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<title>Berkeley DB: DbEnv::lock_get</title>
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<h1>DbEnv::lock_get</h1>
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#include <db_cxx.h>
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DbEnv::lock_get(u_int32_t locker, u_int32_t flags,
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const Dbt *obj, const db_lockmode_t lock_mode, DbLock *lock);
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<p>The DbEnv::lock_get method acquires a lock from the lock table, returning
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information about it in
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the <b>lock</b> argument.
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<p>The <b>locker</b> argument specified to DbEnv::lock_get is an unsigned
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32-bit integer quantity. It represents the entity requesting or releasing
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<p>The <b>flags</b> value must be set to 0 or
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<p><dt><a name="DB_LOCK_NOWAIT">DB_LOCK_NOWAIT</a><dd>If a lock cannot be granted because the requested lock conflicts with an
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return DB_LOCK_NOTGRANTED or throw a
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<a href="../api_cxx/lockng_class.html">DbLockNotGrantedException</a> immediately instead of waiting for
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the lock to become available.
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<p>The <b>obj</b> argument is an untyped byte string that specifies the
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object to be locked or released. Applications using the locking
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subsystem directly while also doing locking via the Berkeley DB access methods
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must take care not to inadvertently lock objects that happen to be equal
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to the unique file IDs used to lock files. See
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<a href="../ref/lock/am_conv.html">Access method locking conventions</a>
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<p>The <b>mode</b> argument is used as an index into the environment's
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lock conflict matrix. When using the default lock conflict matrix,
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<b>mode</b> must be set to one of the following values:
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<dt>DB_LOCK_READ<dd>read (shared)
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<dt>DB_LOCK_WRITE<dd>write (exclusive)
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<dt>DB_LOCK_IWRITE<dd>intention to write (shared)
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<dt>DB_LOCK_IREAD<dd>intention to read (shared)
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<dt>DB_LOCK_IWR<dd>intention to read and write (shared)
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<p>See <a href="../api_cxx/env_set_lk_conflicts.html">DbEnv::set_lk_conflicts</a> and <a href="../ref/lock/stdmode.html">Standard Lock Modes</a> for more information on the lock conflict matrix.
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Otherwise, the DbEnv::lock_get method either returns a non-zero error value or throws an exception that
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encapsulates a non-zero error value on failure, and returns 0 on success.
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<p>The DbEnv::lock_get method may fail and throw an exception or return a non-zero error for the following conditions:
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<p><dt>EINVAL<dd>An invalid flag value or parameter was specified.
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<p><dt>ENOMEM<dd>The maximum number of locks has been reached.
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<p>If the operation was selected to resolve a deadlock, the
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DbEnv::lock_get method will fail and
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and either return <a href="../ref/program/errorret.html#DB_LOCK_DEADLOCK">DB_LOCK_DEADLOCK</a> or
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throw a <a href="../api_cxx/deadlock_class.html">DbDeadlockException</a> exception.
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<p>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.
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If a catastrophic error has occurred, the DbEnv::lock_get method may fail and
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either return <a href="../ref/program/errorret.html#DB_RUNRECOVERY">DB_RUNRECOVERY</a> or throw a
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<a href="../api_cxx/runrec_class.html">DbRunRecoveryException</a>,
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in which case all subsequent Berkeley DB calls will fail in the same way.
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<a href="../api_cxx/env_class.html">DbEnv</a>, <a href="../api_cxx/lock_class.html">DbLock</a>
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<a href="../api_cxx/lock_list.html">Locking Subsystem and Related Methods</a>
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