Thread: Help with simple deadlock detection program

Hello all,

I'm trying to write a program that detects deadlock. Some of the code I already tested in an earlier stage but at this point when I run the code it somehow gets stuck. I believe that it has something to do with a negative integer value. Anyhow, the program should still work if a negative integer comes up. Here's my code so far. I think it's fairly clear on what the idea is, but if you have any questions please let me know.

Code:

#include <stdio.h>


#define FALSE 0
#define TRUE 1


int ALLOC[5][5], REQ[5][5], TOT_RES[5], process, resource, NUMB_RES=5, NUMB_PRO=5;
int TMP[5]={0}, AVAIL[5], CNTR=0, FIN[5]={FALSE}, FLAG;


int main(int argc, char **argv, char **envp) 
{
    srand(time(NULL));
    
    //Create a randomly generated allocation matrix
    //with a value between 0 and 5 for each resource and process
    
    printf("Allocation matrix:\n");


    for(process=0;process<5;process++)
    {
        for(resource=0;resource<5;resource++)
        {
            ALLOC[process][resource]=rand()%4;
            printf("\t%d",ALLOC[process][resource]);
        }
        printf("\n");
    }


    //Create a randomly generated request matrix
    //with a value between 0 and 5 for each resource and process
    
    printf("\nRequest matrix:\n");


    for(process=0;process<5;process++)
    {
        for(resource=0;resource<5;resource++)
        {
            REQ[process][resource]=rand()%4;
            printf("\t%d",REQ[process][resource]);
        }
        printf("\n");
    }


    //Create a randomly generated total resource vector
    //with a value between 10 and 15 for each resource and process
    
    printf("\nResources:\n");


    for(process=0;process<5;process++)
    {
        TOT_RES[process]=rand()%3+NUMB_RES+NUMB_PRO;
        printf("\t%d",TOT_RES[process]);
    }
    
    //display the total number of resources in use


    //printf("\n\nTotal claimed per resource:\n");


    for(process=0;process<5;process++)
    {
        for(resource=0;resource<5;resource++)
        {
            TMP[process]+=ALLOC[resource][process];
        }
        //printf("\t%d", TMP[process]);
    }


    //Display the total number of available resources
    printf("\n\nAvailable:\n");


    for(process=0;process<5;process++)
    {
        AVAIL[process]=TOT_RES[process]-TMP[process];
        printf("\t%d",AVAIL[process]);
    }


    while(TRUE)
    {
        for(process=0;process<5;process++)
        {
            CNTR=0;
            if(FIN[process] == FALSE)
            {
                for(resource=0;resource<5;resource++)
                {
                    //zijn resources beschikbaar?
                    if(REQ[process][resource]<=AVAIL[resource])
                    {
                        //zo ja, verhoog de counter
                        CNTR++;
                    }
                }
                FLAG = FALSE;
                
                //vergelijk counter met aantal resources
                //als counter tot 5 is opgelopen zijn alle resources beschikbaar
                //en kunnen worden teruggegeven aan de available pool
                if(CNTR == NUMB_RES)
                {
                    for(resource=0;resource<5;resource++)
                    {
                        //geef resources terug
                        AVAIL[resource]+=ALLOC[process][resource];
                    }
                    FIN[process]=TRUE;
                    printf("\nProcess number %d is finished\n",process+1);
                }
                else
                FLAG = TRUE;
            }
        }
        CNTR=0;
        for(process=0;process<5;process++)
        {
            if(FIN[process] == TRUE)
            {
                CNTR++;
            }
        }
        if(CNTR==5)
        {
        break;
        }
    }


    for(process=0;process<5;process++)
    {
        if(FIN[process] == FALSE)
        {
            printf("\n Deadlock detected. Responsible process number is: %d\n",process+1);
            return;
        }
    }
}

The program usually gets stuck after producing output displaying the "Available: " text. After that a list of tabbed numbers should appear, but it doesn't. Any help would be much appreciated.

Greetings,

Deheerwassenaar

printf("\t");
printf("%d",AVAIL[process]);

try it like that to see if it works.

if its on linux, you might need a line feed or an fflush to get the 5 printfs after Available to show up. linux doesn't flush the printf output until it sees a \n. if your while loop is not terminating then you never do a linefeed.

Hi all,

@jamesedmonds: I tried your solution, but to no avail unfortunately.

@dmh2000: I tried to use fflush after the for-loop that displays my Available resources, but I didn't solve all my problems.

@ Salem: I think you are right. After rethinking about my while-loop I figured you were on the right track, so I tried to make changes that could help. The first thing I tried was moving the last for-loop within the while-loop, but that still doesn't fix my problem. The reason for letting this for-loop out of the while-loop was so that the while-loop would try to continue, and not just stop after each process had been checked.

I now know what the problem is, and I'm also aware of the solution I think, but I don't know how to implement it.

I think the while loop should end after he checks all processes that aren't finished and nothing changes. Then it should know for sure that new resources will not be available ever. Is someone capable of helping me with this? I tried, but haven't found a solution so far.

Thanks for all the help so far!