159.341_Assignment_2/assignment2_handout.c

/* Dempsey-Jensen, Brychan, 14299890, Assignment 2, 159.341 */
/* Use semaphores to prevent race conditions in a concurrent lift-simulator */

// *************
// Note:
// Uncommenting this definition will print populations & the number of people next to the building

// #define POPULATIONS

// --------------------------------------------------
// ---   159.341 Assignment 2 - Lift Simulator    ---
// --------------------------------------------------
// Written by M. J. Johnson
// Updated by D. P. Playne - 2019
#include <stdio.h>
#include <stddef.h>
#include <stdlib.h>
#include "lift.h"

// --------------------------------------------------
// Define Problem Size
// --------------------------------------------------
#define NLIFTS 4	   // The number of lifts in the building
#define NFLOORS 20	   // The number of floors in the building
#define NPEOPLE 20	   // The number of people in the building
#define MAXNOINLIFT 10 // Maximum number of people in a lift

// --------------------------------------------------
// Define delay times (in milliseconds)
// --------------------------------------------------
//#define SUPERSLOW
//#define SLOW
//#define FAST
#define SUPERFAST // Original FAST

#if defined(SUPERSLOW)
	#define LIFTSPEED 500	  // The time it takes for the lift to move one floor
	#define GETINSPEED 250	  // The time it takes to get into the lift
	#define GETOUTSPEED 250	  // The time it takes to get out of the lift
	#define PEOPLESPEED 10000 // The maximum time a person spends on a floor
#elif defined(SLOW)
	#define LIFTSPEED 250	// The time it takes for the lift to move one floor
	#define GETINSPEED 100	// The time it takes to get into the lift
	#define GETOUTSPEED 100 // The time it takes to get out of the lift
	#define PEOPLESPEED 100 // The maximum time a person spends on a floor
#elif defined(FAST)
	#define LIFTSPEED 25   // The time it takes for the lift to move one floor
	#define GETINSPEED 10  // The time it takes to get into the lift
	#define GETOUTSPEED 10 // The time it takes to get out of the lift
	#define PEOPLESPEED 10 // The maximum time a person spends on a floor
#elif defined(SUPERFAST)
	#define LIFTSPEED 0	  // The time it takes for the lift to move one floor
	#define GETINSPEED 0  // The time it takes to get into the lift
	#define GETOUTSPEED 0 // The time it takes to get out of the lift
	#define PEOPLESPEED 1 // The maximum time a person spends on a floor
#endif

// --------------------------------------------------
// Define lift directions (UP/DOWN)
// --------------------------------------------------
#define UP 1
#define DOWN -1

// Define the lower-case true so that this compiles directly in Windows (GCC 9.2)
#if defined(_WIN32) || defined(WIN32)
#define true TRUE
#endif


// --------------------------------------------------
// Information about a floor in the building
// --------------------------------------------------
typedef struct
{
	int waitingtogoup;			// The number of people waiting to go up
	int waitingtogodown;		// The number of people waiting to go down
	semaphore up_arrow;			// People going up wait on this
	semaphore down_arrow;		// People going down wait on this
	// People can't all press a button at the same time
	semaphore queueInteraction; 
	} floor_info;

// --------------------------------------------------
// Information about a lift
// --------------------------------------------------
typedef struct
{
	int no;						// The lift number (id)
	int position;				// The floor it is on
	int direction;				// Which direction it is going (UP/DOWN)
	int peopleinlift;			// The number of people in the lift
	int stops[NFLOORS];			// How many people are going to each floor
	semaphore stopsem[NFLOORS]; // People in the lift wait on one of these
	// control whether the lift is currently adding someone
	semaphore addToStop;
} lift_info;

// --------------------------------------------------
// Some global variables
// --------------------------------------------------
floor_info floors[NFLOORS];

// keep track of the current target lift on the floor (and a semaphore to prevent this changing prematurely)
lift_info *targetLift[NFLOORS];
semaphore targetLiftSelect[NFLOORS];

// Bind all printing to this semaphore, so that the target position can't be changed before printing.
semaphore printSemaphore;

// If printing people counts, int array and semaphore to keep track of them
#ifdef POPULATIONS
semaphore updateFloorCount;
int floorCount[NFLOORS];
// count of times since value was zero, used to help find a stuck person
int floorCountZeroInc[NFLOORS];

// --------------------------------------------------
// Prints a string, with a delay - but it is zero ms
// --------------------------------------------------
void print_at_xy_fast(int x, int y, const char *s)
{
	semaphore_wait(&printSemaphore);
	gotoxy(x, y);
	Sleep(0);
	printf("%s", s);
	semaphore_signal(&printSemaphore);
}
#endif

