From: Brian Norris <banorris@uci.edu>
Date: Thu, 11 Oct 2012 23:40:05 +0000 (-0700)
Subject: williams-queue: fixup header
X-Git-Tag: pldi2013~34
X-Git-Url: http://plrg.eecs.uci.edu/git/?p=model-checker-benchmarks.git;a=commitdiff_plain;h=52533e63ca15fb03eebc3fa838d274f1943366dc;hp=adc372d8af13fdc07eba357f0c6de4319dbfce10;ds=sidebyside

williams-queue: fixup header

Move the constructor lower, so that member definitions appear earlier
than it in the class definition.

Also, don't assign to members of the atomic structure directly; use a
temporary struct then assign the whole struct.

Still won't compile. Seeing linker errors, probably due to the fact that
this code uses a nonstandrad atomic template:
    std::atomic<counted_node_ptr>

Where counted_node_ptr is a struct with int and pointer members. Thus,
it has size of at least 96 bytes (32+64) and so probably isn't really
supported by atomics... I'm not sure where the author came up with this.

    $ g++ williams-queue.cc --std=c++0x
    /tmp/ccPQgiJC.o: In function `lock_free_queue<int>::lock_free_queue()': williams-queue.cc:(.text._ZN15lock_free_queueIiEC2Ev[_ZN15lock_free_queueIiEC5Ev]+0x92): undefined reference to `std::atomic<lock_free_queue<int>::counted_node_ptr>::load(std::memory_order) const'
    ...
    collect2: ld returned 1 exit status
---

diff --git a/williams-queue/williams-queue.h b/williams-queue/williams-queue.h
index fdf8337..36633db 100644
--- a/williams-queue/williams-queue.h
+++ b/williams-queue/williams-queue.h
@@ -26,22 +26,7 @@ private:
         head.store(old_head->next);
         return old_head;
     }
-public:
-    lock_free_queue():
-        head(new node),tail(head.load())
-    {}
-    // lock_free_queue(const lock_free_queue& other)=delete;
-    // lock_free_queue& operator=(const lock_free_queue& other)=delete;
-    ~lock_free_queue()
-    {
-        while(node* const old_head=head.load())
-        {
-            head.store(old_head->next);
-            delete old_head;
-        }
-    }
 
-private:
     struct counted_node_ptr
     {
         int external_count;
@@ -66,8 +51,9 @@ private:
             new_count.internal_count=0;
             new_count.external_counters=2;
             count.store(new_count);
-            next.ptr=nullptr;
-            next.external_count=0;
+
+	    counted_node_ptr emptynode = {0, nullptr};
+	    next = emptynode;
         }
         void release_ref()
         {
@@ -164,6 +150,23 @@ private:
             current_tail_ptr->release_ref();
     }
 public:
+    lock_free_queue()
+    {
+        counted_node_ptr newnode = {0, new node};
+        head = newnode;
+	tail = head.load();
+    }
+    // lock_free_queue(const lock_free_queue& other)=delete;
+    // lock_free_queue& operator=(const lock_free_queue& other)=delete;
+    ~lock_free_queue()
+    {
+        while(node* const old_head=head.load())
+        {
+            head.store(old_head->next);
+            delete old_head;
+        }
+    }
+
     void push(T new_value)
     {
         std::unique_ptr<T> new_data(new T(new_value));