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<th colspan="3" align="center">DB_ENV->lock_vec()</th>
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<th width="60%" align="center">Chapter 6.
The DB_LOCK Handle
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<div class="sect1" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both"><a id="lockvec"></a>DB_ENV->lock_vec()</h2>
</div>
</div>
</div>
<pre class="programlisting">#include <db.h>
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>
<p>
The <code class="methodname">DB_ENV->lock_vec()</code> method atomically obtains and releases one or
more locks from the lock table. The <code class="methodname">DB_ENV->lock_vec()</code> 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>
<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
<code class="methodname">DB_ENV->lock_vec()</code> returns a non-zero value. In addition, if
<span class="bold"><strong>elistp</strong></span> is not NULL, it is set to
point to the DB_LOCKREQ entry that was being processed when the error
occurred.
</p>
<p>
Unless otherwise specified, the <code class="methodname">DB_ENV->lock_vec()</code> <span>
<span>
method returns a non-zero error value on failure and 0 on success.
</span>
</span>
</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1679175"></a>Parameters</h3>
</div>
</div>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1679210"></a>elistp</h4>
</div>
</div>
</div>
<p>
If an error occurs, and the <span class="bold"><strong>elistp</strong></span>
parameter is non-NULL, it is set to point to the DB_LOCKREQ entry that
was being processed when the error occurred.
</p>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1679257"></a>flags</h4>
</div>
</div>
</div>
<p>
The <span class="bold"><strong>flags</strong></span> parameter must be set to 0
or the following value:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p><a id="vec_DB_LOCK_NOWAIT"></a>
<code class="literal">DB_LOCK_NOWAIT</code>
</p>
<p>
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,
<span class="bold"><strong>elistp</strong></span> identifies the request that
was not granted.
</p>
</li>
</ul>
</div>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1678887"></a>locker</h4>
</div>
</div>
</div>
<p>
The <span class="bold"><strong>locker</strong></span> parameter is an unsigned
32-bit integer quantity. It represents the entity requesting or
releasing the lock.
</p>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1678160"></a>list</h4>
</div>
</div>
</div>
<p>
The <span class="bold"><strong>list</strong></span> array provided to
<code class="methodname">DB_ENV->lock_vec()</code> is typedef'd as DB_LOCKREQ.
</p>
<p>
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
<span class="bold"><strong>memset</strong></span>(3).
</p>
<p>
A DB_LOCKREQ structure has at least the following fields:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p><a id="vec_op"></a>
<code class="literal">lockop_t op;</code>
</p>
<p>
The operation to be performed, which must be set to one of the
following values:
</p>
<div class="itemizedlist">
<ul type="circle">
<li>
<p><a id="vec_DB_LOCK_GET"></a>
<code class="literal">DB_LOCK_GET</code>
</p>
<p>
Get the lock defined by the values of the <span class="bold"><strong>mode</strong></span> and <span class="bold"><strong>obj</strong></span>
structure fields, for the specified
<span class="bold"><strong>locker</strong></span>.
Upon return from <code class="methodname">DB_ENV->lock_vec()</code>,
if the <span class="bold"><strong>lock</strong></span> field is non-NULL, a
reference to the acquired lock is stored there. (This reference is
invalidated by any call to <code class="methodname">DB_ENV->lock_vec()</code> or
<a class="xref" href="lockput.html" title="DB_ENV->lock_put()">DB_ENV->lock_put()</a> that releases
the lock.)
</p>
</li>
<li>
<p><a id="vec_DB_LOCK_GET_TIMEOUT"></a>
<code class="literal">DB_LOCK_GET_TIMEOUT</code>
</p>
<p>
Identical to DB_LOCK_GET except that the value in the <span class="bold"><strong>timeout</strong></span> structure field overrides any
previously specified timeout value for this lock. A value of 0 turns
off any previously specified timeout.
</p>
</li>
<li>
<p><a id="vec_DB_LOCK_PUT"></a>
<code class="literal">DB_LOCK_PUT</code>
</p>
<p>
The lock to which the <span class="bold"><strong>lock</strong></span> structure
field refers is released. The <span class="bold"><strong>locker</strong></span>
parameter, and <span class="bold"><strong>mode</strong></span> and <span class="bold"><strong>obj</strong></span> fields are ignored.
</p>
</li>
<li>
<p><a id="vec_DB_LOCK_PUT_ALL"></a>
<code class="literal">DB_LOCK_PUT_ALL</code>
</p>
<p>
All locks held by the specified <span class="bold"><strong>locker</strong></span> are released. The <span class="bold"><strong>lock</strong></span>, <span class="bold"><strong>mode</strong></span>,
and <span class="bold"><strong>obj</strong></span> structure fields are ignored.
Locks acquired in operations performed by the current call to
<code class="methodname">DB_ENV->lock_vec()</code> 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>
</li>
<li>
<p><a id="vec_DB_LOCK_PUT_OBJ"></a>
<code class="literal">DB_LOCK_PUT_OBJ</code>
</p>
<p>
All locks held on <span class="bold"><strong>obj</strong></span> are released.
