(Solved) : Question Possible Worker Thread Would Never Proceed Past Call Wa Ops Waitforcpu Wa Info Us Q42771238 . . .

Question: Is itpossible that a worker thread would never proceed past the call towa-­‐>ops-­‐>wait_for_cpu(&wa-­‐>info) when using oneof the scheduling policies implemented in this MP?

——————–scheduler.c —- wait_for_cpu() is in thestatic void *worker_proc(void *arg) function —————–

#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <pthread.h>
#include <unistd.h>

#include “scheduler.h”
#include “sched_impl.h”

/* Used to pass thread arguments to worker_proc() */
typedef struct worker_args {
  pthread_t           thread_id;
  int                 iterations;
   worker_thread_ops_t *ops;
  thread_info_t        info;
} worker_args_t;

/* Used to pass thread arguments to sched_proc() */
typedef struct sched_args {
   sched_queue_t *queue;
   sched_ops_t   *sched_ops;
} sched_args_t;

/* The scheduler uses this counter to keep track of whether itshould wait
* for more threads to schedule or exit. If your schedulerimplementation
* is written correctly, it will provide all of thesynchronization
* necessary to mediate access to the num_workers_remainingvariable. */
static int num_workers_remaining = 0;

/* Procedure implementing a worker thread. */
static void *worker_proc(void *arg)
   int i;
   worker_args_t *wa = (worker_args_t *) arg;

   /* Compete with other threads to enter thescheduler queue. */
   printf(“Thread %lu: in scheduler queuen”, (unsignedlong) wa->thread_id);

   for (i = 0; i < wa->iterations; i++) {
       /* Don’t do anything until thescheduler tells us. */

       /* Do some meaningless work…*/
       printf(“Thread %lu: loop %dn”,(unsigned long) wa->thread_id, i);

       /* Let another worker have achance. */

   /* Leave the scheduler queue to make room forsomeone else
   * and decrement the count of remaining threads.*/
   printf(“Thread %lu: exitingn”, (unsigned long)wa->thread_id);


/* Procedure implementing the outline of the scheduler. */
static void *sched_proc(void *arg)
   sched_args_t*sa        = (sched_args_t *)arg;
   sched_queue_t *queue     =sa->queue;
   sched_ops_t   *sched_ops =sa->sched_ops;

   /* Wait until there’s at least one worker thread toschedule. */

   /* Keep scheduling worker threads until we’re done.*/
   while (num_workers_remaining > 0) {
       thread_info_t *info =sched_ops->next_worker(queue);
       /* next_worker() returns NULL ifthe scheduler queue is empty. */
       if (info) {
       } else {
           /* Wait forsomeone to enter the queue. */
   printf(“Scheduler: done!n”);

   return NULL;

/* Print out a message describing usage of the program. */
static void print_help(const char *progname)
   printf(“nusage: %s <sched_impl><queue_size> <num_threads> [iterations]n”,progname);
   printf(“tsched_impl : -fifo or -rr or-dummyn”);
   printf(“tqueue_size : the number of threads that canbe in the scheduler at one timen”);
   printf(“tnum_threads: the number of worker threads torunn”);
   printf(“titerations (optional): the number of loopseach worker thread runsnn”);

/* Display an error and terminate. */
static void exit_error(int err_num)
   fprintf(stderr, “failure: %sn”,strerror(err_num));

/* Create thread_count-many worker threads, each of which runfor iterations-many cycles. */
static worker_args_t *create_workers(worker_thread_ops_t *ops, intthread_count, int iterations, sched_queue_t *queue)
   int i = 0;
   /* Allocate all thread arguments in one big array(makes it easy to deallocate). */
   worker_args_t *argses = (worker_args_t *)malloc(thread_count * sizeof(worker_args_t));

   if (argses == NULL)

   /* Initialize counter used by sched_proc() todetermine when to stop.
   * This is safe assuming sched_ops->wait_for_queue()blocks in sched_proc(). */
   num_workers_remaining = thread_count;

   for (i = 0; i < thread_count; i++) {
       int err = 0;

       /* Set up worker threadarguments. */
       argses[i].iterations =iterations;
       argses[i].ops = ops;
      ops->init_thread_info(&argses[i].info, queue);

       /* Create worker thread.*/
       err =pthread_create(&argses[i].thread_id, NULL, worker_proc, (void*) &argses[i]);
       if (err)

       /* Detach worker thread.*/
       printf(“Main: detaching workerthread %lun”, (unsigned long) argses[i].thread_id);

   /* Arguments can only be deallocated when we’resure the worker
   * threads are done with them. And besides, it containsa handy
   * list of the thread_info_t’s which need to be cleanedup at the
   * end. So return the arguments array. */
   return argses;

/* Launch the scheduler thread. */
static int start_scheduler(pthread_t *thread_id, sched_queue_t*queue, sched_ops_t *ops)
   /* Make arguments static so they’re still valid afterthis function returns. */
   static sched_args_t sa;
   int err;

   /* Set up scheduler thread arguments. */
   sa.queue     = queue;
   sa.sched_ops = ops;

   /* Create the scheduler thread.  */
   err = pthread_create(thread_id, NULL, sched_proc,&sa);
   if (err)

   return err;

/* Deallocate all resources (called at end of program). */
static void clean_up(sched_impl_t *sched, int thread_count,worker_args_t *argses, sched_queue_t *queue)
   int i;
   for (i = 0; i < thread_count; i++)

int smp4_main(int argc, const char **argv)
   int thread_count = 0;
   int queue_size = 0;
   pthread_t sched_thread;
   int iterations = WORKER_ITERATIONS;
   worker_args_t *argses;
   sched_impl_t *sched;
   sched_queue_t queue;

   /* Collect command-line arguments (or exit onerror). */
   if (argc < 4) {

   if (!strcmp(“-fifo”, argv[1])) {
       sched = &sched_fifo;
   } else if (!strcmp(“-rr”, argv[1])) {
       sched = &sched_rr;
   } else if (!strcmp(“-dummy”, argv[1])) {
       sched = &sched_dummy;
   } else {
       printf(“nApologies, I’m unfamiliarwith the “%s” scheduling policy.n”, argv[1]);

   queue_size = atoi(argv[2]);
   thread_count = atoi(argv[3]);
   if (argc >= 5) {
       iterations = atoi(argv[4]);

   /* Begin execution proper. */
   printf(“Main: running %d workers on %d queue_size for%d iterationsn”, thread_count, queue_size, iterations);

   /* Initialize anything that needs to be done forthe scheduler queue. */

   /* Create a thread for the scheduler. */
   start_scheduler(&sched_thread, &queue,&sched->sched_ops);

   /* Create the worker threads and return. */
   argses = create_workers(&sched->worker_ops,thread_count, iterations, &queue);

   printf(“Main: waiting for scheduler %lun”,(unsigned long) sched_thread);
   /* Wait for scheduler to finish. */
   pthread_join(sched_thread, NULL);

   /* Clean up our resources. */
   clean_up(sched, thread_count, argses, &queue);

   /* This will wait for all other threads. */

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Answer to Question: Is it possible that a worker thread would never proceed past the call to wa-­‐>ops-­‐>wait_for_cpu(&wa-�…

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