boost库asio详解1——strand与io_service区别

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:

[cpp] view plaincopyprint?

2013-01-05 17:25:34 626 [8228] DEBUG - id: 4

2013-01-05 17:25:34 631 [8228] DEBUG - count: 1

2013-01-05 17:25:34 634 [5692] DEBUG - id: 1

2013-01-05 17:25:34 637 [5692] DEBUG - count: 2

2013-01-05 17:25:34 640 [5692] DEBUG - id: 2

2013-01-05 17:25:34 642 [5692] DEBUG - count: 3

2013-01-05 17:25:34 646 [5692] DEBUG - id: 3

2013-01-05 17:25:34 649 [5692] DEBUG - count: 4

test_ioserivice的执行结果:

[cpp] view plaincopyprint?

2013-01-05 17:26:28 071 [3236] DEBUG - id: 1

2013-01-05 17:26:28 071 [5768] DEBUG - id: 2

2013-01-05 17:26:28 071 [5108] DEBUG - id: 3

2013-01-05 17:26:28 076 [3236] DEBUG - count: 1

2013-01-05 17:26:28 079 [5768] DEBUG - count: 2

2013-01-05 17:26:28 083 [5108] DEBUG - count: 3

2013-01-05 17:26:28 087 [3236] DEBUG - id: 4

2013-01-05 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.