skiplist/examples/skip.c

#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>

#include "../include/skiplist.h"

// Define a node that contains key and value pair.
struct my_node {
  // Metadata for skiplist node.
  sl_node snode;
  // My data here: {int, int} pair.
  int key;
  int value;
};

// Define a comparison function for `my_node`.
static int
my_cmp(sl_node *a, sl_node *b, void *aux)
{
  // Get `my_node` from skiplist node `a` and `b`.
  struct my_node *aa, *bb;
  aa = sl_get_entry(a, struct my_node, snode);
  bb = sl_get_entry(b, struct my_node, snode);

  // aa  < bb: return neg
  // aa == bb: return 0
  // aa  > bb: return pos
  if (aa->key < bb->key)
    return -1;
  if (aa->key > bb->key)
    return 1;
  return 0;
}

#define NUM_NODES 10000

int
main()
{
  // seed the PRNG
  srandom((unsigned)(time(NULL) | getpid()));

  sl_raw slist;

  // Initialize skiplist.
  sl_init(&slist, my_cmp);

  //   << Insertion >>
  // Allocate & insert NUM_NODES KV pairs: {0, 0}, {1, 10}, {2, 20}.
  struct my_node *nodes[NUM_NODES];
  for (int i = 0; i < NUM_NODES; ++i) {
    // Allocate memory.
    nodes[i] = (struct my_node *)malloc(sizeof(struct my_node));
    // Initialize node.
    sl_init_node(&nodes[i]->snode);
    // Assign key and value.
    nodes[i]->key = i;
    nodes[i]->value = i * 10;
    // Insert into skiplist.
    sl_insert(&slist, &nodes[i]->snode);
  }

  //   << Point lookup >>
  for (int i = 0; i < NUM_NODES; ++i) {
    // Define a query.
    struct my_node query;
    int min = 1, max = NUM_NODES - 1;
    int k = min + (int)random() / (RAND_MAX / (max - min + 1) + 1);
    query.key = k;
    // Find a skiplist node `cursor`.
    sl_node *cursor = sl_find(&slist, &query.snode);
    // If `cursor` is NULL, key doesn't exist.
    if (!cursor)
      continue;
    // Get `my_node` from `cursor`.
    // Note: found->snode == *cursor
    struct my_node *found = sl_get_entry(cursor, struct my_node, snode);
    printf("[point lookup] key: %d, value: %d\n", found->key, found->value);
    if (found->key != found->value / 10) {
      printf("FAILURE: key: %d * 10 !=  value: %d\n", found->key, found->value);
      exit(-1);
    }
    // Release `cursor` (== &found->snode).
    // Other thread cannot free `cursor` until `cursor` is released.
    sl_release_node(cursor);
  }

  //   << Erase >>
  // Erase the KV pair for key 1: {1, 10}.
  {
    // Define a query.
    struct my_node query;
    query.key = 1;
    // Find a skiplist node `cursor`.
    sl_node *cursor = sl_find(&slist, &query.snode);
    // Get `my_node` from `cursor`.
    // Note: found->snode == *cursor
    struct my_node *found = sl_get_entry(cursor, struct my_node, snode);
    printf("[erase] key: %d, value: %d\n", found->key, found->value);

    // Detach `found` from skiplist.
    sl_erase_node(&slist, &found->snode);
    // Release `found`, to free its memory.
    sl_release_node(&found->snode);
    // Free `found` after it becomes safe.
    sl_wait_for_free(&found->snode);
    sl_free_node(&found->snode);
    free(found);
  }

  //   << Iteration >>
  {
    // Get the first cursor.
    sl_node *cursor = sl_begin(&slist);
    while (cursor) {
      // Get `entry` from `cursor`.
      // Note: entry->snode == *cursor
      struct my_node *entry = sl_get_entry(cursor, struct my_node, snode);
      printf("[iteration] key: %d, value: %d\n", entry->key, entry->value);
      // Get next `cursor`.
      cursor = sl_next(&slist, cursor);
      // Release `entry`.
      sl_release_node(&entry->snode);
    }
  }

  //   << Destroy >>
  {
    // Iterate and free all nodes.
    sl_node *cursor = sl_begin(&slist);
    while (cursor) {
      struct my_node *entry = sl_get_entry(cursor, struct my_node, snode);
      printf("[destroy] key: %d, value: %d\n", entry->key, entry->value);
      // Get next `cursor`.
      cursor = sl_next(&slist, cursor);

      // Detach `entry` from skiplist.
      sl_erase_node(&slist, &entry->snode);
      // Release `entry`, to free its memory.
      sl_release_node(&entry->snode);
      // Free `entry` after it becomes safe.
      sl_wait_for_free(&entry->snode);
      sl_free_node(&entry->snode);
      free(entry);
    }
  }

  // Free skiplist.
  sl_free(&slist);

  return 0;
}