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<h1 align="center">The Boost Statechart Library</h1>
<h2 align="center">Future & History</h2>
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<h2>Contents</h2>
<dl class="index">
<dt><a href="#ToDoList">To-do list</a></dt>
<dt><a href="#ChangeHistory">Change history</a></dt>
</dl>
<hr>
<h2><a name="ToDoList" id="ToDoList">To-do list</a></h2>
<p>The library is mostly complete. However, there is some work left
(<font color="#FF0000">red</font> = added as a result of the formal
review):</p>
<ol>
<li>Implement a choice-point-like class, as discussed in
<a href="http://thread.gmane.org/gmane.comp.lib.boost.devel/164460">this
thread</a></li>
<li>Optimize state-entry and state-exit for speed and code-size</li>
<li>Reimplement <code>fifo_scheduler<>::processor_handle</code> so
that <code>fifo_scheduler<>::create_processor<>()</code> and
<code>fifo_scheduler<>::destroy_processor()</code> no longer make
(indirect) calls to global <code>operator new()</code> and <code>operator
delete()</code></li>
<li>Ensure that everything is compileable with C++ RTTI support turned
off (this requires currently lacking support in Boost.Config and probably
a patch for <code>shared_ptr</code>)</li>
<li>Issue an error if <code>BOOST_STATECHART_USE_NATIVE_RTTI</code> is
defined when C++ RTTI is turned off</li>
<li>The current requirement to pass an <code>mpl::list<></code> to
specify inner initial states and reactions is too strict. Check the
requirements on the sequences and document them accordingly (David
Abrahams)</li>
<li>Make compilation performance measurements with mpl::vector and
mpl::deque instead of mpl::list to find out which is fastest. Document a
recommendation for the fastest container and change all examples
accordingly (David Abrahams)</li>
<li>Investigate how a state machine could be serialized. A first glance
at the serialization library revealed that there currently (1.33) is no
support for types that overload <code>operator new</code> (suitable code
is already present in the serialization library but it is currently
commented out due to incompatibilities with certain compilers). Such
support would be essential for Boost.Statechart serialization</li>
<li><font color="#FF0000">Implement a switch-like reaction (Simon
Gittins, Darryl Green)</font></li>
<li>Link incomplete code-snippets in the tutorial to complete example
code where available</li>
<li>Where appropriate, link the reference documentation to examples</li>
<li><font color="#FF0000">Add a description of the implementation and
better explain performance trade-offs (Jonathan Turkanis)</font></li>
<li><font color="#FF0000">Add links to descriptions of alternate
implementations and discuss performance trade-offs (Jonathan
Turkanis)</font></li>
<li><font color="#FF0000">Add a list of applications that use
Boost.Statechart (Paul A. Bristow)</font></li>
<li>Refactor the <code>state_machine</code> class template to reduce code
size in applications with many different state machines</li>
<li>Add a diagram that helps to understand what an unstable state machine
is</li>
<li>Comment MPL-heavy code</li>
<li>Add examples of often made mistakes</li>
<li>Implement <code>priority_scheduler<></code></li>
<li>Eliminate code-duplication in <code>fifo_scheduler</code> with PP
code submitted by Pavel Vozenilek</li>
<li>Add number and label to all diagrams in docs</li>
<li>Add <code>#pragma once</code> to all headers (speeds up compilation
with MS-compatible compilers)</li>
<li>Investigate whether and how <code>fifo_worker<></code> should
accept a policy parameter defining how to lock and wait</li>
</ol>
<h2><a name="ChangeHistory" id="ChangeHistory">Change history</a></h2>
<p>(<font color="#FF0000">red</font> = points raised during formal
review)</p>
<p>1.43.0</p>
<ul>
<li>Generalized the context() functions so that they can also return a
reference to any public base type of a context. This also makes
transition<> & in_state_reaction<> more general, reported
by Igor R</li>
