com.tangosol.io
Class AsyncBinaryStore

java.lang.Object
  com.tangosol.util.Base
      com.tangosol.io.AsyncBinaryStore

All Implemented Interfaces:

BinaryStore

public class AsyncBinaryStore
extends Base
implements BinaryStore

An AsyncBinaryStore is a BinaryStore wrapper that performs the "O" (output) portion of its I/O asynchronously on a daemon thread. The output portion consists of store and erase processing.

Since the "O" portion is passed along to the wrapped BinaryStore on a separate thread, only read operations are blocking, thus the BinaryStore operations on a whole appear much faster. As such, it is somewhat analogous to a write-behind cache.

If an operation fails on the daemon thread, all further operations will occur synchronously, so that exceptions will propagate successfully up. It is assumed that once one exception occurs, the underlying BinaryStore is in a state that will cause more exceptions to occur. Even when an exception occurs on the daemon thread, that write-behind data will not be "lost" because it will still be available in the internal data structures that keeps track of pending writes.

Since:

Coherence 2.5

Author:

cp 2004.06.18

Nested Class Summary

protected class

AsyncBinaryStore.QueueDaemon A daemon that processes queued writes.

Field Summary

protected static int	DEFAULT_LIMIT Default size limit for write-queued data.
protected static Binary	DELETED A special token that is used to signify a queued erase operation.
protected static Object	LOCK_ALL Special key to indicate that all keys should be locked.
protected static long	WAIT_FOREVER Special wait time to indicate that a lock should be blocked on until it becomes available.

Constructor Summary

AsyncBinaryStore(BinaryStore store)
Construct an AsyncBinaryStore.

AsyncBinaryStore(BinaryStore store, int cbMax)
Construct an AsyncBinaryStore.

Method Summary

void	close() Close the store.
protected AsyncBinaryStore.QueueDaemon	ensureQueueDaemon() Obtain the QueueDaemon, if one already exists; otherwise, create and start one.
void	erase(Binary binKey) Remove the specified key from the underlying store if present.
void	eraseAll() Remove all data from the underlying store.
protected void	finalize() Perform cleanup during garbage collection.
void	forceSync() Indicate the future write operations must be synchronous.
BinaryStore	getBinaryStore() Obtain the BinaryStore that this AsyncBinaryStore wraps.
protected ConcurrentMap	getPendingMap() Obtain the map that contains all of the pending store and erase data.
protected AsyncBinaryStore.QueueDaemon	getQueueDaemon()
int	getQueuedLimit() Determine the size, in bytes, of the data that can be queued to be written asynchronously by the QueueDaemon thread.
int	getQueuedSize() Determine the current number of bytes that are pending being written.
protected AsyncBinaryStore.QueueDaemon	instantiateQueueDaemon() Factory method: Instantiate a QueueDaemon.
boolean	isAsync() Determine if the AsyncBinaryStore is operating in an asynchronous manner.
Iterator	keys() Iterate all keys in the underlying store.
Binary	load(Binary binKey) Return the value associated with the specified key, or null if the key does not have an associated value in the underlying store.
protected void	setBinaryStore(BinaryStore store) Specify the underlying BinaryStore.
protected void	setQueueDaemon(AsyncBinaryStore.QueueDaemon daemon)
void	store(Binary binKey, Binary binValue) Store the specified value under the specific key in the underlying store.
String	toString() Return a human readable description of the AsyncBinaryStore.
protected void	updateQueuedSize(int cb) Update the number of bytes that are pending to be written.

Field Detail

DELETED

protected static final Binary DELETED

A special token that is used to signify a queued erase operation.

DEFAULT_LIMIT

protected static final int DEFAULT_LIMIT

Default size limit for write-queued data.

See Also:

Constant Field Values

LOCK_ALL

protected static final Object LOCK_ALL

Special key to indicate that all keys should be locked.

WAIT_FOREVER

protected static final long WAIT_FOREVER

Special wait time to indicate that a lock should be blocked on until it becomes available.

See Also:

Constant Field Values

Constructor Detail

AsyncBinaryStore

public AsyncBinaryStore(BinaryStore store)

Construct an AsyncBinaryStore. An AsyncBinaryStor wrap other BinaryStore objects to provide asynchronous write operations.

The new AsyncBinaryStore will queue a maximum of 4194304 bytes (4 MB) before blocking.

