c++ - MySQL 异常 "connection lost during query"、 "MySQL server has gone away"和 "command out of sync"

Question

我有一个 C++ 代码，它使用 SQLAPI++ 库。在我的代码中，我尝试打开 mysql 连接，然后创建两个使用相同连接的命令，并从两个线程调用该命令。在执行代码期间，我收到异常“查询期间连接丢失”和“MySQL 服务器已消失”。有时我收到异常“命令不同步，您现在无法运行此命令”。我尝试增加wait_timeout 150和max_allowed_pa​​ckage 64M，但我的问题没有解决。下面你可以找到 C++ 代码。

int main()
{

  try
  {
    SAConnection saConnection;
    saConnection.Connect("scada", "root", "123qwerty!@#", SA_MySQL_Client);
    saConnection.setAutoCommit(SA_AutoCommitOff);   

    SACommand saCommand1{&saConnection, "select * from Node"};
    SACommand saCommand2{&saConnection, "select * from Node limit 1"};

    // VM: TODO: saCommand1.setOption("UseStatement") = "TRUE";
    // VM: TODO: saCommand2.setOption("UseStatement") = "TRUE";
    saCommand1.setOption("HandleResult") = "store";
    saCommand2.setOption("HandleResult") = "store";

    auto f1 = std::async(std::launch::async, [&]{ saCommand1.Execute(); saConnection.Commit(); });
    auto f2 = std::async(std::launch::async, [&]{ saCommand2.Execute(); saConnection.Commit(); });
    f1.get();
    f2.get();

    //saConnection.Commit(); // BOOM!

/*
    while (saCommand1.FetchNext())
      std::cerr << "======== fetching a record from saCommand1" << std::endl;
    while (saCommand2.FetchNext())
      std::cerr << "======== fetching a record from saCommand2" << std::endl;
*/
  }
  catch(const SAException& ex)
  {
    std::cerr << "==== ex.what() is " << static_cast<const char*>(ex.ErrText()) << std::endl;
  }

  return 0;
}

Answer 1

您正在使用来自两个 std::async 对象的一个​​连接，可能来自两个线程，这是不受支持的。创建两个到数据库的连接，每个 std::async 一个连接。