Berkeley DB: DbEnv::lock_get
Description: Berkeley DB: An embedded database programmatic toolkit.
Keywords: embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++

### DbEnv::lock_get |

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###

    #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);

### Description: DbEnv::lock_get

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.

### Parameters

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 or throw a DbLockNotGrantedException immediately instead of waiting for the lock to become available.
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 DbEnv::set_lk_conflicts and Standard Lock Modes for more information on the lock conflict matrix.

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

### Errors

The DbEnv::lock_get method may fail and throw DbException, encapsulating one of the following non-zero errors, or return one of the following non-zero errors:

EINVAL
  An invalid flag value or parameter was specified.

If a transactional database environment operation was selected to resolve a deadlock, the DbEnv::lock_get method will fail and either return DB_LOCK_DEADLOCK or throw a DbDeadlockException exception.

If a Berkeley DB Concurrent Data Store database environment configured for lock timeouts was unable to grant a lock in the allowed time, the DbEnv::lock_get method will fail and either return DB_LOCK_NOTGRANTED or throw a DbLockNotGrantedException exception.

If the DB_LOCK_NOWAIT flag or lock timers were configured and the lock could not be granted before the wait-time expired, the DbEnv::lock_get method will fail and either return DB_LOCK_NOTGRANTED or throw a DbLockNotGrantedException exception.

If the maximum number of locks has been reached, the DbEnv::lock_get method will fail and either return ENOMEM or throw a DbMemoryException.

### Class

DbEnv, DbLock

### See Also

Locking Subsystem and Related Methods`

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