Implemented use of hook_user_operations with batch.

custom_users.module

/**
 * Implements hook_user_operations().
 */
function custom_users_user_operations() {
  $operations['custom_users_salesforce'] = array(
    'label' => t('Create Salesforce Account'),
    'callback' => 'custom_users_operations_create_salesforce_callback',
  );
  return $operations;
}

/**
 * Callback function for admin mass generating user salesforce account.
 *
 * @param $uids
 *   An array of user IDs.
 */
function custom_users_operations_create_salesforce_callback(array $uids) {

  $batch = array(
    'title' => t('Creating Salesforce Account'),
    'init_message' => t('Preparing to create salesforce account'),
    'operations' =>array(
      array('custom_users_operations_create_salesforce_batch', array($uids)),
    ),
    'progress_message' => '',
    'finished' => 'custom_users_operations_create_salesforce_batch_finished',
  );
  batch_set($batch);
  batch_process('admin/people');
}


function custom_users_operations_create_salesforce_batch($uids, &$context) {
  if (!isset($context['sandbox']['progress'])) {
    $context['sandbox']['progress'] = 0;
    $context['sandbox']['max'] = count($uids);
    $context['sandbox']['uids'] = $uids;
  }

  // Process nodes by groups of 5.
  $count = min(5, count($context['sandbox']['uids']));
  for ($i = 1; $i <= $count; $i++) {
    // For each nid, load the node, reset the values, and save it.
    $uid = array_shift($context['sandbox']['uids']);
    $account = user_load($uid);

    $result = joc_users_salesforce_account_create($account);

    // Save their JOC & metering data
    if (!empty($result) && $result) {
      $edit = array();
      $edit['data']['JOC'] = $result;
      $edit['roles'] = $account->roles;

      if (empty($edit['roles'][JOC_ROLE_REGISTERED]))
        $edit['roles'][JOC_ROLE_REGISTERED] = 'JOC Registered';

      $account->status = 1;
      // Save user data in drupal
      user_save($account, $edit);
    }
    else {
      watchdog('joc_user_operation', 'Salesforce account for @email is exist or not created',
        array('@email' => $account->mail), WATCHDOG_NOTICE);
    }

    // Store result for post-processing in the finished callback.
    $context['results'][] = $uid;
    // Update our progress information.
    $context['sandbox']['progress']++;
    $context['message'] = t('Processing @current out of @total', array(
      '@current' => $context['sandbox']['progress'],
      '@total' => $context['sandbox']['max'],
    ));
  }

  // Inform the batch engine that we are not finished,
  // and provide an estimation of the completion level we reached.
  if ($context['sandbox']['progress'] != $context['sandbox']['max']) {
    $context['finished'] = $context['sandbox']['progress'] / $context['sandbox']['max'];
  }

}

function custom_users_operations_create_salesforce_batch_finished($success, $results, $operations) {
  if ($success) {
    drupal_set_message(t('The Salesforce account has been created for users.'));
  }
  else {
    drupal_set_message(t('An error occurred and processing did not complete.'), 'error');
    $message = format_plural(count($results), '1 item successfully processed:', '@count items successfully processed:');
    $message .= theme('item_list', array('items' => $results));
    drupal_set_message($message);
  }
}