LPTHREAD_START_ROUTINE / array of classes

Question

I wrote some test code like this which compiled and worked fine...

void threadtest()
{
  HANDLE hThrd;
  DWORD threadId;
  int i;

  for (i = 0;i < 5;i++)
  {
    hThrd = CreateThread(
      NULL,
      0,
      ThreadFunc,
      (LPVOID)i,
      0,
      &threadId );
  }
  // more stuff
}

DWORD WINAPI ThreadFunc(LPVOID n)
{
  // stuff
  return 0;
}

Then I wanted to modify the code to put the ThreadFunc inside a class and then declare an array of those classes. I thought the code should look like this:

class thread_type
{

  public:

  DWORD WINAPI ThreadFunc(LPVOID n)
  {
    // stuff
    return 0;
  }
};

void threadtest()
{
  HANDLE hThrd;
  DWORD threadId;
  int i;
  thread_type *slave;

  slave = new thread_type[5];

  for (i = 0;i < 5;i++)
  {
    hThrd = CreateThread(
    NULL,
    0,
    slave[i].ThreadFunc,
    (LPVOID)i,
    0,
    &threadId );
  }
  // more stuff
}

Unfortunately the compiler complains about the line slave[i].ThreadFunc, I think I may need some special casting but all the permutations I try involving "::" and "&" seem to fail (I'm quite new to C++). The real code has some additional complications which I haven't included for clarity, but I think they are irrelevant.

Answer 1

The following explains the difference between a pointer to a function and a pointer to a member function C++ FAQ Lite. See section 33.2 which explains why what you are doing is a bad idea.

Answer 2

First problem with the code, that the test class is not descendant of the thread_type. Somehow you need to specify the base class. Second is, if you are passing function pointer, that shouldn't be thiscall type. The solution is typically this:

struct thread
{
  virtual void
  run() = 0;

  static thread_func(void* param)
  {
    thread* pThread = (thread*)param;
    thread->run();
  }
}


struct worker : public thread
{
  void
  run()
  {
    (.. code for the thread...)
  }
}

void threadtest()
{
  HANDLE hThrd;
  DWORD threadId;
  int i;
  thread *slave;

  slave = new thread_type[5];
  slave[0] = new worker;
  slave[1] = new worker;
  slave[2] = new worker;
  slave[3] = new worker;
  slave[4] = new worker;

  for (i = 0;i < 5;i++)
  {
    hThrd = CreateThread(
    NULL,
    0,
    &thread::thread_func,
    (LPVOID)slave[i],
    0,
    &threadId );
  }
  // more stuff
}

Note that this could is just a reflection, I couldn't compile now, because I don't have here anything to do so, but the logic should be like this.