【Boost】boost库asio详解1——strand与io_service区别

来源：互联网发布：护照相片制作软件编辑：程序博客网时间：2024/06/06 10:54

namespace{// strand提供串行执行, 能够保证线程安全, 同时被post或dispatch的方法, 不会被并发的执行. // io_service不能保证线程安全boost::asio::io_service m_service;boost::asio::strand m_strand(m_service);boost::mutex m_mutex;void print(int id){// boost::mutex::scoped_lock lock(m_mutex);static int count = 0;PRINT_DEBUG("id: " << boost::lexical_cast<std::string>(id));PRINT_DEBUG("count: " << boost::lexical_cast<std::string>(++count));}void ioRun1(){while(true){m_service.run();}}void ioRun2(){while(true){m_service.run();}}void strand_print1(){// PRINT_DEBUG("Enter print1");m_strand.dispatch(boost::bind(print, 1));// PRINT_DEBUG("Exit print1");}void strand_print2(){// PRINT_DEBUG("Enter print2");m_strand.post(boost::bind(print, 2));// PRINT_DEBUG("Exit print2");}void strand_print3(){// PRINT_DEBUG("Enter print3");              m_strand.post(boost::bind(print, 3));// PRINT_DEBUG("Exit print3");}void strand_print4(){// PRINT_DEBUG("Enter print4");m_strand.post(boost::bind(print, 4));// PRINT_DEBUG("Exit print4");}// 将上面的m_strand换成m_service后，void service_print1(){// PRINT_DEBUG("Enter print1");m_service.dispatch(boost::bind(print, 1));// PRINT_DEBUG("Exit print1");}void service_print2(){// PRINT_DEBUG("Enter print2");m_service.post(boost::bind(print, 2));// PRINT_DEBUG("Exit print2");}void service_print3(){// PRINT_DEBUG("Enter print3");              m_service.post(boost::bind(print, 3));// PRINT_DEBUG("Exit print3");}void service_print4(){// PRINT_DEBUG("Enter print4");m_service.post(boost::bind(print, 4));// PRINT_DEBUG("Exit print4");}}void test_strand(){boost::thread ios1(ioRun1);boost::thread ios2(ioRun2);boost::thread t1(strand_print1);boost::thread t2(strand_print2);boost::thread t3(strand_print3);boost::thread t4(strand_print4);t1.join();t2.join();t3.join();t4.join();m_server.run();}void test_service(){boost::thread ios1(ioRun1);boost::thread ios2(ioRun2);boost::thread t1(service_print1);boost::thread t2(service_print2);boost::thread t3(service_print3);boost::thread t4(service_print4);t1.join();t2.join();t3.join();t4.join();m_service.run();}

test_strand的执行结果:

2013-01-05 17:25:34 626 [8228] DEBUG - id: 42013-01-05 17:25:34 631 [8228] DEBUG - count: 12013-01-05 17:25:34 634 [5692] DEBUG - id: 12013-01-05 17:25:34 637 [5692] DEBUG - count: 22013-01-05 17:25:34 640 [5692] DEBUG - id: 22013-01-05 17:25:34 642 [5692] DEBUG - count: 32013-01-05 17:25:34 646 [5692] DEBUG - id: 32013-01-05 17:25:34 649 [5692] DEBUG - count: 4

test_ioserivice的执行结果:

2013-01-05 17:26:28 071 [3236] DEBUG - id: 12013-01-05 17:26:28 071 [5768] DEBUG - id: 22013-01-05 17:26:28 071 [5108] DEBUG - id: 32013-01-05 17:26:28 076 [3236] DEBUG - count: 12013-01-05 17:26:28 079 [5768] DEBUG - count: 22013-01-05 17:26:28 083 [5108] DEBUG - count: 32013-01-05 17:26:28 087 [3236] DEBUG - id: 42013-01-05 17:26:28 099 [3236] DEBUG - count: 4

从结果可以看到, 在test_strand中print中两个打印函数成对执行, 在test_ioservice两个打印函数就没有线程安全可言了.
如果要保证test_ioservice同步, 就要加上mutex, 在代码中被注释的那句.

注意从日志的线程号中可知: 真正执行print()是主线程, ios1, ios2, 而t1, t2, t3, t4线程只是往ioservice的队列中加入任务.