ms-queue/my_queue.c

   1 #include <threads.h>
   2 #include <stdlib.h>
   3 #include "librace.h"
   4 #include "model-assert.h"
   5
   6 #include "my_queue.h"
   7
   8 #define relaxed memory_order_relaxed
   9 #define release memory_order_release
  10 #define acquire memory_order_acquire
  11
  12 #define MAX_FREELIST 4 /* Each thread can own up to MAX_FREELIST free nodes */
  13 #define INITIAL_FREE 2 /* Each thread starts with INITIAL_FREE free nodes */
  14
  15 static unsigned int (*free_lists)[MAX_FREELIST];
  16
  17 /* Search this thread's free list for a "new" node */
  18 static unsigned int new_node()
  19 {
  20         int i;
  21         int t = get_thread_num();
  22         for (i = 0; i < MAX_FREELIST; i++) {
  23                 unsigned int node = load_32(&free_lists[t][i]);
  24                 if (node) {
  25                         store_32(&free_lists[t][i], 0);
  26                         return node;
  27                 }
  28         }
  29         /* free_list is empty? */
  30         MODEL_ASSERT(0);
  31         return 0;
  32 }
  33
  34 /* Place this node index back on this thread's free list */
  35 static void reclaim(unsigned int node)
  36 {
  37         int i;
  38         int t = get_thread_num();
  39
  40         /* Don't reclaim NULL node */
  41         MODEL_ASSERT(node);
  42
  43         for (i = 0; i < MAX_FREELIST; i++) {
  44                 /* Should never race with our own thread here */
  45                 unsigned int idx = load_32(&free_lists[t][i]);
  46
  47                 /* Found empty spot in free list */
  48                 if (idx == 0) {
  49                         store_32(&free_lists[t][i], node);
  50                         return;
  51                 }
  52         }
  53         /* free list is full? */
  54         MODEL_ASSERT(0);
  55 }
  56
  57 void init_queue(queue_t *q, int num_threads)
  58 {
  59         int i, j;
  60
  61         /* Initialize each thread's free list with INITIAL_FREE NULL "pointers" */
  62         free_lists = malloc(num_threads * sizeof(*free_lists));
  63         for (i = 0; i < num_threads; i++) {
  64                 for (j = 0; j < INITIAL_FREE; j++) {
  65                         free_lists[i][j] = 2 + i * MAX_FREELIST + j;
  66                         atomic_init(&q->nodes[free_lists[i][j]].next, MAKE_POINTER(0, 0));
  67                 }
  68         }
  69
  70         /* initialize queue */
  71         atomic_init(&q->head, MAKE_POINTER(1, 0));
  72         atomic_init(&q->tail, MAKE_POINTER(1, 0));
  73         atomic_init(&q->nodes[1].next, MAKE_POINTER(0, 0));
  74 }
  75
  76 void enqueue(queue_t *q, unsigned int val)
  77 {
  78         int success = 0;
  79         unsigned int node;
  80         pointer tail;
  81         pointer next;
  82         pointer tmp;
  83
  84         node = new_node();
  85         store_32(&q->nodes[node].value, val);
  86         tmp = atomic_load_explicit(&q->nodes[node].next, relaxed);
  87         set_ptr(&tmp, 0); // NULL
  88         atomic_store_explicit(&q->nodes[node].next, tmp, relaxed);
  89
  90         while (!success) {
  91                 tail = atomic_load_explicit(&q->tail, acquire);
  92                 next = atomic_load_explicit(&q->nodes[get_ptr(tail)].next, acquire);
  93                 if (tail == atomic_load_explicit(&q->tail, relaxed)) {
  94                         if (get_ptr(next) == 0) { // == NULL
  95                                 pointer value = MAKE_POINTER(node, get_count(next) + 1);
  96                                 success = atomic_compare_exchange_strong_explicit(&q->nodes[get_ptr(tail)].next,
  97                                                 &next, value, release, release);
  98                         }
  99                         if (!success) {
 100                                 unsigned int ptr = get_ptr(atomic_load_explicit(&q->nodes[get_ptr(tail)].next, acquire));
 101                                 pointer value = MAKE_POINTER(ptr,
 102                                                 get_count(tail) + 1);
 103                                 atomic_compare_exchange_strong_explicit(&q->tail,
 104                                                 &tail, value,
 105                                                 release, release);
 106                                 thrd_yield();
 107                         }
 108                 }
 109         }
 110         atomic_compare_exchange_strong_explicit(&q->tail,
 111                         &tail,
 112                         MAKE_POINTER(node, get_count(tail) + 1),
 113                         release, release);
 114 }
 115
 116 unsigned int dequeue(queue_t *q)
 117 {
 118         unsigned int value;
 119         int success = 0;
 120         pointer head;
 121         pointer tail;
 122         pointer next;
 123
 124         while (!success) {
 125                 head = atomic_load_explicit(&q->head, acquire);
 126                 tail = atomic_load_explicit(&q->tail, relaxed);
 127                 next = atomic_load_explicit(&q->nodes[get_ptr(head)].next, acquire);
 128                 if (atomic_load_explicit(&q->head, relaxed) == head) {
 129                         if (get_ptr(head) == get_ptr(tail)) {
 130                                 if (get_ptr(next) == 0) { // NULL
 131                                         return 0; // NULL
 132                                 }
 133                                 atomic_compare_exchange_strong_explicit(&q->tail,
 134                                                 &tail,
 135                                                 MAKE_POINTER(get_ptr(next), get_count(tail) + 1),
 136                                                 release, release);
 137                                 thrd_yield();
 138                         } else {
 139                                 value = load_32(&q->nodes[get_ptr(next)].value);
 140                                 success = atomic_compare_exchange_strong_explicit(&q->head,
 141                                                 &head,
 142                                                 MAKE_POINTER(get_ptr(next), get_count(head) + 1),
 143                                                 release, release);
 144                                 if (!success)
 145                                         thrd_yield();
 146                         }
 147                 }
 148         }
 149         reclaim(get_ptr(head));
 150         return value;
 151 }