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<title>Berkeley DB: DB_ENV->lock_get</title>
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<h1>DB_ENV->lock_get</h1>
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<h3><pre>
#include <db.h>
<p>
int
DB_ENV->lock_get(DB_ENV *env, u_int32_t locker,
u_int32_t flags, const DBT *obj,
const db_lockmode_t lock_mode, DB_LOCK *lock);
</pre></h3>
<h1>Description</h1>
<p>The DB_ENV->lock_get method acquires a lock from the lock table, returning
information about it in
the <b>lock</b> argument.
<p>The <b>locker</b> argument specified to DB_ENV->lock_get is an unsigned
32-bit integer quantity. It represents the entity requesting or releasing
the lock.
<p>The <b>flags</b> value must be set to 0 or
the following value:
<p><dl compact>
<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
existing lock,
return DB_LOCK_NOTGRANTED immediately instead of waiting
for the lock to become available.
</dl>
<p>The <b>obj</b> 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
<a href="../ref/lock/am_conv.html">Access method locking conventions</a>
for more information.
<p>The <b>mode</b> argument is used as an index into the environment's
lock conflict matrix. When using the default lock conflict matrix,
<b>mode</b> must be set to one of the following values:
<p><dl compact>
<dt>DB_LOCK_READ<dd>read (shared)
<dt>DB_LOCK_WRITE<dd>write (exclusive)
<dt>DB_LOCK_IWRITE<dd>intention to write (shared)
<dt>DB_LOCK_IREAD<dd>intention to read (shared)
<dt>DB_LOCK_IWR<dd>intention to read and write (shared)
</dl>
<p>See <a href="../api_c/env_set_lk_conflicts.html">DB_ENV->set_lk_conflicts</a> and <a href="../ref/lock/stdmode.html">Standard Lock Modes</a> for more information on the lock conflict matrix.
<p>
Otherwise, the DB_ENV->lock_get method returns a non-zero error value on failure and 0 on success.
<h1>Errors</h1>
<p>The DB_ENV->lock_get method may fail and return a non-zero error for the following conditions:
<p><dl compact>
<p><dt>DB_LOCK_DEADLOCK<dd>The operation was selected to resolve a deadlock.
</dl>
<p><dl compact>
<p><dt>EINVAL<dd>An invalid flag value or parameter was specified.
</dl>
<p><dl compact>
<p><dt>ENOMEM<dd>The maximum number of locks has been reached.
</dl>
<p>The DB_ENV->lock_get method may fail and return a non-zero error for errors specified for other Berkeley DB and C library or system functions.
If a catastrophic error has occurred, the DB_ENV->lock_get method may fail and
return <a href="../ref/program/errorret.html#DB_RUNRECOVERY">DB_RUNRECOVERY</a>,
in which case all subsequent Berkeley DB calls will fail in the same way.
<h1>Class</h1>
<a href="../api_c/env_class.html">DB_ENV</a>, <a href="../api_c/lock_class.html">DB_LOCK</a>
<h1>See Also</h1>
<a href="../api_c/lock_list.html">Locking Subsystem and Related Methods</a>
</tt>
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