org.apache.river.mercury

Class TransientEventLog

java.lang.Object

org.apache.river.mercury.TransientEventLog

All Implemented Interfaces:

EventLog

class TransientEventLog
extends Object
implements EventLog

Class that implements the interface for an EventLog. This class encapsulates the details of reading/writing events from/to some non-persistent mechanism. This class makes certain assumptions. First, the next and remove methods are intended to be called in pairs. If remove is not called, then subsequent calls to next will attempt to return the same object. Calling remove essentially advances the read pointer to the next object, if any. There is also an implicit assumption of external synchronization by the caller. That is, only one calling thread will be accessing the log at a time.

Since:

2.0

Author:

Sun Microsystems, Inc.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
private static class	TransientEventLog.RemoteEventHolder Helper class used to hold a remote event and a sequence id.

Field Summary

Fields

Modifier and Type	Field and Description
private boolean	closed Flag that is used to determine whether or not this object has been closed.
private List	entries The associated, non-persistent storage for events
private java.util.concurrent.atomic.AtomicLong	eventCounter Counter used to produce event ids.
private boolean	initialized Flag that is used to determine whether or not this object has been initialized.
private static Logger	persistenceLogger Logger used for persistence-related debugging messages
private Uuid	uuid The associated Uuid for this EventLog.

Constructor Summary

Constructors

Constructor and Description
TransientEventLog(Uuid uuid) Simple constructor that takes a Uuid argument.

Method Summary

Modifier and Type	Method and Description
void	add(RemoteEvent event) Writes the given RemoteEvent to the underlying storage mechanism, if possible.
void	close() Close this log and release any associated runtime resources.
void	delete() Delete associated storage resources for this log.
void	init() Initializes the state of this EventLog object.
boolean	isEmpty() Returns true if this log contains no events and false otherwise.
void	moveAhead(Object cookie) Effectively removes the last set of read events from the log.
RemoteEvent	next() Return the next RemoteEvent to be read.
private void	printControlData(Logger logger, String msg) Output state information to the given Logger.
RemoteEventData[]	readAhead(int maxEvents) Return an array of RemoteEventData with a limit of maxEvents elements.
void	remove() Effectively removes the last read event from the log.
private void	stateCheck() Asserts that the log is in a valid state.

Methods inherited from class java.lang.Object

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

Field Detail

persistenceLogger

private static final Logger persistenceLogger

Logger used for persistence-related debugging messages

uuid

private final Uuid uuid

The associated Uuid for this EventLog.

entries

private final List entries

The associated, non-persistent storage for events

closed

private volatile boolean closed

Flag that is used to determine whether or not this object has been closed.

initialized

private volatile boolean initialized

Flag that is used to determine whether or not this object has been initialized.

eventCounter

private java.util.concurrent.atomic.AtomicLong eventCounter

Counter used to produce event ids.

Constructor Detail

TransientEventLog

TransientEventLog(Uuid uuid)

Simple constructor that takes a Uuid argument.

Throws:

IllegalArgumentException - if the argument is null

Method Detail

init

public void init()
          throws IOException

Description copied from interface: EventLog

Initializes the state of this EventLog object. The required functionality can potentially throw an IOException and has therefore been separated from from object construction.

Specified by:

init in interface EventLog

Throws:

IOException - if an I/O error occurs

stateCheck

private void stateCheck()
                 throws IOException

Asserts that the log is in a valid state.

Throws:

IOException - if the log is in an invalid state

add

public void add(RemoteEvent event)
         throws IOException

Description copied from interface: EventLog

Writes the given RemoteEvent to the underlying storage mechanism, if possible. If an IOException occurs, then the write cannot be guaranteed.

Specified by:

add in interface EventLog

Throws:

IOException - if an I/O error occurs

next

public RemoteEvent next()
                 throws IOException

Description copied from interface: EventLog

Return the next RemoteEvent to be read. Note that next is meant to be used in conjunction with remove. Subsequent calls to next will return the same event until remove is called, which actually updates the read pointer to the next event (indicating that the previously read event was successfully processed).

Specified by:

next in interface EventLog

Throws:

IOException - if an I/O error occurs

readAhead

public RemoteEventData[] readAhead(int maxEvents)
                            throws IOException

Description copied from interface: EventLog

Return an array of RemoteEventData with a limit of maxEvents elements. Note that readAhead is meant to be used in conjunction with moveAhead. Subsequent calls to readAhead with the same argument value will return the same set of events until moveAhead is called, which actually updates the read pointer to the next unread event (indicating that the previously read events were successfully processed).

Specified by:

readAhead in interface EventLog

Parameters:

maxEvents - maximum number of events/elements to return

Throws:

IOException - if an I/O error occurs

isEmpty

public boolean isEmpty()
                throws IOException

Description copied from interface: EventLog

Returns true if this log contains no events and false otherwise.

Specified by:

isEmpty in interface EventLog

Throws:

IOException

remove

public void remove()
            throws IOException

Description copied from interface: EventLog

Effectively removes the last read event from the log. It does this by advancing the read pointer to the next available event, if any.

Specified by:

remove in interface EventLog

Throws:

IOException

moveAhead

public void moveAhead(Object cookie)
               throws IOException

Description copied from interface: EventLog

Effectively removes the last set of read events from the log. It does this by advancing the read pointer to the next available event after the event associated with the provided cookie object.

Specified by:

moveAhead in interface EventLog

Parameters:

cookie - object associated with event to read past. This object should have been obtained from a call to getCookie() on a RemoteEventData object obtained from a call to readAhead on this event log.

Throws:

IOException - if there was a problem advancing the read pointer.

close

public void close()
           throws IOException

Description copied from interface: EventLog

Close this log and release any associated runtime resources.

Specified by:

close in interface EventLog

Throws:

IOException

delete

public void delete()
            throws IOException

Description copied from interface: EventLog

Delete associated storage resources for this log.

Specified by:

delete in interface EventLog

Throws:

IOException - if an IO error occurs

printControlData

private void printControlData(Logger logger,
                              String msg)

Output state information to the given Logger. This is intended for debugging purposes only.