Classes
struct	Conflicting

class	Global_exclusive_latch_guard
	A RAII helper which latches global_latch in exclusive mode during constructor, and unlatches it during destruction, preventing any other threads from activity within lock_sys for it's entire scope. More...

class	Global_exclusive_try_latch
	A RAII helper which tries to exclusively latch the global_lach in constructor and unlatches it, if needed, during destruction, preventing any other threads from activity within lock_sys for it's entire scope, if owns_lock(). More...

class	Global_shared_latch_guard
	A RAII helper which latches global_latch in shared mode during constructor, and unlatches it during destruction, preventing any other thread from acquiring exclusive latch. More...

class	Latches
	The class which handles the logic of latching of lock_sys queues themselves. More...

class	Shard_latch_guard
	A RAII wrapper class which combines Global_shared_latch_guard and Shard_naked_latch_guard to s-latch the global lock_sys latch and latch the mutex protecting the specified shard for the duration of its scope. More...

class	Shard_latches_guard
	A RAII wrapper class which s-latches the global lock_sys shard, and mutexes protecting specified shards for the duration of its scope. More...

class	Shard_naked_latch_guard
	A RAII helper which latches the mutex protecting given shard during constructor, and unlatches it during destruction. More...

class	Shard_naked_latches_guard
	A RAII helper which latches the mutexes protecting specified shards for the duration of its scope. More...

class	Trx_locks_cache
	An object which can be passed to consecutive calls to rec_lock_has_to_wait(trx, mode, lock, is_supremum, trx_locks_cache) for the same trx and heap_no (which is implicitly the bit common to all lock objects passed) which can be used by this function to cache some partial results. More...

class	Unsafe_global_latch_manipulator

Enumerations
enum class	Conflict { HAS_TO_WAIT , NO_CONFLICT , CAN_BYPASS }

Functions
const lock_t *	find_blockers (const lock_t &wait_lock, std::function< bool(const lock_t &)> visitor)
	Calls visitor for each lock_t object which is a reason that wait_lock has to wait. More...

void	find_on_table (const table_id_t table_id, std::function< bool(const lock_t &)> visitor)
	A helper method to access dict_table_t::locks list in a way which is safe against the case another thread is trying to drop or truncate the table. More...

bool	has_to_wait (const lock_t lock1, const lock_t lock2, Trx_locks_cache &lock1_cache)
	Checks if a lock request lock1 has to wait for request lock2. More...

bool	owns_exclusive_global_latch ()
	Tests if lock_sys latch is exclusively owned by the current thread. More...

bool	owns_shared_global_latch ()
	Tests if lock_sys latch is owned in shared mode by the current thread. More...

bool	owns_page_shard (const page_id_t &page_id)
	Tests if given page shard can be safely accessed by the current thread. More...

bool	owns_table_shard (const dict_table_t &table)
	Test if given table shard can be safely accessed by the current thread. More...

bool	owns_lock_shard (const lock_t *lock)
	Checks if shard which contains lock is latched (or that an exclusive latch on whole lock_sys is held) by current thread. More...

template<typename F >
auto	latch_peeked_shard_and_do (const lock_t *peeked_lock, F &&f)
	Temporarily releases trx->mutex, latches the lock-sys shard containing peeked_lock and latches trx->mutex again and calls f under protection of both latches. More...

template<typename F >
void	run_if_waiting (const TrxVersion trx_version, F &&f)
	Given a pointer to trx (which the caller guarantees will not be freed) and the expected value of trx->version, will call the provided function f, only if the trx is still in expected version and waiting for a lock, within a critical section which holds latches on the trx, and the shard containing the waiting lock. More...

static Conflict	rec_lock_check_conflict (const trx_t trx, ulint type_mode, const lock_t lock2, bool lock_is_on_supremum, Trx_locks_cache &trx_locks_cache)
	Checks if a new request for a record lock has to wait for existing request. More...

static bool	rec_lock_has_to_wait (const lock_t lock1, const lock_t lock2, Trx_locks_cache &lock1_cache)
	Checks if a record lock request lock1 has to wait for request lock2. More...

static void	add_to_trx_locks (lock_t *lock)
	Adds the lock to the list of trx's locks. More...

static void	remove_from_trx_locks (lock_t *lock)
	Removes the lock from the list of trx's locks. More...

template<typename F >
static bool	try_relatch_trx_and_shard_and_do (const lock_t *lock, F &&f)
	A helper function which solves a chicken-and-egg problem occurring when one needs to iterate over trx's locks and perform some actions on them. More...

static bool	try_release_read_locks_in_s_mode (trx_t *trx, bool only_gap)
	Tries to release read locks of a transaction without latching the whole lock sys. More...

