ParkNPark.client
Class FaultTolerantClientManager

java.lang.Object
  ParkNPark.client.FaultTolerantClientManager

All Implemented Interfaces:

ClientManagerOperations

public class FaultTolerantClientManager
extends Object
implements ClientManagerOperations

Fault tolerant client manager that wraps a remote ClientManager and rolls over to a new primary server in the presence of failures. Note that this class is not multi-thread safe. Multiple threads should synchronize access or wrap this class with a thread-safe delegate.

Nested Class Summary

protected class	FaultTolerantClientManager.BackgroundThread Background thread that performs the following actions in a loop continuously: Recover from a fault on the primary server if one was detected by either this thread or by the main thread Refresh the list of servers from the naming service Poke each server serially and, upon fault detection, remove that server from the list of servers.
protected class	FaultTolerantClientManager.ReturnValueOrException Return value or an exception along with the return value or the exception object.

Field Summary

protected FaultTolerantClientManager.BackgroundThread	backgroundThread Our background thread that handles name service interactions, fault detections, and fault recoveries
protected int	clientID The server-generated client ID
protected static Method	closeClientManager
protected static Method	enterLot
protected PrintStream	err Original System.err object instance
protected static Method	exitLot
protected ClientManagerFactory	factory The last-known client manager factory instance
protected boolean	fault When true, we are presently processing a fault
protected LogEntry	faultyCallLogEntry A logEntry instance to log to when fault is true
protected static Method	getClientID
protected static Method	getCurrentLevel
protected static Method	getLots
protected static Method	getMaxLevel
protected static Method	getMinLevel
protected static Method	getOtherLotAvailability
protected static PrintStream	inputEater Shared static instance of the input eater output stream wrapped in a PrintStream
private int	interRequestTime Time between requests
protected Logger	logger Our Logger instance
protected static Method	moveDownLevel
protected static Method	moveUpLevel
protected boolean	neverGiveUp When true, never give up when trying to contact the server
protected ClientManager	primaryClientManager The primary client manager
protected Object	primaryClientManagerLock Lock for primaryClientManager, factory, faultyCallLogEntry, systemDown, and fault
protected int	recoveryTimeout The wait timeout to use during fault recoveries
protected int	seq The latest sequence number from the client
protected boolean	systemDown When true, the system is officially down due to no registration of a primary server
protected static String	unexpectedException Message for unexpected exceptions that arise during remote method calls (non-IDL and non-CORBA exceptions)

Constructor Summary

FaultTolerantClientManager(ORB orb, Logger logger, int interRequestTime, boolean neverGiveUp, int detectionTimeout, int recoveryTimeout, PrintStream err)
Creates a new fault-tolerant client manager that automatically fails over to new primary servers on method call failures

Method Summary

protected FaultTolerantClientManager.ReturnValueOrException	callServer(Method method, boolean logAndWait, Object... arguments) Calls the given method on the server with the given arguments and returns a ReturnValueOrException object to indicate a normal or exceptional result and contain the return value or the exception object.
void	closeClientManager() Closes the client manager and frees server resources associated with it, including the client manager's activation in the server's CORBA portable object adapter.
protected boolean	connectToAnyServer(ClientManager faultyClientManager, LogEntry logEntry) Connects to any registered server, which is chosen randomly
PaddedIntegerSeq	enterLot(int seq, int lot) Moves the client's car into the lot with the given lot number and returns an array of level numbers that have available spaces
PaddedVoid	exitLot(int seq) Removes the client's car from the lot that it is currently in
PaddedInteger	getClientID() Returns the client's ID, which can be used in the client manager factory's getExistingClientManager() method
PaddedInteger	getCurrentLevel() Returns the car's current level number
PaddedIntegerSeq	getLots() Returns an array of valid lot numbers in the system, sorted by the lot number in ascending order
PaddedInteger	getMaxLevel() Returns the top level number of the car's current parking lot
PaddedInteger	getMinLevel() Returns the bottom level number of the car's current parking lot
PaddedIntegerSeq	getOtherLotAvailability(int lot) Returns an array of other lots that have availability, sorted by lot distance such that closer lots are listed first
void	hoseServerDatabaseConnection() Hoses the server's database connection.
protected void	interRequestWait() Wait for the configured inter-request wait period or, if none is configured, return immediately.
PaddedInteger	moveDownLevel(int seq) Moves the car from its present level to the level beneath it
PaddedInteger	moveUpLevel(int seq) Moves the car from its present level to the level above it

