gr.uoa.di.madgik.grs.proxy.http.mirror

Class HTTPReaderMirror

java.lang.Object

java.lang.Thread

gr.uoa.di.madgik.grs.proxy.http.mirror.HTTPReaderMirror

All Implemented Interfaces:

IMirror, Runnable

public class HTTPReaderMirror
extends Thread
implements IMirror

This implementation of the IMirror interface specializes the mirroring procedure that needs to be performed from the reader side of the mirroring procedure. The technology employed is communication over HTTP connections. The communication protocol is coupled with the one implemented by the HTTPWriterMirror which is the writer side counterpart of this class.

Author:

Alex Antoniadis

Nested Class Summary

Nested classes/interfaces inherited from class java.lang.Thread

Thread.State, Thread.UncaughtExceptionHandler

Nested classes/interfaces inherited from interface gr.uoa.di.madgik.grs.proxy.mirror.IMirror

IMirror.MirroringState

Field Summary

Fields

Modifier and Type	Field and Description
static long	LongMirrorPeriod The default max period of communication inactivity time span.
static int	ReaderTimout
static long	ShortMirrorPeriod The default min period of communication inactivity time span.

Fields inherited from class java.lang.Thread

MAX_PRIORITY, MIN_PRIORITY, NORM_PRIORITY

Constructor Summary

Constructors

Constructor and Description
HTTPReaderMirror()

Method Summary

Methods

Modifier and Type	Method and Description
void	dispose() Dispose the resources employed by the mirroring implementations
void	dispose(boolean purge) This method disposes the resources that are used by the instance but does so in two phases.
IBuffer	getBuffer() Retrieves the IBuffer that is managed by the IMirror implementation.
GRS2ProxyMirrorProtocolErrorException	getInitializationError() In case the initialization was not successful, and the call to waitInitialization() returned false, this method will return the error that was recorded during the initialization.
void	handle() This invocation of this method starts a new execution thread where the mirroring procedure is executed.
void	overrideBufferCapacity(int capacity) Instructs the mirror to use a different buffer capacity than that transmitted by the respective HTTPWriterMirror.
boolean	pollPartial(long recordIndex, int fieldIndex)
long	requestPartial(long recordIndex, int fieldIndex, IBuffer.TransportOverride override, Object notify) This method is used by the reader side mirror to request payload that belongs to an IBuffer item that has been transfered only partially and more data is requested by the reader client
void	run()
void	setHostname(String hostname) Sets the name of the host where the respective HTTPWriterMirror instance is running
void	setKey(String key) Sets the key on the remote registry that holds the IBuffer this mirror is interested in consuming
void	setPort(int port) Sets the port in the remote host where the respective HTTPWriterMirror is listening
boolean	waitInitialization() This method can be used by HTTPReaderMirror clients, that want to be sure that the initialization procedure of the protocol is completed before they continue their operation.

Methods inherited from class java.lang.Thread

activeCount, checkAccess, clone, countStackFrames, currentThread, destroy, dumpStack, enumerate, getAllStackTraces, getContextClassLoader, getDefaultUncaughtExceptionHandler, getId, getName, getPriority, getStackTrace, getState, getThreadGroup, getUncaughtExceptionHandler, holdsLock, interrupt, interrupted, isAlive, isDaemon, isInterrupted, join, join, join, resume, setContextClassLoader, setDaemon, setDefaultUncaughtExceptionHandler, setName, setPriority, setUncaughtExceptionHandler, sleep, sleep, start, stop, stop, suspend, toString, yield

Methods inherited from class java.lang.Object

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

Field Detail

LongMirrorPeriod

public static final long LongMirrorPeriod

The default max period of communication inactivity time span. Depending on the previous communication exchange this or the respective ShortMirrorPeriod is used. Currently this value is set to 100 milliseconds

See Also:

Constant Field Values

ShortMirrorPeriod

public static final long ShortMirrorPeriod

The default min period of communication inactivity time span. Depending on the previous communication exchange this or the respective LongMirrorPeriod is used. Currently this value is set to 50 milliseconds

See Also:

Constant Field Values

ReaderTimout

public static final int ReaderTimout

See Also:

Constant Field Values

Constructor Detail

HTTPReaderMirror

public HTTPReaderMirror()

Method Detail

setHostname

public void setHostname(String hostname)

Sets the name of the host where the respective HTTPWriterMirror instance is running

Parameters:

hostname - the name of the host

setPort

public void setPort(int port)

Sets the port in the remote host where the respective HTTPWriterMirror is listening

Parameters:

port - the port number

setKey

public void setKey(String key)

Sets the key on the remote registry that holds the IBuffer this mirror is interested in consuming

Parameters:

key - the registry key of the IBuffer to consume

overrideBufferCapacity

public void overrideBufferCapacity(int capacity)

Instructs the mirror to use a different buffer capacity than that transmitted by the respective HTTPWriterMirror. Capacity overriding only takes place if the requested capacity is smaller than the one specified by the respective HTTPWriterMirror, otherwise the latter is used

Parameters:

capacity - The buffer capacity

getBuffer

public IBuffer getBuffer()

Retrieves the IBuffer that is managed by the IMirror implementation. Depending on the mirror side, this instance is either the one the writer is authoring, or the one the reader is accessing.

