umontreal.iro.lecuyer.simprocs
Class SimProcess

java.lang.Object
  umontreal.iro.lecuyer.simprocs.SimProcess

public class SimProcess
extends Object

This abstract class provides process scheduling tools. Each type of process should be defined as a subclass of the class SimProcess, and must provide an implementation of the method actions which describes the life of a process of this class. Whenever a process instance starts, its actions method begins executing.

Just like an event, a process must first be constructed, then scheduled. Scheduling a process is equivalent to placing an event in the event list that will start this process when the simulation clock reaches the specified time. The toString method can be overridden to return information about the process. This information will be returned when formating the event list as a string, if the process is delayed.

A process can be in one of the following states: INITIAL, EXECUTING, DELAYED, SUSPENDED, and DEAD . At most one process can be in the EXECUTING state at any given time, and when there is one, this executing process (called the current process) is said to have control and is executing one of the instructions of its actions method. A process that has been constructed but not yet scheduled is in the INITIAL state. A process is in the DELAYED state if there is a planned event in the event list to activate it (give it control). When a process is scheduled, it is placed in the DELAYED state. It is in the SUSPENDED state if it is waiting to be reactivated (i.e., obtain control) without having an event to do so in the event list. A process can suspends itself by calling suspend directly or indirectly (e.g., by requesting a busy Resource). Usually, a SUSPENDED process must be reactivated by another process or event via the resume method. A process in the DEAD state no longer exists.

To construct new processes, the user needs to extend SimProcess.

Note: the user needs to ensure that the actions method of any process can be terminated, i.e., no infinite loops. For example, using threads process-oriented simulator, if such a method never terminates, threads will not be recycled, causing memory problems.

Field Summary

static int	DEAD The process has terminated its execution.
static int	DELAYED The process is not executing but has an event in the event list to reactivate it later on.
static int	EXECUTING The process is the one currently executing its actions method.
static int	INITIAL The process has been created but not yet scheduled.
static double	STARTING
static int	SUSPENDED The process is not executing and will have to be reactivated by another process or event later on.
static double	WAITING

Constructor Summary

SimProcess()
Constructs a new process without scheduling it and associates this new process with the default simulator; one can get additional knowledge with Simulator static methods.

SimProcess(ProcessSimulator sim)
Constructs a new process associated with sim without scheduling it.

Method Summary

void	actions() This is the method that is called when this process is executing.
boolean	cancel() Cancels the activating event that was supposed to resume this process, and places the process in the SUSPENDED state.
void	delay(double delay) Suspends the execution of the currently executing process and schedules it to resume its execution in delay units of simulation time.
double	getDelay() If the process is in the DELAYED state, returns the remaining time until the planned occurrence of its activating event.
int	getState() Returns the state of the process.
static void	init() This method calls ProcessSimulator.initDefault(), which initializes the default simulator to use processes.
boolean	isAlive() Returns true if the process is alive, otherwise false.
void	kill() Terminates the life of this process and sets its state to DEAD, after canceling its activating event if there is one.
double	priority() Returns the priority of the current variable.
void	reschedule(double delay) If the process is in the DELAYED state, removes it from the event list and reschedules it in delay units of time.
void	resume() Places this process at the beginning of the event list to resume its execution.
void	schedule(double delay) Schedules the process to start in delay time units.
Event	scheduledEvent() Returns the Event associated with the current variable.
void	scheduleNext() Schedules this process to start at the current time, by placing it at the beginning of the event list.
void	setPriority(double priority) Sets the priority assigned to the current variable in the simulation.
void	setScheduledEvent(Event scheduledEvent) Sets the event associated to the current variable.
void	suspend() This method can only be invoked for the EXECUTING or a DELAYED process.

Methods inherited from class java.lang.Object

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

Field Detail

INITIAL

public static final int INITIAL

The process has been created but not yet scheduled.

See Also:

Constant Field Values

EXECUTING

public static final int EXECUTING

The process is the one currently executing its actions method.

