add original source

source/listing_9.3.cpp

@@ -0,0 +1,31 @@
+template<typename Iterator,typename T>
+T parallel_accumulate(Iterator first,Iterator last,T init)
+{
+    unsigned long const length=std::distance(first,last);
+
+    if(!length)
+        return init;
+
+    unsigned long const block_size=25;
+    unsigned long const num_blocks=(length+block_size-1)/block_size;
+
+    std::vector<std::future<T> > futures(num_blocks-1);
+    thread_pool pool;
+
+    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);
+        futures[i]=pool.submit(accumulate_block<Iterator,T>());
+        block_start=block_end;
+    }
+    T last_result=accumulate_block()(block_start,last);
+    T result=init;
+    for(unsigned long i=0;i<(num_blocks-1);++i)
+    {
+        result+=futures[i].get();
+    }
+    result += last_result;
+    return result;
+}