Question

Hi I have the following C++ code,

I have MyThread class in the thread.h file

class MyThread
{ 
    public:
       void start();
       virtual void* task() = 0;
};

I have worker class in the worker.h file

class Worker : public MyThread
{
    virtual ~Worker();
    virtual void* task();   // I have implementation in worker.cpp
};

Have used pthread_create() in the start() in thread.cpp file for creating a thread and I want to make the task() routine defined in the worker.cpp as the start routine . So how can I do that ? What should I pass as the parameter to the start routine in pthread_create ?

I have tried this but it gives an error:

pthread_create(&(this->threadId),&(this->attr),(void *)task,NULL);                        

Answer 1

You can’t use member function as a thread function. You can only use free functions or static member functions, but you can pass arbitrary void* argument to that function and you can pass pointer to this as that argument, that allows you to call member function inside that function:

class MyThread
{ 
    public:
       void start();
       virtual void* task() = 0;

       static void * thread_routine(void* pthis)
       {
            MyThread* t = static_cast<MyThread*>(pthis);
            t->task();
            return 0;
       }
};

Then you launch your thread like this

void MyThread::start()
{
    pthread_create(&(this->threadId),&(this->attr),thread_routine, this);
}