#include <db_cxx.h>
int
DbEnv::lock_get(u_int32_t locker, u_int32_t flags,
const Dbt *object, const db_lockmode_t lock_mode, DbLock *lock);
The DbEnv::lock_get() method acquires a lock from the lock table,
returning information about it in the lock parameter.
The DbEnv::lock_get()
method either returns a non-zero error value or throws an
exception that encapsulates a non-zero error value on
failure, and returns 0 on success.
The locker parameter is an unsigned 32-bit integer quantity. It represents the entity requesting the lock.
The flags parameter must be set to 0 or the following value:
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.
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 DbEnv::set_lk_conflicts() and Standard Lock Modes for more information on the lock conflict matrix.
The DbEnv::lock_get()
method may fail and throw a DbException
exception, encapsulating one of the following non-zero errors, or return one
of the following non-zero errors:
A transactional database environment operation was selected to resolve a deadlock.
DbDeadlockException is thrown if
your Berkeley DB API is configured to throw exceptions.
Otherwise, DB_LOCK_DEADLOCK is returned.
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.
DbLockNotGrantedException is thrown if
your Berkeley DB API is configured to throw exceptions.
Otherwise, DB_LOCK_NOTGRANTED is returned.
The DB_LOCK_NOWAIT flag or lock timers were configured and the lock could not be granted before the wait-time expired.
DbLockNotGrantedException is thrown if
your Berkeley DB API is configured to throw exceptions.
Otherwise, DB_LOCK_NOTGRANTED is returned.
The method was called on an environment which had been opened without being configured for locking.