Fix WFReduceTask compiling error. Add a reducer tutorial.

tutorial/tutorial-20-reducer.cc

@@ -0,0 +1,90 @@
+/*
+  Copyright (c) 2021 Sogou, Inc.
+
+  Licensed under the Apache License, Version 2.0 (the "License");
+  you may not use this file except in compliance with the License.
+  You may obtain a copy of the License at
+
+	  http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License.
+
+  Author: Xie Han (xiehan@sogou-inc.com;63350856@qq.com)
+*/
+
+#include <algorithm>
+#include <stdlib.h>
+#include <stdio.h>
+#include "workflow/WFFacilities.h"
+#include "workflow/WFAlgoTaskFactory.h"
+
+using namespace algorithm;
+
+struct array
+{
+	int *a;
+	int n;
+	size_t size() { return n; }
+};
+
+void reduce(const int *key, ReduceIterator<array> *iter, array *res)
+{
+	const array *v1 = iter->next();
+	const array *v2 = iter->next();
+
+	res->a = new int[v1->n + v2->n];
+	res->n = v1->n + v2->n;
+	std::merge(v1->a, v1->a + v1->n, v2->a, v2->a + v2->n, res->a);
+	delete []v1->a;
+	delete []v2->a;
+}
+
+WFFacilities::WaitGroup wait_group(1);
+
+void callback(WFReduceTask<int, array> *task)
+{
+	ReduceOutput<int, array>& output = *task->get_output();
+	array& res = output[0].second;
+
+	for (int i = 0; i < res.n; i++)
+		printf("%d ", res.a[i]);
+
+	printf("\n");
+	delete []res.a;
+	wait_group.done();
+}
+
+int main(int argc, char *argv[])
+{
+	ReduceInput<int, array> input;
+	array arr;
+	int i;
+
+	if (argc != 2)
+	{
+		fprintf(stderr, "USAGE: %s <num>\n", argv[0]);
+		exit(1);
+	}
+
+	int n = atoi(argv[1]);
+
+	for (i = 0; i < n; i++)
+	{
+		arr.n = 1;
+		arr.a = new int[1];
+		arr.a[0] = random() % 65536;
+		input.emplace_back(0, arr);
+	}
+
+	auto *task = WFAlgoTaskFactory::create_reduce_task("sort", std::move(input),
+													   reduce, callback);
+	task->start();
+
+	wait_group.wait();
+	return 0;
+}
+