org.cache2k.impl

Class ClearStorageBuffer

java.lang.Object

org.cache2k.impl.ClearStorageBuffer

All Implemented Interfaces:

CacheStorage, FlushableStorage, PurgeableStorage

public class ClearStorageBuffer
extends Object
implements CacheStorage, FlushableStorage, PurgeableStorage

Record cache operations during a storage clear and playback later.

By decoupling we still have fast concurrent access on the cache while the storage "does its thing" and remove files, etc. This is now just used for the clear() operation, so it is assumed that the initial state of the storage is empty.

After playback starts, and if the requests come in faster than the storage can handle it we will end up queuing up requests forever, which means we will loose the cache properties and run out of heap space. To avoid this, we slow down the acceptance of new requests as soon as the storage playback starts.

The normal operations like (get, put and remove) fill the playback queue. They also check within the lock whether the storage is online again. This is needed to make the reconnect of the storage atomically. It must be assured that all operations are sent and that the order is kept intact.

Right now, the storage is only operated single threaded by the buffer playback.

TODO-C: Multi threaded storage playback

Author:

Jens Wilke; created: 2014-04-20

Nested Class Summary

Nested classes/interfaces inherited from interface org.cache2k.storage.FlushableStorage

FlushableStorage.FlushContext

Nested classes/interfaces inherited from interface org.cache2k.storage.CacheStorage

CacheStorage.EntryFilter, CacheStorage.EntryVisitor, CacheStorage.MultiThreadedContext, CacheStorage.VisitContext

Nested classes/interfaces inherited from interface org.cache2k.storage.PurgeableStorage

PurgeableStorage.PurgeAction, PurgeableStorage.PurgeContext, PurgeableStorage.PurgeResult

Constructor Summary

Constructors

Constructor and Description
ClearStorageBuffer()

Method Summary

Methods

Modifier and Type	Method and Description
void	clear() Remove all entries from the cache and free resources.
void	close() Free all resources and stop operations immediately.
boolean	contains(Object key) Returns true if there is a mapping for the key.
void	disableOnFailure(Throwable t)
void	flush(FlushableStorage.FlushContext ctx, long now) Stall this thread until the op is executed.
StorageEntry	get(Object key) Retrieve the entry from the storage.
int	getEntryCount()
boolean	isTransferringToStorage()
PurgeableStorage.PurgeResult	purge(PurgeableStorage.PurgeContext ctx, long _valueExpiryTime, long _entryExpiryTime) Does nothing.
void	put(StorageEntry e) Stores the entry in the storage.
boolean	remove(Object key)
void	startTransfer()
void	transfer()
void	visit(CacheStorage.VisitContext ctx, CacheStorage.EntryFilter f, CacheStorage.EntryVisitor v) Iterate over all stored entries and call the entry visitor.

Methods inherited from class java.lang.Object

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

Constructor Detail

ClearStorageBuffer

public ClearStorageBuffer()

Method Detail

flush

public void flush(FlushableStorage.FlushContext ctx,
         long now)
           throws Exception

Stall this thread until the op is executed. However, the op is doing nothing and just notifies us. The flush on the storage can run in parallel with other tasks. This method is only allowed to finish when the flush is done.

Specified by:

flush in interface FlushableStorage

Throws:

Exception

purge

public PurgeableStorage.PurgeResult purge(PurgeableStorage.PurgeContext ctx,
                                 long _valueExpiryTime,
                                 long _entryExpiryTime)

Does nothing. We were cleared lately anyway. Next purge may go to the storage.

Specified by:

purge in interface PurgeableStorage

Parameters:

ctx - Provides a multi-threaded context. Thread resources for purge operations may be more limited or may have lower priority.

_valueExpiryTime - request to remove entries with lower value of StorageEntry.getValueExpiryTime()

_entryExpiryTime - request to remove entries with with lower value of StorageEntry.getEntryExpiryTime()

Returns:

statistical result of the operation, if nothing was done null.

close

public void close()
           throws Exception

Description copied from interface: CacheStorage

Free all resources and stop operations immediately.

Specified by:

close in interface CacheStorage

Throws:

Exception

clear

public void clear()
           throws Exception

Description copied from interface: CacheStorage

Remove all entries from the cache and free resources. This operation is called when there is no other operation concurrently executed on this storage instance.

When a Cache.clear() is initiated there is no obligation to send a CacheStorage.clear() to the persisted storage. Alternatively, all objects can be removed via remove().

Specified by:

clear in interface CacheStorage

Throws:

Exception

put

public void put(StorageEntry e)
         throws Exception

Description copied from interface: CacheStorage

Stores the entry in the storage. The entry instance is solely for transferring the data, no reference may be hold within the storage to it. The callee takes care that the entry data is consistent during the put method call.

If a put operation fails an implementation should try to remove an existing entry bound to the key and then throw the exception.

Specified by:

put in interface CacheStorage

Throws:

IOException - may be thrown if hope is lost

Exception

get

public StorageEntry get(Object key)
                 throws Exception

Description copied from interface: CacheStorage

Retrieve the entry from the storage. If there is no mapping for the key, null is returned.

Depending on the cache configuration, an exception on get is not severe. The cache will try other sources or return null.

Specified by:

get in interface CacheStorage

Throws:

Exception

remove

public boolean remove(Object key)
               throws Exception

Specified by:

remove in interface CacheStorage

Throws:

Exception

contains

public boolean contains(Object key)
                 throws Exception

Description copied from interface: CacheStorage

Returns true if there is a mapping for the key.

An exception on contains is not severe. The cache will try other sources or return null.

Specified by:

contains in interface CacheStorage

Throws:

Exception

visit

public void visit(CacheStorage.VisitContext ctx,
         CacheStorage.EntryFilter f,
         CacheStorage.EntryVisitor v)
           throws Exception

Description copied from interface: CacheStorage

Iterate over all stored entries and call the entry visitor. It is generally safe to return expired entries. If PurgeableStorage is not implemented, returning expired entries is a must, to support the generic purge algorithm.

If the ExecutorService is used, the method may return immediately without the waiting for all threads to finish. This is done by the caller, when needed.

Specified by:

visit in interface CacheStorage

Throws:

Exception

getEntryCount

public int getEntryCount()

Specified by:

getEntryCount in interface CacheStorage

startTransfer

public void startTransfer()

isTransferringToStorage

public boolean isTransferringToStorage()

transfer

public void transfer()
              throws Exception

Throws:

Exception

disableOnFailure

public void disableOnFailure(Throwable t)