The <span class="bold"><strong>locker</strong></span> parameter and the
<span class="bold"><strong>lock</strong></span> and <span class="bold"><strong>mode</strong></span> structure fields are ignored. Locks
acquired in operations performed by the current call to
<code class="methodname">DB_ENV->lock_vec()</code> 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>
</li>
<li>
<p><a id="vec_DB_LOCK_TIMEOUT"></a>
<code class="literal">DB_LOCK_TIMEOUT</code>
</p>
<p>
Cause the specified <span class="bold"><strong>locker</strong></span> 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.
</p>
</li>
</ul>
</div>
</li>
<li>
<p><a id="vec_lock"></a>
<code class="literal">DB_LOCK lock;</code>
</p>
<p>
A lock reference.
</p>
</li>
<li>
<p><a id="vec_mode"></a>
<code class="literal">const lockmode_t mode;</code>
</p>
<p>
The lock mode, used as an index into the environment's lock conflict
matrix. When using the default lock conflict matrix, <span class="bold"><strong>mode</strong></span> must be set to one of the following
values:
</p>
<div class="itemizedlist">
<ul type="circle">
<li>
<p><a id="vec_DB_LOCK_READ"></a>
<code class="literal">DB_LOCK_READ</code>
</p>
<p>
read (shared)
</p>
</li>
<li>
<p><a id="vec_DB_LOCK_WRITE"></a>
<code class="literal">DB_LOCK_WRITE</code>
</p>
<p>
write (exclusive)
</p>
</li>
<li>
<p><a id="vec_DB_LOCK_IWRITE"></a>
<code class="literal">DB_LOCK_IWRITE</code>
</p>
<p>
intention to write (shared)
</p>
</li>
<li>
<p><a id="vec_DB_LOCK_IREAD"></a>
<code class="literal">DB_LOCK_IREAD</code>
</p>
<p>
intention to read (shared)
</p>
</li>
<li>
<p><a id="vec_DB_LOCK_IWR"></a>
<code class="literal">DB_LOCK_IWR</code>
</p>
<p>
intention to read and write (shared)
</p>
</li>
</ul>
</div>
<p>
See <a class="xref" href="envset_lk_conflicts.html" title="DB_ENV->set_lk_conflicts()">DB_ENV->set_lk_conflicts()</a>
and <a href="../../programmer_reference/lock_stdmode.html" class="olink">Standard Lock Modes</a>
for more information on the lock conflict matrix.
</p>
</li>
<li>
<p>
<span class="bold"><a id="obj"></a><strong>const DBT obj;</strong></span>
</p>
<p>
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="../../programmer_reference/lock_am_conv.html" class="olink">Access method locking
conventions</a> in the
<em class="citetitle">Berkeley DB Programmer's Reference Guide</em> for more information.
</p>
</li>
<li>
<p>
<span class="bold"><strong>u_int32_t timeout;</strong></span>
</p>
<p>
The lock timeout value.
</p>
</li>
</ul>
</div>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1679635"></a>nlist</h4>
</div>
</div>
</div>
<p>
The <span class="bold"><strong>nlist</strong></span> parameter specifies the
number of elements in the <span class="bold"><strong>list</strong></span> array.
</p>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1679994"></a>Errors</h3>
</div>
</div>
</div>
<p>
The <code class="methodname">DB_ENV->lock_vec()</code> <span>
<span>
method may fail and return one of the following non-zero errors:
</span>
</span>
</p>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1679480"></a>DB_LOCK_DEADLOCK</h4>
</div>
</div>
</div>
<p>
A transactional database environment operation was selected to resolve
a deadlock.
</p>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1679866"></a>DB_LOCK_NOTGRANTED</h4>
</div>
</div>
</div>
<p>
A Berkeley DB Concurrent Data Store database environment configured
for lock timeouts was unable to grant a lock in the allowed time.
</p>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1679588"></a>DB_LOCK_NOTGRANTED</h4>
</div>
</div>
</div>
<p>
The <a class="link" href="lockvec.html#vec_DB_LOCK_NOWAIT">DB_LOCK_NOWAIT</a>
flag or lock timers were configured and the lock could not be granted
before the wait-time expired.
</p>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1679987"></a>EINVAL</h4>
</div>
</div>
</div>
<p>
An invalid flag value or parameter was specified.
</p>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1679954"></a>ENOMEM</h4>
</div>
</div>
</div>
<p>
The maximum number of locks has been reached.
</p>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1679207"></a>Class</h3>
</div>
</div>
</div>
<p>
<a class="link" href="env.html" title="Chapter 5. The DB_ENV Handle">DB_ENV</a>,
<a class="link" href="lock.html" title="Chapter 6. The DB_LOCK Handle">DB_LOCK</a>
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1679236"></a>See Also</h3>
</div>
</div>
</div>
<p>
<a class="xref" href="lock.html#locklist" title="Locking Subsystem and Related Methods">Locking Subsystem and Related Methods</a>
</p>
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