Parameters:

store - the BinaryStore to wrap

AsyncBinaryStore

public AsyncBinaryStore(BinaryStore store,
                        int cbMax)

Construct an AsyncBinaryStore. An AsyncBinaryStor wrap other BinaryStore objects to provide asynchronous write operations.

Parameters:

store - the BinaryStore to wrap

cbMax - the maximum number of bytes to queue before blocking

Method Detail

load

public Binary load(Binary binKey)

Return the value associated with the specified key, or null if the key does not have an associated value in the underlying store.

Specified by:

load in interface BinaryStore

Parameters:

binKey - key whose associated value is to be returned

Returns:

the value associated with the specified key, or null if no value is available for that key

store

public void store(Binary binKey,
                  Binary binValue)

Store the specified value under the specific key in the underlying store. This method is intended to support both key/value creation and value update for a specific key.

Specified by:

store in interface BinaryStore

Parameters:

binKey - key to store the value under

binValue - value to be stored

Throws:

UnsupportedOperationException - if this implementation or the underlying store is read-only

erase

public void erase(Binary binKey)

Remove the specified key from the underlying store if present.

Specified by:

erase in interface BinaryStore

Parameters:

binKey - key whose mapping is to be removed from the map

Throws:

UnsupportedOperationException - if this implementation or the underlying store is read-only

eraseAll

public void eraseAll()

Remove all data from the underlying store.

Specified by:

eraseAll in interface BinaryStore

Throws:

UnsupportedOperationException - if this implementation or the underlying store is read-only

keys

public Iterator keys()

Iterate all keys in the underlying store.

Specified by:

keys in interface BinaryStore

Returns:

a read-only iterator of the keys in the underlying store

Throws:

UnsupportedOperationException - if the underlying store is not iterable

close

public void close()

Close the store.

getBinaryStore

public BinaryStore getBinaryStore()

Obtain the BinaryStore that this AsyncBinaryStore wraps. The wrapped BinaryStore is also referred to as the "underlying" BinaryStore. All I/O operations are delegated to the underlying BinaryStore; some write operations are performed asynchronously on the QueueDaemon thread.

Returns:

the underlying BinaryStore

setBinaryStore

protected void setBinaryStore(BinaryStore store)

Specify the underlying BinaryStore. When the AsyncBinaryStore is closed, it should clear out its reference to the underlying BinaryStore to indicate that it no longer is open.

Parameters:

store - the underlying BinaryStore

getQueuedLimit

public int getQueuedLimit()

Determine the size, in bytes, of the data that can be queued to be written asynchronously by the QueueDaemon thread. Once the limit is exceeded, operations will be forced to be synchronous to avoid running out of memory or getting too far behind on the I/O operations.

Returns:

the number of bytes allowed to be queued to be written

getQueuedSize

public int getQueuedSize()

Determine the current number of bytes that are pending being written.

Returns:

the number of bytes currently queued to be written

updateQueuedSize

protected void updateQueuedSize(int cb)

Update the number of bytes that are pending to be written.

Parameters:

cb - the number of bytes that the queue length changed by

isAsync

public boolean isAsync()

Determine if the AsyncBinaryStore is operating in an asynchronous manner.

Returns:

true if the AsyncBinaryStore is still operating in an async mode

forceSync

public void forceSync()

Indicate the future write operations must be synchronous.

getPendingMap

protected ConcurrentMap getPendingMap()

Obtain the map that contains all of the pending store and erase data. The key of the map is a Binary key to pass to the underlying store. The corresponding value will be DELETED to indicate an erase operation, otherwise it will be a Binary value.

Returns:

the ConcurrentMap that keeps track of all the pending writes

toString

public String toString()

Return a human readable description of the AsyncBinaryStore.

Returns:

a String description of the AsyncBinaryStore

finalize

protected void finalize()

Perform cleanup during garbage collection.

getQueueDaemon

protected AsyncBinaryStore.QueueDaemon getQueueDaemon()

Returns:

the daemon that manages the write-behind queue

setQueueDaemon

protected void setQueueDaemon(AsyncBinaryStore.QueueDaemon daemon)

Parameters:

daemon - the daemon that manages the write-behind queue

ensureQueueDaemon

protected AsyncBinaryStore.QueueDaemon ensureQueueDaemon()

Obtain the QueueDaemon, if one already exists; otherwise, create and start one.

Returns:

the daemon that manages the write-behind queue

instantiateQueueDaemon

protected AsyncBinaryStore.QueueDaemon instantiateQueueDaemon()

Factory method: Instantiate a QueueDaemon.

Returns:

a new QueueDaemon, but not started