boost::thread 断言的 shared_ptr 失败

Question

class WIFITest
{
public:

  void StartTest();

  void Notify_Test(boost::shared_ptr<basic_msg> basic_msg, ID id );


private:
  void OpenStaMode_test();

private: 
  boost::shared_ptr<boost::thread> OpenStaMode_testThread;

  boost::shared_ptr<basic_msg> VMF_WIFI_NOTIFY_CLIENT_OPEN_MSG;  

  typedef boost::shared_ptr<boost::thread> THREAD;
  typedef boost::shared_ptr<basic_msg> MSG;
  std::map<ID,std::pair<THREAD,MSG>> map;
};  

void WIFITest::StartTest()
{ 
  map[ID::WIFI_REQ_CLIENT_OPEN] = std::make_pair(OpenStaMode_testThread,VMF_WIFI_NOTIFY_CLIENT_OPEN_MSG);

  this->OpenStaMode_testThread.reset(new boost::thread(&WIFITest::OpenStaMode_test,this));
  this->OpenStaMode_testThread->join();

}
void WIFITest::OpenStaMode_test()
{
  unsigned char strData[WIFI_SEND_BUF_SIZE_MIN];
  sendOpenReq(strData);
  try { 
    boost::this_thread::sleep(boost::posix_time::seconds(8));
  }
  catch(const boost::thread_interrupted&) {   

        std::cout<<"OpenStaMode_test success@ \n";

      }
    else {
        goto OpenStaMode_test_fail;
      }

    return;

  }
OpenStaMode_test_fail:
  printf("@WIFITest::OpenStaMode_test FAIL@@@@@@@@@@@@@@ \n");

}

void WIFITest::Notify_Test(boost::shared_ptr<basic_msg> basic_msg, ID id)
{
  map[id].second = basic_msg;

   map[id].first->interrupt();
  printf("@WIFITest::INTERRUPTED @@@@@@@@@@@@@@ \n");

}

首先 main 将创建 StartTest 实例并调用 StartTest()， 当其他代码调用 Notify_Test 时，“map[id].first->interrupt();”这句话将产生以下断言失败，并使程序崩溃。

TestWIFI: ../../boost_1_55_0/boost/smart_ptr/shared_ptr.hpp:653: typename boost::detail::sp_member_access::type boost::shared_ptr::operator->() const [with T = boost::thread, typename boost::detail::sp_member_access::type = boost::thread*]: Assertion `px != 0' failed.

Answer 1

这一行：

map[ID::WIFI_REQ_CLIENT_OPEN] = std::make_pair(OpenStaMode_testThread,VMF_WIFI_NOTIFY_CLIENT_OPEN_MSG);

将OpenStaMode_testThread 的副本存储到地图中，此时该副本为空。

然后您在OpenStaMode_testThread 上调用reset(new boost::thread(&WIFITestSuite::OpenStaMode_test,this))，但这不会影响已存储到地图中的副本。

因此，当您调用map[id].first->interrupt(); 时，您是在一个空的shared_ptr 上调用它，从而导致断言失败。

---

如下所述，如果在线程开始执行之后但在shared_ptr 上的reset() 调用将其存储到映射之前，可能会发生对Notify_Test 的调用，则此处存在竞争条件。要解决此问题，请使用互斥锁：

class WIFITest
{
public:
  /* ... */
private:
  /* ... */

private: 
  boost::mutex mutex_;
  /* ... */
};  



void WIFITest::StartTest()
{ 
  {
    boost::lock_guard<boost::mutex> guard(mutex_);  // Takes ownership of the mutex
    map[ID::WIFI_REQ_CLIENT_OPEN] = std::make_pair(THREAD(), VMF_WIFI_NOTIFY_CLIENT_OPEN_MSG);
    map[ID::WIFI_REQ_CLIENT_OPEN].first.reset(new boost::thread(&WIFITest::OpenStaMode_test,this));
    // At this point the thread has started and the pointer has been stored into the map
  }  // guard is destructed and mutex released here 
     // so that we don't hold the mutex while waiting
     // for the thread to finish.

  map[ID::WIFI_REQ_CLIENT_OPEN].first->join();
}

/* ... */

void WIFITest::Notify_Test(boost::shared_ptr<basic_msg> basic_msg, ID id)
{
  boost::lock_guard<boost::mutex> guard(mutex_); // Takes ownership of the mutex
  map[id].second = basic_msg;
  map[id].first->interrupt();
  printf("@WIFITest::INTERRUPTED @@@@@@@@@@@@@@ \n");

}