ray/src/photon/photon_algorithm.c

#include "photon_algorithm.h"

#include <stdbool.h>
#include "utarray.h"

#include "state/task_log.h"
#include "photon.h"
#include "photon_scheduler.h"

typedef struct {
  /* Object id of this object. */
  object_id object_id;
  /* Handle for the uthash table. */
  UT_hash_handle handle;
} available_object;

/** Part of the photon state that is maintained by the scheduling algorithm. */
struct scheduler_state {
  /** An array of pointers to tasks that are waiting to be scheduled. */
  UT_array *task_queue;
  /** An array of worker indices corresponding to clients that are
   *  waiting for tasks. */
  UT_array *available_workers;
  /** A hash map of the objects that are available in the local Plasma store.
   *  This information could be a little stale. */
  available_object *local_objects;
};

scheduler_state *make_scheduler_state(void) {
  scheduler_state *state = malloc(sizeof(scheduler_state));
  /* Initialize an empty hash map for the cache of local available objects. */
  state->local_objects = NULL;
  /* Initialize the local data structures used for queuing tasks and workers. */
  utarray_new(state->task_queue, &task_ptr_icd);
  utarray_new(state->available_workers, &ut_int_icd);
  return state;
}

void free_scheduler_state(scheduler_state *s) {
  utarray_free(s->task_queue);
  utarray_free(s->available_workers);
  free(s);
}

/**
 * Check if all of the remote object arguments for a task are available in the
 * local object store.
 *
 * @param s The scheduler state.
 * @param task Task specification of the task to check.
 * @return This returns 1 if all of the remote object arguments for the task are
 *         present in the local object store, otherwise it returns 0.
 */
bool can_run(scheduler_state *s, task_spec *task) {
  int64_t num_args = task_num_args(task);
  for (int i = 0; i < num_args; ++i) {
    if (task_arg_type(task, i) == ARG_BY_REF) {
      object_id obj_id = *task_arg_id(task, i);
      available_object *entry;
      HASH_FIND(handle, s->local_objects, &obj_id, sizeof(object_id), entry);
      if (entry == NULL) {
        /* The object is not present locally, so this task cannot be scheduled
         * right now. */
        return false;
      }
    }
  }
  return true;
}

/**
 * If there is a task whose dependencies are available locally, assign it to the
 * worker. This does not remove the worker from the available worker queue.
 *
 * @param s The scheduler state.
 * @param worker_index The index of the worker.
 * @return This returns 1 if it successfully assigned a task to the worker,
 *         otherwise it returns 0.
 */
int find_and_schedule_task_if_possible(scheduler_info *info,
                                       scheduler_state *state,
                                       int worker_index) {
  int found_task_to_schedule = 0;
  /* Find the first task whose dependencies are available locally. */
  task_spec *spec;
  task_instance **task;
  int i = 0;
  for (; i < utarray_len(state->task_queue); ++i) {
    task = (task_instance **) utarray_eltptr(state->task_queue, i);
    spec = task_instance_task_spec(*task);
    if (can_run(state, spec)) {
      found_task_to_schedule = 1;
      break;
    }
  }
  if (found_task_to_schedule) {
    /* This task's dependencies are available locally, so assign the task to the
     * worker. */
    assign_task_to_worker(info, spec, worker_index);
    /* Update the task queue data structure and free the task. */
    free(*task);
    utarray_erase(state->task_queue, i, 1);
  }
  return found_task_to_schedule;
}

void handle_task_submitted(scheduler_info *info,
                           scheduler_state *s,
                           task_spec *task) {
  /* Create a unique task instance ID. This is different from the task ID and
   * is used to distinguish between potentially multiple executions of the
   * task. */
  task_iid task_iid = globally_unique_id();
  task_instance *instance =
      make_task_instance(task_iid, task, TASK_STATUS_WAITING, NIL_ID);
  /* If this task's dependencies are available locally, and if there is an
   * available worker, then assign this task to an available worker. Otherwise,
   * add this task to the local task queue. */
  int schedule_locally =
      (utarray_len(s->available_workers) > 0) && can_run(s, task);
  if (schedule_locally) {
    /* Get the last available worker in the available worker queue. */
    int *worker_index = (int *) utarray_back(s->available_workers);
    /* Tell the available worker to execute the task. */
    assign_task_to_worker(info, task, *worker_index);
    /* Remove the available worker from the queue and free the struct. */
    utarray_pop_back(s->available_workers);
  } else {
    /* Add the task to the task queue. This passes ownership of the task queue.
     * And the task will be freed when it is assigned to a worker. */
    utarray_push_back(s->task_queue, &instance);
  }
  /* Submit the task to redis. */
  task_log_add_task(info->db, instance);
  if (schedule_locally) {
    /* If the task was scheduled locally, we need to free it. Otherwise,
     * ownership of the task is passed to the task_queue, and it will be freed
     * when it is assigned to a worker. */
    free(instance);
  }
}

void handle_worker_available(scheduler_info *info,
                             scheduler_state *state,
                             int worker_index) {
  int scheduled_task =
      find_and_schedule_task_if_possible(info, state, worker_index);
  /* If we couldn't find a task to schedule, add the worker to the queue of
   * available workers. */
  if (!scheduled_task) {
    for (int *p = (int *) utarray_front(state->available_workers); p != NULL;
         p = (int *) utarray_next(state->available_workers, p)) {
      CHECK(*p != worker_index);
    }
    /* Add client_sock to a list of available workers. This struct will be freed
     * when a task is assigned to this worker. */
    utarray_push_back(state->available_workers, &worker_index);
    LOG_INFO("Adding worker_index %d to available workers.\n", worker_index);
  }
}

void handle_object_available(scheduler_info *info,
                             scheduler_state *state,
                             object_id object_id) {
  /* TODO(rkn): When does this get freed? */
  available_object *entry =
      (available_object *) malloc(sizeof(available_object));
  entry->object_id = object_id;
  HASH_ADD(handle, state->local_objects, object_id, sizeof(object_id), entry);

  /* Check if we can schedule any tasks. */
  int num_tasks_scheduled = 0;
  for (int *p = (int *) utarray_front(state->available_workers); p != NULL;
       p = (int *) utarray_next(state->available_workers, p)) {
    /* Schedule a task on this worker if possible. */
    int scheduled_task = find_and_schedule_task_if_possible(info, state, *p);
    if (!scheduled_task) {
      /* There are no tasks we can schedule, so exit the loop. */
      break;
    }
    num_tasks_scheduled += 1;
  }
  utarray_erase(state->available_workers, 0, num_tasks_scheduled);
}