A Simple Discrete-Event Simulation: Part 29

Today I added a Process component. This component is meant to represent a process that takes some amount of time to complete. The time could be zero and there can be other side effects, which usually involve changing properties of the entities being processed, but the time consumed is almost always the salient feature.

The Process component works almost exactly like the Queue component, including the incorporation of the internal array that can hold multiple entities. I don’t do anything special with this yet, but this capability is in place to support special processes of which I’m aware (e.g., a stacked booth where entity A enters first, followed by entity B, and where their process times are independent; if A finishes first it can leave right away but if B finishes first it has to wait for A). For the current implementation the Process component can work with only a single entity at a time.

I also modified the handoff of entities between components. When an entity gets to the far end of a Queue component (which happens instantaneously at present), it queries the next component (the Process component) to see if it can accept an entity. If it can then the entity is passed downstream. If it cannot then nothing happens. On the other end, the downstream component, when it becomes able to accept a new entity, queries the upstream entity to pull the next entity if one is available. This push-pull mechanism requires links to be stored in both directions, and may also be generalized as the mode of connections between all components.

(Click on the “Step” button to advance through the model, refresh the page to run it again.)

Here’s the code for the Process component.

    function ProcessComponent(displayDelay,processTime) {
      setOfEntities.push(this);
      this.componentID = getNewID();
      this.componentName = "Process";
      this.entryTime = "";
      this.currentEntryEntityID = "";
      this.endEntryDisplayTime = 0;
      this.countInQueue = 0;
      this.exitTime = "";
      this.currentExitEntityID = "";
      this.endExitDisplayTime = 0;
      this.endAllDisplayTime = 0;
      this.activity = "";
      this.displayDelay = displayDelay;
      this.processTime = processTime;
      this.openStatus = true;
      this.previousComponent = null;
      this.nextComponent = null;
      this.entityQueue = [];
      //this.nextState = "clearState";

      this.dataGroup = new DisplayGroup(this.componentName,10,127,80,"#00FFFF","#FF0000","#FFFF00");
      this.dataGroup.addValue(this.componentID,"comp. ID","integer");
      this.dataGroup.addValue(this.entryTime,"Entry Time","numdec",5);
      this.dataGroup.addValue(this.currentEntryEntityID,"Entry ID","integer");
      this.dataGroup.addValue(this.countInQueue,"# In Process","numdec","integer");
      this.dataGroup.addValue(this.exitTime,"Exit Time","numdec",5);
      this.dataGroup.addValue(this.currentExitEntityID,"Exit ID","integer");
      this.dataGroup.addValue(this.activity,"Activity","text");
      
      this.assignDisplayValues = function() {
        this.dataGroup.valueList[0].value = this.componentID;
        this.dataGroup.valueList[1].value = this.entryTime;
        this.dataGroup.valueList[2].value = this.currentEntryEntityID;
        this.dataGroup.valueList[3].value = this.countInQueue;
        this.dataGroup.valueList[4].value = this.exitTime;
        this.dataGroup.valueList[5].value = this.currentExitEntityID;
        this.dataGroup.valueList[6].value = this.activity;
      };
      this.drawData = function() {
        this.assignDisplayValues();
        this.dataGroup.drawBasic();
      };
      this.clearEntryDisplay = function() {
        //only clear display if a new one hasn't started a new timer
        if (globalSimClock >= this.endEntryDisplayTime) {
          this.entryTime = "";
          this.currentEntryEntityID = "";
        }
        if (globalSimClock >= this.endAllDisplayTime) {
          this.activity= "";        
        }
        displayProgressText("Process entry "+this.componentID+" clears at time "+globalSimClock.toFixed(6));
      };
      this.clearExitDisplay = function() {
        //only clear display if a new one hasn't started a new timer
        if (globalSimClock >= this.endExitDisplayTime) {
          this.exitTime = "";
          this.currentExitEntityID = "";
        }
        if (globalSimClock >= this.endAllDisplayTime) {
          this.activity= "";        
        }
        displayProgressText("Process exit "+this.componentID+" clears at time "+globalSimClock.toFixed(6));
      };
      this.assignPreviousComponent = function(previous) {
        this.previousComponent = previous;
      };
      this.assignNextComponent = function(next) {
        this.nextComponent = next;
      };
      this.isOpen = function() {
        return this.openStatus;
      };
      this.pullFromPrevious = function() {
        this.previousComponent.forwardEntity();
      };
      this.forwardEntity = function() {
        var entity = this.entityQueue.pop();
        if (entity) {
          //calculate how long item was in process
          var residenceTime = globalSimClock - entity.getLocalEntryTime();
          //now use this to calculate stats for the interval
                   //TODO: calculate stats as needed
          //this.nextComponent.receiveEntity(entity);
          this.countInQueue--;
          this.exitTime = globalSimClock;
          this.currentExitEntityID = entity.entityID;
          this.activity = "New Exit";          
          this.endExitDisplayTime = globalSimClock+this.displayDelay;
          this.endAllDisplayTime = this.endExitDisplayTime;
          feq.newItem(this.endExitDisplayTime,this,"clearExitDisplay");
          displayProgressText("Process comp. "+this.componentID+" forwards entity: "+this.currentExitEntityID+" at time "+globalSimClock.toFixed(6));
          this.openStatus = true;
          this.pullFromPrevious();
        }
      };
      this.receiveEntity = function(entity) {
        //receive the entity
        entity.setLocalEntryTime();  //record time entity entered process
        this.entityQueue.unshift(entity);
        this.countInQueue++;
        //display what was done
        this.entryTime = globalSimClock;
        this.currentEntryEntityID = entity.entityID;
        this.activity = "New Entry";
        //set timer for the process duration
        feq.newItem(globalSimClock+this.processTime,this,"processTimeout");
        //set timer to clear the display after a bit
        this.endEntryDisplayTime = globalSimClock+this.displayDelay;
        this.endAllDisplayTime = this.endEntryDisplayTime;
        feq.newItem(this.endEntryDisplayTime,this,"clearEntryDisplay");
        displayProgressText("Process comp. "+this.componentID+" receives entity: "+this.currentEntryEntityID+" at time "+globalSimClock.toFixed(6));
        this.openStatus = false;
      };

