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<div class="subTitle">org.janusgraph.diskstorage.locking</div>
<h2 title="Interface Locker" class="title">Interface Locker</h2>
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<dt>All Known Implementing Classes:</dt>
<dd><a href="../../../../org/janusgraph/diskstorage/locking/AbstractLocker.html" title="class in org.janusgraph.diskstorage.locking">AbstractLocker</a>, <a href="../../../../org/janusgraph/diskstorage/locking/consistentkey/ConsistentKeyLocker.html" title="class in org.janusgraph.diskstorage.locking.consistentkey">ConsistentKeyLocker</a></dd>
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<pre>public interface <span class="typeNameLabel">Locker</span></pre>
<div class="block">Threadsafe discretionary locking within and between processes JanusGraph.
 <p>
 Locks are identified <a href="../../../../org/janusgraph/diskstorage/util/KeyColumn.html" title="class in org.janusgraph.diskstorage.util"><code>KeyColumn</code></a> instances.
 <code>KeyColumn#equals(Object)</code> should be used to determine whether two
 <code>KeyColumn</code> instances refer to the same or different locks.
 <p>
 Threads taking locks are identified by <a href="../../../../org/janusgraph/diskstorage/keycolumnvalue/StoreTransaction.html" title="interface in org.janusgraph.diskstorage.keycolumnvalue"><code>StoreTransaction</code></a> instances.
 Either <code>equals(...)</code> or reference equality (the <code>==</code> operator)
 can be used to compare these instances.
 <p>
 This interface follows a three-step locking model that supports both
 nonblocking and blocking locking primitives. Not all JanusGraph
 <code>StoreTransaction</code>s will need locks and use this interface. For those
 <code>StoreTransaction</code>s that do take one or more locks, JanusGraph will call the
 methods on this interface in the following order. <code>tx</code> refers to the
 same <code>StoreTransaction</code> instance in each step.
 
 <ol>
 <li><code>writeLock(kc, tx)</code> one or more times per distinct
 <code>KeyColumn kc</code>
 <li><code>checkLocks(tx)</code> once if the user commits <code>tx</code> or never if
 the user aborts <code>tx</code>
 <li><code>deleteLocks(tx)</code> once, regardless of whether
 <code>checkLocks(tx)</code> was called
 </ol>
 
 <p>
 The first step, <code>writeLocks</code>, attempts to take a lock. This may, but
 need not necessarily, indicate whether the attempt succeeded or failed. The
 second step, <code>checkLocks</code>, returns if all previous <code>writeLocks</code>
 succeeded or throws an exception if one or more failed. The final step,
 <code>deleteLocks</code>, releases all locks and associated resources held by the
 <code>tx</code>.
 <p>
 All implementations of this interface must be safe for concurrent use by
 different threads. However, implementations may assume that, for any given
 <code>StoreTransaction tx</code>, all calls to this interface's methods with
 argument <code>tx</code> will either come from a single thread or multiple threads
 using external synchronization to provide the same effect.</div>
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<h3>Method Summary</h3>
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<td class="colFirst"><code>void</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../org/janusgraph/diskstorage/locking/Locker.html#checkLocks-org.janusgraph.diskstorage.keycolumnvalue.StoreTransaction-">checkLocks</a></span>(<a href="../../../../org/janusgraph/diskstorage/keycolumnvalue/StoreTransaction.html" title="interface in org.janusgraph.diskstorage.keycolumnvalue">StoreTransaction</a>&nbsp;tx)</code>
<div class="block">Verify that all previous <a href="../../../../org/janusgraph/diskstorage/locking/Locker.html#writeLock-org.janusgraph.diskstorage.util.KeyColumn-org.janusgraph.diskstorage.keycolumnvalue.StoreTransaction-"><code>writeLock(KeyColumn, StoreTransaction)</code></a>
 calls with <code>tx</code> actually succeeded.</div>
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<td class="colFirst"><code>void</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../org/janusgraph/diskstorage/locking/Locker.html#deleteLocks-org.janusgraph.diskstorage.keycolumnvalue.StoreTransaction-">deleteLocks</a></span>(<a href="../../../../org/janusgraph/diskstorage/keycolumnvalue/StoreTransaction.html" title="interface in org.janusgraph.diskstorage.keycolumnvalue">StoreTransaction</a>&nbsp;tx)</code>
<div class="block">Release every lock currently held by <code>tx</code>.</div>
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<td class="colFirst"><code>void</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../org/janusgraph/diskstorage/locking/Locker.html#writeLock-org.janusgraph.diskstorage.util.KeyColumn-org.janusgraph.diskstorage.keycolumnvalue.StoreTransaction-">writeLock</a></span>(<a href="../../../../org/janusgraph/diskstorage/util/KeyColumn.html" title="class in org.janusgraph.diskstorage.util">KeyColumn</a>&nbsp;lockID,
         <a href="../../../../org/janusgraph/diskstorage/keycolumnvalue/StoreTransaction.html" title="interface in org.janusgraph.diskstorage.keycolumnvalue">StoreTransaction</a>&nbsp;tx)</code>
<div class="block">Attempt to acquire/take/claim/write the lock named by <code>lockID</code>.</div>
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<h4>writeLock</h4>
<pre>void&nbsp;writeLock(<a href="../../../../org/janusgraph/diskstorage/util/KeyColumn.html" title="class in org.janusgraph.diskstorage.util">KeyColumn</a>&nbsp;lockID,
               <a href="../../../../org/janusgraph/diskstorage/keycolumnvalue/StoreTransaction.html" title="interface in org.janusgraph.diskstorage.keycolumnvalue">StoreTransaction</a>&nbsp;tx)
        throws <a href="../../../../org/janusgraph/diskstorage/locking/TemporaryLockingException.html" title="class in org.janusgraph.diskstorage.locking">TemporaryLockingException</a>,
               <a href="../../../../org/janusgraph/diskstorage/locking/PermanentLockingException.html" title="class in org.janusgraph.diskstorage.locking">PermanentLockingException</a></pre>
<div class="block">Attempt to acquire/take/claim/write the lock named by <code>lockID</code>.
