Re: [boost] Threads and mutexes : assign_to error

From: Douglas Gregor (gregod_at_[hidden])
Date: 2003-04-30 09:15:08

On Wednesday 30 April 2003 08:44 am, Jacques Kerner wrote:
> Hi,
>
> I get the following error :
>
> error C2664: 'void boost::function0<R,Allocator>::assign_to(Functor)' :
> unable to convert parameter 1 from 'const CTaskManager' to 'CTaskManager'
>
> when doing this :
>
> class CTaskManager
> {
>     public:
>         CTaskManager();
>         ~CTaskManager();
>         void operator()() {}
>
>     private:
>         boost::mutex m_mutex;
> }
>
> and
>
> CTaskManager taskManager;
> boost::thread_group mainThreadGroup;
> mainThreadGroup.create_thread(taskManager);
> mainThreadGroup.join_all();
>
> The error dissapears when I remove the mutex from the definition of
> CTaskManager ... (?!!)
>
> So what is the right way to use mutex and threads together? Do I have to
> declare the mutex outside of the
> functor? Why?

Mutexes are not copyable, and when you pass taskManager to create_thread it 
tries to make a local copy of the function object . If you would prefer to 
pass a reference to taskManager to create_thread, do this:

  mainThreadGroup.create_thread(boost::ref(taskManager));

        Doug