<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE section PUBLIC "-//Boost//DTD BoostBook XML V1.0//EN"
  "http://www.boost.org/tools/boostbook/dtd/boostbook.dtd">
<section last-revision="$Date$">

<title>Introduction</title>

<note>
<para><emphasis role="bold">Boost.Signals is no longer being actively maintained.</emphasis>
Do not use Boost.Signals for new development (use 
<link linkend="signals2">Boost.Signals2</link>
instead). If you have existing Boost.Signals-based code, it will
continue to work, but consider moving to Boost.Signals2. There is
<link linkend="signals2.porting">
a porting guide</link> in the Signals2 documentation.</para>
</note>

<para>The Boost.Signals library is an implementation of a managed
signals and slots system. Signals represent callbacks with multiple
targets, and are also called publishers or events in similar
systems. Signals are connected to some set of slots, which are
callback receivers (also called event targets or subscribers), which
are called when the signal is "emitted."</para>

<para>Signals and slots are managed, in that signals and slots (or,
more properly, objects that occur as part of the slots) track all
connections and are capable of automatically disconnecting signal/slot
connections when either is destroyed. This enables the user to make
signal/slot connections without expending a great effort to manage the
lifetimes of those connections with regard to the lifetimes of all
objects involved.</para>

<para>When signals are connected to multiple slots, there is a
question regarding the relationship between the return values of the
slots and the return value of the signals. Boost.Signals allows the
user to specify the manner in which multiple return values are
combined.</para>

</section>
