[Boost-users] [boost.signals] documentation suggestion + thread-safe partial implementation

From: Frank Hess (frank.hess_at_[hidden])
Date: 2007-01-26 10:52:15

Hi,

I'd like to suggest a sentence be added to the boost.signals documentation 
describing how to connect one signal directly to another signal.  It took 
me a while to realize I could do things like

signal.connect(boost::bind(boost::ref(otherSignal), _2));

wrapping a signal object in a boost::ref() call before passing it to 
boost::bind(), to get around signals being noncopyable.  Before this 
epiphany, I kept writing trivial wrapper functions to use as slots when I 
wanted to connect two signals :)  I imagine others who are new to 
boost.signals and boost in general would resort to similar tactics.

By the way, I hacked up a partial implementation of boost.signals which is 
intended to be thread-safe, since I missed boost.signals so much in my 
multi-threaded code.  Would anyone would be interested in this?  It's just 
a few header files, and depends on boost (although not on boost.signals).  

I just did the bare minimum I need for my own use: a signal template class, 
signalslib::connection, and signalslib::scoped_connection.  I didn't 
implement return values because I don't use them.  I didn't implement 
boost::trackable because I don't see how to make automatic connection 
management thread-safe when a signal is connected to an object's member 
function.  You really want to insure the slot is disconnected from the 
signal before the object providing the slot is destroyed.  Inheriting the 
object from boost::trackable wouldn't seem to be good enough, since the 
boost::trackable destructor wouldn't get called until after the object's 
destructor.  So you pretty much have to manually disconnect the connection 
at the beginning of the object's destructor.

-- 
Frank