Question

Modify the program q1.c by adding calls to uthread_join (and making no other changes) so that it always prints the lines “zero” to “three” in order; i.e., its output must always be the following.

q1.c code as below:

#include <stdlib.h>
#include <stdio.h>
#include "uthread.h"

uthread_t t0, t1, t2;

void randomStall() {
int i, r = random() >> 16;
while (i++<r);
}

void* p0(void* v) {
randomStall();
printf("zero\n");
return NULL;
}

void* p1(void* v) {
randomStall();
printf("one\n");
return NULL;
}

void* p2(void* v) {
randomStall();
printf("two\n");
return NULL;
}

int main(int arg, char** arv) {
uthread_init(4);
t0 = uthread_create(p0, NULL);
t1 = uthread_create(p1, NULL);
t2 = uthread_create(p2, NULL);
randomStall();
printf("three\n");
printf("------\n");
}

Answer 1

Concept of Thread Join

a calling thread i.e the one which is executing the current statement, will wait until the called thread finish executing its function

e.g:

thread2.start(); // do more stuff here thread2.join(); System.out.println("Done");

in the above code the current thread i.e which will be executing these statements will for thread2 to finish its work and that will print Done

Modified Source Code

#include <stdlib.h>

#include <stdio.h>

#include "uthread.h"

uthread_t t0, t1, t2;

void randomStall() {

int i, r = random() >> 16;

while (i++<r);

}

void* p0(void* v) {

randomStall();

printf("zero\n");

return NULL;

}

void* p1(void* v) {

randomStall();

printf("one\n");

return NULL;

}

void* p2(void* v) {

randomStall();

printf("two\n");

return NULL;

}

int main(int arg, char** arv) {

uthread_init(4);

t0 = uthread_create(p0, NULL);

//make main thread wait for t0 to finish its work

t0.uthread_join();

t1 = uthread_create(p1, NULL);

//make main thread wait for t1 to finish its work

t1.uthread_join();

t2 = uthread_create(p2, NULL);

//make main thread wait for t2 to finish its work

t2.uthread_join();

randomStall();

//main thread print three after t0, t1, t2 has already done printing their text

printf("three\n");

printf("------\n");

}