justwillim/sml

[Boost].SML: C++14 State Machine Library

---

[Boost].SML (formerly called [Boost].MSM-lite)

Your scalable C++14 header State Machine Library with no dependencies (Try it online!)

Let's release a TCP connection!

// $CXX -std=c++14 -O2 -fno-exceptions -Wall -Wextra -Werror -pedantic -pedantic-errors tcp_release.cpp
// cl /std:c++14 /Ox /W3 tcp_release.cpp (***)

#include <cassert>
#include <boost/sml.hpp>

namespace sml = boost::sml;

//dependencies
struct sender {
  template<class T>
  void send(const T&) {}
};

// events
struct ack { bool valid = true; };
struct fin { bool valid = true;};
struct release {};
struct timeout {};

// guards
const auto is_valid = [](const auto& event) { return event.valid; };

// actions
const auto send_fin = [](sender& s) { s.send(fin{}); };
const auto send_ack = [](const auto& event, sender& s) { s.send(event); };

struct tcp_release {
  auto operator()() const {
    using namespace sml;
    /**
     * Initial state: *initial_state
     * Transition DSL: src_state + event [ guard ] / action = dst_state
     */
    return make_transition_table(
      *"established"_s + event<release> / send_fin          = "fin wait 1"_s,
       "fin wait 1"_s  + event<ack> [ is_valid ]            = "fin wait 2"_s,
       "fin wait 2"_s  + event<fin> [ is_valid ] / send_ack = "timed wait"_s,
       "timed wait"_s  + event<timeout> / send_ack          = X
    );
  }
};

int main() {
  using namespace sml;

  sender s;
  sm<tcp_release> sm{s}; // pass dependencies via ctor...
  assert(sm.is("established"_s));

  sm.process_event(release{}); // complexity O(1) -> jump table
  assert(sm.is("fin wait 1"_s));

  sm.process_event(ack{});
  assert(sm.is("fin wait 2"_s));

  sm.process_event(fin{});
  assert(sm.is("timed wait"_s));

  sm.process_event(timeout{});
  assert(sm.is(X));  // released
}

(***) MSVC-2015 (Example)

• use state<class state_name> instead of "state_name"_s
• expliclty state a lambda's result type auto action = [] -> void {}

Benchmark

<td rowspan="4">
  <a href="http://boost-experimental.github.io/sml/benchmarks/index.html#benchmarks">More Benchmarks</a>
</td>

	Clang-3.8	GCC-6	MSVC-2015
Compilation Time	0.102s	0.118s	0.296s
Binary size (stripped)	6.2kb	6.2kb	105kb
ASM x86-64	process_event: movb $1, (%r8) // current state = 1 movl $1, %eax // handled ret main: leaq 14(%rsp), %r8 leaq 15(%rsp), %rdi movb $0, 14(%rsp) movq %r8, %rcx movq %r8, %rdx movq %r8, %rsi call *process_event // jump table ...

---

Documentation

• Introduction
  • UML State Machine
  • Do I need a State Machine?
  • Real Life examples?
  • Why [Boost].SML?
  • Problems with Boost.MSM - eUML
  • [Boost].SML design goals
  • What 'lite' implies?
  • Supported UML features
  • Additional features
  • Related materials
  • Acknowledgements
• Overview
  • Quick Start
  • Dependencies
  • Supported/Tested compilers
  • Configuration
  • Exception Safety
  • Thread Safety
  • Design
  • Error messages
• Features/Benchmarks
  • Features
  • Benchmarks
• Tutorial
  • 0. Read Boost.MSM - eUML documentation
  • 1. Create events and states
  • 2. Create guards and actions
  • 3. Create a transition table
  • 4. Set initial states
  • 5. Create a state machine
  • 6. Process events
  • 8. Handle errors
  • 9. Test it
  • 10. Debug it
• UML vs SML
  • Unified Modeling Language™ (UML®) Version 2.5
  • Initial Pseudostate
  • Terminate Pseudostate
  • External transition
  • Anonymous transition
  • Internal transition
  • Entry/Exit action
  • Self transition
  • Sub/Composite
  • Orthogonal regions
  • Deep History
  • Shallow History
  • Event defering
• User Guide
  • transitional [concept]
  • configurable [concept]
  • callable [concept]
  • dispatchable [concept]
  • state [core]
  • event [core]
  • make_transition_table [state machine]
  • sm [state machine]
  • policies [state machine]
  • testing::sm [testing]
  • make_dispatch_table [utility]
• Examples
  • Hello World
  • Events
  • States
  • Actions Guards
  • Transitions
  • Defer/Process
  • Orthogonal Regions
  • Composite
  • History
  • Error handling
  • Logging
  • Testing
  • Runtime Dispatcher
  • eUML Emulation
  • Dependencies
  • Dependency Injection
  • SDL2 Integration
  • Plant UML Integration
• FAQ
• CHANGELOG
  • [1.1.0] - 2016-2017-XX-XX
  • [1.0.1] - 2016-2017-05-06
  • [1.0.0] - 2016-2017-01-28
• TODO

---

Disclaimer Boost.SML is not an official Boost library.