INodeMap

INodeMap利用LightWeightGSet来存储INode对象，为什么可以存储INode ID和INode的映射呢？因为INode的equals和hashCode方法都已经重载，并且只根据id判断，那么知道id之后，其它字段为空的Inode对象，就可以得到映射的对象。equals和hashCode 方法如下：

@Override
public final boolean equals(Object that) {
if (this == that) {
return true;
}
if (that == null || !(that instanceof INode)) {
return false;
}
return getId() == ((INode) that).getId();
}

@Override
public final int hashCode() {
long id = getId();
return (int)(id^(id>>>32));
}

INodeMap的源代码：

/**
* Storing all the {@link INode}s and maintaining the mapping between INode ID
* and INode.
*/
public class INodeMap {

static INodeMap newInstance(INodeDirectory rootDir) {
// Compute the map capacity by allocating 1% of total memory
int capacity = LightWeightGSet.computeCapacity(1, "INodeMap");
GSet<INode, INodeWithAdditionalFields> map
= new LightWeightGSet<INode, INodeWithAdditionalFields>(capacity);
map.put(rootDir);
return new INodeMap(map);
}

/** Synchronized by external lock. */
private final GSet<INode, INodeWithAdditionalFields> map;

public Iterator<INodeWithAdditionalFields> getMapIterator() {
return map.iterator();
}

private INodeMap(GSet<INode, INodeWithAdditionalFields> map) {
Preconditions.checkArgument(map != null);
this.map = map;
}

/**
* Add an {@link INode} into the {@link INode} map. Replace the old value if
* necessary.
* @param inode The {@link INode} to be added to the map.
*/
public final void put(INode inode) {
if (inode instanceof INodeWithAdditionalFields) {
map.put((INodeWithAdditionalFields)inode);
}
}

/**
* Remove a {@link INode} from the map.
* @param inode The {@link INode} to be removed.
*/
public final void remove(INode inode) {
map.remove(inode);
}

/**
* @return The size of the map.
*/
public int size() {
return map.size();
}

/**
* Get the {@link INode} with the given id from the map.
* @param id ID of the {@link INode}.
* @return The {@link INode} in the map with the given id. Return null if no
*         such {@link INode} in the map.
*/
public INode get(long id) {
INode inode = new INodeWithAdditionalFields(id, null, new PermissionStatus(
"", "", new FsPermission((short) 0)), 0, 0) {

@Override
void recordModification(int latestSnapshotId)
throws QuotaExceededException {
}

@Override
public void destroyAndCollectBlocks(BlocksMapUpdateInfo collectedBlocks,
List<INode> removedINodes) {
// Nothing to do
}

@Override
public Counts computeQuotaUsage(Counts counts, boolean useCache,
int lastSnapshotId) {
return null;
}

@Override
public ContentSummaryComputationContext computeContentSummary(
ContentSummaryComputationContext summary) {
return null;
}

@Override
public Counts cleanSubtree(int snapshotId, int priorSnapshotId,
BlocksMapUpdateInfo collectedBlocks, List<INode> removedINodes,
boolean countDiffChange) throws QuotaExceededException {
return null;
}

@Override
public byte getStoragePolicyID(){
return BlockStoragePolicySuite.ID_UNSPECIFIED;
}

@Override
public byte getLocalStoragePolicyID() {
return BlockStoragePolicySuite.ID_UNSPECIFIED;
}
};

return map.get(inode);
}

/**
* Clear the {@link #map}
*/
public void clear() {
map.clear();
}
}