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<div class="subTitle">org.apache.hadoop.hdfs.server.datanode</div>
<h2 title="Class ShortCircuitRegistry" class="title">Class ShortCircuitRegistry</h2>
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<li>org.apache.hadoop.hdfs.server.datanode.ShortCircuitRegistry</li>
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<pre>public class <span class="typeNameLabel">ShortCircuitRegistry</span>
extends <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true" title="class or interface in java.lang">Object</a></pre>
<div class="block">Manages client short-circuit memory segments on the DataNode.
DFSClients request shared memory segments from the DataNode. The
ShortCircuitRegistry generates and manages these segments. Each segment
has a randomly generated 128-bit ID which uniquely identifies it. The
segments each contain several "slots."
Before performing a short-circuit read, DFSClients must request a pair of
file descriptors from the DataNode via the REQUEST_SHORT_CIRCUIT_FDS
operation. As part of this operation, DFSClients pass the ID of the shared
memory segment they would like to use to communicate information about this
replica, as well as the slot number within that segment they would like to
use. Slot allocation is always done by the client.
Slots are used to track the state of the block on the both the client and
datanode. When this DataNode mlocks a block, the corresponding slots for the
replicas are marked as "anchorable". Anchorable blocks can be safely read
without verifying the checksum. This means that BlockReaderLocal objects
using these replicas can skip checksumming. It also means that we can do
zero-copy reads on these replicas (the ZCR interface has no way of
verifying checksums.)
When a DN needs to munlock a block, it needs to first wait for the block to
be unanchored by clients doing a no-checksum read or a zero-copy read. The
DN also marks the block's slots as "unanchorable" to prevent additional
clients from initiating these operations in the future.
The counterpart of this class on the client is <code>DfsClientShmManager</code>.</div>
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<td class="colFirst"><code>static class&nbsp;</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/hadoop/hdfs/server/datanode/ShortCircuitRegistry.NewShmInfo.html" title="class in org.apache.hadoop.hdfs.server.datanode">ShortCircuitRegistry.NewShmInfo</a></span></code>&nbsp;</td>
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<tr class="rowColor">
<td class="colFirst"><code>static class&nbsp;</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/hadoop/hdfs/server/datanode/ShortCircuitRegistry.RegisteredShm.html" title="class in org.apache.hadoop.hdfs.server.datanode">ShortCircuitRegistry.RegisteredShm</a></span></code>&nbsp;</td>
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<tr class="altColor">
<td class="colFirst"><code>static interface&nbsp;</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/hadoop/hdfs/server/datanode/ShortCircuitRegistry.Visitor.html" title="interface in org.apache.hadoop.hdfs.server.datanode">ShortCircuitRegistry.Visitor</a></span></code>&nbsp;</td>
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<td class="colFirst"><code>static org.slf4j.Logger</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/hadoop/hdfs/server/datanode/ShortCircuitRegistry.html#LOG">LOG</a></span></code>&nbsp;</td>
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<td class="colOne"><code><span class="memberNameLink"><a href="../../../../../../org/apache/hadoop/hdfs/server/datanode/ShortCircuitRegistry.html#ShortCircuitRegistry-org.apache.hadoop.conf.Configuration-">ShortCircuitRegistry</a></span>(org.apache.hadoop.conf.Configuration&nbsp;conf)</code>&nbsp;</td>
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<td class="colFirst"><code><a href="../../../../../../org/apache/hadoop/hdfs/server/datanode/ShortCircuitRegistry.NewShmInfo.html" title="class in org.apache.hadoop.hdfs.server.datanode">ShortCircuitRegistry.NewShmInfo</a></code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/hadoop/hdfs/server/datanode/ShortCircuitRegistry.html#createNewMemorySegment-java.lang.String-org.apache.hadoop.net.unix.DomainSocket-">createNewMemorySegment</a></span>(<a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a>&nbsp;clientName,
org.apache.hadoop.net.unix.DomainSocket&nbsp;sock)</code>
<div class="block">Handle a DFSClient request to create a new memory segment.</div>
</td>
</tr>
<tr id="i1" class="rowColor">
