Briefly explain why PTHREAD_CANCEL_ASYNCHRONOUS is used in this MP (see below).

#include "enzyme.h"

int please_quit; int use_yield; int workperformed;

// The code each enzyme executes. void *run_enzyme(void *data) { /* This function should : 1. cast the void* pointer to thread_info_t* 2. initialize the swapcount to zero 3. Set the cancel type to PTHREAD_CANCEL_ASYNCHRONOUS 4. If the first letter of the string is a C then call pthread_cancel on this thread. 5. Create a while loop that only exits when please_quit is nonzero 6. Within this loop: if the first character of the string has an ascii value greater than the second (s[0] >s[1]) then - Set workperformed=1, increment swapcount for this thread, then swap the two characters around If "use_yield" is nonzero then call pthread_yield at the end of the loop. 7. Return a pointer to the updated structure. */ while(0) { sched_yield(); }; return NULL; }

// Make threads to sort string. // Returns the number of threads created. // There is a memory bug in this function. int make_enzyme_threads(pthread_t * enzymes, char *string, void *(*fp)(void *)) { int i,rv,len; thread_info_t *info; len = strlen(string); info = (thread_info_t *)malloc(sizeof(thread_info_t));

for(i=0;istring = string+i; rv = pthread_create(enzymes+i,NULL,fp,info); if (rv) { fprintf(stderr,"Could not create thread %d : %s ", i,strerror(rv)); exit(1); } } return len-1; }

// Join all threads at the end. // Returns the total number of swaps. int join_on_enzymes(pthread_t *threads, int n) { int i; int totalswapcount = 0; int whatgoeshere=0; // just to make the code compile // you will need to edit the code below for(i=0;i

if(whatgoeshere) { fprintf(stderr,"Can't join thread %d:%s. ",i,strerror(rv)); continue; }

if ((void*)whatgoeshere == PTHREAD_CANCELED) { continue; } else if (status == NULL) { printf("Thread %d did not return anything ",i); } else { printf("Thread %d exited normally: ",i);// Don't change this line int threadswapcount = whatgoeshere; // Hint - you will need to cast something. printf("%d swaps. ",threadswapcount); // Don't change this line totalswapcount += threadswapcount;// Don't change this line } } return totalswapcount; }

/* Wait until the string is in order. Note, we need the workperformed flag just in case a thread is in the middle of swapping characters so that the string temporarily is in order because the swap is not complete. */ void wait_till_done(char *string, int n) { int i; while(1) { sched_yield(); workperformed=0; for(i=0;i string[i+1]) { workperformed=1; } if(workperformed==0) break; } }

void * sleeper_func(void *p) { sleep( (int) p); // Actually this may return before p seconds because of signals. // See man sleep for more information printf("sleeper func woke up - exiting the program "); exit(1); }

int smp2_main(int argc, char **argv) { pthread_t enzymes[MAX]; int n,totalswap; char string[MAX];

if (argc <= 1) { fprintf(stderr,"Usage: %s ",argv[0]); exit(1); } strncpy(string,argv[1],MAX); // Why is this necessary? Why cant we give argv[1] directly to the thread functions?

please_quit = 0; use_yield =1; printf("Creating threads... "); n = make_enzyme_threads(enzymes,string,run_enzyme); printf("Done creating %d threads. ",n); pthread_t sleeperid; pthread_create(&sleeperid,NULL,sleeper_func,(void*)5);

wait_till_done(string,n); please_quit = 1; printf("Joining threads... "); totalswap = join_on_enzymes(enzymes, n); printf("Total: %d swaps ",totalswap); printf("Sorted string: %s ",string); exit(0); }