// --------------------------------------------------
// Print a string on the screen at position (x,y)
// --------------------------------------------------
void print_at_xy(int x, int y, const char *s)
{
	// Lock our print to just one thread (stops x,y from changing)
	semaphore_wait(&printSemaphore);
	// Move cursor to (x,y)
	gotoxy(x, y);

	// Slow things down
	Sleep(1);

	// Print the string
	printf("%s", s);

	// Move cursor out of the way
	gotoxy(42, NFLOORS + 2);
	// flush the stream and release the semaphore
	//fflush(stdout);
	semaphore_signal(&printSemaphore);
}

// --------------------------------------------------
// Function for a lift to pick people waiting on a
// floor going in a certain direction
// --------------------------------------------------
void get_into_lift(lift_info *lift, int direction)
{
	// Local variables
	int *waiting;
	semaphore *s;

	// Check lift direction
	if (direction == UP)
	{
		// Use up_arrow semaphore
		s = &floors[lift->position].up_arrow;

		// Number of people waiting to go up
		waiting = &floors[lift->position].waitingtogoup;
	}
	else
	{
		// Use down_arrow semaphore
		s = &floors[lift->position].down_arrow;

		// Number of people waiting to go down
		waiting = &floors[lift->position].waitingtogodown;
	}

	// Waiting can begin to be decremented while another thread enters the loop. Therefore we
	// need to prevent an attempt to remove someone who has already been removed
	while (*waiting)
	{
		// Check if lift is empty
		if (lift->peopleinlift == 0)
		{
			// Set the direction of the lift
			lift->direction = direction;
		}

		// Prevent other threads from evaluating the conditional until waiting is decremented
		semaphore_wait(&floors[lift->position].queueInteraction);
		if (lift->peopleinlift < MAXNOINLIFT && *waiting)
		{
			// Add person to the lift
			lift->peopleinlift++;
			print_at_xy(NLIFTS * 4 + floors[lift->position].waitingtogodown + floors[lift->position].waitingtogoup, NFLOORS - lift->position, " ");

			(*waiting)--;
			semaphore_signal(&floors[lift->position].queueInteraction);

			// Wait for person to get into lift
			Sleep(GETINSPEED);


			// Wait to set the current lift for the floor as our current lift. We maintain this lock,
			// while the person whom is later signalled will relase it
			semaphore_wait(&targetLiftSelect[lift->position]);
			targetLift[lift->position] = lift;
			// lock the addtostop, to prevent the lift leaving without the passenger
			semaphore_wait(&lift->addToStop);
			// Finally, "open the doors and let someone in"
			semaphore_signal(s);
		}
		else
		{
			// There is no-one else waiting; so release our lock
			semaphore_signal(&floors[lift->position].queueInteraction);
			break;
		}
	}
}

// --------------------------------------------------
// Function for the Lift Threads
// --------------------------------------------------
void *lift_thread(void *p)
{
	// Local variables
	lift_info lift;
	int no = (long long)p;
	int i;

	// Set up Lift
	lift.no = no;		   // Set lift number
	lift.position = 0;	   // Lift starts on ground floor
	lift.direction = UP;   // Lift starts going up
	lift.peopleinlift = 0; // Lift starts empty
	// A lift can load a single person at a time
	semaphore_create(&lift.addToStop, 1);

	for (i = 0; i < NFLOORS; i++)
	{
		lift.stops[i] = 0;					   // No passengers waiting
		semaphore_create(&lift.stopsem[i], 0); // Initialise semaphores
	}

	// Randomise lift
	randomise();

	// Wait for random start up time (up to a second)
	Sleep(rnd(1000));

	// Loop forever
	while (true)
	{
		// Print current position of the lift
		print_at_xy(no * 4 + 1, NFLOORS - lift.position, lf);
		// Wait for a while
		Sleep(LIFTSPEED);

		// Print the number of people in the lift
#ifdef POPULATIONS
		char str[12];
		sprintf(str, "%d", lift.peopleinlift);
		print_at_xy_fast(no * 4 + 1, NFLOORS + 5, "  ");
		print_at_xy_fast(no * 4 + 1, NFLOORS + 5, str);
#endif

		// Drop off passengers on this floor
		while (lift.stops[lift.position] != 0)
		{
			// These are sequential operations on just one thread (this lift), so don't need protecting here -
			// The passenger is told to get out and then does work on the floor

			// One less passenger in lift
			lift.peopleinlift--;

			// One less waiting to get off at this floor
			lift.stops[lift.position]--;
			
			// Wait for exit lift delay
			Sleep(GETOUTSPEED);

			// Signal passenger to leave lift
			semaphore_signal(&lift.stopsem[lift.position]);
			

