is the qdatastream thread safe or not ?

nicker player

I just used the QJsonObject in the new std::thread .and the heob debugger give me a tip:

<unique>0x000860F2</unique>
  <tid>26</tid>
  <kind>Leak_DefinitelyLost</kind>
  <xwhat>
    <text>160816 bytes in 1 blocks are lost in loss record 12 of 81505 (#549106)</text>
    <leakedbytes>160816</leakedbytes>
    <leakedblocks>1</leakedblocks>
  </xwhat>
  <stack>
    <frame>
      <fn>malloc</fn>
    </frame>
    <frame>
      <ip>0x673B1B17</ip>
      <obj>D:\program\qt\5.14.1\msvc2017\bin\Qt5Cored.dll</obj>
      <fn>class QDataStream &amp; operator&gt;&gt;(class QDataStream &amp;,class QJsonObject &amp;)</fn>
    </frame>
    <frame>
      <ip>0x673AEDD2</ip>
      <obj>D:\program\qt\5.14.1\msvc2017\bin\Qt5Cored.dll</obj>
      <fn>bool QJsonObject::detach2(unsigned int)</fn>
    </frame>
    <frame>
      <ip>0x673B09F3</ip>
      <obj>D:\program\qt\5.14.1\msvc2017\bin\Qt5Cored.dll</obj>
      <fn>class QDataStream &amp; operator&gt;&gt;(class QDataStream &amp;,class QJsonObject &amp;)</fn>
    </frame>
    <frame>
      <ip>0x673B0D92</ip>
      <obj>D:\program\qt\5.14.1\msvc2017\bin\Qt5Cored.dll</obj>
      <fn>class QDataStream &amp; operator&gt;&gt;(class QDataStream &amp;,class QJsonObject &amp;)</fn>
    </frame>
    <frame>
      <ip>0x673AEA5E</ip>
      <obj>D:\program\qt\5.14.1\msvc2017\bin\Qt5Cored.dll</obj>
      <fn>class QJsonObject::iterator QJsonObject::insert(class QStringView,class QJsonValue const &amp;)</fn>
    </frame>
    <frame>
      <ip>0x673AE96B</ip>
      <obj>D:\program\qt\5.14.1\msvc2017\bin\Qt5Cored.dll</obj>
      <fn>class QJsonObject::iterator QJsonObject::insert(class QString const &amp;,class QJsonValue const &amp;)</fn>
    </frame>

I just use the std::mutex to lock the data write and read.
so I think maybe its not safe with using the std::mutex to read and write the qjsonobject? dose i need to change the std::mutex into the QMutex ?

Christian Ehrlicher

No Qt object or function is thread safe except it is explicitly stated in the documentation.

nicker player

so if I used the std::thread and the std::mutex to lock the data.what should I do the make sure that writting and reading the data is safe .

class A:QObject{
....
private:
       QJsonObject t_data;
public:
       void writing(const QString & value){
                t_data.insert("data",value);
                do_otherthings_such_as_update_the_ui_value();
        }
}

//std thread functions what is detached from the main thread.
int testfunction(){
       //heres  to modify and send the data into the writing method.
       A aobject;
       aobject.writing("somevalue");
}

so dose i need to lock the the t_data by using the QMutex or using the emit method to to the other data what is in the main thread instead of using the lock way.what should i do.please.

Christian Ehrlicher

When you only access an object from a single thread why do you ask about thread safeness and mutexes here?

nicker player

In fact.
I wrote the data in a new std::thread and then post the result to the qt ui main loop.
Now I just used the emit way to send the data to the ui loop.