ms-queue/my_queue.c

   1 #include <threads.h>
   2 #include <stdlib.h>
   3
   4 #include "my_queue.h"
   5
   6 static unsigned int *node_nums;
   7
   8 static unsigned int new_node()
   9 {
  10         return node_nums[get_thread_num()];
  11 }
  12
  13 static void reclaim(unsigned int node)
  14 {
  15         node_nums[get_thread_num()] = node;
  16 }
  17
  18 void init_queue(queue_t *q, int num_threads)
  19 {
  20         unsigned int i;
  21         pointer head;
  22         pointer tail;
  23         pointer next;
  24
  25         node_nums = malloc(num_threads * sizeof(*node_nums));
  26         for (i = 0; i < num_threads; i++)
  27                 node_nums[i] = 2 + i;
  28
  29         /* initialize queue */
  30         head = MAKE_POINTER(1, 0);
  31         tail = MAKE_POINTER(1, 0);
  32         next = MAKE_POINTER(0, 0); // (NULL, 0)
  33
  34         atomic_init(&q->nodes[0].next, 0); // assumed inititalized in original example
  35
  36         atomic_store(&q->head, head);
  37         atomic_store(&q->tail, tail);
  38         atomic_store(&q->nodes[1].next, next);
  39
  40         /* initialize avail list */
  41         for (i = 2; i < MAX_NODES; i++) {
  42                 next = MAKE_POINTER(i + 1, 0);
  43                 atomic_store(&q->nodes[i].next, next);
  44         }
  45
  46         next = MAKE_POINTER(0, 0); // (NULL, 0)
  47         atomic_store(&q->nodes[MAX_NODES].next, next);
  48 }
  49
  50 void enqueue(queue_t *q, unsigned int val)
  51 {
  52         int success = 0;
  53         unsigned int node;
  54         pointer tail;
  55         pointer next;
  56         pointer tmp;
  57
  58         node = new_node();
  59         q->nodes[node].value = val;
  60         tmp = atomic_load(&q->nodes[node].next);
  61         set_ptr(&tmp, 0); // NULL
  62         atomic_store(&q->nodes[node].next, tmp);
  63
  64         while (!success) {
  65                 tail = atomic_load(&q->tail);
  66                 next = atomic_load(&q->nodes[get_ptr(tail)].next);
  67                 if (tail == atomic_load(&q->tail)) {
  68                         if (get_ptr(next) == 0) { // == NULL
  69                                 pointer value = MAKE_POINTER(node, get_count(next) + 1);
  70                                 success = atomic_compare_exchange_weak(&q->nodes[get_ptr(tail)].next,
  71                                                 &next, value);
  72                         }
  73                         if (!success) {
  74                                 unsigned int ptr = get_ptr(atomic_load(&q->nodes[get_ptr(tail)].next));
  75                                 pointer value = MAKE_POINTER(ptr,
  76                                                 get_count(tail) + 1);
  77                                 atomic_compare_exchange_strong(&q->tail,
  78                                                 &tail, value);
  79                                 thrd_yield();
  80                         }
  81                 }
  82         }
  83         atomic_compare_exchange_strong(&q->tail,
  84                         &tail,
  85                         MAKE_POINTER(node, get_count(tail) + 1));
  86 }
  87
  88 unsigned int dequeue(queue_t *q)
  89 {
  90         unsigned int value;
  91         int success = 0;
  92         pointer head;
  93         pointer tail;
  94         pointer next;
  95
  96         while (!success) {
  97                 head = atomic_load(&q->head);
  98                 tail = atomic_load(&q->tail);
  99                 next = atomic_load(&q->nodes[get_ptr(head)].next);
 100                 if (atomic_load(&q->head) == head) {
 101                         if (get_ptr(head) == get_ptr(tail)) {
 102                                 if (get_ptr(next) == 0) { // NULL
 103                                         return 0; // NULL
 104                                 }
 105                                 atomic_compare_exchange_strong(&q->tail,
 106                                                 &tail,
 107                                                 MAKE_POINTER(get_ptr(next), get_count(tail) + 1));
 108                                 thrd_yield();
 109                         } else {
 110                                 value = q->nodes[get_ptr(next)].value;
 111                                 success = atomic_compare_exchange_weak(&q->head,
 112                                                 &head,
 113                                                 MAKE_POINTER(get_ptr(next), get_count(head) + 1));
 114                                 if (!success)
 115                                         thrd_yield();
 116                         }
 117                 }
 118         }
 119         reclaim(get_ptr(head));
 120         return value;
 121 }