[Boost-users] Re: Problem using Boost.thread : Class destructor called several times!

From: Raoul Gough (RaoulGough_at_[hidden])
Date: 2003-10-03 08:04:37

"Huck finn" <huckfinn19_at_[hidden]> writes:

> Hi there, still a newbie question for you guys...
>
> I changed a bit the sample example from thread.cpp :
>
> here's the new code i'm trying:
> -----------------
> boost::mutex io_mutex; // The iostreams are not guaranteed to be
> thread-safe!
> class FakeClass
> {
> public:
> 	FakeClass(int NewID):ID(NewID)
> 	{
> 		boost::mutex::scoped_lock scoped_lock(io_mutex);
> 		std::cout<<"FakeClass #"<<ID<<" says : "<<"I'm alive!"<<std::endl;
> 	}

FakeClass (FakeClass const &copy) : ID (copy.ID) {
  boost::mutex::scoped_lock scoped_lock(io_mutex);
  std::cout<<"FakeClass #"<<ID<<" says : "<<"I've been copied!"<<std::endl;
}

> 	~FakeClass()
> 	{
> 		boost::mutex::scoped_lock scoped_lock(io_mutex);
> 		std::cout<<"FakeClass #"<<ID<<" says : "<<"I'm being
> destroyed!"<<std::endl;
> 	}
> 	void operator()()
> 	{
> 		boost::mutex::scoped_lock scoped_lock(io_mutex);
> 		std::cout<<"Thread for FakeClass #"<<ID<<" has been started!"<<std::endl;
> 	}
> private:
> 	int ID;
> };
> void main ()
> {
> 	boost::thread_group group;
> 	FakeClass item1(1),item2(2);
>
> 	group.create_thread(item1);
> 	group.create_thread(item2);
> 	group.join_all();
> 	std::cout<<"   main ending..."<<std::endl;
> }
> -----------------------------
>
> here's what I get when executing :
>
> FakeClass #1 says : I'm alive!
> FakeClass #2 says : I'm alive!
> FakeClass #1 says : I'm being destroyed!
> FakeClass #1 says : I'm being destroyed!
> FakeClass #1 says : I'm being destroyed!
> Thread for FakeClass #1 has been started!
> FakeClass #2 says : I'm being destroyed!
> FakeClass #1 says : I'm being destroyed!
> FakeClass #2 says : I'm being destroyed!
> FakeClass #2 says : I'm being destroyed!
> Thread for FakeClass #2 has been started!
> FakeClass #2 says : I'm being destroyed!
>    main ending...
> FakeClass #2 says : I'm being destroyed!
> FakeClass #1 says : I'm being destroyed!
> Press any key to continue
>
>
> 1- I'm wondering why the destructor of my FakeClass is called 4 times
> for each items ???
>
> 2- It says in the doc that the function that creates a thread "copies
> the function wrapped by threadfunc" and threadfunc would be in this
> case item1 and item2, does this means that the copy constructor is
> called every time a thread is created with an object?

Adding an explicit copy constructor with tracing will tell you for
sure - it certainly looks like some copies are being made in this
case.

-- 
Raoul Gough.
(setq dabbrev-case-fold-search nil)