#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.

• 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.
  
  

• 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.

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

• 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.

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

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

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

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

• An invalid flag value or parameter was specified.

• The maximum number of locks has been reached.