docs/lock.rd

## 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.