Pthread Help

Anonymous_guy · #1 29-Jun-2009, 14:31

So this is the first time I've ever done ANYTHING with pthreads what so ever. I have an assignment that deals with them and I'm having quite a bit of trouble at the moment.

Essentially the program will take in a file such as:

Code:

W:9,7
w:3,2
e:13,3
e:12,5
W:15,2
w:11,10
e:7,1
E:1,7
w:14,9

Where the first letter represents the direction and priority. W being high priority west, and w being low priority west. Same for E and e. The first number represents the time it takes the train to load passengers (So the time the thread has to wait before it can see if the main track is empty.) The next number represents the time it takes to cross the main track.

The rules enforced by the automated control system are:
1. Only one train is on the main track at any given time.

2. Only loaded trains can cross the main track.

3. If there are multiple loaded trains, the one with the high priority crosses.

4. If two loaded trains have the same priority, then:

(a) If they are both traveling in the same direction, the train which finished loading first gets the clearance to cross. If they finished loading at the same time, the one appeared first in the input file gets the clearance to cross.
(b) If they are traveling in opposite directions, pick the train which will travel in the direction opposite of which the last train to cross the main track traveled.

So all in all, to the input given above the output would be:

Code:

Train  7 is ready to go East
Train  7 is ON the main track going East
Train  1 is ready to go West
Train  6 is ready to go East
Train  7 is OFF the main track after going East
Train  1 is ON the main track going West
Train  0 is ready to go West
Train  1 is OFF the main track after going West
Train  0 is ON the main track going West
Train  5 is ready to go West
Train  3 is ready to go East
Train  2 is ready to go East
Train  8 is ready to go West
Train  4 is ready to go West
Train  0 is OFF the main track after going West
Train  4 is ON the main track going West
Train  4 is OFF the main track after going West
Train  6 is ON the main track going East
Train  6 is OFF the main track after going East
Train  5 is ON the main track going West
Train  5 is OFF the main track after going West
Train  3 is ON the main track going East
Train  3 is OFF the main track after going East
Train  8 is ON the main track going West
Train  8 is OFF the main track after going West
Train  2 is ON the main track going East
Train  2 is OFF the main track after going East

Now after all that. Right now my program takes in the input file and creates an array of Trains. Each Train contains a number, priority, direction, loading and crossing times as well as a thread. I then sorted the array by loading times. But at this point I'm stuck and really have no idea what to do. ANY help is greatly appreciated.

CPP / C++ / C Code:

#include <pthread.h>
#include <string>
#include <iostream>
#include <fstream>
#include <queue>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

using namespace std;
#define DIGIT 10
#define W 1
#define w 2
#define E 3
#define e 4

class train{
	public:
	int loadingTime;
	int crossingTime;
	int number;
	int priority;
	
	
	train()
	{
		loadingTime = 0;
		crossingTime = 0;
		number = 0;
		priority = 0;
	};
	train(int lTime, int cTime, int num, int pri)
	{
		loadingTime = lTime;
		crossingTime = cTime;
		number = num;
		priority = pri;
	};
	
	int getLoading()
	{
		return loadingTime;
	}
	int getCrossing()
	{
		return crossingTime;
	}
	int getNumber()
	{
		return number;
	}
	int getPriority()
	{
		return priority;
	}
	string getDirection()
	{
		if(priority == 1 || priority == 2)
		{
			return "West";
		}
		else
		{
			return "East";
		}
	}
	
	
};


void BubbleSort(train *num, int numLength)
{
      int i, j, flag = 1;    
      train temp;           
      for(i = 1; (i <= numLength) && flag; i++)
     {
          flag = 0;
          for (j=0; j < (numLength -1); j++)
         {
               if (num[j+1].getLoading() < num[j].getLoading())      
              { 
                    temp = num[j];            
                    num[j] = num[j+1];
                    num[j+1] = temp;
                    flag = 1;               
               }
          }
     }
     return;
}



int main(int argc, char **argv)
{
	if(argc != 3)
	{
		cout<<"Please enter two paramaters, the name of the file followed by the number of trains."<<endl;
	}
	
	int numTrains = atoi(argv[2]);
	int i;
	int loadingTimes[numTrains];
	int crossingTimes[numTrains];
	char direction;
	int dirFlag = 0;
	char temp;
	int tempOnes = 0, tempTens = 0;
	
	train trainArray[numTrains];
	