Specified by:

getBuffer in interface IMirror

Returns:

the IBuffer that is managed by the IMirror implementation

See Also:

IMirror.getBuffer()

handle

public void handle()
            throws GRS2ProxyMirrorInvalidOperationException

This invocation of this method starts a new execution thread where the mirroring procedure is executed. The created thread of execution is executed in the background and as a daemon service.

Throws:

GRS2ProxyMirrorInvalidOperationException - if the mirroring state does not allow the operation to be executed

dispose

public void dispose()

Dispose the resources employed by the mirroring implementations

This method actually invokes the respective dispose(boolean) with an argument of false. This is because the actual disposing needs to take place when the mirroring thread is prepared to gracefully exit its execution

Specified by:

dispose in interface IMirror

See Also:

IMirror.dispose()

dispose

public void dispose(boolean purge)

This method disposes the resources that are used by the instance but does so in two phases. One can request the disposal passing an argument of false which puts the mirroring thread in a state where the needed actions are taken to gracefully exit this part of the protocol but also notify the respective HTTPWriterMirror to stop the mirroring procedure gracefully. When the method in again invoked with a true argument from the protocol implementing thread, all resources are disposed.

Parameters:

purge - whether the resources need to be immediately disposed, or this need to wait until the protocol thread is ready to purge the involved resources

waitInitialization

public boolean waitInitialization()

This method can be used by HTTPReaderMirror clients, that want to be sure that the initialization procedure of the protocol is completed before they continue their operation. If someone invokes this method before communication has been successfully been established with the remote HTTPWriterMirror, and the involved IBuffer information including the RecordDefinitions are exchanged and the IBuffer is initialized, the method will block him. After this operation is completed, and for any later invocation, the method will return control immediately

Returns:

true if the initialization was successful, false if there was an error during initialization

getInitializationError

public GRS2ProxyMirrorProtocolErrorException getInitializationError()

In case the initialization was not successful, and the call to waitInitialization() returned false, this method will return the error that was recorded during the initialization. If no error was recorded, null is returned

Returns:

the initialization error or null if no error was recorded

pollPartial

public boolean pollPartial(long recordIndex,
                  int fieldIndex)
                    throws GRS2ProxyMirrorDisposedException

the management of the partial requests is performed using PartialRequestManager

Specified by:

pollPartial in interface IMirror

Parameters:

recordIndex - The record index / id, for which the requester has requested data to be delivered

fieldIndex - The field index of the specific record for which data are requested

Returns:

false if the requester needs to wait again until data is returned false otherwise. In case true is returned, the data have either been retrieved, or no more data is expected to be send, possibly because of a closed connection

Throws:

GRS2ProxyMirrorDisposedException - the mirror is already disposed

See Also:

IMirror.pollPartial(long, int)

requestPartial

public long requestPartial(long recordIndex,
                  int fieldIndex,
                  IBuffer.TransportOverride override,
                  Object notify)
                    throws GRS2ProxyMirrorInvalidOperationException,
                           GRS2ProxyMirrorDisposedException

This method is used by the reader side mirror to request payload that belongs to an IBuffer item that has been transfered only partially and more data is requested by the reader client

The indicative time returned for the next poll operation is the amount defined as ShortMirrorPeriod

Specified by:

requestPartial in interface IMirror

Parameters:

recordIndex - The index of the record whose payload is requested. As described in Record, this index coincides with the record id.

fieldIndex - The index of the field belonging to the defined record for which additional data is requested

override - whether or not the field's IBuffer.TransportDirective should be overridden as explained in IBuffer

notify - A synchronization object that can be used for the requester to block on until the required data is provided

Returns:

An indicative amount of time that the requester can wait before the data is available. This value is only indicative and it does not imply that after this period the data will be available. For this. the IMirror.pollPartial(long, int) should be used

Throws:

GRS2ProxyMirrorDisposedException - the mirror is already disposed

GRS2ProxyMirrorInvalidOperationException - if the PartialRequestManager has not been initialized

See Also:

IMirror.requestPartial(long, int, gr.uoa.di.madgik.grs.buffer.IBuffer.TransportOverride, java.lang.Object)

run

public void run()

In the context of the mirroring procedure, the execution of this thread includes the following actions.
Initially, a connection to the remote HTTPWriterMirror is established, the details of the employed IBuffer are retrieved, as well as the RecordDefinitions that describe the Record s that will be retrieved. The appropriate IBuffer implementation is instantiated, configured and set with all the retrieved information.
After the initialization is completed, any blocked clients waiting to be notified on initialization completion are notified.
The main protocol loop is then initialized. On every iteration, a request is send to the remote HTTPWriterMirror with the number of records that could be added to the local IBuffer, any partial data requests, as well as the status of the consumption procedure.
In the next step, any event emitted from the reader is send over to the writer
The next step is to retrieve from the HTTPWriterMirror any Records send as well as partial data from the requested ones. The respective information is used to either populate new Records and add them to the local IBuffer, or to locate and enhance the Fields for which additional data have been received.
Any events that are send from the writer are also received
The remote status is also retrieved and the protocol loop continues unless it should be teardown based on the remote status.
If the remote mirror has responded with the information requested, then the period of the next protocol loop is defined as the minimum defined in ShortMirrorPeriod while in case no needed information was received the period is set to the maximum defined in LongMirrorPeriod

Specified by:

run in interface Runnable

Overrides:

run in class Thread

See Also:

Thread.run()