Re: [Boost-users] boost::thread queries

From: Peter Dimov (pdimov_at_[hidden])
Date: 2006-10-11 17:19:37

Rob Caldecott wrote:
> I have just started to investigate the boost::thread library and have
> a couple of questions (Win32/VS2005):
>
> 1. I have an application that creates lots of relatively short-lived
> threads. When a thread is created I store the handle in an array, and
> at regular intervals, I remove completed threads from the array by
> checking the thread state via ::GetExitCodeThread.  The application
> runs 24/7 so I don't want an array containing thousands of "dead"
> handles.
>
> I thought I'd replace this code with a boost::thread_group, but I
> cannot see any way to remove completed threads from the internal
> list.  This means the std::list used by boost::thread_group would
> keep on increasing in size until the application exits, which I want
> to avoid.  If I decide to roll my own thread group code, how can I
> check if a boost::thread is still active or not?

You can't.

Interesting timing; I submitted a proposal for a threading API to the C++ 
committee:

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2090.html

that lets you do that. You can keep a vector< thread::handle > and 
periodically sweep it using thread::try_join as a predicate. I've been 
having troubles convincing some committee members of its utility, though.

That said, why do you even have to keep the boost::thread objects? There 
aren't many useful things that you could do with a boost::thread; if you run 
24/7 you should be able to just spawn the threads "detached":

boost::thread( f );

without keeping them in a thread group.

> 2. I am getting a memory leak when my application exits, which has
> already been mentioned here.  Does anyone have a fix for this which I
> can apply to the 1.33.1 source (then rebuilding the thread lib by
> hand)?  It would be much appreciated. I am also unsure if this leak
> will be fixed for 1.34 - does anyone know for certain?

You can replace your version of tss_hooks.cpp with this one:

http://boost.cvs.sourceforge.net/*checkout*/boost/boost/libs/thread/src/tss_hooks.cpp?revision=1.4

and rebuild.

1.34 does contain a fix for that too, albeit a different one.