			// Check if that was the last passenger waiting for this floor
			if (!lift.stops[lift.position])
			{
				// Clear the "-"
				print_at_xy(no * 4 + 1 + 2, NFLOORS - lift.position, " ");
			}
		}
		// Check if lift is going up or is empty
		if (lift.direction == UP || !lift.peopleinlift)
		{
			// Pick up passengers waiting to go up
			get_into_lift(&lift, UP);
		}
		// Check if lift is going down or is empty
		if (lift.direction == DOWN || !lift.peopleinlift)
		{
			// Pick up passengers waiting to go down
			get_into_lift(&lift, DOWN);
		}

		// Erase lift from screen
		print_at_xy(no * 4 + 1, NFLOORS - lift.position, (lift.direction + 1 ? " " : lc));

		// Move lift, but make sure it doesn't move before someone is fully loaded
		// this really could go anywhere, but it fits the metaphor to wrap it here (doesn't have to wrap anything)
		semaphore_wait(&lift.addToStop);
		lift.position += lift.direction;
		semaphore_signal(&lift.addToStop);

		// Check if lift is at top or bottom
		if (lift.position == 0 || lift.position == NFLOORS - 1)
		{
			// Change lift direction
			lift.direction = -lift.direction;
		}
	}

	return NULL;
}

// --------------------------------------------------
// Function for the Person Threads
// --------------------------------------------------
void *person_thread(void *p)
{
	// Local variables
	int from = 0, to; // Start on the ground floor
	lift_info *lift;
	// Randomise
	randomise();

	// Stay in the building forever
	while (true)
	{
		// Work for a while
		Sleep(rnd(PEOPLESPEED));
		do
		{
			// Randomly pick another floor to go to
			to = rnd(NFLOORS);
		} while (to == from);
		semaphore *s;
		// Check which direction the person is going (UP/DOWN)
		if (to > from)
		{
			// One more person waiting to go up
			// Only one can press the button at a time. Ensure the person is printed to the console before releasing the
			// semaphore so that there are no ghosts left in the console
			semaphore_wait(&floors[from].queueInteraction);
			floors[from].waitingtogoup++;
			print_at_xy(NLIFTS * 4 + floors[from].waitingtogoup + floors[from].waitingtogodown, NFLOORS - from, pr);
			semaphore_signal(&floors[from].queueInteraction);

			s = &floors[from].up_arrow;
			// Wait for a lift to arrive (going up)
		}
		else
		{
			semaphore_wait(&floors[from].queueInteraction);
			// One more person waiting to go down
			floors[from].waitingtogodown++;
			print_at_xy(NLIFTS * 4 + floors[from].waitingtogoup + floors[from].waitingtogodown, NFLOORS - from, pr);
			semaphore_signal(&floors[from].queueInteraction);

			s = &floors[from].down_arrow;
			// Wait for a lift to arrive (going down)
		}

		// We've pressed our button
		// waiting for a lift's doors to open
		semaphore_wait(s);
		// Which lift we are getting into. The targetLift has locked the variable, so once we have our reference,
		lift = targetLift[from];
		// Realease the targetLift ASAP so another lift can load someone
		semaphore_signal(&targetLiftSelect[lift->position]);

		// GetIntoLift() continues its loop, from here (this passenger is signalled to enter; so we definitely need to hold a lock around
		// this value)
		// When GetIntoLift() decides that a passenger should enter, it obtains a lock of addToStop. 
		// We release that lock here. Finally, once all passengers have been picked up and the lift decides to move on, if this lock is
		// still held, then the lift wont change floor (protecting against unloading issues)

		// We could do this by extending the targetLiftSelect semaphore through the same condition, but that would affect the performance of all lifts on this floor
		lift->stops[to]++;
		
		if (lift->stops[to] == 1)
		{
			// Print light for destination
			print_at_xy(lift->no * 4 + 1 + 2, NFLOORS - to, "-");
		}
		// Person are fully added
		semaphore_signal(&lift->addToStop);

		semaphore_wait(&lift->stopsem[to]);
		// Wait until we are at the right floor

#ifdef POPULATIONS
		// Prints the current location of all people in a line below the building
		semaphore_wait(&updateFloorCount);
		floorCount[to]++;
		floorCount[from]--;
		semaphore_signal(&updateFloorCount);
		// Print the current person's floor
		char str[3];
		sprintf(str, "%d", to);
		print_at_xy_fast((long long)p * 4 + 1, NFLOORS + 8, "  ");
		print_at_xy_fast((long long)p * 4 + 1, NFLOORS + 8, str);
#endif
		// Finally, exit the lift
		from = to;
	}

	return NULL;
}

// --------------------------------------------------
//	Print the building on the screen
// --------------------------------------------------
void printbuilding(void)
{

	// Local variables
	int l, f;

	// Clear Screen
	system(clear_screen);
	// Print the whole building before anything else
	// Print Roof
	printf("%s", tl);
	for (l = 0; l < NLIFTS - 1; l++)
	{
		printf("%s%s%s%s", hl, td, hl, td);
	}
	printf("%s%s%s%s\n", hl, td, hl, tr);

