跨线程复制 boost::exception 崩溃

Question

下面的示例代码将 boost::exception 对象从 1 个线程复制/传输到另一个线程，由于在破坏 exception/exception_ptr 内部状态期间的竞争条件而崩溃。我不确定解决它的最佳方法是什么。

使用的 boost 版本是 1.42，平台是在双核 Intel m/c 上运行的 Ubuntu Lucid。编译器是 gcc 4.4.3。

#include <iostream>

#include <boost/exception/all.hpp>
#include <boost/thread.hpp>

struct Exception
    : public virtual std::exception
    , public virtual boost::exception
{
};

struct MyException : public virtual Exception {};

struct MyTag {};

typedef boost::error_info<MyTag, std::string> MyError;

struct Test
{
    Test()
    {
        _t.reset(new boost::thread(boost::bind(&Test::executor, this)));
    }

    ~Test()
    {
        _t->join();
    }

    void executor()
    {
        std::cerr << "executor: starting ...\n";
        for (;;)
        {
            boost::unique_lock<boost::mutex> lk(_mx);
            while(_q.empty())
            {
                _cv.wait(lk);
            }
            {
                boost::shared_ptr<boost::promise<int> > pt = _q.front();
                _q.pop_front();
                lk.unlock();
                pt->set_exception(boost::copy_exception(MyException() << MyError("test")));
            }
        }
    }

    void run_impl()
    {
        try
        {
            boost::shared_ptr< boost::promise<int> > pm(new boost::promise<int>());

            boost::unique_future<int> fu = pm->get_future();
            {
                boost::unique_lock<boost::mutex> lk(_mx);
                _q.push_back(pm);
                pm.reset();
            }
            _cv.notify_one();

            fu.get();
            assert(false);
        }
        catch (const MyException& e)
        {
            throw;
        }
        catch (const boost::exception& )
        {
            assert(false);
        }
        catch (...)
        {
            assert(false);
        }
    }

    void run()
    {
        std::cerr << "run: starting ...\n";
        for (;;)
        {
            try
            {
                run_impl();
            }
            catch (...)
            {
            }
        }
    }

private:

    boost::mutex _mx;
    std::list< boost::shared_ptr< boost::promise<int> > > _q;
    boost::shared_ptr<boost::thread> _t;
    boost::condition_variable_any _cv;
};

int main()
{
    Test test;
    test.run();
}

/*
#0  0x080526bd in boost::exception_detail::refcount_ptr<boost::exception_detail::error_info_container>::release (this=0x806e26c) at /boost_1_42_0/boost/exception/exception.hpp:79            
#1  0x0804f7c5 in ~refcount_ptr (this=0x806e26c, __in_chrg=<value optimized out>) at /boost_1_42_0/boost/exception/exception.hpp:34                                                           
#2  0x0804bb61 in ~exception (this=0x806e268, __in_chrg=<value optimized out>) at /boost_1_42_0/boost/exception/exception.hpp:254                                                             
#3  0x0805579a in ~clone_impl (this=0x806e260, __in_chrg=<value optimized out>, __vtt_parm=<value optimized out>) at /boost_1_42_0/boost/exception/exception.hpp:391                          
#4  0x001ff633 in ?? () from /usr/lib/libstdc++.so.6                                                                                                                                                           
#5  0x0027233d in _Unwind_DeleteException () from /lib/libgcc_s.so.1                                                                                                                                           
#6  0x001fe110 in __cxa_end_catch () from /usr/lib/libstdc++.so.6                                                                                                                                              
#7  0x0804f7a4 in Test::run (this=0xbffff74c) at ex_org.cpp:89                                                                                                                                                 
#8  0x0804b869 in main () at ex_org.cpp:106 
*/

Answer 1

我不是 boost 专家，但我注意到了一些比赛问题，它在调试模式下运行正常吗？

对于执行者我会这样写

void executor()
{
    std::cerr << "executor: starting ...\n";

    for (;;)
    {            
        _cv.wait(lk);

        boost::unique_lock<boost::mutex> lk(_mx);

        __sync_synchronize (); // Tells the compiler to prevent optimizations

        if ( !_q.empty() ) {                
            boost::shared_ptr<boost::promise<int> > pt = _q.front();
            _q.pop_front();
            pt->set_exception(boost::copy_exception(MyException() << MyError("test")));
        }
    }
}

还有

void run_impl()
{
    try
    {
        boost::shared_ptr< boost::promise<int> > pm(new boost::promise<int>());

        boost::unique_future<int> fu = pm->get_future();

        {
            boost::unique_lock<boost::mutex> lk(_mx);

            // prevent the compiler from mixing above and below code
            __sync_synchronize ();

            _q.push_back(pm);
            pm.reset();
        }

        _cv.notify_one();

        // This one is the paranoïd's one ;), one must check without ! 
        __sync_synchronize ();

        {
            // since fu must holds an internal reference pm being currently 
            // changed by the other thread !
            boost::unique_lock<boost::mutex> lk(_mx);

            // Then you are assured that everything is coherent at this point
            // the stack frame holding the exception stuffs won't be corrupted

            fu.get();
        }

        assert(false);
    }