chase-lev-deque/deque.c

   1 #include <stdatomic.h>
   2 #include <inttypes.h>
   3 #include "deque.h"
   4 #include <stdlib.h>
   5
   6 Deque * create() {
   7         Deque * q = (Deque *) calloc(1, sizeof(Deque));
   8         Array * a = (Array *) calloc(1, sizeof(Array)+2*sizeof(atomic_int));
   9         atomic_store_explicit(&q->array, a, memory_order_relaxed);
  10         atomic_store_explicit(&q->top, 0, memory_order_relaxed);
  11         atomic_store_explicit(&q->bottom, 0, memory_order_relaxed);
  12         atomic_store_explicit(&a->size, 2, memory_order_relaxed);
  13         return q;
  14 }
  15
  16 int take(Deque *q) {
  17         size_t b = atomic_load_explicit(&q->bottom, memory_order_relaxed) - 1;
  18         Array *a = (Array *) atomic_load_explicit(&q->array, memory_order_relaxed);
  19         atomic_store_explicit(&q->bottom, b, memory_order_relaxed);
  20         atomic_thread_fence(memory_order_seq_cst);
  21         size_t t = atomic_load_explicit(&q->top, memory_order_relaxed);
  22         int x;
  23         if (t <= b) {
  24                 /* Non-empty queue. */
  25                 x = atomic_load_explicit(&a->buffer[b % atomic_load_explicit(&a->size,memory_order_relaxed)], memory_order_relaxed);
  26                 if (t == b) {
  27                         /* Single last element in queue. */
  28                         if (!atomic_compare_exchange_strong_explicit(&q->top, &t, t + 1, memory_order_seq_cst, memory_order_relaxed))
  29                                 /* Failed race. */
  30                                 x = EMPTY;
  31                         atomic_store_explicit(&q->bottom, b + 1, memory_order_relaxed);
  32                 }
  33         } else { /* Empty queue. */
  34                 x = EMPTY;
  35                 atomic_store_explicit(&q->bottom, b + 1, memory_order_relaxed);
  36         }
  37         return x;
  38 }
  39
  40 void resize(Deque *q) {
  41         Array *a = (Array *) atomic_load_explicit(&q->array, memory_order_relaxed);
  42         size_t size=atomic_load_explicit(&a->size, memory_order_relaxed);
  43         size_t new_size=size << 1;
  44         Array *new_a = (Array *) calloc(1, new_size * sizeof(atomic_int) + sizeof(Array));
  45         size_t top=atomic_load_explicit(&q->top, memory_order_relaxed);
  46         size_t bottom=atomic_load_explicit(&q->bottom, memory_order_relaxed);
  47         atomic_store_explicit(&new_a->size, new_size, memory_order_relaxed);
  48         size_t i;
  49         for(i=top; i < bottom; i++) {
  50                 atomic_store_explicit(&new_a->buffer[i % new_size], atomic_load_explicit(&a->buffer[i % size], memory_order_relaxed), memory_order_relaxed);
  51         }
  52         atomic_store_explicit(&q->array, new_a, memory_order_relaxed);
  53 }
  54
  55 void push(Deque *q, int x) {
  56         size_t b = atomic_load_explicit(&q->bottom, memory_order_relaxed);
  57         size_t t = atomic_load_explicit(&q->top, memory_order_acquire);
  58         Array *a = (Array *) atomic_load_explicit(&q->array, memory_order_relaxed);
  59         if (b - t > atomic_load_explicit(&a->size, memory_order_relaxed) - 1) /* Full queue. */ {
  60                 resize(q);
  61                 //Bug in paper...should have next line...
  62                 a = (Array *) atomic_load_explicit(&q->array, memory_order_relaxed);
  63         }
  64         atomic_store_explicit(&a->buffer[b % atomic_load_explicit(&a->size, memory_order_relaxed)], x, memory_order_relaxed);
  65         atomic_thread_fence(memory_order_release);
  66         atomic_store_explicit(&q->bottom, b + 1, memory_order_relaxed);
  67 }
  68
  69 int steal(Deque *q) {
  70         size_t t = atomic_load_explicit(&q->top, memory_order_acquire);
  71         atomic_thread_fence(memory_order_seq_cst);
  72         size_t b = atomic_load_explicit(&q->bottom, memory_order_acquire);
  73         int x = EMPTY;
  74         if (t < b) {
  75                 /* Non-empty queue. */
  76                 Array *a = (Array *) atomic_load_explicit(&q->array, memory_order_relaxed);
  77                 x = atomic_load_explicit(&a->buffer[t % atomic_load_explicit(&a->size, memory_order_relaxed)], memory_order_relaxed);
  78                 if (!atomic_compare_exchange_strong_explicit(&q->top, &t, t + 1, memory_order_seq_cst, memory_order_relaxed))
  79                         /* Failed race. */
  80                         return ABORT;
  81         }
  82         return x;
  83 }