<li>Added triggering_event()</li>
<li>Fixed Bug #3329 (shadow variable warnings), reported by Grant
Erickson</li>
<li>Fixed Bug #3963 (state_machine<>::post_event() should be
protected), reported by Arne Babnik</li>
</ul>
<p>1.40.0</p>
<ul>
<li>Fixed a bug that prevented the use of boost::ref() with
fifo_scheduler<>::create_processor<>, reported by Steve
Hawkes</li>
<li>Fixed bug #3092 (regression test failures in VC10 beta 1), reported by
Richard Webb</li>
</ul>
<p>1.38.0</p>
<ul>
<li>Fixed gcc-4.3 warning in state_machine.hpp (ticket #2389), reported by
Bryan Silverthorn</li>
</ul>
<p>1.36.0</p>
<ul>
<li>Removed all permanent warning suppressions from library headers
and avoided the resulting warnings with other means (suggested by
Steven Watanabe; thanks to Peter Dimov and Yuval Ronen for insight
into when C4511 & C4512 are issued)</li>
<li>Added the FAQ item <a href="faq.html#AssertInStateDestructor">Why
do I get an assert when I access the state machine from a state
destructor?</a> (due to feedback from Jiang Miao)</li>
<li>Added defaults for the last two template parameters of <a href=
"reference.html#ClassTemplatein_state_reaction">in_state_reaction<></a>
(due to feedback from Sean Kelly)</li>
<li>Adapted fifo_scheduler<> to the changed allocator interface of
boost::function</li>
<li>Changed the PingPong example to demonstrate how the inner workings of
an asynchronous_state_machine<> subclass can be hidden</li>
</ul>
<p>1.35.0</p>
<ul>
<li>Added placement new overload to <code>event<></code> (due to
feedback from Federico J. Fernández)</li>
<li>Made <code>event<></code> copy-assignable (Federico J.
Fernández)</li>
</ul>
<p>1.34.0</p>
<ul>
<li>Fixed a bug that prevented compilation of exception_translator.hpp
(reported by Oliver Kowalke) and adapted TransitionTest.cpp to also test
the exception_translator class</li>
<li>Fixed an allocator-related bug that led to compiler errors in many
tests on GCC >= 4.0</li>
<li>Fixed a number of issues that led to compile-time failures on Intel
9.0 and Code Warrior</li>
<li>Added compile-link tests for all examples</li>
<li>Documented <code>state_machine<>::post_event</code> and added a
<code>const event_base &</code> overload</li>
<li>example/Jamfile.v2 now also stages the dlls necessary to launch the
multithreaded PingPong examples</li>
<li>Added a FAQ item regarding UML2.0 conformance</li>
<li>Made the documentation of <code>unconsumed_event</code> more
visible</li>
<li>Declared <code>state_base::~state_base virtual</code> for GCC. This
makes state exit slightly slower but does away with loads of "has virtual
functions but non-virtual destructor" warnings</li>
<li>Made transitions to history UML2.0 compliant, see <a href=
"faq.html#Uml2">here</a> for more information</li>
<li>Tidied all html files & validated them with <a href=
"http://validator.w3.org/">http://validator.w3.org/</a></li>
<li>Fixed broken links</li>
<li>Fixed a few conformance problems that led to errors on HP compilers</li>
<li>Corrected documentation regarding allocation of states and events</li>
</ul>
<p>17 December, 2005</p>
<ul>
<li>Added detailed performance data to the performance document</li>
<li>Added the Performance "example" and the associated Performance.xls,
which were used to perform the more detailed measurements and draw the
associated charts that can now be found in the performance document</li>
<li>Simplified the BitMachine example (the performance measurement
functions are no longer needed)</li>
<li><font color="#FF0000">Removed the to-do item "Investigate how
constant-time dispatch for non-orthogonal state machines can be
implemented" suggested by David Abrahams, Jonathan Turkanis, Rob Steward
and Dave Gomboc. The more detailed performance measurements have shown
that the time spent for event dispatch is almost always small compared to
the time spent for state-entry and state-exit. See <a href=
"performance.html#SpeedVersusScalabilityTradeoffs">Speed versus
scalability tradeoffs</a> in the performance document for more
information</font></li>
