add original source

source/listing_8.8.cpp

@@ -0,0 +1,24 @@
+template<typename Iterator,typename Func>
+void parallel_for_each(Iterator first,Iterator last,Func f)
+{
+    unsigned long const length=std::distance(first,last);
+
+    if(!length)
+        return;
+
+    unsigned long const min_per_thread=25;
+
+    if(length<(2*min_per_thread))
+    {
+        std::for_each(first,last,f);
+    }
+    else
+    {
+        Iterator const mid_point=first+length/2;
+        std::future<void> first_half=
+            std::async(&parallel_for_each<Iterator,Func>,
+                       first,mid_point,f);
+        parallel_for_each(mid_point,last,f);
+        first_half.get();
+    }
+}