From a183b6355e22b4d701da4ae5e3243c3ebdeeb1e8 Mon Sep 17 00:00:00 2001
From: Pixel <pixel@nobis-crew.org>
Date: Thu, 12 Nov 2009 00:35:43 -0800
Subject: Adding atomic queues.

---
 include/Atomic.h | 69 +++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 68 insertions(+), 1 deletion(-)

diff --git a/include/Atomic.h b/include/Atomic.h
index 35edbf1..3b325f2 100644
--- a/include/Atomic.h
+++ b/include/Atomic.h
@@ -21,7 +21,8 @@ template <class T> T Increment(volatile T * ptr, T delta = 1) { __sync_fetch_and
 template <class T> T Decrement(volatile T * ptr, T delta = 1) { __sync_fetch_and_sub(ptr, delta); }
 };
 
-template <class T> T CmpXChg(volatile T * ptr, T xch, T cmp) { return __sync_val_compare_and_swap(ptr, cmp, xch); }
+template <class T> T CmpXChgVal(volatile T * ptr, T xch, T cmp) { return __sync_val_compare_and_swap(ptr, cmp, xch); }
+template <class T> bool CmpXChgBool(volatile T * ptr, T xch, T cmp) { return __sync_bool_compare_and_swap(ptr, cmp, xch); }
 
 template <class T> T Exchange32(volatile T * ptr, T exchange) {
 #if defined(i386) || defined (__x86_64)
@@ -64,6 +65,72 @@ template <class T> T * ExchangePtr(T * volatile * ptr, T * exchange) {
 #endif
 }
 
+// Based on "Simple, Fast, and Practical Non-Blocking and Blocking Concurrent Queue Algorithms"
+template <class T>
+class Queue {
+  public:
+      Queue() : Head(new node_t()), Tail(Head) { }
+    void enqueue(const T & val) {
+        node_t * node = new node_t(val);
+        ptr_t tail, next;
+        while(true) {
+            tail = Tail;
+            next = tail.ptr->next;
+            if (tail == Tail) {
+                if (next.ptr == NULL) {
+                    ptr_t new_ptr(node, next.count + 1);
+                    if (CmpXChgBool(&tail.ptr->next, new_ptr, next))
+                        break;
+                } else {
+                    ptr_t new_ptr(next.ptr, tail.count + 1);
+                    CmpXChgBool(&Tail, new_ptr, tail);
+                }
+            }
+        }
+        ptr_t new_ptr(node, tail.count + 1);
+        CmpXChgBool(&Tail, new_ptr, tail);
+    }
+    bool dequeue(T * pval) {
+        ptr_t head, tail, next;
+        while(true) {
+            head = Head;
+            tail = Tail;
+            next = head->next;
+            if (head == Head) {
+                if (head.ptr == tail.ptr) {
+                    if (next.ptr == NULL)
+                        return false;
+                    ptr_t new_ptr(next.ptr, tail.count + 1);
+                    CmpXChgBool(&Tail, new_ptr, tail);
+                } else {
+                    *pval = next.ptr->value;
+                    ptr_t new_ptr(next.ptr, head.count + 1);
+                    if (CmpXChgBool(&Head, new_ptr, head))
+                        break;
+                }
+            }
+        }
+        delete head.ptr;
+        return true;
+    }
+  private:
+    struct node_t;
+    struct ptr_t {
+        ptr_t() : ptr(NULL), count(0) { }
+        ptr_t(node_t * ptr, unsigned int count = 0) : ptr(ptr), count(count) { }
+        ptr_t(const ptr_t & c) : ptr(c.ptr), count(c.count) { }
+        node_t * ptr;
+        unsigned int count;
+    };
+    struct node_t {
+        node_t() { }
+        node_t(const T & val) : val(val) { }
+        T val;
+        ptr_t next;
+    };
+    ptr_t Head, Tail;
+};
+
 };
 
 #endif
-- 
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