<li>Fixed an order of declaration bug which caused a compile-time error
in event_base.hpp when compiled with GCC3.4.2 on HP-UX (the error neither
showed up on GCC3.4.2 on MinGW nor on MSVC7.1)</li>
<li>Tested with 1.33.1 version of the boost distribution</li>
</ul>
<p>14 August, 2005</p>
<ul>
<li><b>This release will only work with the 1.33.0 version of the boost
distribution</b></li>
<li><font color="#FF0000"><b>B</b></font><b><font color="#FF0000">reaking
change:</font></b> <font color="#FF0000">Added
<code>simple_state<>::operator new</code> &
<code>simple_state<>::operator delete</code> forwarding to the
allocator passed to <code>state_machine</code> (Peter Petrov). This
considerably simplifies memory management customization. A user now only
needs to pass his own allocator to <code>state_machine<></code> and
no longer has to separately overload <code>operator
new</code>/<code>delete</code> for his state classes. Existing state
classes for which memory management is not customized will thus
automatically use the allocator passed to
<code>state_machine<></code>. Existing state classes for which
<code>operator new</code>/<code>delete</code> is overloaded
<b>directly</b> will continue to work as before. The only case where
existing code will refuse to compile is when a state class inherits from
an additional base with overloaded <code>operator
new</code>/<code>delete</code> (leading to ambiguous call errors).
Forwarding functions need to be added to such state classes (see
BitMachine for an example)</font></li>
<li><b>Breaking change</b>: Added an Allocator parameter to the
<code>event</code> class template and added <code>event<>::operator
new</code>/<code>delete</code>. This makes customizing memory management
easier but could also break existing code (see previous point)</li>
<li>Added Jamfile.v2 files</li>
<li>Added <code>event_base</code> specializations to all reactions and
updated the reference accordingly. This allows to implement reactions
triggered by an event of any type</li>
<li>Added a facility allowing to specially handle events that did not
trigger a reaction. See point 10 of <a href=
"reference.html#process_event">process_event</a>() effects for more
information. Updated tests and docs accordingly</li>
<li><font color="#FF0000">Added a FAQ item explaining how to
trouble-shoot compile-time errors (John Spalding)</font></li>
<li><font color="#FF0000">Added a FAQ item that presents code for a
StopWatch variant that does not use state-local storage and explains the
drawbacks of that approach (Jeff Garland, Rob Steward)</font></li>
<li>Added a FAQ item explaining the pitfalls of dynamically linked
state-machines. Also added associated tests to find out whether and how
FSMs can be put into DLLs</li>
<li><font color="#FF0000">Removed the to-do item "Eliminate the need to
wrap a single templated inner initial state into an
<code>mpl::list<></code>" suggested by Jonathan Turkanis because I
don't currently see how this can be implemented without big ugly
workarounds. A description of the problem can be found here: <a href=
"http://thread.gmane.org/gmane.comp.lib.boost.devel/128741">http://thread.gmane.org/gmane.comp.lib.boost.devel/128741</a></font></li>
<li><font color="#FF0000">Put all remarks about code as comments inside
the code (Pavel Vozenilek, Augustus Saunders)</font></li>
<li>On suitable platforms the library should now be compileable with
exception support turned off (untested due to lacking access to such a
platform)</li>
<li>Added allocator support for broken std libs. Thanks to Joaquín
M López Muñoz for adding his allocator workarounds to
boost/detail</li>
</ul>
<p>19 June, 2005</p>
<ul>
<li>Updated the documentation for the new reaction specification
interface</li>
<li><font color="#FF0000">Invalid calls to reaction functions now always
lead to a failing runtime assert (Jonathan Turkanis). In debug mode the
<code>result</code> type is a class with destructive copy semantics,
enabling the detection of a wider range of reaction function abuses.
