edu.rice.hj.experimental.actors

Class ReaderWriterActor<MsgType>

java.lang.Object

edu.rice.hj.experimental.actors.Selector<ReadWriteEnum.ReaderWriterMessage<MsgType>>

edu.rice.hj.experimental.actors.ReaderWriterActor<MsgType>

public abstract class ReaderWriterActor<MsgType>
extends Selector<ReadWriteEnum.ReaderWriterMessage<MsgType>>

A ReaderWriterActor enables intra-actor parallelism by allowing multiple read messages to be processed in parallel. This allows for a greater level of concurrency in accessing shared data than that permitted by actors which process only one message at a time. It exploits the fact that while only a single thread at a time (a writer message) can modify the shared data, in many cases any number of threads can concurrently read the data (hence reader messages). In theory, the increase in concurrency permitted by the use of a read-write actors will lead to performance improvements over the use of a 'regular' actor. In practice this increase in concurrency will only be fully realized on a multi-processor, and then only if the access patterns for the shared data are suitable.

Messages are sent to this actor using the sendReadMessage() and sendWriteMessage() methods. Users are discouraged from using the send() method directly to send messages.

Policy decisions in the implementation: The messages are processed using an arrival-order policy, reader-first policy, or writer-first policy. By default we use the writer-first policy (i.e. writer messages get processed before reader messages). A writer is given preference as writes are expected to be short and infrequent. Preference to the writer can reduce the potential for concurrency. As soon as a write message is seen, any subsequent messages are prevented from being processed. The runtime waits until all in-flight read messages have been completely processed, then the write message is processed before enabling processing of messages following the write message.

The actual implementation uses DataDrivenControl instances to wait and trigger the execution of write messages when there are read messages in-flight.

Author:

Shams Imam (shams@rice.edu)

Field Summary

Fields inherited from class edu.rice.hj.experimental.actors.Selector

numClassifiers

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	ReaderWriterActor()
protected	ReaderWriterActor(ReaderWriterPolicy policy)

Method Summary

Modifier and Type	Method and Description
protected void	process(ReadWriteEnum.ReaderWriterMessage<MsgType> theMsg) Callback allowing user to have custom behavior while processing messages.
protected abstract void	processRead(MsgType theMsg) Callback allowing user to have custom behavior while processing 'read' messages.
protected abstract void	processWrite(MsgType theMsg) Callback allowing user to have custom behavior while processing 'write' messages.
void	sendReadMessage(MsgType message)
void	sendWriteMessage(MsgType message)

Methods inherited from class edu.rice.hj.experimental.actors.Selector

disable, disable, disableAllExcept, disableAllExcept, enable, enable, enableAll, exit, handleThrowable, hasStarted, isEnabled, isEnabled, onPostExit, onPostStart, onPreExit, onPreStart, send, send, start, start, tryProcessMessage

Methods inherited from class java.lang.Object

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

Constructor Detail

ReaderWriterActor

protected ReaderWriterActor()

Throws:

NullPointerException - if enumClass is null

IllegalArgumentException - if enumClass does not represent an enum

ReaderWriterActor

protected ReaderWriterActor(ReaderWriterPolicy policy)

Parameters:

policy - The reader-writer policy to use

Throws:

NullPointerException - if enumClass is null

IllegalArgumentException - if enumClass does not represent an enum

Method Detail

sendWriteMessage

public final void sendWriteMessage(MsgType message)

sendReadMessage

public final void sendReadMessage(MsgType message)

process

protected final void process(ReadWriteEnum.ReaderWriterMessage<MsgType> theMsg)

Description copied from class: Selector

Callback allowing user to have custom behavior while processing messages.

Specified by:

process in class Selector<ReadWriteEnum.ReaderWriterMessage<MsgType>>

Parameters:

theMsg - message to process

processWrite

protected abstract void processWrite(MsgType theMsg)

Callback allowing user to have custom behavior while processing 'write' messages.

Parameters:

theMsg - message to process

processRead

protected abstract void processRead(MsgType theMsg)

Callback allowing user to have custom behavior while processing 'read' messages.

Parameters:

theMsg - message to process