Re: [Boost-users] Boost thread library wrapper

10 Feb 2006

      Dhanvi Kapila wrote:
...
by exit handlers I mean some special function that would be gauranteed 
to be called whenever the thread is exiting.
Technically, this depends entirely on whether the underlying operating 
system provides such a mechanism. Win32 doesn't. A thread killed by 
TerminateThread, or simply ended by ExitThread, is dead immediately, and 
no code is ever again executed on its stack. The only thing that still 
gets executed (not necessarily on the existing thread) are the DLL entry 
functions.
Thus, Boost.Thread cannot possibly supply a reliable version of such a 
feature across all platforms, and as such, it's probably best that it 
doesn't supply the feature at all.

If you want to guarantee execution of a function on thread end under 
normal circumstances (i.e. normal return or exception stack unwinding), 
you should use a sentry object that executes that code in the destructor:

void thread_entry()
{
  thread_sentry sentry;

  // Code here

}

You can easily make a reusable object for this:

class thread_sentry : public boost::noncopyable
{
  boost::function exit_func_;
public:
  thread_sentry(boost::function exit_func)
    : exit_func_(exit_func)
  {}

  ~thread_sentry()
  {
    if(exit_func_) exit_func_();
  }
};

Now you can do:

void exit_function()
{
  // Cleanup code.
}

void thread_entry
{
  thread_sentry sentry(exit_function);

  // Code here

}

Usually such code can be avoided by using RAII objects for all resources 
in the first place.

Sebastian Redl