[C] Printer queue emulation with child processes

[Scuzz]

Just showing another project I did while I was at Uni.

I dont know if it works, it should work as i submitted it as complete. But knowing me, i probably didnt care if it did work or not.

I’m pretty sure we had to emulate a printer queue. Each printer job was a child process.
Unix based OS only.

Producer

Producer
/* Some printf functions are comment out, these are for debuggin purposes. */

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>

void fChildProcess();

int main(int argc, char *argv[])
{
	if (argc != 3) //Error out if correct command isnt entered
	{	
		printf("Usage: %s SizeOfQueue NumberOfJobs\n", argv[0]);
		exit(0);
	}
	
	int columns = 2;
	int rows;
	int row;
	int *matrix;
	int shmid;
	int i, k, j, iNoj, iSoq;
	
	iSoq = atoi (argv[1]);
	iNoj = atoi (argv[2]); 
	
	if (iNoj > iSoq) //Error if number of jobs is > than the size of the queue
	{
		printf("Number of Jobs has to be less than the Size of queue\n");
		exit(0);
	}
	
	FILE *fp;
	pid_t pid;
	key_t key;
	key = 1220; //Identifier for shared memory
	rows = iSoq; //Sets the rows in the shared memory to +1 so there is space for flags
	k = 1;
	
	/* Makes a file that has the size of the queue in it */
	fp = fopen("size", "w");
	fprintf(fp, "%d", rows);
	fclose(fp);
	
	shmid = shmget(key, sizeof(int)*rows*columns, IPC_CREAT | 0666);
	if(shmid < 0)
	{
		perror("shmget");
		_Exit(1);
	}
	//printf("Segment created\n");
	matrix = (int *)shmat(shmid, 0, 0);	//Attatch
	matrix[0*2 + 0] = 0; // Read/write flag
	matrix[0*2 + 1] = 1;
	
	//printf("%d\t%d\n", matrix[0*2 + 0], matrix[0*2 + 1]);
	

	while(1)
	{
		//printf("WHILE LOOP\n");
		if(matrix[0*2 + 0] == 0)
		{
			for(i = 0; i < iNoj; i++)
			{
				if(matrix[0*2 + 1] <= iSoq)
				{
					//printf("FOR LOOP\n");
					pid = fork();
					if(pid < 0)
					{
						printf("fork Error");
						exit(1);
					}
					if(pid == 0)
					{
						fChildProcess();
					}
					else
					{
						//printf("PARENT\n");
						k = matrix[0*2 + 1];
						matrix[k*2 + 0] = pid; //Adds PID to shared memory
						matrix[0*2 + 1]++;	
						printf("PID %d added\n", matrix[k*2 + 0]);
					}
				}
			}
			//printf("SHARED MEM\n");
			//for(i = 0; i < iSoq; i++)
			//{
				//printf("%d\t%d\n", matrix[(i+1)*2 + 0], matrix[(i+1)*2 + 1]);
			//}
			matrix[0*2 + 0] = 1; 
		}
		else
		{
			sleep(1); //Wait for consumer
			wait(1); //Wait for child process
		}
			
	}	
	shmctl( shmid, IPC_RMID, 0 );
}

void fChildProcess()
{
	for(;;); //infinite loop, child process runs forever.
}

Consumer

Consumer
/* Some printf functions are commented out, they are used for debugging purpses*/

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/signal.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>

int main (int argc, char *argv[])
{
	if (argc != 2)	 //Errors out if correct arguments are not entered
	{
		printf ("Usage: %s AmmountToDelete\n", argv[0]);
		exit(1);
	}
	
	int rows;
	int columns = 2;
	int *matrix;
	int shmid;
	int i, j, iAtd;
	
	iAtd = atoi(argv[1]);
	
	FILE *fp;
	key_t key;

	//Opens the size file to get the size of the queue
	fp = fopen("size", "r"); 
	fscanf(fp, "%d", &rows);
	fclose(fp);
	
	if(iAtd > rows)
	{
		printf("Please enter a number <= %d\n", rows);
		exit(0);
	}
	
	k = 0;
	key = 1220;
	shmid = shmget(key, sizeof(int)*rows*columns, 0666);
	if(shmid < 0)
	{
		perror("shmget"); 	//Error out if shared mem not found
		exit(EXIT_FAILURE);
	}
	printf("Segment found\n");
	matrix = (int *)shmat(shmid, 0, 0); //Attatch
	
	//printf("Shared mem\n");
	//for(i = 0; i < rows; i++)
	//{
	//	printf("SHARED MEM\n%d\t%d\n", matrix[i*2 + 0], matrix[i*2 + 1]);
	//}
	
	while(1)
	{
		if(matrix[0*2 + 0] == 1)
		{
			//printf("SHARED MEM BEFORE\n");
			//for(i = 0; i < rows; i++)
			//{
			//	printf("%d\t%d\n", matrix[(i+1)*2 + 0], matrix[(i+1)*2 + 1]);
			//}
			//printf("KILLING PIDs\n");
			for(i = 0; i < iAtd; i++)
			{
				if(matrix[(i+1)*2 + 0] > 0)
				{
					printf("KILLING\t%d\n", matrix[(i+1)*2 + 0]);
					kill(matrix[(i+1)*2 + 0], SIGTERM); //Kills the process
					printf("KILLED\t%d\n", matrix[(i+1)*2 + 0]);
					matrix[0*2 + 1]--;
				}
			}
			for(j = 0; j < matrix[0*2 + 1]; j++) 
			{
				matrix[(j + 1)*2 + 0] = matrix[(j + 2)*2 + 0];
			}
			//printf("SHARED MEM AFTER\n");
			//for(i = 0; i < rows; i++)
			//{
			//	printf("%d\t%d\n", matrix[(i+1)*2 + 0], matrix[(i+1)*2 + 1]);
			//}
			matrix[0*2 + 0] = 0;
		}
		else
		{
			sleep(1);
		}
	}
	exit(0);
}