Yarn下分片和分块源代码分析

public class FileSplit extends InputSplit implements Writable {
	private Path file;
	private long start;
	private long length;
	private String[] hosts;

	public FileSplit() {
	}

	public FileSplit(Path file, long start, long length, String[] hosts) {
		this.file = file;
		this.start = start;
		this.length = length;
		this.hosts = hosts;
	}

	public Path getPath() {
		return this.file;
	}

	public long getStart() {
		return this.start;
	}

	public long getLength() {
		return this.length;
	}

	public String toString() {
		return this.file + ":" + this.start + "+" + this.length;
	}

	public void write(DataOutput out) throws IOException {
		Text.writeString(out, this.file.toString());
		out.writeLong(this.start);
		out.writeLong(this.length);
	}

	public void readFields(DataInput in) throws IOException {
		this.file = new Path(Text.readString(in));
		this.start = in.readLong();
		this.length = in.readLong();
		this.hosts = null;
	}

	public String[] getLocations() throws IOException {
		if (this.hosts == null) {
			return new String[0];
		}
		return this.hosts;
	}
}

代码比较简单， 四部分组成  文件路径 ，启始位置，长度，Host列表

Host为什么是个列表

看分片的时候创建函数

splits.add(makeSplit(path, length - bytesRemaining,
                                splitSize, blkLocations[blkIndex].getHosts()));

再来看块的源代码

public class BlockLocation {
    private String[] hosts;
    private String[] names;
    private String[] topologyPaths;
    private long offset;
    private long length;
    private boolean corrupt;

    public BlockLocation() {
        this(new String[0], new String[0], 0L, 0L);
    }

    public BlockLocation(String[] names, String[] hosts, long offset,
            long length) {
        this(names, hosts, offset, length, false);
    }

    public BlockLocation(String[] names, String[] hosts, long offset,
            long length, boolean corrupt) {
        if (names == null)
            this.names = new String[0];
        else {
            this.names = names;
        }
        if (hosts == null)
            this.hosts = new String[0];
        else {
            this.hosts = hosts;
        }
        this.offset = offset;
        this.length = length;
        this.topologyPaths = new String[0];
        this.corrupt = corrupt;
    }

    public BlockLocation(String[] names, String[] hosts,
            String[] topologyPaths, long offset, long length) {
        this(names, hosts, topologyPaths, offset, length, false);
    }

    public BlockLocation(String[] names, String[] hosts,
            String[] topologyPaths, long offset, long length, boolean corrupt) {
        this(names, hosts, offset, length, corrupt);
        if (topologyPaths == null)
            this.topologyPaths = new String[0];
        else
            this.topologyPaths = topologyPaths;
    }

    public String[] getHosts() throws IOException {
        if ((this.hosts == null) || (this.hosts.length == 0)) {
            return new String[0];
        }
        return this.hosts;
    }

    public String[] getNames() throws IOException {
        if ((this.names == null) || (this.names.length == 0)) {
            return new String[0];
        }
        return this.names;
    }

    public String[] getTopologyPaths() throws IOException {
        if ((this.topologyPaths == null) || (this.topologyPaths.length == 0)) {
            return new String[0];
        }
        return this.topologyPaths;
    }

    public long getOffset() {
        return this.offset;
    }

    public long getLength() {
        return this.length;
    }

    public boolean isCorrupt() {
        return this.corrupt;
    }

    public void setOffset(long offset) {
        this.offset = offset;
    }

    public void setLength(long length) {
        this.length = length;
    }

    public void setCorrupt(boolean corrupt) {
        this.corrupt = corrupt;
    }

    public void setHosts(String[] hosts) throws IOException {
        if (hosts == null)
            this.hosts = new String[0];
        else
            this.hosts = hosts;
    }

    public void setNames(String[] names) throws IOException {
        if (names == null)
            this.names = new String[0];
        else
            this.names = names;
    }

    public void setTopologyPaths(String[] topologyPaths) throws IOException {
        if (topologyPaths == null)
            this.topologyPaths = new String[0];
        else
            this.topologyPaths = topologyPaths;
    }

    public String toString() {
        StringBuilder result = new StringBuilder();
        result.append(this.offset);
        result.append(',');
        result.append(this.length);
        if (this.corrupt) {
            result.append("(corrupt)");
        }
        for (String h : this.hosts) {
            result.append(',');
            result.append(h);
        }
        return result.toString();
    }
}