Package lcm.lcm

Class MessageAggregator

java.lang.Object

lcm.lcm.MessageAggregator

All Implemented Interfaces:

LCMSubscriber

public class MessageAggregator
extends Object
implements LCMSubscriber

Accumulates received LCM messages in a queue.

LCM normally delivers messages asynchronously by invoking the messageReceived method on a subscriber as soon as a message is received. This class provides an alternate way to receive messages by storing them in an internal queue, and then delivering them to synchronously to the user.

The aggregator has configurable limits. If too many messages are aggregated without having been retrieved, then older messages are discarded.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
class	MessageAggregator.Message	A received message.

Constructor Summary

Constructors

Constructor	Description
MessageAggregator()

Method Summary

Modifier and Type	Method	Description
long	getMaxBufferSize()	Retrieves the maximum amount of memory that will be used to store messages.
int	getMaxMessages()	Retrieves the maximum number of unretrieved message that will be queued up by the aggregator.
MessageAggregator.Message	getNextMessage()	Retrieves the next message, waiting if necessary.
MessageAggregator.Message	getNextMessage(long timeout_ms)	Attempt to retrieve the next received LCM message.
void	messageReceived(LCM lcm, String channel, lcm.lcm.LCMDataInputStream dins)	Internal method, called by LCM when a message is received.
int	numMessagesAvailable()	Returns the number of received messages waiting to be retrieved.
void	setMaxBufferSize(long val)	Sets the maximum amount of memory that will be used to store messages.
void	setMaxMessages(int val)	Sets the maximum number of unretrieved message that will be queued up by the aggregator.

Methods inherited from class java.lang.Object

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

Constructor Details

MessageAggregator

public MessageAggregator()

Method Details

messageReceived

public void messageReceived(LCM lcm,
 String channel,
 lcm.lcm.LCMDataInputStream dins)

Internal method, called by LCM when a message is received.

Specified by:

messageReceived in interface LCMSubscriber

Parameters:

lcm - the LCM instance that received the message.

channel - the channel on which the message was received.

dins - the message contents.

setMaxBufferSize

public void setMaxBufferSize(long val)

Sets the maximum amount of memory that will be used to store messages. This is an alternative way to limit the messages stored by the aggregator. Messages are discarded oldest-first to ensure that the total size of unretrieved messages stays under this limit.

Parameters:

val - memory limit, in bytes.

getMaxBufferSize

public long getMaxBufferSize()

Retrieves the maximum amount of memory that will be used to store messages.

setMaxMessages

public void setMaxMessages(int val)

Sets the maximum number of unretrieved message that will be queued up by the aggregator. Messages are discarded oldest-first to ensure that the number of unretrieved messages stays under this limit.

getMaxMessages

public int getMaxMessages()

Retrieves the maximum number of unretrieved message that will be queued up by the aggregator.

getNextMessage

public MessageAggregator.Message getNextMessage(long timeout_ms)

Attempt to retrieve the next received LCM message.

Parameters:

timeout_ms - Max # of milliseconds to wait for a message. If 0, then don't wait. If less than 0, then wait indefinitely.

Returns:

a Message, or null if no message was received.

getNextMessage

public MessageAggregator.Message getNextMessage()

Retrieves the next message, waiting if necessary.

numMessagesAvailable

public int numMessagesAvailable()

Returns the number of received messages waiting to be retrieved.