X-Git-Url: http://plrg.eecs.uci.edu/git/?p=model-checker-benchmarks.git;a=blobdiff_plain;f=ms-queue%2Fmy_queue.c;h=6c0ccd4bea4c0f49b2a1fdd4f9b24d992dc0f749;hp=dfdf819574e49bf4914f0b5b819390bf3236c1eb;hb=f19c4f0d0d8c054fdea82137c57dc0dca3059704;hpb=647601d3f341bb2a2a79534b3d044c039695839d

diff --git a/ms-queue/my_queue.c b/ms-queue/my_queue.c
index dfdf819..6c0ccd4 100644
--- a/ms-queue/my_queue.c
+++ b/ms-queue/my_queue.c
@@ -1,6 +1,7 @@
 #include <threads.h>
 #include <stdlib.h>
 #include "librace.h"
+#include "model-assert.h"
 
 #include "my_queue.h"
 
@@ -8,49 +9,71 @@
 #define release memory_order_release
 #define acquire memory_order_acquire
 
-static unsigned int *node_nums;
+#define MAX_FREELIST 4 /* Each thread can own up to MAX_FREELIST free nodes */
+#define INITIAL_FREE 2 /* Each thread starts with INITIAL_FREE free nodes */
 
+#define POISON_IDX 0x666
+
+static unsigned int (*free_lists)[MAX_FREELIST];
+
+/* Search this thread's free list for a "new" node */
 static unsigned int new_node()
 {
-	return node_nums[get_thread_num()];
+	int i;
+	int t = get_thread_num();
+	for (i = 0; i < MAX_FREELIST; i++) {
+		unsigned int node = load_32(&free_lists[t][i]);
+		if (node) {
+			store_32(&free_lists[t][i], 0);
+			return node;
+		}
+	}
+	/* free_list is empty? */
+	MODEL_ASSERT(0);
+	return 0;
 }
 
+/* Place this node index back on this thread's free list */
 static void reclaim(unsigned int node)
 {
-	node_nums[get_thread_num()] = node;
-}
+	int i;
+	int t = get_thread_num();
 
-void init_queue(queue_t *q, int num_threads)
-{
-	unsigned int i;
-	pointer head;
-	pointer tail;
-	pointer next;
+	/* Don't reclaim NULL node */
+	MODEL_ASSERT(node);
 
-	node_nums = malloc(num_threads * sizeof(*node_nums));
-	for (i = 0; i < num_threads; i++)
-		node_nums[i] = 2 + i;
+	for (i = 0; i < MAX_FREELIST; i++) {
+		/* Should never race with our own thread here */
+		unsigned int idx = load_32(&free_lists[t][i]);
 
-	/* Note: needed to add this init manually */
-	atomic_init(&q->nodes[0].next, 0);
+		/* Found empty spot in free list */
+		if (idx == 0) {
+			store_32(&free_lists[t][i], node);
+			return;
+		}
+	}
+	/* free list is full? */
+	MODEL_ASSERT(0);
+}
 
-	/* initialize queue */
-	head = MAKE_POINTER(1, 0);
-	tail = MAKE_POINTER(1, 0);
-	next = MAKE_POINTER(0, 0); // (NULL, 0)
-
-	atomic_init(&q->head, head);
-	atomic_init(&q->tail, tail);
-	atomic_init(&q->nodes[1].next, next);
-
-	/* initialize avail list */
-	for (i = 2; i < MAX_NODES; i++) {
-		next = MAKE_POINTER(i + 1, 0);
-		atomic_init(&q->nodes[i].next, next);
+void init_queue(queue_t *q, int num_threads)
+{
+	int i, j;
+
+	/* Initialize each thread's free list with INITIAL_FREE pointers */
+	/* The actual nodes are initialized with poison indexes */
+	free_lists = malloc(num_threads * sizeof(*free_lists));
+	for (i = 0; i < num_threads; i++) {
+		for (j = 0; j < INITIAL_FREE; j++) {
+			free_lists[i][j] = 2 + i * MAX_FREELIST + j;
+			atomic_init(&q->nodes[free_lists[i][j]].next, MAKE_POINTER(POISON_IDX, 0));
+		}
 	}
 
-	next = MAKE_POINTER(0, 0); // (NULL, 0)
-	atomic_init(&q->nodes[MAX_NODES].next, next);
+	/* initialize queue */
+	atomic_init(&q->head, MAKE_POINTER(1, 0));
+	atomic_init(&q->tail, MAKE_POINTER(1, 0));
+	atomic_init(&q->nodes[1].next, MAKE_POINTER(0, 0));
 }
 
 void enqueue(queue_t *q, unsigned int val)
@@ -61,7 +84,6 @@ void enqueue(queue_t *q, unsigned int val)
 	pointer next;
 	pointer tmp;
 
