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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 *obj, const db_lockmode_t lock_mode, DbLock *lock);
Description
The DbEnv::lock_get method acquires a lock from the lock table, returning
information about it in
the lock argument.
The locker argument specified to DbEnv::lock_get 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 granted because the requested lock conflicts with an
existing lock, return immediately instead of waiting for the lock to
become available.
The obj argument is an untyped byte string that specifies the
object to be locked or released. 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 mode argument is used as an index into the environment's
lock conflict matrix. When using the default lock conflict matrix,
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.
If a lock is requested that cannot be immediately granted, and the
flags parameter was set to DB_LOCK_NOWAIT, the
DbEnv::lock_get method may
return or throw an exception encapsulating
DB_LOCK_NOTGRANTED.
Otherwise, 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.
Errors
The DbEnv::lock_get method may fail and throw an exception or 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 DbEnv::lock_get method may fail and throw an exception or return a non-zero error for errors specified for other Berkeley DB and C library or system methods.
If a catastrophic error has occurred, the DbEnv::lock_get method may fail and either
return DB_RUNRECOVERY or throw an exception encapsulating
DB_RUNRECOVERY, in which case all subsequent Berkeley DB calls will fail
in the same way.
Class
DbEnv, DbLock
See Also
DbEnv::set_lk_conflicts,
DbEnv::set_lk_detect,
DbEnv::set_lk_max_lockers,
DbEnv::set_lk_max_locks,
DbEnv::set_lk_max_objects,
DbEnv::lock_detect,
DbEnv::lock_get,
DbEnv::lock_id,
DbEnv::lock_id_free,
DbEnv::lock_put,
DbEnv::lock_stat,
and
DbEnv::lock_vec.
Copyright Sleepycat Software
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