1 files changed, 88 insertions, 0 deletions
diff --git a/lock_free_queue.c b/lock_free_queue.c
new file mode 100644
index 0000000..217fb0b
--- /dev/null
+++ b/lock_free_queue.c
@@ -0,0 +1,88 @@
+/*
+ * File     : lock_free_queue.c
+ * Author   : Jérémy Zurcher  <jeremy@asynk.ch>
+ * Date     : 01/11/09 
+ * License  : stolen from http://www.cs.rochester.edu/~scott/papers/1996_PODC_queues.pdf
+ */
+
+#include "stdlib.h"
+#include "cas.h"
+#include "lock_free_queue.h"
+#ifdef DEBUG
+#include "stdio.h"
+#endif
+
+void init( lfq_t *q ) {
+    node_t *node = (node_t*)malloc(sizeof(node_t));
+    node->next.split.ptr = NULL;
+    node->next.split.count = 0;
+    q->head.split.ptr = q->tail.split.ptr = node;
+    q->head.split.count = q->tail.split.count = 0;
+}
+
+void enqueue( lfq_t *q, void *data ) {
+    node_t *node;
+    pointer_t tail;
+    pointer_t next;
+    pointer_t tmp;
+
+    node = (node_t*)malloc(sizeof(node_t));
+    node->data = data;
+    node->next.split.ptr = NULL;
+    /* node->next.split.count = 0; */
+    for(;;) {
+        tail.concat = q->tail.concat;                   /* copy tail pointer */
+        next.concat = tail.split.ptr->next.concat;      /* copy next pointer */
+        if (tail.concat == q->tail.concat) {            /* tail is still consistent */
+            if (next.split.ptr == NULL) {               /* next is still the last node */
+                /* if tail->next is the same as next, link node at the end of the list */
+                tmp.split.ptr = node;
+                tmp.split.count = next.split.count+1;
+                if ( compare_and_swap( &tail.split.ptr->next.concat, next.concat, tmp.concat ) ) break;
+            } else {
+                /* try to swing tail to the next node, if q-> tail is still tail => next is ok */
+                tmp.split.ptr = next.split.ptr;
+                tmp.split.count = tail.split.count+1;
+                compare_and_swap( &q->tail.concat, tail.concat, tmp.concat );
+            }
+        }
+    }
+    /* try to swing tail to the next node, may have been done by a concurrent push */
+    tmp.split.ptr = node;
+    tmp.split.count = tail.split.count+1;
+    compare_and_swap( &q->tail.concat, tail.concat, tmp.concat );
+}
+
+void* dequeue( lfq_t *q ) {
+    void *data;
+    pointer_t head;
+    pointer_t tail;
+    node_t *next;
+    pointer_t tmp;
+    
+    for(;;) {
+        head.concat = q->head.concat;
+        tail.concat = q->tail.concat;
+        next = (node_t *)head.split.ptr;
+        if (head.concat == q->head.concat) {
+            if (head.split.ptr == tail.split.ptr) {     /* still consistent */
+                if (next->next.split.ptr == NULL) {     /* queue empty */
+                    return NULL;
+                }
+                /* new node has been linked, but tail is behind, should advance it */
+                tmp.split.ptr = next->next.split.ptr;
+                tmp.split.count = tail.split.count+1;
+                compare_and_swap( &q->tail.concat, tail.concat, tmp.concat );
+            } else {
+                data = next->data;
+                /* try to swing head to the next node */
+                tmp.split.ptr = next->next.split.ptr;
+                tmp.split.count = head.split.count+1;
+                if( compare_and_swap( &q->head.concat, head.concat, tmp.concat ) ) break;
+            }
+        }
+    }
+    free((void*)head.split.ptr);
+    return data;
+}
+