static bool	try_release_read_locks_in_x_mode (trx_t *trx, bool only_gap)
	Release read locks of a transaction latching the whole lock-sys in exclusive mode, which is a bit too expensive to do by default. More...

static bool	try_release_all_locks (trx_t *trx)
	Releases transaction locks, and releases possible other transactions waiting because of these locks. More...

static void	rec_queue_validate_latched (const buf_block_t block, const rec_t rec, const dict_index_t index, const ulint offsets)
	Validates the lock queue on a single record. More...

static void	rec_queue_latch_and_validate (const buf_block_t block, const rec_t rec, const dict_index_t index, const ulint offsets)
	Validates the lock queue on a single record. More...

static void	rec_queue_latch_and_validate (const buf_block_t block, const rec_t rec, const dict_index_t *index)
	Validates the lock queue on a single record. More...

Variables
constexpr auto	MAX_CS_DURATION = std::chrono::seconds{1}
	We don't want to hold the Global latch for too long, even in S mode, not to starve threads waiting for X-latch on it such as lock_wait_timeout_thread(). More...

Enumeration Type Documentation

◆ Conflict

enum class locksys::Conflict

strong

Enumerator
HAS_TO_WAIT
NO_CONFLICT
CAN_BYPASS

Function Documentation

◆ add_to_trx_locks()

static void locksys::add_to_trx_locks ( lock_t * lock )

static

Adds the lock to the list of trx's locks.

Requires lock->trx to be already set. Bumps the trx_lock_version.

Parameters

[in,out] lock The lock that we want to add to lock->trx->lock.trx_locks

◆ find_blockers()

const lock_t * locksys::find_blockers	(	const lock_t &	wait_lock,
		std::function< bool(const lock_t &)>	visitor
	)

Calls visitor for each lock_t object which is a reason that wait_lock has to wait.

It is assumed that the wait_lock is waiting, and the caller has latched the shard which contains the wait_lock

Parameters

[in]	wait_lock	the waiting lock
[in]	visitor	a function to be called for each lock, s.t. locksys::has_to_wait(wait_lock, lock) is true. To stop iteration the visitor can return true, in which case the lock for which it happened will be returned.

Returns: the first lock for which visitor returned true (in which case the search ends) or nullptr if visitor never returned true (so all waiters were visited).

◆ find_on_table()

void locksys::find_on_table	(	const table_id_t	table_id,
		std::function< bool(const lock_t &)>	visitor
	)

A helper method to access dict_table_t::locks list in a way which is safe against the case another thread is trying to drop or truncate the table.

The main challenge it solves is how to do that without acquiring an MDL.

Parameters

[in]	table_id	The id of the table, locks of which we want to visit
[in]	visitor	The visitor function which will be called for each lock on the table. It might be not called at all, in case the table is no longer found in the hash, or has no locks. If it is called, then it is called under protection of shard mutex for this table_id. To stop iteration the visitor can return true.

◆ has_to_wait()

bool locksys::has_to_wait	(	const lock_t *	lock1,
		const lock_t *	lock2,
		Trx_locks_cache &	lock1_cache
	)

Checks if a lock request lock1 has to wait for request lock2.

It returns the same result as

See also: lock_has_to_wait(lock1, lock2), but in case these are record locks, it might use lock1_cache object to speed up the computation. If the same lock1_cache is passed to multiple calls of this method, then lock1 also needs to be the same.

Parameters

[in]	lock1	A waiting lock
[in]	lock2	Another lock; NOTE that it is assumed that this has a lock bit set on the same record as in lock1 if the locks are record locks.
[in]	lock1_cache	An object which can be passed to consecutive calls to this function for the same lock1 which can be used by this function to cache some partial results.

Returns: true if lock1 has to wait for lock2 to be removed

◆ latch_peeked_shard_and_do()

template<typename F >

auto locksys::latch_peeked_shard_and_do	(	const lock_t *	peeked_lock,
		F &&	f
	)

Temporarily releases trx->mutex, latches the lock-sys shard containing peeked_lock and latches trx->mutex again and calls f under protection of both latches.

The latch on lock-sys shard will be released immediately after f returns. It is a responsibility of the caller to handle shared lock-sys latch, trx->mutex and verify inside f that the trx has not been finished, and the lock was not released meanwhile.

Parameters

[in]	peeked_lock	A lock of the trx. (While trx->mutex is held it can't be freed, but can be released). It is used to determine the lock-sys shard to latch.
[in]	f	The callback to call once the lock-sys shard is latched and trx->mutex is relatched.

Returns: The value returned by f.

◆ owns_exclusive_global_latch()

bool locksys::owns_exclusive_global_latch ( )

Tests if lock_sys latch is exclusively owned by the current thread.

