add original source

source/listing_8.10.cpp

@@ -0,0 +1,45 @@
+template<typename Iterator,typename MatchType>
+Iterator parallel_find_impl(Iterator first,Iterator last,MatchType match,
+                            std::atomic<bool>& done)
+{
+    try
+    {
+        unsigned long const length=std::distance(first,last);
+        unsigned long const min_per_thread=25;
+        if(length<(2*min_per_thread))
+        {
+            for(;(first!=last) && !done.load();++first)
+            {
+                if(*first==match)
+                {
+                    done=true;
+                    return first;
+                }
+            }
+            return last;
+        }
+        else
+        {
+            Iterator const mid_point=first+(length/2);
+            std::future<Iterator> async_result=
+                std::async(&parallel_find_impl<Iterator,MatchType>,
+                           mid_point,last,match,std::ref(done));
+            Iterator const direct_result=
+                parallel_find_impl(first,mid_point,match,done);
+            return (direct_result==mid_point)?
+                async_result.get():direct_result;
+        }
+    }
+    catch(...)
+    {
+        done=true;
+        throw;
+    }
+}
+
+template<typename Iterator,typename MatchType>
+Iterator parallel_find(Iterator first,Iterator last,MatchType match)
+{
+    std::atomic<bool> done(false);
+    return parallel_find_impl(first,last,match,done);
+}