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<title>Berkeley DB: DB_ENV->lock_vec</title>
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<h1>DB_ENV->lock_vec</h1>
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<h3><pre>
#include <db.h>
<p>
int
DB_ENV->lock_vec(DB_ENV *env, u_int32_t locker, u_int32_t flags,
DB_LOCKREQ list[], int nlist, DB_LOCKREQ **elistp);
</pre></h3>
<h1>Description</h1>
<p>The DB_ENV->lock_vec method atomically obtains and releases one or more locks
from the lock table. The DB_ENV->lock_vec method is intended to support
acquisition or trading of multiple locks under one lock table semaphore,
as is needed for lock coupling or in multigranularity locking for lock
escalation.
<p>The <b>locker</b> argument specified to DB_ENV->lock_vec is an unsigned
32-bit integer quantity. It represents the entity requesting or releasing
the locks.
<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. In this case, if non-NULL,
<b>elistp</b> identifies the request that was not granted.
</dl>
<p>The <b>list</b> array provided to DB_ENV->lock_vec is typedef'd as
DB_LOCKREQ. A DB_LOCKREQ structure has at least the following fields.
In order to ensure compatibility with future releases of Berkeley DB, all
fields of the DB_LOCKREQ structure that are not explicitly set should
be initialized to 0 before the first time the structure is used. Do
this by declaring the structure external or static, or by calling
<b>memset</b>(3).
<p><dl compact>
<p><dt>lockop_t <a name="op">op</a>;<dd>The operation to be performed, which must be set to one of the
following values:
<p><dl compact>
<p><dt><a name="DB_LOCK_GET">DB_LOCK_GET</a><dd>Get the lock defined by the values of the <b>mode</b> and <b>obj</b>
structure fields, for the specified <b>locker</b>. Upon return from
DB_ENV->lock_vec, if the <b>lock</b> field is non-NULL, a reference
to the acquired lock is stored there. (This reference is invalidated
by any call to DB_ENV->lock_vec or <a href="../api_c/lock_put.html">DB_ENV->lock_put</a> that releases the
lock.)
<p><dt><a name="DB_LOCK_GET_TIMEOUT">DB_LOCK_GET_TIMEOUT</a><dd>Identical to DB_LOCK_GET except that the value in the <b>timeout</b>
structure field overrides any previously specified timeout value for
this lock. A value of 0 turns off any previously specified timeout.
<p><dt><a name="DB_LOCK_PUT">DB_LOCK_PUT</a><dd>The lock to which the <b>lock</b> structure field refers is released.
The <b>locker</b> argument, and <b>mode</b> and <b>obj</b> fields
are ignored.
<p><dt><a name="DB_LOCK_PUT_ALL">DB_LOCK_PUT_ALL</a><dd>All locks held by the specified <b>locker</b> are released. The
<b>lock</b>, <b>mode</b>, and <b>obj</b> structure fields are
ignored. Locks acquired in operations performed by the current call to
DB_ENV->lock_vec which appear before the DB_LOCK_PUT_ALL
operation are released; those acquired in operations appearing after
the DB_LOCK_PUT_ALL operation are not released.
<p><dt><a name="DB_LOCK_PUT_OBJ">DB_LOCK_PUT_OBJ</a><dd>All locks held on the object <b>obj</b> are released. The
<b>locker</b> argument and the <b>lock</b> and <b>mode</b> structure
fields are ignored. Locks acquired in operations performed by the
current call to DB_ENV->lock_vec that appear before the
DB_LOCK_PUT_OBJ operation are released; those acquired in
operations appearing after the DB_LOCK_PUT_OBJ operation are
not released.
<p><dt><a name="DB_LOCK_TIMEOUT">DB_LOCK_TIMEOUT</a><dd>Cause the specified <b>locker</b> to timeout immediately. If the
database environment has not configured automatic deadlock detection,
the transaction will timeout the next time deadlock detection is
performed. As transactions acquire locks on behalf of a single locker
ID, timing out the locker ID associated with a transaction will time
out the transaction itself.
</dl>
<p><dt>DB_LOCK <a name="lock">lock</a>;<dd>A lock reference.
<p><dt>const lockmode_t <a name="mode">mode</a>;<dd>The lock mode, 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><a name="DB_LOCK_READ">DB_LOCK_READ</a><dd>read (shared)
<dt><a name="DB_LOCK_WRITE">DB_LOCK_WRITE</a><dd>write (exclusive)
<dt><a name="DB_LOCK_IWRITE">DB_LOCK_IWRITE</a><dd>intention to write (shared)
<dt><a name="DB_LOCK_IREAD">DB_LOCK_IREAD</a><dd>intention to read (shared)
<dt><a name="DB_LOCK_IWR">DB_LOCK_IWR</a><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><dt>const DBT <a name="obj">obj</a>;<dd>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><dt>u_int32_t timeout;<dd>The lock timeout value.
</dl>
<p>The <b>nlist</b> argument specifies the number of elements in the
<b>list</b> array.
<p>If any of the requested locks cannot be acquired, or any of the locks to
be released cannot be released, the operations before the failing
operation are guaranteed to have completed successfully, and
DB_ENV->lock_vec returns a non-zero value. In addition, if <b>elistp</b>
is not NULL, it is set to point to the DB_LOCKREQ entry that was being
processed when the error occurred.
<p>
Otherwise, the DB_ENV->lock_vec method returns a non-zero error value on failure and 0 on success.
<h1>Errors</h1>
<p>The DB_ENV->lock_vec 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_vec 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_vec 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>
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