-	/* Get a fresh node, set its value field, then set it's next reference to null */
 	node = new_node();
 	store_32(&q->nodes[node].value, val);
 	tmp = atomic_load_explicit(&q->nodes[node].next, relaxed);
@@ -69,62 +91,71 @@ void enqueue(queue_t *q, unsigned int val)
 	atomic_store_explicit(&q->nodes[node].next, tmp, relaxed);
 
 	while (!success) {
-		//tail isn't actually synchronization point
-		tail = atomic_load_explicit(&q->tail, relaxed);
-		//acquire reference...
-		next = atomic_load_explicit(&q->nodes[get_ptr(tail)].next, memory_order_seq_cst);
-		if (tail == atomic_load_explicit(&q->tail, memory_order_seq_cst)) {
+		tail = atomic_load_explicit(&q->tail, acquire);
+		next = atomic_load_explicit(&q->nodes[get_ptr(tail)].next, acquire);
+		if (tail == atomic_load_explicit(&q->tail, relaxed)) {
+
+			/* Check for uninitialized 'next' */
+			MODEL_ASSERT(get_ptr(next) != POISON_IDX);
+
 			if (get_ptr(next) == 0) { // == NULL
 				pointer value = MAKE_POINTER(node, get_count(next) + 1);
 				success = atomic_compare_exchange_strong_explicit(&q->nodes[get_ptr(tail)].next,
-						&next, value, memory_order_seq_cst, memory_order_seq_cst);
+						&next, value, release, release);
 			}
 			if (!success) {
-				unsigned int ptr = get_ptr(atomic_load_explicit(&q->nodes[get_ptr(tail)].next, memory_order_relaxed));
+				unsigned int ptr = get_ptr(atomic_load_explicit(&q->nodes[get_ptr(tail)].next, acquire));
 				pointer value = MAKE_POINTER(ptr,
 						get_count(tail) + 1);
 				atomic_compare_exchange_strong_explicit(&q->tail,
 						&tail, value,
-						memory_order_seq_cst, memory_order_seq_cst);
+						release, release);
+				thrd_yield();
 			}
 		}
 	}
 	atomic_compare_exchange_strong_explicit(&q->tail,
 			&tail,
 			MAKE_POINTER(node, get_count(tail) + 1),
-			memory_order_seq_cst, memory_order_seq_cst);
+			release, release);
 }
 
-unsigned int dequeue(queue_t *q)
+bool dequeue(queue_t *q, unsigned int *retVal)
 {
-	unsigned int value;
 	int success = 0;
 	pointer head;
 	pointer tail;
 	pointer next;
 
 	while (!success) {
-		head = atomic_load_explicit(&q->head, memory_order_seq_cst);
-		tail = atomic_load_explicit(&q->tail, memory_order_seq_cst);
-		next = atomic_load_explicit(&q->nodes[get_ptr(head)].next, memory_order_seq_cst);
-		if (atomic_load_explicit(&q->head, memory_order_seq_cst) == head) {
+		head = atomic_load_explicit(&q->head, acquire);
+		tail = atomic_load_explicit(&q->tail, relaxed);
+		next = atomic_load_explicit(&q->nodes[get_ptr(head)].next, acquire);
+		if (atomic_load_explicit(&q->head, relaxed) == head) {
 			if (get_ptr(head) == get_ptr(tail)) {
+
+				/* Check for uninitialized 'next' */
+				MODEL_ASSERT(get_ptr(next) != POISON_IDX);
+
 				if (get_ptr(next) == 0) { // NULL
-					return 0; // NULL
+					return false; // NULL
 				}
 				atomic_compare_exchange_strong_explicit(&q->tail,
 						&tail,
 						MAKE_POINTER(get_ptr(next), get_count(tail) + 1),
-						memory_order_seq_cst, memory_order_seq_cst);
+						release, release);
+				thrd_yield();
 			} else {
-				value = load_32(&q->nodes[get_ptr(next)].value);
+				*retVal = load_32(&q->nodes[get_ptr(next)].value);
 				success = atomic_compare_exchange_strong_explicit(&q->head,
 						&head,
 						MAKE_POINTER(get_ptr(next), get_count(head) + 1),
-						memory_order_seq_cst, memory_order_seq_cst);
+						release, release);
+				if (!success)
+					thrd_yield();
 			}
 		}
 	}
 	reclaim(get_ptr(head));
-	return value;
+	return true;
 }