# uSCXML ReadMe [![Build Status](https://travis-ci.org/sradomski/uscxml.png?branch=master)](https://travis-ci.org/sradomski/uscxml) **Table of Contents** - [General](#general) - [Test Reports](#test-reports) - [License](#license) - [Download](#download) - [Usage](#usage) - [Advanced Topics](#advanced-topics) - [Embedding uSCXML](#embedding-uscxml) - [Extending uSCXML](#extending-uscxml) - [Miscellaneous](#miscellaneous) - [Acknowledgments](#acknowledgments) ## General uSCXML is a SCXML interpreter written in C/C++. It is [standards compliant](#test-reports) and [easily extended](#extending-uscxml) even in C# and Java. It runs on Linux, Windows, Raspberry Pi and Mac OSX, each 32- as well as 64Bits as well as iOS. * Datamodels * Full [ECMAScript datamodel](https://github.com/tklab-tud/uscxml/tree/master/src/uscxml/plugins/datamodel/ecmascript) using Google's v8 (and JavaScriptCore on MacOSX and iOS) * Simplified support for [Web Storage](http://www.w3.org/TR/2013/REC-webstorage-20130730/) in document.localStorage * Support for binary data via [TypedArrays](https://www.khronos.org/registry/typedarray/specs/latest/) (will not throw exceptions yet) * Full [NULL datamodel](https://github.com/tklab-tud/uscxml/tree/master/src/uscxml/plugins/datamodel/null) with required In predicate * [Prolog datamodel](https://github.com/tklab-tud/uscxml/tree/master/src/uscxml/plugins/datamodel/prolog/swi) using SWI prolog * Experimental [Promela datamodel](https://github.com/tklab-tud/uscxml/tree/master/src/uscxml/plugins/datamodel/promela) for use with the [SPIN](http://spinroot.com/spin/whatispin.html) model-checker * Early support for a [Lua datamodel](https://github.com/tklab-tud/uscxml/tree/master/src/uscxml/plugins/datamodel/lua) * Rudimentary support for [XPath datamodel](https://github.com/tklab-tud/uscxml/tree/master/src/uscxml/plugins/datamodel/xpath) * Invokers * scxml: Invoke a nested scxml interpreter * dirmon: Watches a directory for changes to files * scenegraph: Simplified 3D scenegraphs with custom markup * heartbeat: Periodically sends events * umundo: Subscribe to channels and publish events * [Many others](https://github.com/tklab-tud/uscxml/tree/master/src/uscxml/plugins/invoker) * DOM * DOM Core Level 2 + XPath extensions available for ecmascript datamodel * Namespace aware to embed custom markup for special invokers * Communication * Features the standard basichttp io-processor * Features the required SCXML io-processor * No DOM io-processor * Early support for [WebSockets](http://datatracker.ietf.org/doc/rfc6455/) * Can actually respond to HTTP requests with data via <response> * Language Bindings * PHP module for apache and cli interpreter * Java bindings ### Test Reports * We continuously run the [W3C IRP tests](http://www.w3.org/Voice/2013/scxml-irp/) for SCXML. * Have a look at the [result](http://uscxml.tk.informatik.tu-darmstadt.de/cdash/index.php?project=uscxml) for the various platforms. * The manual and XPath specific tests are [excluded](https://github.com/tklab-tud/uscxml/blob/master/contrib/ctest/CTestCustom.ctest.in). uSCXML still fails the following ecmascript tests:
Test#StatusDescriptionComment
326 / 329 Fail for v8 "test that _ioprocessors stays bound till the session ends" / "test that none of the system variables can be modified" The v8 implementation will return a new _ioprocessor object for each access.
579 Failed "Before the parent state has been visited for the first time, if a transition is executed that takes the history state as its target, the SCXML processor MUST execute any executable content in the transition after the parent state's onentry content and any content in a possible initial transition." Functionality was recently added and is not yet supported.