<td class="colFirst"><code><a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a></code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/hadoop/hdfs/server/datanode/ShortCircuitRegistry.html#getClientNames-org.apache.hadoop.hdfs.ExtendedBlockId-">getClientNames</a></span>(org.apache.hadoop.hdfs.ExtendedBlockId&nbsp;blockId)</code>&nbsp;</td>
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<td class="colFirst"><code>int</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/hadoop/hdfs/server/datanode/ShortCircuitRegistry.html#getShmNum--">getShmNum</a></span>()</code>&nbsp;</td>
</tr>
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<td class="colFirst"><code>void</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/hadoop/hdfs/server/datanode/ShortCircuitRegistry.html#processBlockInvalidation-org.apache.hadoop.hdfs.ExtendedBlockId-">processBlockInvalidation</a></span>(org.apache.hadoop.hdfs.ExtendedBlockId&nbsp;blockId)</code>
<div class="block">Invalidate any slot associated with a blockId that we are invalidating
(deleting) from this DataNode.</div>
</td>
</tr>
<tr id="i4" class="altColor">
<td class="colFirst"><code>void</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/hadoop/hdfs/server/datanode/ShortCircuitRegistry.html#processBlockMlockEvent-org.apache.hadoop.hdfs.ExtendedBlockId-">processBlockMlockEvent</a></span>(org.apache.hadoop.hdfs.ExtendedBlockId&nbsp;blockId)</code>
<div class="block">Process a block mlock event from the FsDatasetCache.</div>
</td>
</tr>
<tr id="i5" class="rowColor">
<td class="colFirst"><code>boolean</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/hadoop/hdfs/server/datanode/ShortCircuitRegistry.html#processBlockMunlockRequest-org.apache.hadoop.hdfs.ExtendedBlockId-">processBlockMunlockRequest</a></span>(org.apache.hadoop.hdfs.ExtendedBlockId&nbsp;blockId)</code>
<div class="block">Mark any slots associated with this blockId as unanchorable.</div>
</td>
</tr>
<tr id="i6" class="altColor">
<td class="colFirst"><code>void</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/hadoop/hdfs/server/datanode/ShortCircuitRegistry.html#registerSlot-org.apache.hadoop.hdfs.ExtendedBlockId-org.apache.hadoop.hdfs.shortcircuit.ShortCircuitShm.SlotId-boolean-">registerSlot</a></span>(org.apache.hadoop.hdfs.ExtendedBlockId&nbsp;blockId,
org.apache.hadoop.hdfs.shortcircuit.ShortCircuitShm.SlotId&nbsp;slotId,
boolean&nbsp;isCached)</code>&nbsp;</td>
</tr>
<tr id="i7" class="rowColor">
<td class="colFirst"><code>void</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/hadoop/hdfs/server/datanode/ShortCircuitRegistry.html#removeShm-org.apache.hadoop.hdfs.shortcircuit.ShortCircuitShm-">removeShm</a></span>(org.apache.hadoop.hdfs.shortcircuit.ShortCircuitShm&nbsp;shm)</code>&nbsp;</td>
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<td class="colFirst"><code>void</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/hadoop/hdfs/server/datanode/ShortCircuitRegistry.html#shutdown--">shutdown</a></span>()</code>&nbsp;</td>
</tr>
<tr id="i9" class="rowColor">
<td class="colFirst"><code>void</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/hadoop/hdfs/server/datanode/ShortCircuitRegistry.html#unregisterSlot-org.apache.hadoop.hdfs.shortcircuit.ShortCircuitShm.SlotId-">unregisterSlot</a></span>(org.apache.hadoop.hdfs.shortcircuit.ShortCircuitShm.SlotId&nbsp;slotId)</code>&nbsp;</td>
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<td class="colFirst"><code>boolean</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/hadoop/hdfs/server/datanode/ShortCircuitRegistry.html#visit-org.apache.hadoop.hdfs.server.datanode.ShortCircuitRegistry.Visitor-">visit</a></span>(<a href="../../../../../../org/apache/hadoop/hdfs/server/datanode/ShortCircuitRegistry.Visitor.html" title="interface in org.apache.hadoop.hdfs.server.datanode">ShortCircuitRegistry.Visitor</a>&nbsp;visitor)</code>&nbsp;</td>
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<pre>public static final&nbsp;org.slf4j.Logger LOG</pre>
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<h4>ShortCircuitRegistry</h4>
<pre>public&nbsp;ShortCircuitRegistry(org.apache.hadoop.conf.Configuration&nbsp;conf)
throws <a href="https://docs.oracle.com/javase/8/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</a></pre>
<dl>
<dt><span class="throwsLabel">Throws:</span></dt>
<dd><code><a href="https://docs.oracle.com/javase/8/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</a></code></dd>
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<h4>removeShm</h4>