 <p>
 Returns on success and throws an exception on failure.</div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>lockID</code> - the lock to acquire</dd>
<dd><code>tx</code> - the transaction attempting to acquire the lock</dd>
<dt><span class="throwsLabel">Throws:</span></dt>
<dd><code><a href="../../../../org/janusgraph/diskstorage/locking/TemporaryLockingException.html" title="class in org.janusgraph.diskstorage.locking">TemporaryLockingException</a></code> - a failure likely to disappear if the call is retried</dd>
<dd><code><a href="../../../../org/janusgraph/diskstorage/locking/PermanentLockingException.html" title="class in org.janusgraph.diskstorage.locking">PermanentLockingException</a></code> - a failure unlikely to disappear if the call is retried</dd>
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<h4>checkLocks</h4>
<pre>void&nbsp;checkLocks(<a href="../../../../org/janusgraph/diskstorage/keycolumnvalue/StoreTransaction.html" title="interface in org.janusgraph.diskstorage.keycolumnvalue">StoreTransaction</a>&nbsp;tx)
         throws <a href="../../../../org/janusgraph/diskstorage/locking/TemporaryLockingException.html" title="class in org.janusgraph.diskstorage.locking">TemporaryLockingException</a>,
                <a href="../../../../org/janusgraph/diskstorage/locking/PermanentLockingException.html" title="class in org.janusgraph.diskstorage.locking">PermanentLockingException</a></pre>
<div class="block">Verify that all previous <a href="../../../../org/janusgraph/diskstorage/locking/Locker.html#writeLock-org.janusgraph.diskstorage.util.KeyColumn-org.janusgraph.diskstorage.keycolumnvalue.StoreTransaction-"><code>writeLock(KeyColumn, StoreTransaction)</code></a>
 calls with <code>tx</code> actually succeeded.
 <p>
 Returns on success and throws an exception on failure.</div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>tx</code> - the transaction attempting to check the result of previous
            <code>writeLock(..., tx)</code> calls in which it was the
            <code>tx</code> argument</dd>
<dt><span class="throwsLabel">Throws:</span></dt>
<dd><code><a href="../../../../org/janusgraph/diskstorage/locking/TemporaryLockingException.html" title="class in org.janusgraph.diskstorage.locking">TemporaryLockingException</a></code> - a failure likely to disappear if the call is retried</dd>
<dd><code><a href="../../../../org/janusgraph/diskstorage/locking/PermanentLockingException.html" title="class in org.janusgraph.diskstorage.locking">PermanentLockingException</a></code> - a failure unlikely to disappear if the call is retried</dd>
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<h4>deleteLocks</h4>
<pre>void&nbsp;deleteLocks(<a href="../../../../org/janusgraph/diskstorage/keycolumnvalue/StoreTransaction.html" title="interface in org.janusgraph.diskstorage.keycolumnvalue">StoreTransaction</a>&nbsp;tx)
          throws <a href="../../../../org/janusgraph/diskstorage/locking/TemporaryLockingException.html" title="class in org.janusgraph.diskstorage.locking">TemporaryLockingException</a>,
                 <a href="../../../../org/janusgraph/diskstorage/locking/PermanentLockingException.html" title="class in org.janusgraph.diskstorage.locking">PermanentLockingException</a></pre>
<div class="block">Release every lock currently held by <code>tx</code>.
 <p>
 Returns on success and throws an exception on failure.</div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>tx</code> - the transaction attempting to delete locks taken in previous
            <code>writeLock(..., tx)</code> calls in which it was the
            <code>tx</code> argument</dd>
<dt><span class="throwsLabel">Throws:</span></dt>
<dd><code><a href="../../../../org/janusgraph/diskstorage/locking/TemporaryLockingException.html" title="class in org.janusgraph.diskstorage.locking">TemporaryLockingException</a></code> - a failure likely to disappear if the call is retried</dd>
<dd><code><a href="../../../../org/janusgraph/diskstorage/locking/PermanentLockingException.html" title="class in org.janusgraph.diskstorage.locking">PermanentLockingException</a></code> - a failure unlikely to disappear if the call is retried</dd>
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