Methods inherited from class java.lang.Object

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

Field Detail

primaryClientManager

protected ClientManager primaryClientManager

The primary client manager

factory

protected ClientManagerFactory factory

The last-known client manager factory instance

fault

protected boolean fault

When true, we are presently processing a fault

systemDown

protected boolean systemDown

When true, the system is officially down due to no registration of a primary server

faultyCallLogEntry

protected LogEntry faultyCallLogEntry

A logEntry instance to log to when fault is true

primaryClientManagerLock

protected Object primaryClientManagerLock

Lock for primaryClientManager, factory, faultyCallLogEntry, systemDown, and fault

backgroundThread

protected FaultTolerantClientManager.BackgroundThread backgroundThread

Our background thread that handles name service interactions, fault detections, and fault recoveries

seq

protected int seq

The latest sequence number from the client

clientID

protected int clientID

The server-generated client ID

interRequestTime

private int interRequestTime

Time between requests

logger

protected Logger logger

Our Logger instance

neverGiveUp

protected boolean neverGiveUp

When true, never give up when trying to contact the server

recoveryTimeout

protected int recoveryTimeout

The wait timeout to use during fault recoveries

err

protected PrintStream err

Original System.err object instance

getClientID

protected static final Method getClientID

enterLot

protected static final Method enterLot

exitLot

protected static final Method exitLot

getOtherLotAvailability

protected static final Method getOtherLotAvailability

getLots

protected static final Method getLots

moveUpLevel

protected static final Method moveUpLevel

moveDownLevel

protected static final Method moveDownLevel

getCurrentLevel

protected static final Method getCurrentLevel

getMaxLevel

protected static final Method getMaxLevel

getMinLevel

protected static final Method getMinLevel

closeClientManager

protected static final Method closeClientManager

unexpectedException

protected static final String unexpectedException

Message for unexpected exceptions that arise during remote method calls (non-IDL and non-CORBA exceptions)

See Also:

Constant Field Values

inputEater

protected static PrintStream inputEater

Shared static instance of the input eater output stream wrapped in a PrintStream

Constructor Detail

FaultTolerantClientManager

public FaultTolerantClientManager(ORB orb,
                                  Logger logger,
                                  int interRequestTime,
                                  boolean neverGiveUp,
                                  int detectionTimeout,
                                  int recoveryTimeout,
                                  PrintStream err)
                           throws ServiceUnavailableException

Creates a new fault-tolerant client manager that automatically fails over to new primary servers on method call failures

Parameters:

orb - The object request broker instance to use

logger - The Logger instance to write performance data to

interRequestTime - The time to wait between method invocations

neverGiveUp - When true, the client will never give up its attempt to contact the server, even if no primary is registered

detectionTimeout - The wait timeout to use during fault detections

recoveryTimeout - The wait timeout to use during fault recoveries

The - System.err instance to use

Throws:

ServiceUnavailableException - Thrown when a primary server could not be located or contacted

Method Detail

callServer

protected FaultTolerantClientManager.ReturnValueOrException callServer(Method method,
                                                                       boolean logAndWait,
                                                                       Object... arguments)

Calls the given method on the server with the given arguments and returns a ReturnValueOrException object to indicate a normal or exceptional result and contain the return value or the exception object. If server communication or service unavailability exceptions arise, this method will automatically fail over to the new primary after that becomes available. Server communication and service unavailability exceptions are only returned if no primary server is registered

Parameters:

method - The method to call on our client manager on the primary server

logAndWait - When true, this method call will be logged and, after returning from that call, this method will wait for the inter-request time before returning

arguments - The arguments to pass to the given method's parameters

Returns:

A ReturnValueOrException indicating a normal or exceptional result

getClientID

public PaddedInteger getClientID()
                          throws ServiceUnavailableException

Returns the client's ID, which can be used in the client manager factory's getExistingClientManager() method

Specified by:

getClientID in interface ClientManagerOperations

Returns:

The client's ID

Throws:

ServiceUnavailableException - Thrown when the log is closed and the server is shutting down

enterLot

public PaddedIntegerSeq enterLot(int seq,
                                 int lot)
                          throws AlreadyInLotException,
                                 LotNotFoundException,
                                 LotFullException,
                                 ServiceUnavailableException

Moves the client's car into the lot with the given lot number and returns an array of level numbers that have available spaces

Specified by:

enterLot in interface ClientManagerOperations

Parameters:

seq - The latest sequence number of the client

lot - The lot number to enter

Returns:

An array of level numbers that have available spaces [Category: Baseline; Requirements: 1, 2, and 3]

Throws:

AlreadyInLotException - Thrown when the client's car is already in a lot

LotNotFoundException - Thrown if the given lot number is not known to the system

LotFullException - Thrown if the given lot is full

ServiceUnavailableException - Thrown if the database cannot be contacted or if some other reason prevents the car from entering the lot

exitLot

public PaddedVoid exitLot(int seq)
                   throws NotInLotException,
                          NotOnExitLevelException,
                          ServiceUnavailableException

Removes the client's car from the lot that it is currently in

Specified by:

exitLot in interface ClientManagerOperations

Parameters:

seq - The latest sequence number of the client

Throws:

NotInLotException - Thrown if the car is not in a lot

NotOnExitLevelException - Thrown if the car is in a lot but is not on a permitted exit level

ServiceUnavailableException - Thrown if the database cannot be contacted or if some other reason prevents the car from exiting the lot [Category: Baseline; Requirement: 7]

getOtherLotAvailability

public PaddedIntegerSeq getOtherLotAvailability(int lot)
                                         throws LotNotFoundException,
                                                ServiceUnavailableException

