Berkeley DB: lock_vec
Description: Berkeley DB: An embedded database programmatic toolkit.
Keywords: embedded,database,programmatic,toolkit,b+tree,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,java,C,C++

# lock_vec |

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    #include <db.h>

    int
    lock_vec(DB_ENV *env, u_int32_t locker, u_int32_t flags,
        DB_LOCKREQ list[], int nlist, DB_LOCKREQ **elistp);

# Description

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.

The locker argument specified to lock_vec is an unsigned 32-bit integer quantity. It represents the entity requesting or releasing the lock.

The flags value must be set to 0 or the following value:

DB_LOCK_NOWAIT
  If a lock cannot be immediately granted because the requested lock conflicts with an existing lock, return instead of waiting for the lock to become available.

The list array provided to lock_vec is typedef'd as DB_LOCKREQ. A DB_LOCKREQ structure has at least the following fields, which must be initialized before calling lock_vec:

lockop_t op;
  The operation to be performed, which must be set to one of the following values:

  DB_LOCK_GET
    Get a lock, as defined by the values of locker, obj, and mode. Upon return from lock_vec, if the lock field is non-NULL, a reference to the acquired lock is stored there. (This reference is invalidated by any call to lock_vec or lock_put that releases the lock.)

  DB_LOCK_PUT
    The lock referenced by the contents of the lock field is released.

  DB_LOCK_PUT_ALL
    All locks held by the locker are released. (Any locks acquired as a part of the current call to lock_vec that appear after the DB_LOCK_PUT_ALL entry are not considered for this operation).

  DB_LOCK_PUT_OBJ
    All locks held on the object obj are released. The mode and locker parameters are ignored. Note that any locks acquired as a part of the current call to lock_vec that occur before the DB_LOCK_PUT_OBJ will also be released; those acquired afterwards will not be released.

const DBT obj;
  An untyped byte string that specifies the object to be locked or released.

const lockmode_t mode;
  The lock mode, used as an index into the environment's lock conflict array. See DBENV->set_lk_conflicts and Standard Lock Modes for a description of that array.

DB_LOCK lock;
  A lock reference.

The nlist argument specifies the number of elements in the list array.

If any of the requested locks cannot be acquired, or any of the locks to be released cannot be released, the operations before the failing operation are guaranteed to have completed successfully, and lock_vec returns a non-zero value. In addition, if elistp is not NULL, it is set to point to the DB_LOCKREQ entry that was being processed when the error occurred.

The lock_vec function may return one of the following values:

DB_LOCK_NOTGRANTED
  A lock was requested that could not be immediately granted and the flag parameter was set to DB_LOCK_NOWAIT. In this case, if non-NULL, elistp identifies the request that was not granted.

Otherwise, the lock_vec function returns a non-zero error value on failure and 0 on success.

# Errors

The lock_vec function may fail and return a non-zero error for the following conditions:

DB_LOCK_DEADLOCK
  The operation was selected to resolve a deadlock.

EINVAL
  An invalid flag value or parameter was specified.

ENOMEM
  The maximum number of locks has been reached.

The lock_vec function may fail and return a non-zero error for errors specified for other Berkeley DB and C library or system functions. If a catastrophic error has occurred, the lock_vec function may fail and return DB_RUNRECOVERY, in which case all subsequent Berkeley DB calls will fail in the same way.

# See Also

DBENV->set_lk_conflicts, DBENV->set_lk_detect, DBENV->set_lk_max, lock_detect, lock_get, lock_id, lock_put, lock_stat and lock_vec.`

Copyright Sleepycat Software