      this.activate = function(nextState) {
        if (nextState == "processTimeout") {
          this.forwardEntity();
        } else if (nextState == "clearEntryDisplay") {
          this.clearEntryDisplay();
        } else if (nextState == "clearExitDisplay") {
          this.clearExitDisplay();
        } else {
          errorUndefinedAdvanceState(this.entityID,this.nextState);
        }      
      };  //this.activate
      
    }  //ProcessComponent

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

function ProcessComponent(displayDelay,processTime) {

setOfEntities.push(this);

this.componentID = getNewID();

this.componentName = "Process";

this.entryTime = "";

this.currentEntryEntityID = "";

this.endEntryDisplayTime = 0;

this.countInQueue = 0;

this.exitTime = "";

this.currentExitEntityID = "";

this.endExitDisplayTime = 0;

this.endAllDisplayTime = 0;

this.activity = "";

this.displayDelay = displayDelay;

this.processTime = processTime;

this.openStatus = true;

this.previousComponent = null;

this.nextComponent = null;

this.entityQueue = [];

//this.nextState = "clearState";

this.dataGroup = new DisplayGroup(this.componentName,10,127,80,"#00FFFF","#FF0000","#FFFF00");

this.dataGroup.addValue(this.componentID,"comp. ID","integer");

this.dataGroup.addValue(this.entryTime,"Entry Time","numdec",5);

this.dataGroup.addValue(this.currentEntryEntityID,"Entry ID","integer");

this.dataGroup.addValue(this.countInQueue,"# In Process","numdec","integer");

this.dataGroup.addValue(this.exitTime,"Exit Time","numdec",5);

this.dataGroup.addValue(this.currentExitEntityID,"Exit ID","integer");

this.dataGroup.addValue(this.activity,"Activity","text");

this.assignDisplayValues = function() {

this.dataGroup.valueList[0].value = this.componentID;

this.dataGroup.valueList[1].value = this.entryTime;

this.dataGroup.valueList[2].value = this.currentEntryEntityID;

this.dataGroup.valueList[3].value = this.countInQueue;

this.dataGroup.valueList[4].value = this.exitTime;

this.dataGroup.valueList[5].value = this.currentExitEntityID;

this.dataGroup.valueList[6].value = this.activity;

};

this.drawData = function() {

this.assignDisplayValues();

this.dataGroup.drawBasic();

};

this.clearEntryDisplay = function() {

//only clear display if a new one hasn't started a new timer

if (globalSimClock >= this.endEntryDisplayTime) {

this.entryTime = "";

this.currentEntryEntityID = "";

}

if (globalSimClock >= this.endAllDisplayTime) {

this.activity= "";

}

displayProgressText("Process entry "+this.componentID+" clears at time "+globalSimClock.toFixed(6));

