Start thread with derived class's member function

Question

Similar to this question: Start thread with member function and this one: std::thread calling method of class

However I have the following:

#include <thread>
#include <iostream>
class myAbstractClass {
public:
  virtual void myFunction() = 0;//abstract class
}

class myFirstClass : public myAbstractClass {
public:
  void myFunction() { std::cout << "First class here";}
}

class mySecondClass : public myAbstractClass {
public:
  void myFunction() { std::cout << "Second class here";}
}

Then I have to call myFunction() from a different place in a new thread, but the following does not compile (and I can't think of anything else to try):

public void callMemberFunctionInThread(myAbstractClass& myInstance) {
  std::thread myThread (&myAbstractClass::myFunction, myInstance);
  //supposed to call myInstance.myFunction() on myThread
}

"does not compile" isn't very specific. What error messages are you getting? — Andrew Henle, Apr 09 '17 at 14:15
Intellisense doesn't complain, compilation starts and then it gives `C2259 'myAbstractClass': cannot instantiate abstract class` in file `tuple` located in `C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.10.25017\include` (line 199) — ProgrammingMachine5000, Apr 09 '17 at 14:24
Please fix your program so that it is an [mcve] first. Lots of trivial syntax error here. — kennytm, Apr 09 '17 at 14:25
The abstract class member function should be `virtual` if the derived classes are supposed to override it. Don't know if that works with `std::thread` anyway. — Bo Persson, Apr 09 '17 at 14:42
@peppe Thanks a lot, that fixed it. Do you want me to post it as a new answer so that other people searching for it can find it more quickly? — ProgrammingMachine5000, Apr 09 '17 at 14:44
@Programming - If you have a complete working example of starting a thread with a virtual function, that would make an interesting answer. Haven't really considered that before. — Bo Persson, Apr 09 '17 at 14:55

score 1 · Accepted Answer · answered Apr 09 '17 at 14:52

Pass std::ref(myInstance). Note that std::thread constructor will make a copy of the arguments passed to it (see here), and you can't copy a myAbstractClass.

(Then, all of this will still work because std::thread functionality is described in terms of std::invoke, which unwraps the std::reference_wrapper obtained by std::ref and calls the pointer to member function onto it. See here).

Start thread with derived class's member function

1 Answers1