boost::asio学习 - multithreaded programs
今天在测试boost::asio Tutorial中的 Timer.5 - Synchronising handlers in multithreaded programs 程序时，发现数据处理始终是在主线程中执行的，为了验证“If you find yourself running into these limitations, an alternative approach is to have a pool of threads calling io_service::run()”遂对timer.cpp进行了一些修改：
1.取消使用boost::asio::strand::wrap()来封装回调函数；
2.在printer::print1()中强制线程sleep(1)来检测多线程的并发处理；
完整代码如下：
timer.cpp
1 #include <iostream>
2 #include <boost/asio.hpp>
3 #include <boost/thread.hpp>
4 #include <boost/bind.hpp>
5 #include <boost/date_time/posix_time/posix_time.hpp>
6
7 class printer
8 {
9 public:
10 printer(boost::asio::io_service& io)
11 : strand_(io),
12 timer1_(io, boost::posix_time::seconds(1)),
13 timer2_(io, boost::posix_time::seconds(1)),
14 count_(0)
15 {
16 timer1_.async_wait(boost::bind(&printer::print1, this));
17 timer2_.async_wait(boost::bind(&printer::print2, this));
18 }
19
20 ~printer()
21 {
22 std::cout << "Final count is " << count_ << "\n";
23 }
24
25 void print1()
26 {
27 std::cout << boost::this_thread::get_id() << "\n";
28
29 if (count_ < 10)
30 {
31 std::cout << "Timer 1: " << count_ << "\n";
32 ++count_;
33
34 timer1_.expires_at(timer1_.expires_at() + boost::posix_time::seconds(1));
35 timer1_.async_wait(boost::bind(&printer::print1, this));
36 }
37 sleep(1);
38 }
39
40 void print2()
41 {
42 std::cout << boost::this_thread::get_id() << "\n";
43
44 if (count_ < 10)
45 {
46 std::cout << "Timer 2: " << count_ << "\n";
47 ++count_;
48
49 timer2_.expires_at(timer2_.expires_at() + boost::posix_time::seconds(1));
50 timer2_.async_wait(boost::bind(&printer::print2, this));
51 }
52 }
53
54 private:
55 boost::asio::strand strand_;
56 boost::asio::deadline_timer timer1_;
57 boost::asio::deadline_timer timer2_;
58 int count_;
59 };
60
61 int main()
62 {
63 std::cout << boost::this_thread::get_id() << "\n";
64
65 boost::asio::io_service io;
66 printer p(io);
67 boost::thread t(boost::bind(&boost::asio::io_service::run, &io));
68 io.run();
69 t.join();
70
71 return 0;
72 }
程序运行输出：
0x850e050
0x850e050
Timer 1: 0
0x850e810
Timer 2: 1
0x850e810
Timer 1: 2
0x850e050
Timer 2: 3
0x850e050
Timer 1: 4
0x850e810
Timer 2: 5
0x850e810
Timer 1: 6
0x850e050
Timer 2: 7
0x850e050
Timer 1: 8
0x850e810
Timer 2: 9
0x850e810
0x850e050
从输出结果可以看出：当多个线程运行同一个io_service::run()时，它们将并发执行该io_service上的待处理的handlers！
