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## org.apache.hadoop.filecache
Class TrackerDistributedCacheManager

    java.lang.Object
      org.apache.hadoop.filecache.TrackerDistributedCacheManager

    public class TrackerDistributedCacheManager

extends Object

Manages a single machine's instance of a cross-job cache. This class would typically be instantiated by a TaskTracker (or something that emulates it, like LocalJobRunner). This class is internal to Hadoop, and should not be treated as a public interface.

Nested Class Summary
`protected class` | `TrackerDistributedCacheManager.BaseDirManager` This class holds properties of each base directories and is responsible for clean up unused cache files in base directories.
`protected class` | `TrackerDistributedCacheManager.CleanupThread` A thread to check and cleanup the unused files periodically

Field Summary
`protected TrackerDistributedCacheManager.BaseDirManager` | `baseDirManager`
`protected TrackerDistributedCacheManager.CleanupThread` | `cleanupThread`

Constructor Summary
`TrackerDistributedCacheManager(Configuration conf, TaskController controller)`

Method Summary
`static void` | `createAllSymlink(Configuration conf, File jobCacheDir, File workDir)` This method create symlinks for all files in a given dir in another directory.
`static void` | `determineCacheVisibilities(Configuration job)` Determines the visibilities of the distributed cache files and archives.
`static void` | `determineTimestamps(Configuration job)` Determines timestamps of files to be cached, and stores those in the configuration.
`static long` | `downloadCacheObject(Configuration conf, URI source, Path destination, long desiredTimestamp, boolean isArchive, FsPermission permission)` Download a given path to the local file system.
`static boolean[]` | `getArchiveVisibilities(Configuration conf)` Get the booleans on whether the archives are public or not.
`static void` | `getDelegationTokens(Configuration job, Credentials credentials)` For each archive or cache file - get the corresponding delegation token
`static boolean[]` | `getFileVisibilities(Configuration conf)` Get the booleans on whether the files are public or not.
`TaskDistributedCacheManager` | `newTaskDistributedCacheManager(JobID jobId, Configuration taskConf)`
`void` | `purgeCache()` Clear the entire contents of the cache and delete the backing files.
`void` | `setArchiveSizes(JobID jobId, long[] sizes)`
`void` | `startCleanupThread()` Start the background thread
`void` | `stopCleanupThread()` Stop the background thread
`static void` | `validate(Configuration conf)` This is part of the framework API.

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

### baseDirManager

    protected TrackerDistributedCacheManager.BaseDirManager baseDirManager

### cleanupThread

    protected TrackerDistributedCacheManager.CleanupThread cleanupThread

Constructor Detail

### TrackerDistributedCacheManager

    public TrackerDistributedCacheManager(Configuration conf,
                                          TaskController controller)
                                   throws IOException

Throws:
  `IOException`

Method Detail

### downloadCacheObject

    public static long downloadCacheObject(Configuration conf,
                                           URI source,
                                           Path destination,
                                           long desiredTimestamp,
                                           boolean isArchive,
                                           FsPermission permission)
                                    throws IOException

  Download a given path to the local file system.

  Parameters:
    `conf` - the job's configuration
    `source` - the source to copy from
    `destination` - where to copy the file. must be local fs
    `desiredTimestamp` - the required modification timestamp of the source
    `isArchive` - is this an archive that should be expanded
    `permission` - the desired permissions of the file.
  Returns:
    for archives, the number of bytes in the unpacked directory
  Throws:
    `IOException`

### createAllSymlink

    public static void createAllSymlink(Configuration conf,
                                        File jobCacheDir,
                                        File workDir)
                                 throws IOException

  This method create symlinks for all files in a given dir in another directory. Should not be used outside of DistributedCache code.

  Parameters:
    `conf` - the configuration
    `jobCacheDir` - the target directory for creating symlinks
    `workDir` - the directory in which the symlinks are created
  Throws:
    `IOException`

### purgeCache

    public void purgeCache()

  Clear the entire contents of the cache and delete the backing files. This should only be used when the server is reinitializing, because the users are going to lose their files.

### newTaskDistributedCacheManager

    public TaskDistributedCacheManager newTaskDistributedCacheManager(JobID jobId,
                                                                      Configuration taskConf)
                                                               throws IOException

  Throws:
    `IOException`

### setArchiveSizes

    public void setArchiveSizes(JobID jobId,
                                long[] sizes)
                         throws IOException

  Throws:
    `IOException`

### determineTimestamps

    public static void determineTimestamps(Configuration job)
                                    throws IOException

  Determines timestamps of files to be cached, and stores those in the configuration. This is intended to be used internally by JobClient after all cache files have been added. This is an internal method!

  Parameters:
    `job` - Configuration of a job.
  Throws:
    `IOException`

### determineCacheVisibilities

    public static void determineCacheVisibilities(Configuration job)
                                           throws IOException

  Determines the visibilities of the distributed cache files and archives. The visibility of a cache path is "public" if the leaf component has READ permissions for others, and the parent subdirs have EXECUTE permissions for others

  Parameters:
    `job` -
  Throws:
    `IOException`

### getFileVisibilities

    public static boolean[] getFileVisibilities(Configuration conf)

  Get the booleans on whether the files are public or not. Used by internal DistributedCache and MapReduce code.

  Parameters:
    `conf` - The configuration which stored the timestamps
  Returns:
    array of booleans
  Throws:
    `IOException`

### getArchiveVisibilities

    public static boolean[] getArchiveVisibilities(Configuration conf)

  Get the booleans on whether the archives are public or not. Used by internal DistributedCache and MapReduce code.

  Parameters:
    `conf` - The configuration which stored the timestamps
  Returns:
    array of booleans

### getDelegationTokens

    public static void getDelegationTokens(Configuration job,
                                           Credentials credentials)
                                    throws IOException

  For each archive or cache file - get the corresponding delegation token

  Parameters:
    `job` -
    `credentials` -
  Throws:
    `IOException`

### validate

    public static void validate(Configuration conf)
                         throws InvalidJobConfException

  This is part of the framework API. It's called within the job submission code only, not by users. In the non-error case it has no side effects and returns normally. If there's a URI in both mapred.cache.files and mapred.cache.archives, it throws its exception.

  Parameters:
    `conf` - a `Configuration` to be cheked for duplication in cached URIs
  Throws:
    `InvalidJobConfException`

### startCleanupThread

    public void startCleanupThread()

  Start the background thread

### stopCleanupThread

    public void stopCleanupThread()

  Stop the background thread

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