Assignment #03 Race conditions and context switching.

Programming Assignment #03

Experience the race conditions and context switching.
/*=========================================================*/
/* race.c --- for playing with ECE437 */
/*=========================================================*/
#include <unistd.h
#include <stdio.h
#include <stdlib.h
#include <pthread.h
struct {int balance[2];} Bank={{100,100}}; //global variable defined
void* MakeTransactions() { //routine for thread execution
int i, j, tmp1, tmp2, rint; double dummy;
for (i=0; i < 100; i++) {
rint = (rand()%30)-15;
if (((tmp1=Bank.balance[0])+rint)=0 && ((tmp2=Bank.balance[1])-rint)=0) {
Bank.balance[0] = tmp1 + rint;
for (j=0; j < rint*1000; j++) {dummy=2.345*8.765/1.234;} // spend time on purpose
Bank.balance[1] = tmp2 - rint;
}
}
return NULL;
}
int main(int argc, char **argv) {
int i; void* voidptr=NULL; pthread_t tid[2];
srand(getpid());
printf("Init balances A:%d + B:%d == %d!\n",
Bank.balance[0],Bank.balance[1],Bank.balance[0]+Bank.balance[1]);
for (i=0; i<2; i++) if (pthread_create(&tid[i],NULL,MakeTransactions, NULL)) {
perror("Error in thread creating\n"); return(1); }
for (i=0; i<2; i++) if (pthread_join(tid[i], (void*)&voidptr)) {
perror("Error in thread joining\n"); return(1);}
printf("Let's check the balances A:%d + B:%d == %d ?= 200\n",
Bank.balance[0],Bank.balance[1],Bank.balance[0]+Bank.balance[1]);
return 0;
}
Q1) (25%) Compile then run the above code for 10-20 times. Write a paragraph to explain.
Q2) (25%) Use thread library calls (mutex lock and unlock) to modify the code in Q1) to remove any
potential race conditions. Show your modification of the code and explain the outcome with your
modification
Q3) (25%) Rewrite your code in Q1) replacing threads by processes.
• Instead of creating two threads to call “MakeTransactions”, you will use fork() to create a child
process. Both parent and child processes will call procedure “MakeTransactions”.
• Since two processes will not share a common address space, you will need to rewrite code to
allocate “Bank” as a shared variable (by applying shared memory IPC, see Slide M02c).
• Other parts (i.e., set up initial values, print the initial values and balance, and print the ending
values and balance) stay the same.
Show your implementation code in the written report, compile then run your new process-based code
for 10-20 times. Write a paragraph to explain if the race condition still exists.
Q4) (25%) Use semaphore system calls to modify your code in Q3 in order to remove any potential
race conditions. Show your modification of the code and explain the outcome with your modification.
Note:
1. You do not need to submit your source code, only submit a written report which may contain
some copy/paste your code segments (you may highlight/using a different font color to indicate
your modified codes).
2. You can continue to work as a group of two or individually. If you work as a group of two, you still
have to submit a separate report without copying with each other. Also, if you work as a group of
two, you have to indicate the group member in the report.