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NodeIdMap.java
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NodeIdMap.java
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package org.softwareheritage.graph.maps;
import org.softwareheritage.graph.Graph;
import org.softwareheritage.graph.SWHID;
import java.io.IOException;
/**
* Mapping between internal long node id and external SWHID.
* <p>
* Mappings in both directions are pre-computed and dumped on disk in the {@link NodeMapBuilder}
* class, then they are loaded here using mmap().
*
* @author The Software Heritage developers
* @see NodeMapBuilder
*/
public class NodeIdMap {
/** Fixed length of full SWHID */
public static final int SWHID_LENGTH = 50;
/** Fixed length of long node id */
public static final int NODE_ID_LENGTH = 20;
/** Fixed length of binary SWHID buffer */
public static final int SWHID_BIN_SIZE = 22;
/** Fixed length of binary node id buffer */
public static final int NODE_ID_BIN_SIZE = 8;
/** Graph path and basename */
String graphPath;
/** Number of ids to map */
long nbIds;
/** mmap()-ed SWHID_TO_NODE file */
MapFile swhToNodeMap;
/** mmap()-ed NODE_TO_SWHID file */
MapFile nodeToSwhMap;
/**
* Constructor.
*
* @param graphPath full graph path
* @param nbNodes number of nodes in the graph
*/
public NodeIdMap(String graphPath, long nbNodes) throws IOException {
this.graphPath = graphPath;
this.nbIds = nbNodes;
this.swhToNodeMap = new MapFile(graphPath + Graph.SWHID_TO_NODE, SWHID_BIN_SIZE + NODE_ID_BIN_SIZE);
this.nodeToSwhMap = new MapFile(graphPath + Graph.NODE_TO_SWHID, SWHID_BIN_SIZE);
}
/**
* Converts SWHID to corresponding long node id.
*
* @param swhid node represented as a {@link SWHID}
* @return corresponding node as a long id
* @see SWHID
*/
public long getNodeId(SWHID swhid) {
/*
* The file is sorted by swhid, hence we can binary search on swhid to get corresponding nodeId
*/
long start = 0;
long end = nbIds - 1;
while (start <= end) {
long lineNumber = (start + end) / 2L;
byte[] buffer = swhToNodeMap.readAtLine(lineNumber);
byte[] swhidBuffer = new byte[SWHID_BIN_SIZE];
byte[] nodeBuffer = new byte[NODE_ID_BIN_SIZE];
System.arraycopy(buffer, 0, swhidBuffer, 0, SWHID_BIN_SIZE);
System.arraycopy(buffer, SWHID_BIN_SIZE, nodeBuffer, 0, NODE_ID_BIN_SIZE);
String currentSWHID = SWHID.fromBytes(swhidBuffer).getSWHID();
long currentNodeId = java.nio.ByteBuffer.wrap(nodeBuffer).getLong();
int cmp = currentSWHID.compareTo(swhid.toString());
if (cmp == 0) {
return currentNodeId;
} else if (cmp < 0) {
start = lineNumber + 1;
} else {
end = lineNumber - 1;
}
}
throw new IllegalArgumentException("Unknown SWHID: " + swhid);
}
/**
* Converts a node long id to corresponding SWHID.
*
* @param nodeId node as a long id
* @return corresponding node as a {@link SWHID}
* @see SWHID
*/
public SWHID getSWHID(long nodeId) {
/*
* Each line in NODE_TO_SWHID is formatted as: swhid The file is ordered by nodeId, meaning node0's
* swhid is at line 0, hence we can read the nodeId-th line to get corresponding swhid
*/
if (nodeId < 0 || nodeId >= nbIds) {
throw new IllegalArgumentException("Node id " + nodeId + " should be between 0 and " + nbIds);
}
return SWHID.fromBytes(nodeToSwhMap.readAtLine(nodeId));
}
/**
* Closes the mapping files.
*/
public void close() throws IOException {
swhToNodeMap.close();
nodeToSwhMap.close();
}
}

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