add original source

source/listing_8.12.cpp

@@ -0,0 +1,24 @@
+class barrier
+{
+    unsigned const count;
+    std::atomic<unsigned> spaces;
+    std::atomic<unsigned> generation;
+public:
+    explicit barrier(unsigned count_):
+        count(count_),spaces(count),generation(0)
+    {}
+    void wait()
+    {
+        unsigned const my_generation=generation;
+        if(!--spaces)
+        {
+            spaces=count;
+            ++generation;
+        }
+        else
+        {
+            while(generation==my_generation)
+                std::this_thread::yield();
+        }
+    }
+};