Returns: true iff the current thread owns exclusive global lock_sys latch

◆ owns_lock_shard()

bool locksys::owns_lock_shard ( const lock_t * lock )

Checks if shard which contains lock is latched (or that an exclusive latch on whole lock_sys is held) by current thread.

Parameters

[in] lock lock which belongs to a shard we want to check

Returns: true iff the current thread owns exclusive global lock_sys latch or both a shared global lock_sys latch and mutex protecting the shard containing the specified lock

◆ owns_page_shard()

bool locksys::owns_page_shard ( const page_id_t & page_id )

Tests if given page shard can be safely accessed by the current thread.

Parameters

page_id specifies the page

Returns: true iff the current thread owns exclusive global lock_sys latch or both a shared global lock_sys latch and mutex protecting the page shard

◆ owns_shared_global_latch()

bool locksys::owns_shared_global_latch ( )

Tests if lock_sys latch is owned in shared mode by the current thread.

Returns: true iff the current thread owns shared global lock_sys latch

◆ owns_table_shard()

bool locksys::owns_table_shard ( const dict_table_t & table )

Test if given table shard can be safely accessed by the current thread.

Parameters

table the table

Returns: true iff the current thread owns exclusive global lock_sys latch or both a shared global lock_sys latch and mutex protecting the table shard

◆ rec_lock_check_conflict()

static Conflict locksys::rec_lock_check_conflict	(	const trx_t *	trx,
		ulint	type_mode,
		const lock_t *	lock2,
		bool	lock_is_on_supremum,
		Trx_locks_cache &	trx_locks_cache
	)

inlinestatic

Checks if a new request for a record lock has to wait for existing request.

Parameters

[in]	trx	The trx requesting the new lock
[in]	type_mode	precise mode of the new lock to set: LOCK_S or LOCK_X, possibly ORed to LOCK_GAP or LOCK_REC_NOT_GAP, LOCK_INSERT_INTENTION
[in]	lock2	another record lock; NOTE that it is assumed that this has a lock bit set on the same record as in the new lock we are setting
[in]	lock_is_on_supremum	true if we are setting the lock on the 'supremum' record of an index page: we know then that the lock request is really for a 'gap' type lock
[in]	trx_locks_cache	An object which can be passed to consecutive calls to this function for the same trx and heap_no (which is implicitly the bit common to all lock2 objects passed) which can be used by this function to cache some partial results.

Return values

NO_CONFLICT	the trx does not have to wait for lock2
CAN_BYPASS	the trx does not have to wait for lock2, as it can bypass it
HAS_TO_WAIT	the trx has to wait for lock2

◆ rec_lock_has_to_wait()

static bool locksys::rec_lock_has_to_wait	(	const lock_t *	lock1,
		const lock_t *	lock2,
		Trx_locks_cache &	lock1_cache
	)

inlinestatic

Checks if a record lock request lock1 has to wait for request lock2.

Parameters

[in]	lock1	waiting record lock
[in]	lock2	another record lock; NOTE that it is assumed that this has a lock bit set on the same record as in lock1
[in]	lock1_cache	Cached info gathered during calls with lock1

Returns: true if lock1 has to wait for lock2 to be removed

◆ rec_queue_latch_and_validate() [1/2]

static void locksys::rec_queue_latch_and_validate	(	const buf_block_t *	block,
		const rec_t *	rec,
		const dict_index_t *	index
	)

static

Validates the lock queue on a single record.

Parameters

[in]	block	buffer block containing rec
[in]	rec	record to look at
[in]	index	index, or NULL if not known

◆ rec_queue_latch_and_validate() [2/2]

static void locksys::rec_queue_latch_and_validate	(	const buf_block_t *	block,
		const rec_t *	rec,
		const dict_index_t *	index,
		const ulint *	offsets
	)

static

Validates the lock queue on a single record.

Parameters

[in]	block	buffer block containing rec
[in]	rec	record to look at
[in]	index	index, or NULL if not known
[in]	offsets	rec_get_offsets(rec, index)

◆ rec_queue_validate_latched()

static void locksys::rec_queue_validate_latched	(	const buf_block_t *	block,
		const rec_t *	rec,
		const dict_index_t *	index,
		const ulint *	offsets
	)

static

Validates the lock queue on a single record.

Parameters

[in]	block	buffer block containing rec
[in]	rec	record to look at
[in]	index	index, or NULL if not known
[in]	offsets	rec_get_offsets(rec, index)

◆ remove_from_trx_locks()

static void locksys::remove_from_trx_locks ( lock_t * lock )

static

Removes the lock from the list of trx's locks.

Bumps the trx_lock_version.