	
	FILE *inFile;
	inFile = fopen(argv[1],"r");
	if (inFile == NULL) 
	{
		cout<< "Unable to open file"<<endl;
		exit(1);   // call system to stop
	}
	for(i = 0; i < numTrains; i++)
	{
		
		cout<<"Train number: "<<i<<endl;
		direction = getc(inFile);
		if(direction == 'e')
		{
			dirFlag = e;
			cout<<"East bound low priority"<<endl;
		}
		if(direction == 'E')
		{
			dirFlag = E;
			cout<<"East bound high priority"<<endl;
		}
		if(direction == 'w')
		{
			dirFlag = w;
			cout<<"West bound low priority"<<endl;
		}
		if(direction == 'W')
		{
			dirFlag = W;
			cout<<"West bound high priority"<<endl;
		}
		getc(inFile);
		temp = getc(inFile);
		tempTens = atoi(&temp);
		if((temp = getc(inFile)) == ',')
		{
			loadingTimes[i] = tempTens;
		}
		else
		{
			tempOnes = atoi(&temp);
			tempTens *= DIGIT;
			loadingTimes[i] = tempTens+tempOnes;
			getc(inFile);
			
		}
		tempOnes = 0;
		tempTens = 0;
		cout<<"Loading Time: "<<loadingTimes[i]<<endl;
		
		temp = getc(inFile);
		tempTens = atoi(&temp);
		if((temp = getc(inFile)) == '\n')
		{
			crossingTimes[i] = tempTens;
		}
		else
		{
			tempOnes = atoi(&temp);
			tempTens *= DIGIT;
			crossingTimes[i] = tempTens+tempOnes;
			getc(inFile);
		}
		tempOnes = 0;
		tempTens = 0;
		cout<<"Crossing Time: "<<crossingTimes[i]<<endl;
		
		train temp(loadingTimes[i], crossingTimes[i], i, dirFlag);
		trainArray[i] = temp;
	}
	BubbleSort(trainArray, numTrains);
	for(i = 0; i < numTrains; i++)
	{
		if (i == 0)
		{
			sleep(trainArray[i].getLoading());
		}
		else
		{
			sleep((trainArray[i].getLoading() - trainArray[i-1].getLoading()));
		}
		
		cout<<"Train "<<trainArray[i].getNumber()<<" is ready to go "<<trainArray[i].getDirection()<<"."<<endl;
	}
	

	
	
	return 0;
}

Mexican Bob · #2 30-Jun-2009, 23:25

Other than including the pthreads header, you are STILL not doing ANYTHING with pthreads

You probably want to decide whether this is a C program or a C++ program. Currently, it is a rather poor mixture of both languages. Since the pthreads library is a C-centric API, I'd probably recommend sticking with C, unless this is specifically a C++ class and C++ is expected.

For example, we tend not to have public data in a class definition and if we do decide that it is useful, there is absolutely no "good" reason for accessor/mutator operations.

Perhaps you should take a moment to explain the objective. I'm guessing that we have to have all of the trains, load and then cross the main track and then presumably unload. Are these to run (based on priority) continuously until interrupted? From your narrative, is seems as if you want each train to run as a separate thread. Perhaps a restatement of the problem will add additional clarity?

Should we assume that you also want no "starving" of lower priority trains such that all trains are able to be loaded and eventually unloaded in some kind of manner that gives each thread the opportunity to run to completion on every pass through the priority queue? Do you want to use priority inversioning?

Another aspect for you to consider is that you may want to explain your design methodology. How do you expect to implement the objective through code versus what your code actually does. Obviously the code is a WIP (work-in-progress), so unless we have a better idea of what must be done and what design goals you hope/expect to achieve, the only thing that I can do is point out problems like mixing C and C++ and public data in a C++ class.

Also, if each line of your input file equals one train, then you do not need to ask the user for the number of trains...unless you want to constrain the system so that it can process a subset of the data file. Generally speaking, we do not want to ask the user for the number of "records" in a file, because how would the user know without opening the file in some manner, presumedly by using our program?

MxB

Anonymous_guy · #3 01-Jul-2009, 01:21

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