Piss Pott Ohne Raceconditions mit Semaphoren

pisspott2.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/sem.h>
#include <sys/wait.h>
#include <errno.h>
#include <string.h>

#define MAXCOUNT ((FUSS_B+FUSS_A)*17)
#define FUSS_B 15.51337
#define FUSS_A 13.13123
#define SHM_ERROR "Shared Memory konnte nicht erstellt werden!\n"
#define FORK_ERROR "fork() konnte keinen Kindprozess erzeugen!\n"
#define SEM_ERROR "Fehler bei Semaphore !\n"

int main(int argc, char * argv[])
{
	/* Hilfsvariablen*/
	int i, sleep_time;
	if(argc <= 1)
	{
		fprintf(stderr,"Zeit in us angeben !\n");
		return EXIT_FAILURE;
	}
	sleep_time = strtol(argv[1],NULL,10);
	/* Semaphore initialisieren*/
	int sem_id,sem_check;
	unsigned short marker[1];	
	sem_id = semget (IPC_PRIVATE, 1, IPC_CREAT|0644);	/*anlegen*/
	if(sem_id == -1) 
	{
		fprintf(stderr,SEM_ERROR);
		return EXIT_FAILURE;
	}
	marker[0] = 1;
	sem_check=semctl(sem_id, 1, SETALL, marker);
	if(sem_check < 0)
	{
		fprintf(stderr,SEM_ERROR);
		return EXIT_FAILURE;
	}
	/* PIDs der Kindprozesse*/
	int pid[2];
	/*Shared Memory fuer IPS*/
	int *sperr_fuer_kind,id_sperr,id;
	id_sperr = shmget( IPC_PRIVATE, sizeof(int),0600);
	if(id_sperr == -1)
	{
		fprintf(stderr,SHM_ERROR);
		return EXIT_FAILURE;
	}
	sperr_fuer_kind = (int*)shmat(id_sperr,0,0);
	if(sperr_fuer_kind == NULL)
	{
		fprintf(stderr,SHM_ERROR);
		return EXIT_FAILURE;
	}
	/*Shared Memory fuer PissPott*/
	double *area;
	id = shmget( IPC_PRIVATE, sizeof(double),0600);
	if(id == -1)
	{
		fprintf(stderr,SHM_ERROR);
		return EXIT_FAILURE;
	}
	area = (double*)shmat(id,0,0);
	if(area == NULL)
	{
		fprintf(stderr,SHM_ERROR);
		return EXIT_FAILURE;
	}
	/* Semaphore Strukturen zum sperren und freigeben*/
	struct sembuf enter, leave;
	enter.sem_num = 0;	/* Semaphor 0 in der Gruppe*/
	enter.sem_op = -1;	/* blockieren*/
	enter.sem_flg = SEM_UNDO;
	leave.sem_num = 0;	/* Semaphor 0 in der Gruppe*/
	leave.sem_op = 1;	/* freigeben*/
	leave.sem_flg = SEM_UNDO;
	/* Bereich zuruecksetzen*/
	*area = MAXCOUNT;
	*sperr_fuer_kind = 0;
	/* 1 Kindprozesse erzeugen*/
	pid[0] = fork();
	if(pid[0] == -1)
	{
		fprintf(stderr,FORK_ERROR);
		return EXIT_FAILURE;
	}
	if(pid[0] == 0)	/* KIND 1*/
	{
		while(1)
		{
			/*KRITISCHER BEREICH BETRETEN*/
			if( semop(sem_id,&enter,1) < 0)
			{
				fprintf(stderr,SEM_ERROR);
				return EXIT_FAILURE;
			}
			if(*sperr_fuer_kind == 1 && *area > 0){
				/*KRITISCHER BEREICH VERLASSEN*/
				if( semop(sem_id,&leave,1) < 0)
				{
					fprintf(stderr,SEM_ERROR);
					return EXIT_FAILURE;
				}
				continue;
			}
			if(*area > 0)
			{
				*area -= FUSS_A;
			}else{break;}
			*sperr_fuer_kind = 1;
			/*KRITISCHER BEREICH VERLASSEN*/
			if( semop(sem_id,&leave,1) < 0)
			{
				fprintf(stderr,SEM_ERROR);
				return EXIT_FAILURE;
			}
			printf("POTT - %lf\n",*area);
			fflush(stdout);
			usleep(sleep_time);
			
		}
		return EXIT_SUCCESS;
	}
	else
	{	
		/* 2 Kindprozesse erzeugen*/
		pid[1] = fork();
		if(pid[1] == -1)
		{
			fprintf(stderr,FORK_ERROR);
			return EXIT_FAILURE;
		}
		if(pid[1] == 0)	/* KIND 2*/
		{
			while(1)
			{
				/*KRITISCHER BEREICH BETRETEN*/
				if( semop(sem_id,&enter,1) < 0)
				{
					fprintf(stderr,SEM_ERROR);
					return EXIT_FAILURE;
				}
				if(*sperr_fuer_kind == 2 && *area > 0){
					/*KRITISCHER BEREICH VERLASSEN*/
					if( semop(sem_id,&leave,1) < 0)
					{
						fprintf(stderr,SEM_ERROR);
						return EXIT_FAILURE;
					}
					continue;
				}
				if(*area > 0)
				{
					*area -= FUSS_B;
				}else{break;}
				*sperr_fuer_kind = 2;
				/*KRITISCHER BEREICH VERLASSEN*/
				if( semop(sem_id,&leave,1) < 0)
				{
					fprintf(stderr,SEM_ERROR);
					return EXIT_FAILURE;
				}
				printf("PISS - %lf\n",*area);
				fflush(stdout);
				usleep(sleep_time);
			}
			return EXIT_SUCCESS;
		}
		/* VATER wartet auf alle Kinder*/
		for(i=0;i<2;i++)
		{
			waitpid(*(pid+i),NULL,0);
		}
	}
	/* Semaphore freigeben*/
	semctl(sem_id, 0, IPC_RMID);
	/* ENDE*/
	/* return EXIT_SUCCESS;*/
	if(*area < 0.1 && *area > -0.1)
	{
		/* Shared Memory loesen*/
		shmdt(area);
		shmdt(sperr_fuer_kind);
		shmctl(id, IPC_RMID, 0);
		shmctl(id_sperr, IPC_RMID, 0);
		printf("OK\n");
		return EXIT_SUCCESS;
	}
	else
	{
		/* Shared Memory loesen*/
		shmdt(area);
		shmdt(sperr_fuer_kind);
		shmctl(id, IPC_RMID, 0);
		shmctl(id_sperr, IPC_RMID, 0);
		printf("Nicht OK\n");
		return EXIT_FAILURE;
	}
}