};

this.clearExitDisplay = function() {

//only clear display if a new one hasn't started a new timer

if (globalSimClock >= this.endExitDisplayTime) {

this.exitTime = "";

this.currentExitEntityID = "";

}

if (globalSimClock >= this.endAllDisplayTime) {

this.activity= "";

}

displayProgressText("Process exit "+this.componentID+" clears at time "+globalSimClock.toFixed(6));

};

this.assignPreviousComponent = function(previous) {

this.previousComponent = previous;

};

this.assignNextComponent = function(next) {

this.nextComponent = next;

};

this.isOpen = function() {

return this.openStatus;

};

this.pullFromPrevious = function() {

this.previousComponent.forwardEntity();

};

this.forwardEntity = function() {

var entity = this.entityQueue.pop();

if (entity) {

//calculate how long item was in process

var residenceTime = globalSimClock - entity.getLocalEntryTime();

//now use this to calculate stats for the interval

//TODO: calculate stats as needed

//this.nextComponent.receiveEntity(entity);

this.countInQueue--;

this.exitTime = globalSimClock;

this.currentExitEntityID = entity.entityID;

this.activity = "New Exit";

this.endExitDisplayTime = globalSimClock+this.displayDelay;

this.endAllDisplayTime = this.endExitDisplayTime;

feq.newItem(this.endExitDisplayTime,this,"clearExitDisplay");

displayProgressText("Process comp. "+this.componentID+" forwards entity: "+this.currentExitEntityID+" at time "+globalSimClock.toFixed(6));

this.openStatus = true;

this.pullFromPrevious();

}

};

this.receiveEntity = function(entity) {

//receive the entity

entity.setLocalEntryTime(); //record time entity entered process

this.entityQueue.unshift(entity);

this.countInQueue++;

//display what was done

this.entryTime = globalSimClock;

this.currentEntryEntityID = entity.entityID;

this.activity = "New Entry";

//set timer for the process duration

feq.newItem(globalSimClock+this.processTime,this,"processTimeout");

//set timer to clear the display after a bit

this.endEntryDisplayTime = globalSimClock+this.displayDelay;

this.endAllDisplayTime = this.endEntryDisplayTime;

feq.newItem(this.endEntryDisplayTime,this,"clearEntryDisplay");

displayProgressText("Process comp. "+this.componentID+" receives entity: "+this.currentEntryEntityID+" at time "+globalSimClock.toFixed(6));

this.openStatus = false;

};

this.activate = function(nextState) {

if (nextState == "processTimeout") {

this.forwardEntity();

} else if (nextState == "clearEntryDisplay") {

this.clearEntryDisplay();

} else if (nextState == "clearExitDisplay") {

this.clearExitDisplay();

} else {

errorUndefinedAdvanceState(this.entityID,this.nextState);

}

}; //this.activate

} //ProcessComponent

Here’s the code that initializes all the components.

    //schedule for six hours of arrivals in half-hour blocks
    var arrivalSchedule = [0,0,1,3,4,4,5,6,3,2,1,0]; 
    
    var arrival1 = new ArrivalsComponent(30.0,arrivalSchedule);

    var entry1 = new EntryComponent(2.0);
    
    arrival1.assignNextComponent(entry1);
    
    var queue1 = new QueueComponent(2.0);
    
    entry1.assignNextComponent(queue1);
    
    var process1 = new ProcessComponent(2.0,9.0);
    process1.assignPreviousComponent(queue1);
    
    queue1.assignNextComponent(process1);

    //process1.assignNextComponent(NULL);  //need to assign something real eventually

//schedule for six hours of arrivals in half-hour blocks

var arrivalSchedule = [0,0,1,3,4,4,5,6,3,2,1,0];

var arrival1 = new ArrivalsComponent(30.0,arrivalSchedule);

var entry1 = new EntryComponent(2.0);

arrival1.assignNextComponent(entry1);

var queue1 = new QueueComponent(2.0);

entry1.assignNextComponent(queue1);

var process1 = new ProcessComponent(2.0,9.0);

process1.assignPreviousComponent(queue1);

queue1.assignNextComponent(process1);

//process1.assignNextComponent(NULL); //need to assign something real eventually

The processing time was set to nine seconds so we can watch a nice collection of entities build up in the queue but which allows the system to completely empty out by the end of the simulation. Once the queue is continually not empty the process is engaged continuously.

Stepping through the simulation in this mode takes some patience, so once I get the Exit component incorporated I’m going to change things up a bit.

A Simple Discrete-Event Simulation: Part 29

Leave a Reply Cancel reply

Recent Posts

Recent Comments

Categories

Meta