if (element == MY_ERRPTR)
return TRUE;
else if (element->flushed)
{
struct timespec abstime;
set_timespec(abstime, wait_timeout);
return element->share->wait_for_old_version(thd, &abstime, deadlock_weight);
}
tdc_unlock_share(element);
return FALSE;
}
/**
Iterate table definition cache.
Object is protected against removal from table definition cache.
@note Returned TABLE_SHARE is not guaranteed to be fully initialized:
tdc_acquire_share() added new share, but didn't open it yet. If caller
needs fully initializer share, it must lock table share mutex.
*/
struct eliminate_duplicates_arg
{
HASH hash;
MEM_ROOT root;
my_hash_walk_action action;
void *argument;
};
static uchar *eliminate_duplicates_get_key(const uchar *element, size_t *length,
my_bool)
{
LEX_STRING *key= (LEX_STRING *) element;
*length= key->length;
return (uchar *) key->str;
}
static my_bool eliminate_duplicates(void *el, void *a)
{
TDC_element *element= static_cast<TDC_element*>(el);
eliminate_duplicates_arg *arg= static_cast<eliminate_duplicates_arg*>(a);
LEX_STRING *key= (LEX_STRING *) alloc_root(&arg->root, sizeof(LEX_STRING));
if (!key || !(key->str= (char*) memdup_root(&arg->root, element->m_key,
element->m_key_length)))
return TRUE;
key->length= element->m_key_length;
if (my_hash_insert(&arg->hash, (uchar *) key))
return FALSE;
return arg->action(element, arg->argument);
}
int tdc_iterate(THD *thd, my_hash_walk_action action, void *argument,
bool no_dups)
{
eliminate_duplicates_arg no_dups_argument;
LF_PINS *pins;
myf alloc_flags= 0;
uint hash_flags= HASH_UNIQUE;
int res;
if (thd)
{
fix_thd_pins(thd);
pins= thd->tdc_hash_pins;
alloc_flags= MY_THREAD_SPECIFIC;
hash_flags|= HASH_THREAD_SPECIFIC;
}
else
pins= lf_hash_get_pins(&tdc_hash);
if (!pins)
return ER_OUTOFMEMORY;
if (no_dups)
{
init_alloc_root(PSI_INSTRUMENT_ME, &no_dups_argument.root, 4096, 4096, MYF(alloc_flags));
my_hash_init(PSI_INSTRUMENT_ME, &no_dups_argument.hash, &my_charset_bin,
tdc_records(), 0, 0, eliminate_duplicates_get_key, 0,
hash_flags);
no_dups_argument.action= action;
no_dups_argument.argument= argument;
action= eliminate_duplicates;
argument= &no_dups_argument;
}
res= lf_hash_iterate(&tdc_hash, pins, action, argument);
if (!thd)
lf_hash_put_pins(pins);
if (no_dups)
{
my_hash_free(&no_dups_argument.hash);
free_root(&no_dups_argument.root, MYF(0));
}
return res;
}
int show_tc_active_instances(THD *thd, SHOW_VAR *var, void *buff,
system_status_var *, enum enum_var_type scope)
{
var->type= SHOW_UINT;
var->value= buff;
*(reinterpret_cast<uint32_t*>(buff))=
tc_active_instances.load(std::memory_order_relaxed);
return 0;
}
/**
Waits until ref_count goes down to given number
@param my_refs Number of references owned by the caller
Caller must own at least one TABLE_SHARE reference.
Even though current thread holds exclusive metadata lock on this share,
concurrent FLUSH TABLES threads may be in process of closing unused table
instances belonging to this share. E.g.:
thr1 (FLUSH TABLES): table= share->tdc.free_tables.pop_front();
thr1 (FLUSH TABLES): share->tdc.all_tables.remove(table);
thr2 (ALTER TABLE): tdc_remove_table();
thr1 (FLUSH TABLES): intern_close_table(table);
Current remove type assumes that all table instances (except for those
that are owned by current thread) must be closed before
thd_remove_table() returns. Wait for such tables now.
intern_close_table() decrements ref_count and signals COND_release. When
ref_count drops down to number of references owned by current thread
waiting is completed.
Unfortunately TABLE_SHARE::wait_for_old_version() cannot be used here
because it waits for all table instances, whereas we have to wait only
for those that are not owned by current thread.
*/
void TDC_element::wait_for_refs(uint my_refs)
{
while (ref_count > my_refs)
mysql_cond_wait(&COND_release, &LOCK_table_share);
}
/**
Flushes unused TABLE instances
@param thd Thread context
@param mark_flushed Whether to destroy TABLE_SHARE when released
Caller is allowed to own used TABLE instances.
There must be no TABLE objects used by other threads and caller must own
exclusive metadata lock on the table.
*/
void TDC_element::flush(THD *thd, bool mark_flushed)
{
DBUG_ASSERT(thd->mdl_context.is_lock_owner(MDL_key::TABLE, share->db.str,
share->table_name.str,
MDL_EXCLUSIVE));
flush_unused(mark_flushed);
mysql_mutex_lock(&LOCK_table_share);
All_share_tables_list::Iterator it(all_tables);
uint my_refs= 0;
while (auto table= it++)
{
if (table->in_use == thd)
my_refs++;
}
wait_for_refs(my_refs);
#ifndef DBUG_OFF
it.rewind();
while (auto table= it++)
DBUG_ASSERT(table->in_use == thd);
#endif
mysql_mutex_unlock(&LOCK_table_share);
}
/**
Flushes unused TABLE instances
*/
void TDC_element::flush_unused(bool mark_flushed)
{
Share_free_tables::List purge_tables;
mysql_mutex_lock(&LOCK_table_share);
if (mark_flushed)
flushed= true;
tc_remove_all_unused_tables(this, &purge_tables);
mysql_mutex_unlock(&LOCK_table_share);
while (auto table= purge_tables.pop_front())
intern_close_table(table);
}
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