Added appropriate tests and updated the documentation</font></li>
<li><font color="#FF0000">Separated performance-related docs from the
rationale into a page of its own (Pavel Vozenilek)</font></li>
<li><font color="#FF0000">Added clone functionality to events so that
stack-allocated events can now be deferred and posted. Updated the
documentation and tests accordingly (Jonathan Turkanis)</font></li>
<li><font color="#FF0000">Clarified the definition of context (John
Spalding)</font></li>
<li><font color="#FF0000">Implemented
<code>in_state_reaction<></code>. Updated the documentation and
tests accordingly (Darryl Green)</font></li>
</ul>
<p>12 May, 2005</p>
<ul>
<li><font color="#FF0000"><b>Breaking change</b>: Changed the library
namespace from <code>fsm</code> to <code>statechart</code> (Alexander
Nasonov, David Abrahams)</font></li>
<li><font color="#FF0000"><b>Breaking change</b>: Changed the library
name from boost::fsm to Boost.Statechart (Alexander Nasonov, David
Abrahams)</font></li>
<li><font color="#FF0000"><b>Breaking change</b>: Reactions are now
specified with a <code>reactions</code> member typedef in a state class
declaration instead of a template parameter (Alexander Nasonov), not yet
documented.</font></li>
</ul>
<p>03 May, 2005</p>
<ul>
<li>Removed the to-do item for the <code>std::type_info</code>
replacement. Thanks to Jody Hagins for taking care of that!</li>
<li>Added to-do items for the issues uncovered during the review</li>
<li>Fixed documentation bugs in the effects descriptions for
<code>state_machine::initiate()</code>,
<code>state_machine::terminate()</code> and
<code>state_machine::process_event()</code></li>
<li><font color="#FF0000">Moved "Getting started" and "Audience" into
index.html (Augustus Saunders)</font></li>
<li><font color="#FF0000">Added Basic topics and Intermediate topics
headings and shortened the "How to read this tutorial" section (Augustus
Saunders)</font></li>
</ul>
<p>21 February, 2005</p>
<ul>
<li>Corrected the review period length mentioned above (absolutely no
changes to code and documentation)</li>
</ul>
<p>20 February, 2005</p>
<ul>
<li><b>Breaking change</b>: Incorporated a part of
<code>exception_translator::operator()</code> code into the
<code>state_machine</code> class template. This simplifies custom
exception translators and makes implementing them less error-prone</li>
<li><b>Breaking change</b>: A request to defer an exception event is no
longer honored and ultimately results in the exception being rethrown.
This change is the result of the rule that during the processing of an
exception no non-user code must be called that could itself propagate an
exception and thus mask the original exception (for event deferral
<code>operator new</code> must be called, which could throw). Exception
event deferral has always been a strange concept anyway</li>
<li>Various code brush-ups</li>
</ul>
<p>09 February, 2005</p>
<ul>
<li>Added exception testing to TransitionTest</li>
<li>Fixed a bug that led to an access violation when orthogonal region 0
of a state was terminated before exiting the state (either through
another termination or a transition)</li>
<li>Various minor changes</li>
</ul>
<p>07 February, 2005</p>
<ul>
<li>Added FifoSchedulerTest, TerminationTest, CustomReactionTest,
StateIterationTest, TypeInfoTest, StateCastTest, HistoryTest and tests
for inconsistent uses of history, unsupported types of deep history and
invalid statecharts</li>
<li>Fixed a bug that led to a compile-time error when
<code>state_downcast</code> was instantiated with a reference target</li>
<li>Fixed a bug that led to a null function pointer dereference when
history was cleared before making a transition to history</li>
<li>Updated the "Speed versus scalability tradeoffs" section</li>
<li>Fixed previously failing builds of single-threaded variants of the
PingPong example</li>
<li>Moved the "Incompatible compilers" section to index.html</li>
<li>Added explanation for the BitMachine & Handcrafted examples</li>
