Re: [boost] Threads and mutexes : assign_to error

From: Jacques Kerner (jacques.kerner_at_[hidden])
Date: 2003-04-30 09:54:29

Douglas Gregor wrote:

>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
>
>_______________________________________________
>Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
>
>  
>
Thank you very much, it works great. I had missed the fact that 
create_thread makes a copy
of the functor. Thanks again!