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 #define POISON_IDX 0x666
  16
  17 static unsigned int (*free_lists)[MAX_FREELIST];
  18
  19 /* Search this thread's free list for a "new" node */
  20 static unsigned int new_node()
  21 {
  22         int i;
  23         int t = get_thread_num();
  24         for (i = 0; i < MAX_FREELIST; i++) {
  25                 unsigned int node = load_32(&free_lists[t][i]);
  26                 if (node) {
  27                         store_32(&free_lists[t][i], 0);
  28                         return node;
  29                 }
  30         }
  31         /* free_list is empty? */
  32         MODEL_ASSERT(0);
  33         return 0;
  34 }
  35
  36 /* Place this node index back on this thread's free list */
  37 static void reclaim(unsigned int node)
  38 {
  39         int i;
  40         int t = get_thread_num();
  41
  42         /* Don't reclaim NULL node */
  43         MODEL_ASSERT(node);
  44
  45         for (i = 0; i < MAX_FREELIST; i++) {
  46                 /* Should never race with our own thread here */
  47                 unsigned int idx = load_32(&free_lists[t][i]);
  48
  49                 /* Found empty spot in free list */
  50                 if (idx == 0) {
  51                         store_32(&free_lists[t][i], node);
  52                         return;
  53                 }
  54         }
  55         /* free list is full? */
  56         MODEL_ASSERT(0);
  57 }
  58
  59 void init_queue(queue_t *q, int num_threads)
  60 {
  61         int i, j;
  62
  63         /* Initialize each thread's free list with INITIAL_FREE pointers */
  64         /* The actual nodes are initialized with poison indexes */
  65         free_lists = malloc(num_threads * sizeof(*free_lists));
  66         for (i = 0; i < num_threads; i++) {
  67                 for (j = 0; j < INITIAL_FREE; j++) {
  68                         free_lists[i][j] = 2 + i * MAX_FREELIST + j;
  69                         atomic_init(&q->nodes[free_lists[i][j]].next, MAKE_POINTER(POISON_IDX, 0));
  70                 }
  71         }
  72
  73         /* initialize queue */
  74         atomic_init(&q->head, MAKE_POINTER(1, 0));
  75         atomic_init(&q->tail, MAKE_POINTER(1, 0));
  76         atomic_init(&q->nodes[1].next, MAKE_POINTER(0, 0));
  77 }
  78
  79 void enqueue(queue_t *q, unsigned int val)
  80 {
  81         int success = 0;
  82         unsigned int node;
  83         pointer tail;
  84         pointer next;
  85         pointer tmp;
  86
  87         node = new_node();
  88         store_32(&q->nodes[node].value, val);
  89         tmp = atomic_load_explicit(&q->nodes[node].next, relaxed);
  90         set_ptr(&tmp, 0); // NULL
  91         atomic_store_explicit(&q->nodes[node].next, tmp, relaxed);
  92
  93         while (!success) {
  94                 tail = atomic_load_explicit(&q->tail, acquire);
  95                 next = atomic_load_explicit(&q->nodes[get_ptr(tail)].next, acquire);
  96                 if (tail == atomic_load_explicit(&q->tail, relaxed)) {
  97
  98                         /* Check for uninitialized 'next' */
  99                         MODEL_ASSERT(get_ptr(next) != POISON_IDX);
 100
 101                         if (get_ptr(next) == 0) { // == NULL
 102                                 pointer value = MAKE_POINTER(node, get_count(next) + 1);
 103                                 success = atomic_compare_exchange_strong_explicit(&q->nodes[get_ptr(tail)].next,
 104                                                 &next, value, release, release);
 105                         }
 106                         if (!success) {
 107                                 unsigned int ptr = get_ptr(atomic_load_explicit(&q->nodes[get_ptr(tail)].next, acquire));
 108                                 pointer value = MAKE_POINTER(ptr,
 109                                                 get_count(tail) + 1);
 110                                 atomic_compare_exchange_strong_explicit(&q->tail,
 111                                                 &tail, value,
 112                                                 release, release);
 113                                 thrd_yield();
 114                         }
 115                 }
 116         }
 117         atomic_compare_exchange_strong_explicit(&q->tail,
 118                         &tail,
 119                         MAKE_POINTER(node, get_count(tail) + 1),
 120                         release, release);
 121 }
 122
 123 unsigned int dequeue(queue_t *q)
 124 {
 125         unsigned int value;
 126         int success = 0;
 127         pointer head;
 128         pointer tail;
 129         pointer next;
 130
 131         while (!success) {
 132                 head = atomic_load_explicit(&q->head, acquire);
 133                 tail = atomic_load_explicit(&q->tail, relaxed);
 134                 next = atomic_load_explicit(&q->nodes[get_ptr(head)].next, acquire);
 135                 if (atomic_load_explicit(&q->head, relaxed) == head) {
 136                         if (get_ptr(head) == get_ptr(tail)) {
 137
 138                                 /* Check for uninitialized 'next' */
 139                                 MODEL_ASSERT(get_ptr(next) != POISON_IDX);
 140
 141                                 if (get_ptr(next) == 0) { // NULL
 142                                         return 0; // NULL
 143                                 }
 144                                 atomic_compare_exchange_strong_explicit(&q->tail,
 145                                                 &tail,
 146                                                 MAKE_POINTER(get_ptr(next), get_count(tail) + 1),
 147                                                 release, release);
 148                                 thrd_yield();
 149                         } else {
 150                                 value = load_32(&q->nodes[get_ptr(next)].value);
 151                                 success = atomic_compare_exchange_strong_explicit(&q->head,
 152                                                 &head,
 153                                                 MAKE_POINTER(get_ptr(next), get_count(head) + 1),
 154                                                 release, release);
 155                                 if (!success)
 156                                         thrd_yield();
 157                         }
 158                 }
 159         }
 160         reclaim(get_ptr(head));
 161         return value;
 162 }