### License uSCXML itself is distributed under the Simplified BSD license as in, do not sue us and do not misrepresent authorship. Please have a look at the licenses of the [libraries we depend upon](https://github.com/tklab-tud/uscxml/blob/master/docs/BUILDING.md#build-dependencies) as well. ### Download We do not yet feature installers. Please download the source and have a look at the [build instructions](https://github.com/tklab-tud/uscxml/blob/master/docs/BUILDING.md). ## Usage In order to use the interpreter, you need to #include "uscxml/Interpreter.h" and instantiate objects of uscxml::Interpreter. ### Non-Blocking Interpretation with SCXML from URL Interpreter scxml = Interpreter::fromURL("http://www.example.com/fancy.scxml"); scxml.start(); // non-blocking in own thread There are some cases, i.e. with graphical invokers, where the main thread is required in order to react to UI events. You will have to deligate control flow from the main thread into the interpreter every now and then: interpreter.runOnMainThread(25); This will perform a single iteration on the invoked components with a maximum of 25 frames per seconds or return immediately. You will have to call this method every now and then if you are using e.g. the scenegraph invoker. ### Blocking Interpretation with inline SCXML Interpreter scxml = Interpreter::fromXML(""); scxml.interpret(); // blocking When using blocking interpretation, it is assumed that it is running on the main thread and it will call runOnMainThread between stable configurations. ### Interleaved Interpretation with inline SCXML Interpreter scxml = Interpreter::fromXML(""); InterpreterState state; do { state = interpreter.step(true); // boolean argument causes blocking or not } while(state > 0) Using step, you can run a single macrostep of the interpreter and interleave interpretation with the rest of your code. ### Callbacks for an Interpreter You can register an InterpreterMonitor prior to start in order to receive control-flow upon various events in the Interpreter. class StatusMonitor : public uscxml::InterpreterMonitor { void onStableConfiguration(...) void beforeCompletion(...) void afterCompletion(...) void beforeMicroStep(...) void beforeTakingTransitions(...) void beforeEnteringStates(...) void afterEnteringStates(...) void beforeExitingStates(...) void afterExitingStates(...) }; StatusMonitor statMon; Interpreter scxml = Interpreter::fromXML(""); scxml.addMonitor(&statMon); scxml.start(); This will cause the interpreter to invoke the callbacks from the monitor whenever the corresponding internal phase is reached. ## Advanced Topics ### Embedding uSCXML There are bindings for [Java](https://github.com/tklab-tud/uscxml/tree/master/embedding/java) and [C#](https://github.com/tklab-tud/uscxml/tree/master/embedding/csharp) with some examples in the embedding directory. The bindings consist of two parts each 1. The C++ uscxml interpreter compiled as a loadable module for the target language and 2. A target language specific module (uscxml.jar / uscxmlCSharp.dll) with the wrapper classes. The first one is loaded by the target language (System.loadLibrary / SetDLLDirectory) while the second is to be included in your actual project. Have a look at the examples in embedding and adapt the paths to reflect your setup. See the [build instructions](https://github.com/tklab-tud/uscxml/blob/master/docs/BUILDING.md) for details on how to build these. ### Extending uSCXML The uSCXML interpreter can be extended by introducing new 1. DataModels as embedded scripting languages (e.g. ECMAScript, Prolog and XPath) 2. Invokers to represent external components that deliver and accept events (e.g. iCal, SceneGraph, DirectoryMonitor) 3. I/O-Processors to provide communication with external systems (e.g. BasicHTTP, SCXML). 4. Elements for Executable Content (e.g. <respond>, <fetch>, <postpone>). The basic approach to extend the interpreter is the same in all cases: 1. Write a class inheriting the abstract base class (e.g. DataModelImpl, InvokerImpl, IOProcessorImpl, ExecutableContentImpl). 2. Instantiate your class and register it as a prototype at the Factory via one of its static register* methods. 1. You can register at the global Factory Singleton via Factory::register*(prototypeInstance) 2. Or provide a new Factory instance to selected interpreters as an in-between. 