Parameters

[in,out] lock The lock that we want to remove from lock->trx->lock.trx_locks

◆ run_if_waiting()

template<typename F >

void locksys::run_if_waiting	(	const TrxVersion	trx_version,
		F &&	f
	)

Given a pointer to trx (which the caller guarantees will not be freed) and the expected value of trx->version, will call the provided function f, only if the trx is still in expected version and waiting for a lock, within a critical section which holds latches on the trx, and the shard containing the waiting lock.

If the transaction has meanwhile finished waiting for a lock, or committed or rolled back etc. the f will not be called. It may happen that the lock for which the trx is waiting during exectuion of f is not the same as the lock it was waiting at the moment of invocation.

Parameters

[in]	trx_version	The version of the trx that we intend to wake up
[in]	f	The callback to call if trx is still waiting for a lock and is still in version trx_version

◆ try_relatch_trx_and_shard_and_do()

template<typename F >

static bool locksys::try_relatch_trx_and_shard_and_do	(	const lock_t *	lock,
		F &&	f
	)

static

A helper function which solves a chicken-and-egg problem occurring when one needs to iterate over trx's locks and perform some actions on them.

Iterating over this list requires trx->mutex (or exclusive global lock_sys latch), and operating on a lock requires lock_sys latches, yet the latching order requires lock_sys latches to be taken before trx->mutex. One way around it is to use exclusive global lock_sys latch, which heavily deteriorates concurrency. Another is to try to reacquire the latches in needed order, veryfing that the list wasn't modified meanwhile. This function performs following steps:

releases trx->mutex,
acquires proper lock_sys shard latch for given lock,
reaquires trx->mutex
executes f unless trx's locks list has changed Before and after this function following should hold:

the shared global lock_sys latch is held
the trx->mutex is held
Parameters

[in] lock the lock we are interested in

[in] f the function to execute when the shard is latched

Returns
true if f was called, false if it couldn't be called because trx locks have changed while relatching trx->mutex

◆ try_release_all_locks()

static bool locksys::try_release_all_locks ( trx_t * trx )

static

Releases transaction locks, and releases possible other transactions waiting because of these locks.

Parameters

[in,out] trx transaction

Returns: true if and only if it succeeded to do the job

◆ try_release_read_locks_in_s_mode()

static bool locksys::try_release_read_locks_in_s_mode	(	trx_t *	trx,
		bool	only_gap
	)

static

Tries to release read locks of a transaction without latching the whole lock sys.

This may fail, if there are many concurrent threads editing the list of locks of this transaction (for example due to B-tree pages being merged or split, or due to implicit-to-explicit conversion). It is called during XA prepare to release locks early.

Parameters

[in,out]	trx	transaction
[in]	only_gap	release only GAP locks

Returns: true if and only if it succeeded to do the job

◆ try_release_read_locks_in_x_mode()

static bool locksys::try_release_read_locks_in_x_mode	(	trx_t *	trx,
		bool	only_gap
	)

static

Release read locks of a transaction latching the whole lock-sys in exclusive mode, which is a bit too expensive to do by default.

It is called during XA prepare to release locks early.

Parameters

[in,out]	trx	transaction
[in]	only_gap	release only GAP locks

Returns: true if and only if it succeeded to do the job

Variable Documentation

◆ MAX_CS_DURATION

constexpr auto locksys::MAX_CS_DURATION = std::chrono::seconds{1}

constexpr

We don't want to hold the Global latch for too long, even in S mode, not to starve threads waiting for X-latch on it such as lock_wait_timeout_thread().

This defines the longest allowed critical section duration.

[in]	lock	the lock we are interested in
[in]	f	the function to execute when the shard is latched

Classes

Enumerations

Functions

Variables

Enumeration Type Documentation

◆ Conflict

Function Documentation

◆ add_to_trx_locks()

◆ find_blockers()

◆ find_on_table()

◆ has_to_wait()

◆ latch_peeked_shard_and_do()

◆ owns_exclusive_global_latch()

◆ owns_lock_shard()

◆ owns_page_shard()

◆ owns_shared_global_latch()

◆ owns_table_shard()

◆ rec_lock_check_conflict()

◆ rec_lock_has_to_wait()

◆ rec_queue_latch_and_validate() [1/2]

◆ rec_queue_latch_and_validate() [2/2]

◆ rec_queue_validate_latched()

◆ remove_from_trx_locks()

◆ run_if_waiting()

◆ try_relatch_trx_and_shard_and_do()

◆ try_release_all_locks()

◆ try_release_read_locks_in_s_mode()

◆ try_release_read_locks_in_x_mode()

Variable Documentation

◆ MAX_CS_DURATION