<pre>public&nbsp;void&nbsp;removeShm(org.apache.hadoop.hdfs.shortcircuit.ShortCircuitShm&nbsp;shm)</pre>
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<h4>processBlockMlockEvent</h4>
<pre>public&nbsp;void&nbsp;processBlockMlockEvent(org.apache.hadoop.hdfs.ExtendedBlockId&nbsp;blockId)</pre>
<div class="block">Process a block mlock event from the FsDatasetCache.</div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>blockId</code> - The block that was mlocked.</dd>
</dl>
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<h4>processBlockMunlockRequest</h4>
<pre>public&nbsp;boolean&nbsp;processBlockMunlockRequest(org.apache.hadoop.hdfs.ExtendedBlockId&nbsp;blockId)</pre>
<div class="block">Mark any slots associated with this blockId as unanchorable.</div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>blockId</code> - The block ID.</dd>
<dt><span class="returnLabel">Returns:</span></dt>
<dd>True if we should allow the munlock request.</dd>
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<pre>public&nbsp;void&nbsp;processBlockInvalidation(org.apache.hadoop.hdfs.ExtendedBlockId&nbsp;blockId)</pre>
<div class="block">Invalidate any slot associated with a blockId that we are invalidating
(deleting) from this DataNode. When a slot is invalid, the DFSClient will
not use the corresponding replica for new read or mmap operations (although
existing, ongoing read or mmap operations will complete.)</div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>blockId</code> - The block ID.</dd>
</dl>
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<h4>getClientNames</h4>
<pre>public&nbsp;<a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a>&nbsp;getClientNames(org.apache.hadoop.hdfs.ExtendedBlockId&nbsp;blockId)</pre>
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<h4>createNewMemorySegment</h4>
<pre>public&nbsp;<a href="../../../../../../org/apache/hadoop/hdfs/server/datanode/ShortCircuitRegistry.NewShmInfo.html" title="class in org.apache.hadoop.hdfs.server.datanode">ShortCircuitRegistry.NewShmInfo</a>&nbsp;createNewMemorySegment(<a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a>&nbsp;clientName,
org.apache.hadoop.net.unix.DomainSocket&nbsp;sock)
throws <a href="https://docs.oracle.com/javase/8/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</a></pre>
<div class="block">Handle a DFSClient request to create a new memory segment.</div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>clientName</code> - Client name as reported by the client.</dd>
<dd><code>sock</code> - The DomainSocket to associate with this memory
segment. When this socket is closed, or the
other side writes anything to the socket, the
segment will be closed. This can happen at any
time, including right after this function returns.</dd>
<dt><span class="returnLabel">Returns:</span></dt>
<dd>A NewShmInfo object. The caller must close the
NewShmInfo object once they are done with it.</dd>
<dt><span class="throwsLabel">Throws:</span></dt>
<dd><code><a href="https://docs.oracle.com/javase/8/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</a></code> - If the new memory segment could not be created.</dd>
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<h4>registerSlot</h4>
<pre>public&nbsp;void&nbsp;registerSlot(org.apache.hadoop.hdfs.ExtendedBlockId&nbsp;blockId,
org.apache.hadoop.hdfs.shortcircuit.ShortCircuitShm.SlotId&nbsp;slotId,
boolean&nbsp;isCached)
throws org.apache.hadoop.fs.InvalidRequestException</pre>
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<dt><span class="throwsLabel">Throws:</span></dt>
<dd><code>org.apache.hadoop.fs.InvalidRequestException</code></dd>
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<pre>public&nbsp;void&nbsp;unregisterSlot(org.apache.hadoop.hdfs.shortcircuit.ShortCircuitShm.SlotId&nbsp;slotId)
throws org.apache.hadoop.fs.InvalidRequestException</pre>
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<dt><span class="throwsLabel">Throws:</span></dt>
<dd><code>org.apache.hadoop.fs.InvalidRequestException</code></dd>
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<pre>public&nbsp;void&nbsp;shutdown()</pre>
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<pre>public&nbsp;boolean&nbsp;visit(<a href="../../../../../../org/apache/hadoop/hdfs/server/datanode/ShortCircuitRegistry.Visitor.html" title="interface in org.apache.hadoop.hdfs.server.datanode">ShortCircuitRegistry.Visitor</a>&nbsp;visitor)</pre>
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<pre>public&nbsp;int&nbsp;getShmNum()</pre>
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