Re: [Boost-users] functor for boost::thread_group threads: which one is correct?

Subject: Re: [Boost-users] functor for boost::thread_group threads: which one is correct?
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2009-08-23 15:06:20

AMDG

Boost lzw wrote:
> I have two versions (VERSION1 and VERSION2) of a group_helper functor to be
> called from boost::thread_group, which one of them is correct?
>
> class FileThread
> {
> public:
> void print() {...}
> void find() {...}
> };
>
> class group_helper
> {
> private:
>     boost::shared_ptr<FileThread> m_object;
> public:
>    //VISION1
>     group_helper(boost::shared_ptr<FileThread>& object) : m_object(object) {
> }
>
>    //VISION2
>     group_helper() : m_object(boost::shared_ptr<FileThread>(new FileThread))
> { }
>
>     void operator()() { m_object->find(); m_object->print(); }
> };
>   

Both are correct depending on whether you want to pass an external 
FileThread
or create a new FileThread in the constructor.

> On another matter, why the following code results in a runtime exception
> from the group_helper's dtor?
>
> #include <iostream>
> #include "boost/thread/thread.hpp"
>
> class FileThread
> {
> public:
> 	void find() { }
> 	void print() { }
> };
>
> class group_helper			
> {							
> private:
> 	FileThread* m_object;	
> public:			
> 	group_helper() : m_object(new FileThread) {}
> 	void operator()() { m_object->find(); m_object->print(); }
> 	~group_helper() { if (m_object) delete m_object; }// EXCEPTION from dtor
> };
>   

group_helper is copied and both copies try to
delete m_object.

> int main()
> {
> 	group_helper gh;
> 	boost::thread thrd(gh);						
> 	thrd.join();
> }
>   

In Christ,
Steven Watanabe