org.apache.slider.core.persist

Class ConfPersister

java.lang.Object

org.apache.slider.core.persist.ConfPersister

public class ConfPersister
extends Object

Class to implement persistence of a configuration. This code contains the logic to acquire and release locks. # writelock MUST be acquired exclusively for writes. This is done by creating the file with no overwrite # shared readlock MUST be acquired for reads. This is done by creating the readlock file with overwrite forbidden -but treating a failure as a sign that the lock exists, and therefore the operation can continue. # releaselock is only released if the client created it. # after acquiring either lock, client must check for the alternate lock existing. If it is, release lock and fail. There's one small race here: multiple readers; first reader releases lock while second is in use. Strict Fix: client checks for readlock after read completed. If it is not there, problem: fail. But this massively increases the risk of false negatives. This isn't 100% perfect, because of the condition where the owner releases a lock, a writer grabs its lock & writes to it, the reader gets slightly contaminated data: own-share-delete-write-own-release(shared)-delete We are assuming that the rate of change is low enough that this is rare, and of limited damage. ONCE A CLUSTER IS RUNNING, ONLY THE AM MAY PERSIST UPDATES VIA ITS APIs That is: outside the AM, a writelock MUST only be acquired after verifying there is no running application.

Constructor Summary

Constructors

Constructor and Description
ConfPersister(CoreFileSystem coreFS, org.apache.hadoop.fs.Path persistDir)

Method Summary

Methods

Modifier and Type	Method and Description
org.apache.hadoop.fs.Path	getPersistDir() Get the target directory
void	load(AggregateConf conf) Load the configuration.
void	mkPersistDir() Make the persistent directory
void	save(AggregateConf conf, LockHeldAction action) Save the configuration
String	toString()

Methods inherited from class java.lang.Object

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

Constructor Detail

ConfPersister

public ConfPersister(CoreFileSystem coreFS,
             org.apache.hadoop.fs.Path persistDir)

Method Detail

getPersistDir

public org.apache.hadoop.fs.Path getPersistDir()

Get the target directory

Returns:

the directory for persistence

mkPersistDir

public void mkPersistDir()
                  throws IOException

Make the persistent directory

Throws:

IOException - IO failure

toString

public String toString()

Overrides:

toString in class Object

save

public void save(AggregateConf conf,
        LockHeldAction action)
          throws IOException,
                 SliderException,
                 LockAcquireFailedException

Save the configuration

Parameters:

conf - configuration to fill in

action -

Throws:

IOException - IO problems

LockAcquireFailedException - the lock could not be acquired

SliderException

load

public void load(AggregateConf conf)
          throws FileNotFoundException,
                 IOException,
                 SliderException,
                 LockAcquireFailedException

Load the configuration. If a lock failure is raised, the contents of the configuration MAY have changed -lock race conditions are looked for on exit

Parameters:

conf - configuration to fill in

Throws:

IOException - IO problems

LockAcquireFailedException - the lock could not be acquired

FileNotFoundException

SliderException