GUI thread blocked using QThread.

[wysota]

I'm not sure why you are making things so complex, try this:

class LogEvent : public QEvent {
public:
  LogEvent(const QString &str) : QEvent(QEvent::MaxUser-1), m_str(str){}
  const QString &string() const { return m_str; }
private:
  QString m_str;
};
 
class Log : public QThread {
public:
  Log(){}
  void run(){ exec(); }
  static void log(const QString &str){ QCoreApplication::postEvent(new LogEvent(str)); }
protected:
  void customEvent(QEvent *e){
    if(e->type()==QEvent::MaxUser-1){
        logData(static_cast<LogEvent*>(e)->string());
    }
  }
};

class LogEvent : public QEvent {
public:
  LogEvent(const QString &str) : QEvent(QEvent::MaxUser-1), m_str(str){}
  const QString &string() const { return m_str; }
private:
  QString m_str;
};

class Log : public QThread {
public:
  Log(){}
  void run(){ exec(); }
  static void log(const QString &str){ QCoreApplication::postEvent(new LogEvent(str)); }
protected:
  void customEvent(QEvent *e){
    if(e->type()==QEvent::MaxUser-1){
        logData(static_cast<LogEvent*>(e)->string());
    }
  }
};

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No need for any mutexes or artificial event queues.