Package org.apache.hadoop.fs

Class HardLink

java.lang.Object

org.apache.hadoop.fs.HardLink

Direct Known Subclasses:

FileUtil.HardLink

public class HardLink
extends Object

Class for creating hardlinks. Supports Unix/Linux, Windows via winutils , and Mac OS X. The HardLink class was formerly a static inner class of FSUtil, and the methods provided were blatantly non-thread-safe. To enable volume-parallel Update snapshots, we now provide static threadsafe methods that allocate new buffer string arrays upon each call. We also provide an API to hardlink all files in a directory with a single command, which is up to 128 times more efficient - and minimizes the impact of the extra buffer creations.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	HardLink.LinkStats	HardLink statistics counters and methods.

Field Summary

Fields

Modifier and Type	Field	Description
final HardLink.LinkStats	linkStats

Constructor Summary

Constructors

Constructor	Description
HardLink()

Method Summary

Modifier and Type	Method	Description
static void	createHardLink(File file, File linkName)	Creates a hardlink.
static void	createHardLinkMult(File parentDir, String[] fileBaseNames, File linkDir)	Creates hardlinks from multiple existing files within one parent directory, into one target directory.
static int	getLinkCount(File fileName)	Retrieves the number of links to the specified file.
static boolean	supportsHardLink(File f)	Determines whether the system supports hardlinks.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

linkStats

public final HardLink.LinkStats linkStats

Constructor Details

HardLink

public HardLink()

Method Details

createHardLink

public static void createHardLink(File file,
 File linkName)
                           throws IOException

Creates a hardlink.

Parameters:

file - - existing source file

linkName - - desired target link file

Throws:

IOException - raised on errors performing I/O.

createHardLinkMult

public static void createHardLinkMult(File parentDir,
 String[] fileBaseNames,
 File linkDir)
                               throws IOException

Creates hardlinks from multiple existing files within one parent directory, into one target directory.

Parameters:

parentDir - - directory containing source files

fileBaseNames - - list of path-less file names, as returned by parentDir.list()

linkDir - - where the hardlinks should be put. It must already exist.

Throws:

IOException - raised on errors performing I/O.

supportsHardLink

public static boolean supportsHardLink(File f)

Determines whether the system supports hardlinks.

Parameters:

f - - file to examine

Returns:

true if hardlinks are supported, false otherwise

getLinkCount

public static int getLinkCount(File fileName)
                        throws IOException

Retrieves the number of links to the specified file.

Parameters:

fileName - file name.

Returns:

link count.

Throws:

IOException - raised on errors performing I/O.