The only reason you aren't seeing a problem with that code is because it
exits very quickly after ~B() is called, before the other thread gets a
chance to be scheduled again. In a large program, shutdown might not be so
fast. Try putting a sleep(1) at the end of B::~B() -- you'll see that the
destructor is called with the background thread still running.
On Fri, Mar 6, 2009 at 11:13 AM, Marc Vaillant <m...@jhu.edu> wrote:
> On Fri, Mar 06, 2009 at 09:52:07AM -0800, Kenton Varda wrote:
> > On Fri, Mar 6, 2009 at 5:50 AM, marc <vaill...@cis.jhu.edu> wrote:
> >
> > Isn't this a common scenario in C++ for which stdlib provides a
> simple
> > solution, std::auto_ptr? std::auto_ptr is a lightweight class
> designed
> > to "RAIIify" pointers. What am I missing?
> >
> >
> > Deleting the objects on shutdown is easy. The problem is that doing so
> while
> > another thread is still using them may crash the program. If your
> program is
> > careful to shut down all background threads before exiting, then it's
> fine, but
> > many people write code which isn't so clean, and some of these people
> insist
> > that libraries should not delete their objects at exit for exactly this
> reason.
>
> I'm referring to having a static auto_ptr variable. I'm not familiar
> with how this can manifest the danger you describe. Can you point it
> out in the following example?
>
>
> #include <pthread.h>
> #include <memory>
> #include <iostream>
>
>
> class B
> {
> public:
> ~B()
> {
> std::cout<<"destructor called"<<std::endl;
> }
>
> int alive()
> {
> return 1;
> }
>
> };
>
> class A
> {
> public:
> static std::auto_ptr<B> b;
> };
>
> std::auto_ptr<B> A::b(new B);
>
> void *threadFunc(void* p)
> {
> while(1)
> {
> std::cout<<A::b->alive()<<" ";
> }
> }
>
> int main()
> {
> pthread_t t;
> int rc;
> int p;
> rc = pthread_create(&t, NULL, threadFunc, (void *)p);
> sleep(1);
>
> return 1;
> }
>
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