<li>Various minor changes</li>
</ul>
<p>25 November, 2004</p>
<ul>
<li>Adapted to the changes in the 1.32.0 distribution (mainly MPL
changes). The library no longer works with 1.31.0</li>
<li>Fixed a bug that led to a failing runtime assert during state machine
destruction</li>
<li>Fixed a bug that led to events deferred in a composite state not
being released when that state was left</li>
<li>Added TransitionTest and DeferralTest</li>
</ul>
<p>19 October, 2004</p>
<ul>
<li><b>Breaking change</b>: Out of the box, a state machine no longer
uses <code>exception_translator<></code> to translate exceptions
propagated into the framework. Instead,
<code>null_exception_translator</code> is now used, which does not catch
or translate any exceptions. Updated docs accordingly</li>
<li>Implemented <a href="tutorial.html#TwoStageExit">two stage exit</a>
and updated docs accordingly</li>
<li>Implemented an experimental feature that allows a transition action
to be a member of the transition source or any of its direct or indirect
contexts, see <a href=
"configuration.html#ApplicationDefinedMacros">BOOST_STATECHART_RELAX_TRANSITION_CONTEXT</a></li>
<li>Various small code and documentation improvements</li>
</ul>
<p>22 May, 2004</p>
<ul>
<li>Integrated the Intel 7.0 workarounds provided by Pavel Vozenilek
(most are std library workarounds)</li>
<li>Added the Intel 7.0 section to the configuration page</li>
<li>Updated copyright notices</li>
</ul>
<p>12 May, 2004</p>
<ul>
<li>Fixed a bug that could have led to an <code>exception_thrown</code>
event being sent to a state that is <b>not</b> the outermost unstable
state in an unstable state machine (as documented in the reference).
Instead, the event was sent to the state where the entry action of a
direct inner state threw an exception, which is only correct for state
machines without orthogonal regions. Also updated the <a href=
"tutorial.html#ExceptionHandling">Exception handling</a> section in the
tutorial, which now explains this behavior in detail</li>
<li>Fixed bug that, under extremely rare circumstances, would have
prevented the correct handling of out of memory situations</li>
<li>Fixed an inconsistency in the state entry sequence when a state in an
orthogonal region is the target of a transition originating outside its
direct outer state. Now the states are always entered according to the
number of their orthogonal region, i.e. orthogonal region 0 first, then
orthogonal region 1 and so on. Since the documentation did not define the
sequence (it does now) users should not notice any difference</li>
<li>Changed the implementation of <code>state_machine::terminate()</code>
so that orthogonal regions are now exited strictly from highest to lowest
number instead of arbitrarily as before. Updated docs accordingly</li>
</ul>
<p>22 April, 2004</p>
<ul>
<li>Removed the previously added BCC 5.6.4 fixes (the BCC port was
postponed due to lack of knowledge how to work around certain bugs)</li>
<li>Replaced all uses of <code>BOOST_STATIC_CONSTANT</code> with their
mpl counterparts (<code>bool_</code>, <code>integral_c</code>). As a
result, ports to buggy compilers should become easier</li>
<li>Clarified some bits in the tutorial and added StopWatch2.cpp, which
details an alternative way of retrieving state machine state</li>
</ul>
<p>10 April, 2004</p>
<ul>
<li>Added two BCC 5.6.4 fixes contributed by Pavel Vozenilek;
Boost.Statechart does not yet work on BCC though</li>
<li>Implemented a few of the documentation and code improvements
suggested by Pavel Vozenilek, including the new "UML to Boost.Statechart
mapping summary" document</li>
</ul>
<p>26 March, 2004</p>
<ul>
<li>Fixed a small Intel 8.0 bug in the BitMachine example</li>
</ul>
<p>25 March, 2004</p>
<ul>
<li>Now everything compiles warning-free on Intel 8.0</li>
</ul>
<p>21 March, 2004</p>
<ul>
<li><b>Breaking change</b>: <code>fifo_scheduler<></code> and
<code>fifo_worker<></code> now always work non-blocking by
default</li>
<li>Added gcc makefiles, contributed by Mitsuo Fukasawa</li>
