add original source

source/listing_8.9.cpp

@@ -0,0 +1,76 @@
+template<typename Iterator,typename MatchType>
+Iterator parallel_find(Iterator first,Iterator last,MatchType match)
+{
+    struct find_element
+    {
+        void operator()(Iterator begin,Iterator end,
+                        MatchType match,
+                        std::promise<Iterator>* result,
+                        std::atomic<bool>* done_flag)
+        {
+            try
+            {
+                for(;(begin!=end) && !done_flag->load();++begin)
+                {
+                    if(*begin==match)
+                    {
+                        result->set_value(begin);
+                        done_flag->store(true);
+                        return;
+                    }
+                }
+            }
+            catch(...)
+            {
+                try
+                {
+                    result->set_exception(std::current_exception());
+                    done_flag->store(true);
+                }
+                catch(...)
+                {}
+            }
+        }
+    };
+
+    unsigned long const length=std::distance(first,last);
+
+    if(!length)
+        return last;
+
+    unsigned long const min_per_thread=25;
+    unsigned long const max_threads=
+        (length+min_per_thread-1)/min_per_thread;
+
+    unsigned long const hardware_threads=
+        std::thread::hardware_concurrency();
+
+    unsigned long const num_threads=
+        std::min(hardware_threads!=0?hardware_threads:2,max_threads);
+
+    unsigned long const block_size=length/num_threads;
+
+    std::promise<Iterator> result;
+    std::atomic<bool> done_flag(false);
+    std::vector<std::thread> threads(num_threads-1);
+    {
+        join_threads joiner(threads);
+
+        Iterator block_start=first;
+        for(unsigned long i=0;i<(num_threads-1);++i)
+        {
+            Iterator block_end=block_start;
+            std::advance(block_end,block_size);
+            threads[i]=std::thread(find_element(),
+                                   block_start,block_end,match,
+                                   &result,&done_flag);
+            block_start=block_end;
+        }
+        find_element()(block_start,last,match,&result,&done_flag);
+    }
+    if(!done_flag.load())
+    {
+        return last;
+    }
+    return result.get_future().get();
+}