3. Write an interpreter using your new functionality. Note: Within the language bindings, you will have to inherit the base classes without the Impl suffix. Have a look at the examples in embedding for examples. #### Ad-hoc Extensions Sometimes, it is more suited to provide an interpreter with an already instantiated extension (e.g. an IOProcessor with an existing connection). In this case, it is somewhat awkward to register a prototype and have all initialization in its create(Interpreter interpreter) method. While you can still dispatch over the interpreter instance and access information from some global Interpreter->Data map, there is a more straight-forward approach, e.g. in Java: Interpreter interpreter = Intepreter.fromURI(uri); AdhocIOProcessor ioProc = new AdhocIOProcessor(Whatever youLike); ioProc.setParameter1(something); interpreter.addIOProcessor(ioProc); This will cause the interpreter to use the given instance for all send requests targeting one of the types returned by ioProc.getNames() and not instantiate an instance via the factory. The instance can deliver events into the interpreter via returnEvent(Event e, boolean toExternalQueue). The same approach can be used for invokers: Interpreter interpreter = Intepreter.fromURI(uri); TestAdhocInvoker invoker1 = new TestAdhocInvoker(Whatever youLike); invoker1.setParameter1(something); interpreter.setInvoker("invokeId", invoker1); This will cause the interpreter to use the given instance for a given invokeId and not instantiate via the factory. Similarly, datamodels can be registered via interpreter.setDataModel(DataModel dm). Note: Providing ad-hoc extensions is only supported before the interpreter is started. If you change instances with a running interpreter, the behavior is undefined. # Miscellaneous ## Ad-hoc extensions are deallocated by their interpreter If you register any ad-hoc extension with an interpreter, be it in C++ or a language binding, this extension's instance belongs to the interpreter. This means i.e. that (i) the interpreter's destructor will deallocate the extension instance, (ii) you cannot reuse it for another interpreter and (iii) you may not call its destructor. For the language bindings, this means furthermore that you have to call swigReleaseOwnership() on the extension instance to prevent the target language's memory managment form calling the instances C++ native destructor. The destructor can only be called once and the interpreter's destructor will do it. If allocating additional extension instances per interpreter is expensive, consider using aggregation as a "has a" relationship with the expensive part. ## Not all exceptions are propagated into the target languages Only exceptions raised during the following methods are propagated into the target language: Interpreter::fromXML Interpreter::fromURI Interpreter::step Interpreter::interpret If you dig around in the exposed APIs, there are other methods that may raise exceptions (e.g. interpreter.getDataModel().eval()). Be careful when calling these. Ultimately, all exceptions ought to be propagated into the target language to be handled accordingly. We are currently evaluating different approaches to do so. ## Where is the Android Port? When I originally tried to compile the required libraries for uSCXML on Android (libevent, curl, libxml2), it would not work out of the box and I postponed. If there is a demand for an Android port, I can have another look. uSCXML itself is written in a subset of C++99 and ought to compile just fine. ## UTF8 support Currently, we use std::string to represent all strings. This is not a problem as e.g. the ECMAScript datamodels will just interpret these as character arrays and handle Unicode respectively. Though it is a problem if you like to use non-ASCII characters e.g. in the id attribute of states. ## Performance The performance of uSCXML depends on many things like the employed datamodel and the platform it runs on. Using a MacBook Pro with an Intel i7 @2.4Ghz and the ECMAScript datamodel (test/uscxml/test-performance.scxml), we achieve about 20.000 events/sec. On a Raspberry Pi, however, only 350 events/sec are achieved. If performance ought to be increased further, the first place to look would be most likely the employed DOM implementation, which uses the rather expensive dynamic_cast somewhat too liberally. For a real performance boost, the explicit SCXML DOM representation at runtime might be dropped in favor of some simple structs representing the states and transitions. This has been no priority for us so far as even 350 events/sec is plenty for our use-cases. ## What about some code documentation? Up until recently, the APIs of uSCXML were still subject to rather substantial changes. If there is one thing worse than no documentation, it is wrong documentation, so we did not document the source. Another stumbling block was the fact that documentation would not show up in the language bindings. Both issues are resolved by now: The APIs have not changed substantially in about 8 month and the new version of SWIG will allow doxygen comments to be show up in various target languages; so we will document somewhen soon. # Acknowledgments This SCXML interpreter is developed at the [Telekooperation Group](http://www.tk.informatik.tu-darmstadt.de) of the Technical University of Darmstadt as part of the [SmartVortex](http://smartvortex.eu) project funded by the [7th European framework program](http://ec.europa.eu/research/fp7/index_en.cfm).