Description
(40pts) 1. Read the following code. Find out how many processes are
created when the code is run, and point out the relation (i.e., the
parent-child relation) existing among these processes.
#include <unistd.h>
#include <stdio.h>
void main(int argc, char *argv[])
{
int tmp;
tmp=fork();
if(tmp>0){
int tmp;
tmp=fork();
if(tmp==0) fork();
}
tmp=fork();
printf(“This is process: %d\n”, getpid());
}
For example, when the following code is executed, two processes are
created. Suppose these processes are P0 and P1. P0 is the parent of P1.
#include <stdio.h>
#include <unistd.h>
int main( ){
fork();
}
(30pts) 2. Using the program shown below, identify the values of pid,
pid1 and value at lines A, B, C, D, E and F. (Note: Function getpid()
returns the ID of the calling process. Assume: the IDs of the parent and
child processes are 3000 and 5000, respectively.)
#include <sys/types.h>
#include <stdio.h>
#include <unistd.h>
int main( ){
pid_t pid, pid1;
int value;
pid = fork( );
value=0;
if (pid < 0) {
printf(“Fork Failed\n” );
exit(1);
}
else if (pid == 0){
value+=1;
pid1 = getpid( );
printf(“chid: pid = %d\n”, pid); /* A */
printf(“child: pid = %d\n”, pid1); /* B */
printf(“child: value=%d\n”, value); /* C */
}else{
value+=2;
pid1 = getpid( );
printf(“parent: pid = %d\n”, pid); /* D */
printf(“parent: pid = %d\n”, pid1); /* E */
wait(NULL);
printf(“parent: value=%d\n”, value); /* F */
}
return 0;
}
(30pts) 3. Read the following program and find out what are the outputs.
If there are multiple possibilies, list all the possible outputs.
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
void main()
{
int fd0[2],fd1[2];
pid_t pid;
char buf[255];
pipe(fd0);
pipe(fd1);
pid=fork();
if(pid==0){
read(fd0[0],buf,255);
printf(“This is child process 1.\n”);
write(fd1[1],”hello”,sizeof(“hello”));
exit(0);
}else{
pid=fork();
if(pid==0){
printf(“This is child process 2.\n”);
write(fd0[1],”hello”,sizeof(“hello”));
exit(0);
}
read(fd1[0],buf,255);
printf(“This is parent process.\n”);
}
}