Returns an array of other lots that have availability, sorted by lot distance such that closer lots are listed first

Specified by:

getOtherLotAvailability in interface ClientManagerOperations

Parameters:

lot - The lot to get lot distances from

Returns:

An array of other lots that have availability [Category: Baseline; Requirement: 4]

Throws:

LotNotFoundException - Thrown if the given lot number is not known to the system

ServiceUnavailableException - Thrown if the database cannot be contacted or if some other reason prevents the system from discovering the availability of other lots

getLots

public PaddedIntegerSeq getLots()
                         throws ServiceUnavailableException

Returns an array of valid lot numbers in the system, sorted by the lot number in ascending order

Specified by:

getLots in interface ClientManagerOperations

Returns:

An array of valid lot numbers in the system [Category: Baseline; Requirement: 12]

Throws:

ServiceUnavailableException - Thrown if the database cannot be contacted or if some other reason prevents the system from discovering the its defined lots

moveUpLevel

public PaddedInteger moveUpLevel(int seq)
                          throws NotInLotException,
                                 AtTopLevelException,
                                 ServiceUnavailableException

Moves the car from its present level to the level above it

Specified by:

moveUpLevel in interface ClientManagerOperations

Parameters:

seq - The latest sequence number of the client

Returns:

The level number that the client's car is now on [Category: Baseline; Requirement: 6]

Throws:

NotInLotException - Thrown if the car is not in a lot

AtTopLevelException - Thrown if the car is already on the highest level

ServiceUnavailableException - Thrown if the database cannot be contacted or if some other reason prevents the car from moving to the next highest level

moveDownLevel

public PaddedInteger moveDownLevel(int seq)
                            throws NotInLotException,
                                   AtBottomLevelException,
                                   ServiceUnavailableException

Moves the car from its present level to the level beneath it

Specified by:

moveDownLevel in interface ClientManagerOperations

Parameters:

seq - The latest sequence number of the client

Returns:

The level number that the client's car is now on [Category: Baseline; Requirement: 6]

Throws:

NotInLotException - Thrown if the car is not in a lot

AtTopLevelException - Thrown if the car is already on the lowest level

ServiceUnavailableException - Thrown if the database cannot be contacted or if some other reason prevents the car from moving to the lower level

AtBottomLevelException

getCurrentLevel

public PaddedInteger getCurrentLevel()
                              throws NotInLotException,
                                     ServiceUnavailableException

Returns the car's current level number

Specified by:

getCurrentLevel in interface ClientManagerOperations

Returns:

The car's current level number [Category: Baseline; Requirement: 6]

Throws:

NotInLotException - Thrown if the car is not in a lot

ServiceUnavailableException - Thrown if the database cannot be contacted or if some other reason prevents the system from returning the car's current level

getMaxLevel

public PaddedInteger getMaxLevel()
                          throws NotInLotException,
                                 ServiceUnavailableException

Returns the top level number of the car's current parking lot

Specified by:

getMaxLevel in interface ClientManagerOperations

Returns:

The top level number of the car's current parking lot [Category: Baseline; Requirement: 6]

Throws:

NotInLotException - Thrown if the car is not in a lot

ServiceUnavailableException - Thrown if the database cannot be contacted or if some other reason prevents the system from returning the current lot's highest level

getMinLevel

public PaddedInteger getMinLevel()
                          throws NotInLotException,
                                 ServiceUnavailableException

Returns the bottom level number of the car's current parking lot

Specified by:

getMinLevel in interface ClientManagerOperations

Returns:

The bottom level number of the car's current parking lot [Category: Baseline; Requirement: 6]

Throws:

NotInLotException - Thrown if the car is not in a lot

ServiceUnavailableException - Thrown if the database cannot be contacted or if some other reason prevents the system from returning the current lot's lowest level

closeClientManager

public void closeClientManager()
                        throws ServiceUnavailableException

Closes the client manager and frees server resources associated with it, including the client manager's activation in the server's CORBA portable object adapter. AFter calling this method, you should not use this FaultTolerantClientManager instance again

Specified by:

closeClientManager in interface ClientManagerOperations

Throws:

ServiceUnavailableException - Thrown if the database cannot be contacted or if some other reason prevents the system from closing the client manager. The client manager remains open if this exception gets thrown

interRequestWait

protected void interRequestWait()

Wait for the configured inter-request wait period or, if none is configured, return immediately. Note that interrupting the calling Thread will cause this method to return immediately after being interrupted

hoseServerDatabaseConnection

public void hoseServerDatabaseConnection()

Hoses the server's database connection. This is primarily used for fault injection

connectToAnyServer

protected boolean connectToAnyServer(ClientManager faultyClientManager,
                                     LogEntry logEntry)

Connects to any registered server, which is chosen randomly

Parameters:

faultyClientManager - The ClientManager that was deemed to be faulty, or null if no ClientManager is faulty

logEntry - The LogEntry object to write performance data to when not null

Returns:

True when a connection with a server was successfully established or false if a server connection could not be established