Copy DBserver.c above into a file in your filespace named lab05q1.c Modify lab05q1.c so that it has the same functionality as DBserver.c above, except that it uses USER-LEVEL threads (using the pthread library). "Clean up" your new code to make it more clear and concise. - you can join threads much more simply.

DBserver.c:

/* 3 users use the DB (for each, a thread is spawned). Thread i does queryNo[i] queries for its user. A global "total_queries" is maintained. Each thread updates it after each of its queries.

This has a race condition on variable total_queries.

Note that if you have maxed out your allotted clones, one (or more) child may never execute its function, although it exists. So parent can't terminate because it waits forever for child (do ps -lu USERID and kill the offending child)

*/

#define _GNU_SOURCE //for Ubuntu #include #include #include #include #include #include #include #include

int queryNo[3] = {1011, 1012, 1013};

int total_queries = 0;

int userThread (void *p) { int i; int q = (int)(long)p;

//set thread q on CPU q cpu_set_t set; CPU_ZERO( &set ); CPU_SET( q, &set ); if (sched_setaffinity( getpid(), sizeof( cpu_set_t ), &set )) { perror( "sched_setaffinity" ); _exit(0); }

for (i = 0; i < queryNo[q]; i++) { //handle queries total_queries = total_queries + 1; } _exit(0); }

int main(int argc, char *argv[]) { const int STACK_SIZE = 65536; char *stack; char *stackTop[3]; pid_t cret[3], wret; int i;

for (i = 0; i < 3; i++) { //do 3 child threads stack = malloc(STACK_SIZE); if (stack == NULL) { perror("malloc"); exit(1); } stackTop[i] = stack + STACK_SIZE; /* Assume stack grows downward */ cret[i] = clone(userThread, stackTop[i], CLONE_VM|SIGCHLD, (void *)(long)i); //make child signal when done if (cret[i] == -1) { perror("clone"); exit(0); } //parent keeps going here } //for (i=0;i<3;i++) waitpid(cret[i],0,0);

for (i = 0; i < 3; i++) { wret = waitpid(-1, 0, 0); if (wret == -1) { perror("waitpid"); exit(3); } //a useless double-check that we got our own children... if (wret != cret[0] && wret != cret[1] && wret != cret[2] ) { perror("waitpid wret"); exit(2); } } sleep(1); printf("%d total_queries should be 3036 and it is %d ", getpid(), total_queries); return 0; }