	// Print Floors and Lifts
	for (f = NFLOORS - 1; f >= 0; f--)
	{
		for (l = 0; l < NLIFTS; l++)
		{
			printf("%s%s%s ", vl, lc, vl);
			if (l == NLIFTS - 1)
			{
				printf("%s\n", vl);
			}
		}
	}

	// Print Ground
	printf("%s", bl);
	for (l = 0; l < NLIFTS - 1; l++)
	{
		printf("%s%s%s%s", hl, tu, hl, tu);
	}
	printf("%s%s%s%s\n", hl, tu, hl, br);

	// Print Message
	printf("Lift Simulation - Press CTRL-Break to exit\n");

#ifdef POPULATIONS
	gotoxy(0, NFLOORS + 7);
	printf("People\'s Destination Floors:");
	gotoxy(0, NFLOORS + 4);
	printf("Lift Occupants:");
	gotoxy(4 * NLIFTS + NPEOPLE + 5, 0);
	printf("Number of People on Floor:");
#endif
	// Ensure buffer is written
	fflush(stdout);
	// Once the building has been printed, then we can those waiting to print that they may do so
	semaphore_signal(&printSemaphore);
}


#ifdef POPULATIONS
// --------------------------------------------------
// Iterate through the floors and update the queue size
// --------------------------------------------------
void *update_floor_counts(void *p)
{
	int i;
	int k;
	// Iterations since the count on the floor was zero
	char str2[18] = {';',' ','\t', 'i', 't', 'e', 'r', 's', ' ', 's', 'i', 'n', 'c', 'e', ' ', '0', ':', ' '};
	while (true)
	{
		for (i = -1; i < NFLOORS; i++)
		{
			char str[48];
			char str3[12];
			if (i != -1)
			{
				if (floorCount[i] != 0){
					floorCountZeroInc[i]++;
				}
				else{
					floorCountZeroInc[i] = 0;
				}
				sprintf(str, "%d", floorCount[i]);
				sprintf(str3, "%d", floorCountZeroInc[i]);
				strcat(str, str2);
				strcat(str, str3);
				print_at_xy_fast(4 * NLIFTS + NPEOPLE + 5, NFLOORS - i, "                                          ");
				print_at_xy_fast(4 * NLIFTS + NPEOPLE + 5, NFLOORS - i, str);
			}
			else
			{
				int ttl = 0;
				for (k = 0; k < NFLOORS; k++)
				{
					ttl += floorCount[k];
				}
				sprintf(str, "%d", ttl);
				if (ttl != NPEOPLE)
				{
					break;
				}
				print_at_xy_fast(4 * NLIFTS + NPEOPLE + 5, NFLOORS - i, str);
			}
			
		}
	}
	//Sleep(0);
}
#endif

// --------------------------------------------------
// Main starts the threads and then waits.
// --------------------------------------------------
int main()
{
	// Intro stage:
	printf("|------------------------------------------|\n");
	printf("|  159.341 2021 Semester 1, Assignment 2   |\n");
	printf("|  Submitted by Brychan Dempsey, 14299890  |\n");
	printf("|------------------------------------------|\n");
	printf("\nPress \'enter\' to begin.");
	char c;
	do {
    	c = getchar();
  	} while (!(c == 10 || c == 12)); // Char is not \r or \n
	
	// Local variables
	unsigned long i;
	// init the print semaphore
	semaphore_create(&printSemaphore, 0);
	// Initialise Building
	for (i = 0; i < NFLOORS; i++)
	{
		floors[i].waitingtogoup = 0;
		floors[i].waitingtogodown = 0;
		semaphore_create(&floors[i].up_arrow, 0);
		semaphore_create(&floors[i].down_arrow, 0);

		semaphore_create(&floors[i].queueInteraction, 1);
		semaphore_create(&targetLiftSelect[i], 1);
#ifdef POPULATIONS
		if (i == 0)
		{
			semaphore_create(&updateFloorCount, 1);
			floorCount[0] = NPEOPLE;
			floorCountZeroInc[0] = 0;
		}
		else
		{
			floorCount[i] = 0;
			floorCountZeroInc[i] = 0;
		}
#endif

	}

	// Print Building
	printbuilding();

	// Create Lifts
	for (i = 0; i < NLIFTS; i++)
	{
		// Create Lift Thread
		create_thread(lift_thread, (void *)i);
	}

	// Create People
	for (i = 0; i < NPEOPLE; i++)
	{
		// Create Person Thread
		create_thread(person_thread, (void *)i);
	}
#ifdef POPULATIONS
	create_thread(update_floor_counts, (void *)i);
#endif
	// Go to sleep for 86400 seconds (one day)
	Sleep(86400000ULL);
}