1 /*
2     Copyright (c) 2023 Intel Corporation
3 
4     Licensed under the Apache License, Version 2.0 (the "License");
5     you may not use this file except in compliance with the License.
6     You may obtain a copy of the License at
7 
8         http://www.apache.org/licenses/LICENSE-2.0
9 
10     Unless required by applicable law or agreed to in writing, software
11     distributed under the License is distributed on an "AS IS" BASIS,
12     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13     See the License for the specific language governing permissions and
14     limitations under the License.
15 */
16 
17 #include "task_emulation_layer.h"
18 
19 #include <iostream>
20 #include <numeric>
21 #include <utility>
22 
23 int cutoff;
24 
25 long serial_fib(int n) {
26     return n < 2 ? n : serial_fib(n - 1) + serial_fib(n - 2);
27 }
28 
29 struct fib_continuation : task_emulation::base_task {
30     fib_continuation(int& s) : sum(s) {}
31 
32     void execute() override {
33         sum = x + y;
34     }
35 
36     int x{ 0 }, y{ 0 };
37     int& sum;
38 };
39 
40 struct fib_computation : task_emulation::base_task {
41     fib_computation(int n, int* x) : n(n), x(x) {}
42 
43     void execute() override {
44         if (n < cutoff) {
45             *x = serial_fib(n);
46         }
47         else {
48             // Continuation passing
49             auto& c = *this->create_continuation<fib_continuation>(/* children_counter = */ 2, *x);
50             task_emulation::run_task(c.create_child_of_continuation<fib_computation>(n - 1, &c.x));
51 
52             // Recycling
53             this->recycle_as_child_of_continuation(c);
54             n = n - 2;
55             x = &c.y;
56 
57             // Bypass is not supported by task_emulation and next_task executed directly.
58             // Howewer, the old-TBB bypass behavior can be achieved with
59             // `return task_group::defer()` (check Migration Guide).
60             // Consider submit another task if recursion call is not acceptable
61             // i.e. instead of Recycling + Direct Body call
62             // submit task_emulation::run_task(c.create_child_of_continuation<fib_computation>(n - 2, &c.y));
63             this->operator()();
64         }
65     }
66 
67     int n;
68     int* x;
69 };
70 
71 int fibonacci(int n) {
72     int sum{};
73     tbb::task_group tg;
74     tg.run_and_wait(
75         task_emulation::create_root_task<fib_computation>(/* for root task = */ tg, n, &sum));
76     return sum;
77 }
78 
79 template <typename F>
80 std::pair</* result */ unsigned long, /* time */ unsigned long> measure(F&& f,
81                                                                         int number,
82                                                                         unsigned long ntrial) {
83     std::vector<unsigned long> times;
84 
85     unsigned long result;
86     for (unsigned long i = 0; i < ntrial; ++i) {
87         auto t1 = std::chrono::steady_clock::now();
88         result = f(number);
89         auto t2 = std::chrono::steady_clock::now();
90 
91         auto time = std::chrono::duration_cast<std::chrono::milliseconds>(t2 - t1).count();
92         times.push_back(time);
93     }
94 
95     return std::make_pair(
96         result,
97         static_cast<unsigned long>(std::accumulate(times.begin(), times.end(), 0) / times.size()));
98 }
99 
100 int main(int argc, char* argv[]) {
101     int numbers = argc > 1 ? strtol(argv[1], nullptr, 0) : 50;
102     cutoff = argc > 2 ? strtol(argv[2], nullptr, 0) : 16;
103     unsigned long ntrial = argc > 3 ? (unsigned long)strtoul(argv[3], nullptr, 0) : 20;
104 
105     auto res = measure(fibonacci, numbers, ntrial);
106     std::cout << "Fibonacci N = " << res.first << " Avg time = " << res.second << " ms"
107               << std::endl;
108 }
109