Lock system

The lock subsystem provides interprocess and intraprocess concurrency control mechanisms. While the locking system is used extensively by the Berkeley DB access methods and transaction system, it may also be used as a stand-alone subsystem to provide concurrency control to any set of designated resources.

The lock subsystem is created, initialized, and opened by calls to BDB::Env#open with the DBD::INIT_LOCK or DBB::INIT_CDB flags specified.

The following options can be given when the environnement is created

"set_lk_conflicts"

Set lock conflicts matrix

"set_lk_detect"

Set automatic deadlock detection

"set_lk_max"

Set maximum number of locks

BDB::LockError

Exception generated by lock call

BDB::LockHeld

Lock not held by locker

BDB::LockGranted

Lock not granted

BDB::LockDead

Locker killed to resolve a deadlock

BDB::Lockid

A lock ID can be obtained with BDB::Env#lock_id

See also BDB::Env#lock_stat and BDB::Env#lock_detect

Methods

get(string, mode , flags = 0)

lock_get(string, mode [, flags])

The lock_get function acquires a lock from the lock table, it return an object BDB::Lock

string specifies the object to be locked or released.

mode is an index into the environment's lock conflict array

flags value must be set to 0 or the value BDBD::LOCK_NOWAIT in this case if a lock cannot be granted because the requested lock conflicts with an existing lock, raise an error BDB::LockGranted

vec(array , flags = 0)

lock_vec(array [, flags])

The lock_vec function atomically obtains and releases one or more locks from the lock table. The lock_vec function is intended to support acquisition or trading of multiple locks under one lock table semaphore, as is needed for lock coupling or in multigranularity locking for lock escalation.

array

ARRAY of HASH with the following keys

"op"

the operation to be performed, which must be set to one of the following values BDB::LOCK_GET, BDB::LOCK_PUT, BDB::LOCK_PUT_ALL or BDB::LOCK_PUT_OBJ

"obj"

the object (String) to be locked or released

"mode"

is an index into the environment's lock conflict array

"lock"

an object BDB::Lock

flags

value must be set to 0 or the value BDBD::LOCK_NOWAIT in this case if a lock cannot be granted because the requested lock conflicts with an existing lock, raise an error BDB::LockGrantedreturn immediately

BDB::Lock

Methods

put()

lock_put()

release()

delete()

The lock_put function releases lock from the lock table.