<li>Added a fixed version of atomic_count_gcc.hpp to fsm.zip, see
<a href="http://lists.boost.org/MailArchives/boost/msg57537.php">http://lists.boost.org/MailArchives/boost/msg57537.php</a>
for more information</li>
</ul>
<p>16 March, 2004</p>
<ul>
<li><b>Breaking change</b>: Added the <code>FifoWorker</code> template
parameter to <code>fifo_scheduler<></code> and updated
documentation and examples accordingly</li>
</ul>
<p>13 March, 2004</p>
<ul>
<li><b>Breaking change</b>: Renamed <code>worker<></code> to
<code>fifo_scheduler<></code> and updated documentation and
examples accordingly</li>
<li>Changed the <code>fifo_scheduler<></code> implementation so
that a custom worker implementation needs to duplicate less code</li>
<li>Various other small code and doc changes</li>
</ul>
<p>03 March, 2004</p>
<ul>
<li><b>Breaking change</b>: Redesigned the <code>worker<></code>
and <code>asynchronous_state_machine<></code> class templates and
updated documentation accordingly. Event processors can now be added and
removed while a worker is running. Moreover, the new design allows for
custom workers with non-FIFO queueing schemes</li>
<li>The StopWatch example now uses <code>std::time()</code> instead of
<code>std::clock()</code></li>
</ul>
<p>09 February, 2004</p>
<ul>
<li>Integrated the standard conformance fixes contributed by Peter
Petrov. The library now also works on GCC 3.2 and should be much easier
to port to other highly conforming compilers</li>
<li>Added the state type information facility to
<code>simple_state</code></li>
<li>Added the function templates
<code>simple_state::clear_shallow_history()</code> and
<code>simple_state::clear_deep_history()</code></li>
</ul>
<p>11 January, 2004</p>
<ul>
<li>Finished reference documentation</li>
<li>Updated Copyright notices</li>
</ul>
<p>12 December, 2003</p>
<ul>
<li><b>Thanks to Mitsuo Fukasawa the tutorial is now also available in
Japanese!!!</b></li>
<li>Added a state type information facility</li>
<li>Added reference (unfinished) and configuration documentation and
updated other documents</li>
<li>Various code brush-ups (no breaking changes)</li>
</ul>
<p>12 October, 2003</p>
<ul>
<li><b>Breaking change</b>: Removed <code>rtti_policy<></code> from
the interface. By default, the library now uses its own (often faster)
RTTI implementation. Users can demand the use of native C++ RTTI by
defining <code>BOOST_STATECHART_USE_NATIVE_RTTI</code>. This change only
affects users who customized <code>state_machine<></code>,
<code>asynchronous_state_machine<></code> or
<code>worker<></code></li>
<li><b>Breaking change</b>: Reordered template arguments of
<code>state_machine<></code> and
<code>asynchronous_state_machine<></code>. This change only affects
users who customized <code>state_machine<></code> or
<code>asynchronous_state_machine<></code></li>
<li>Added shallow/deep history support and updated documentation
accordingly</li>
<li>Added various compile-time sanity checks</li>
<li>Added 1 FAQ (asked by Mitsuo Fukasawa)</li>
</ul>
<p>16 August, 2003</p>
<ul>
<li>Added <code>asynchronous_state_machine<></code> and
<code>worker<></code> and updated documentation accordingly</li>
<li>Various minor bug fixes and code improvements (no breaking interface
changes)</li>
<li>Added Keyboard and PingPong examples</li>
<li>Added .pdf documentation</li>
</ul>
<p>08 June, 2003</p>
<ul>
<li>Added 3 FAQs (asked by Bohdan) & 1 definition</li>
<li>Removed the superfluous public derivation specifiers in the tutorial
and the examples as suggested by Aleksey Gurtovoy</li>
<li>Various code improvements (no interface changes)</li>
<li>Various html improvements</li>
</ul>
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<p>Revised 04 April, 2010</p>
<p><i>Copyright © 2003-2010 <a href="contact.html">Andreas Huber
Dönni</a></i></p>
<p><i>Distributed under the Boost Software License, Version 1.0. (See
accompanying file <a href="../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or
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