Re: [boost] [signals/threadsafe version] Atomic disconnects

From: Johan Torp (johan.torp_at_[hidden])
Date: 2008-03-09 05:21:10

Frank Mori Hess wrote:
> 
> To have the connection disconnect on the Foo object's destruction, you're 
> supposed to pass a shared_ptr owning the object (either directly or 
> indirectly) to slot::track() before connecting the slot.  This insures the 
> object is not destroyed while a slot invocation is in progress (the signal 
> converts its weak_ptr copy to a shared_ptr while the slot runs), and 
> disconnects the slot when the tracked weak_ptr expires.  It does have the 
> drawback that you often can't track connections made in the constructor 
> though, since enable_shared_from_this doesn't work there.  I did provide 
> postconstructible/deconstruct_ptr to support postconstructors, although it 
> does all add up to a bit more typing.
> 

Thanks for the clarification. This solution forces the use of shared_ptrs
and might keep a Foo instance alive a little bit longer. Especially the
latter requirement is a no-no for me. 

I created my own thread safe signals implementation which requires a
"CallbackRequester" to connect a synchronous slot to an asynchronous signal:

class CallbackRequester { virtual void callLater(const
boost::function<void()>& callback) = 0; }; 

The callbackrequester implementation -typically a queue - switches to the
thread which the synchronous slot "belongs" to. This is of course very
intrusive to the entire design of an application - callbackrequesters
implementations need to exist for all threads and be passed around all over
the application. However, it made it possible to implement a safe
scoped_connection with RAII semantics. User code look something like this:

AsyncSignal<void()> sig;

class Foo{
Foo(boost::weak_ptr<CallbackRequester> req)
: con(sig, boost::bind(&Foo::SomeFunc, this), req) {}
 
void SomeFunc() { ...}

AsyncSignalConnection con;
};
 

Johan
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