See Also:

Constant Field Values

DELAYED

public static final int DELAYED

The process is not executing but has an event in the event list to reactivate it later on.

See Also:

Constant Field Values

SUSPENDED

public static final int SUSPENDED

The process is not executing and will have to be reactivated by another process or event later on.

See Also:

Constant Field Values

DEAD

public static final int DEAD

The process has terminated its execution.

See Also:

Constant Field Values

STARTING

public static final double STARTING

See Also:

Constant Field Values

WAITING

public static final double WAITING

See Also:

Constant Field Values

Constructor Detail

SimProcess

public SimProcess()

Constructs a new process without scheduling it and associates this new process with the default simulator; one can get additional knowledge with Simulator static methods. It will have to be scheduled later on. The process is in the INITIAL state.

SimProcess

public SimProcess(ProcessSimulator sim)

Constructs a new process associated with sim without scheduling it. It will have to be scheduled later on. The process is in the INITIAL state.

Parameters:

sim - Link the current variable to ProcessSimulator sim

Method Detail

schedule

public void schedule(double delay)

Schedules the process to start in delay time units. This puts the process in the DELAYED state.

Parameters:

delay - delay, in simulation time, before the process starts

scheduleNext

public void scheduleNext()

Schedules this process to start at the current time, by placing it at the beginning of the event list. This puts the process in the DELAYED state.

scheduledEvent

public Event scheduledEvent()

Returns the Event associated with the current variable.

setScheduledEvent

public void setScheduledEvent(Event scheduledEvent)

Sets the event associated to the current variable.

Parameters:

scheduledEvent - new scheduledEvent for the current variable

priority

public double priority()

Returns the priority of the current variable.

Returns:

priority of the current variable.

setPriority

public void setPriority(double priority)

Sets the priority assigned to the current variable in the simulation. This method should never be called after the event has been scheduled, otherwise the events will not execute in ascending priority order anymore.

Parameters:

priority - priority assigned to the current variable in the simulation

isAlive

public final boolean isAlive()

Returns true if the process is alive, otherwise false.

Returns:

true if the process is not in the DEAD state

getState

public int getState()

Returns the state of the process.

Returns:

one of the process states INITIAL, EXECUTING, DELAYED, SUSPENDED, or DEAD.

getDelay

public double getDelay()

If the process is in the DELAYED state, returns the remaining time until the planned occurrence of its activating event. Otherwise, an illegal state exception will be thrown printing an error message.

Returns:

remaining delay before the process starts

Throws:

IllegalStateException - if the process is not in DELAYED state

reschedule

public void reschedule(double delay)

If the process is in the DELAYED state, removes it from the event list and reschedules it in delay units of time. Example: If the process p has called delay(5.0) at time 10.0, and another process invokes reschedule(p, 6.2) at time 13.5, then the process p will resume at time 13.5 + 6.2 = 19.7.

Parameters:

delay - new delay, in simulation time units, before the process starts or is resumed

resume

public void resume()

Places this process at the beginning of the event list to resume its execution. If the process was DELAYED, cancels its earlier activating event.

cancel

public boolean cancel()

Cancels the activating event that was supposed to resume this process, and places the process in the SUSPENDED state. This method can be invoked only for a process in the DELAYED state.

Returns:

true if the process was canceled successfully

delay

public void delay(double delay)

Suspends the execution of the currently executing process and schedules it to resume its execution in delay units of simulation time. It moves in the DELAYED state. Only the process in the EXECUTING state can call this method.

suspend

public void suspend()

This method can only be invoked for the EXECUTING or a DELAYED process. If the process is EXECUTING, suspends execution. If the process is DELAYED, cancels its activating event. This places the process in the SUSPENDED state.

kill

public void kill()

Terminates the life of this process and sets its state to DEAD, after canceling its activating event if there is one.

actions

public void actions()

This is the method that is called when this process is executing. Every subclass of SimProcess that is to be instantiated must provide an implementation of this method.

init

public static void init()

This method calls ProcessSimulator.initDefault(), which initializes the default simulator to use processes.