Re: [boost] [thread] countdown_latch

22 Apr 2013

      Le 22/04/13 00:55, Michael Marcin a écrit :
...
On 4/21/2013 4:53 PM, Vicente J. Botet Escriba wrote:
...
You are surely right. My first approach would be option 3, but it has a
lot of troubles as you note.
I suspect that the completion_latch needs a latch internally to ensure
that all the waiters have been finished.
The best would be to prototype these ideas and see what can be done.
Back to the original example with widget for a second whether it is a 
latch or a barrier it is only used on construction but then kept 
around as member for the entire lifetime of the object.
This seems unnecessary but also seems to be the pattern I've seen 
everywhere.
Would it be better to do something like:
class widget
{
public:
    widget()
    {
        countdown_latch latch(1);
        thread_ = std::thread( [&]{ thread_func( latch ); }
        latch.wait();
    }
private:
    void setup();
    void run();
void thread_func( countdown_latch& latch )
    {
        setup();
        latch.count_down();
        // from here on latch is a dangling reference don't use
run();
    }
std::thread thread_;
};
Or is there something cleaner?
++ It reduce the size of the widget.
- dangling reference (but that can be mastered.

I don't know your constraints:
Why do you need to run the setup on the new created thread?
Could it be executed directly on the widget constructor?
If yes

class widget {
public:
     widget()     {
         setup();
         thread_ = std::thread( [&]{ run(  ); } );
     }
private:
     void setup();
     void run();
     std::thread thread_;
};

Do you need to manage the thread? if not, detaching the thread allows 
you to don't include it on the widget context.

class widget {
public:
     widget()     {
...
         std::thread( [&]{ thread_func( latch ); }).detach();
...
     }
private:
     void setup();
     void run();
};

Best,
Vicente