I origially posted this in another group but this group is more
appropriate so I am reposting it here.
I am trying to create a tree of processes. The code below works,
however, my initial call to the procTree function is passed depth-2. I
arrived at this via trial and error and am not sure why this works?
Can anyone spot what I am doing wrong? Or is that right for some reason
I don't understand?


int i=-1;
int pid;
int numberOfProcesses=-1;

void procTree(int depth)
{
for(i=0;i<numberOfProcesses;i=i+1){
int socko=socket(2,1,0);
struct sockaddr_in addr;
addr.sin_family=2;
addr.sin_addr.s_addr=htonl((127<<24)+1);
addr.sin_port=0;
bind(socko,(struct sockaddr *)&addr,16);
if((pid=fork())< 0){
printf("Fork failed");
exit(1);
}
if(pid==0){
//then in child
if(depth>0){
procTree(depth-1);
}

// do other child stuff
return;
}
if(pid){
//then in parent
}
}
}

int main(int argc, char *argv[]){
char input[MAXBUFFER];//create a character array to hold input
from the user
char output[MAXBUFFER];//create a character array to hold output
int depth=atoi(argv[2]);
numberOfProcesses=atoi(argv[1]);

procTree(depth-2);

read(0,input,MAXBUFFER);
sprintf(output,"%s",input);
write(1,output,strlen(output));
}

What I really really want to know is why I need to set depth to depth-2
in my fist call to procTree? I just iteratated the value a few times to
find one that works but I have no idea why!!
I kept looking at ps output until the tree looked correct to me.
i.e.
$ ps -ef | grep "2 2"
jani     2244  1979  0 15:34 ttyp1    00:00:00 ./a.out 2 2
jani     2245  2244  0 15:34 ttyp1    00:00:00 ./a.out 2 2
jani     2246  2244  0 15:34 ttyp1    00:00:00 ./a.out 2

[ Post a follow-up to this message ]

Jani Yusef <jani@persian.com> writes:

> I origially posted this in another group but this group is more
> appropriate so I am reposting it here.
> I am trying to create a tree of processes. The code below works,
> however, my initial call to the procTree function is passed depth-2. I
> arrived at this via trial and error and am not sure why this works?
> Can anyone spot what I am doing wrong? Or is that right for some
> reason I don't understand?
> [...]
> void procTree(int depth)
>         {
>             for(i=0;i<numberOfProcesses;i=i+1){
> [...]
>                 if((pid=fork())< 0){
>                     printf("Fork failed");
>                     exit(1);
>                 }
>                 if(pid==0){
>                     //then in child
>                     if(depth>0){
>                       procTree(depth-1);
>                     }
>
>                     // do other child stuff
>                     return;
>                 }
> [...]
> What I really really want to know is why I need to set depth to depth-2
> in my fist call to procTree? I just iteratated the value a few times to
> find one that works but I have no idea why!!

That's just a problem of recursion and counting.

First, you have already one root process, so your minimum depth is 1,
not 0, and when you set depth=1, you don't want to fork any
child. That means, you should test the depth before trying to fork!


void procTree(int depth){
if(1<depth){
for(i=0;i<number_of_children;i++){
int pid=fork();
switch(pid){
case 0: /* in child */
depth--;
procTree(depth);
return;
case -1:
perror("fork");
return;
default: /* in parent */
break; }}}}


int main(int argc,char** argv){
/* ... */
int depth=argv[2]?atoi(argv[2]):1;
procTree(depth);
/* ... */ }


(If you use procps ps, you can use ps -f to get a display of your
process tree (or use pstree)).

--
__Pascal Bourguignon__                     http://www.informatimago.com/

Our enemies are innovative and resourceful, and so are we. They never
stop thinking about new ways to harm our country and our people, and
neither do we.

[ Post a follow-up to this message ]

Jani Yusef wrote:
> I origially posted this in another group but this group is more
> appropriate so I am reposting it here.
> I am trying to create a tree of processes. The code below works,
> however, my initial call to the procTree function is passed depth-2. I
> arrived at this via trial and error and am not sure why this works?
> Can anyone spot what I am doing wrong? Or is that right for some reason
> I don't understand?
>
>
> int i=-1;
> int pid;
> int numberOfProcesses=-1;
>
> void procTree(int depth)
>        {
>            for(i=0;i<numberOfProcesses;i=i+1){
>                int socko=socket(2,1,0);
>                struct sockaddr_in addr;
>                addr.sin_family=2;
>                addr.sin_addr.s_addr=htonl((127<<24)+1);
>                addr.sin_port=0;
>                bind(socko,(struct sockaddr *)&addr,16);
>                if((pid=fork())< 0){
>                    printf("Fork failed");
>                    exit(1);
>                }
>                if(pid==0){
>                    //then in child
>                    if(depth>0){
>                      procTree(depth-1);
>                    }
>
>                    // do other child stuff
>                    return;
>                }
>                if(pid){
>                    //then in parent
>                }
>            }
>        }
>
> int main(int argc, char *argv[]){
>          char input[MAXBUFFER];//create a character array to hold inpu
t
> from the user
>          char output[MAXBUFFER];//create a character array to hold out
put
>          int depth=atoi(argv[2]);
>          numberOfProcesses=atoi(argv[1]);
>
>          procTree(depth-2);
>
>          read(0,input,MAXBUFFER);
>          sprintf(output,"%s",input);
>          write(1,output,strlen(output));
> }
>
> What I really really want to know is why I need to set depth to depth-2
> in my fist call to procTree? I just iteratated the value a few times to
> find one that works but I have no idea why!!
> I kept looking at ps output until the tree looked correct to me.
> i.e.
> $ ps -ef | grep "2 2"
> jani     2244  1979  0 15:34 ttyp1    00:00:00 ./a.out 2 2
> jani     2245  2244  0 15:34 ttyp1    00:00:00 ./a.out 2 2
> jani     2246  2244  0 15:34 ttyp1    00:00:00 ./a.out 2
>

In your code, you do not modify your depth value.  Instead of saying
proctree(depth-1) say proctree(--depth).

--

Fletcher Glenn

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