DB_ENV->lock_get()

#include <db.h>

int
DB_ENV->lock_get(DB_ENV *env, u_int32_t locker,
    u_int32_t flags, const DBT *object,
    const db_lockmode_t lock_mode, DB_LOCK *lock);  

The DB_ENV->lock_get() method acquires a lock from the lock table, returning information about it in the lock parameter.

The DB_ENV->lock_get() method returns a non-zero error value on failure and 0 on success.

Parameters

locker

The locker parameter is an unsigned 32-bit integer quantity. It represents the entity requesting the lock.

flags

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

• DB_LOCK_NOWAIT

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

object

The object parameter is an untyped byte string that specifies the object to be locked. Applications using the locking subsystem directly while also doing locking via the Berkeley DB access methods must take care not to inadvertently lock objects that happen to be equal to the unique file IDs used to lock files. See Access method locking conventions in the Berkeley DB Programmer's Reference Guide for more information.

lock_mode

The lock_mode parameter is used as an index into the environment's lock conflict matrix. When using the default lock conflict matrix, lock_mode must be set to one of the following values:

• DB_LOCK_READ

  read (shared)

• DB_LOCK_WRITE

  write (exclusive)

• DB_LOCK_IWRITE

  intention to write (shared)

• DB_LOCK_IREAD

  intention to read (shared)

• DB_LOCK_IWR

  intention to read and write (shared)

See DB_ENV->set_lk_conflicts() and Standard Lock Modes for more information on the lock conflict matrix.

lock

The DB_ENV->lock_get() method returns the lock information in lock.

Errors

The DB_ENV->lock_get() method may fail and return one of the following non-zero errors:

DB_LOCK_DEADLOCK

A transactional database environment operation was selected to resolve a deadlock.

DB_LOCK_NOTGRANTED

A Berkeley DB Concurrent Data Store database environment configured for lock timeouts was unable to grant a lock in the allowed time.

You attempted to open a database handle that is configured for no waiting exclusive locking, but the exclusive lock could not be immediately obtained. See DB->set_lk_exclusive() for more information.

DB_LOCK_NOTGRANTED

The DB_LOCK_NOWAIT flag or lock timers were configured and the lock could not be granted before the wait-time expired.

EINVAL

An invalid flag value or parameter was specified.

EINVAL

The method was called on an environment which had been opened without being configured for locking.

ENOMEM

The maximum number of locks has been reached.

Class

DB_ENV, DB_LOCK

See Also

Locking Subsystem and Related Methods