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Event-driven programming
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<h2 id="event-loop">Event loop</h2> <p class="note">Main article: <a href="/facts/Event_loop/NNcN8Auy">Event loop</a></p><p>Because the <a href="/facts/Main_loop/NNcN8Auy">event loop</a> of retrieving/dispatching of events are common amongst applications, many programming frameworks take care of their implementation and expect the user to provide only the code for the event handlers. </p><p><a href="/facts/IBM_RPG/yNSN1Ga1">RPG</a>, an early programming language from <a href="/facts/IBM/QszA7nwd">IBM</a>, whose 1960s design concept was similar to event-driven programming discussed above, provided a built-in main <a href="/facts/I/O/WQTE8Jas">I/O</a> loop (known as the "program cycle") where the calculations responded in accordance to 'indicators' (<a href="/facts/Flag_(computing)/fWgTjqvX">flags</a>) that were set earlier in the cycle. </p> <h3>Event handlers</h3> <p>The actual logic is contained in event-handler routines. These routines handle the events to which the main program will respond. For example, a single left-button mouse-click on a command button in a <a href="/facts/Graphical_user_interface/wBlQFWDP">GUI</a> program may trigger a routine that will open another window, save data to a <a href="/facts/Database/VYcpkevb">database</a> or exit the application. Many <a href="/facts/Integrated_development_environment/jbEINSQf">IDEs</a> provide the programmer with GUI event templates, allowing the programmer to focus on writing the event code. </p><p>Keeping track of history is normally trivial in a sequential program. Because event handlers execute in response to external events, correctly structuring the handlers to work when called in any order can require special attention and planning in an event-driven program. </p><p>In addition to writing the event handlers, event handlers also need to be bound to events so that the correct function is called when the event takes place. For UI events, many IDEs combine the two steps: double-click on a button, and the editor creates an (empty) event handler associated with the user clicking the button and opens a text window so you can edit the event handler. </p> <h2 id="common-uses">Common uses</h2> <p>Most existing GUI architectures use event-driven programming.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> Windows has an <a href="/facts/Message_loop_in_Microsoft_Windows/G2LJtpgA">event loop</a>. The Java AWT framework processes all UI changes on a single thread, called the <a href="/facts/Event_dispatching_thread/ML9oHBSg">Event dispatching thread</a>. Similarly, all UI updates in the Java framework <a href="/facts/JavaFX/hWrAAmny">JavaFX</a> occur on the JavaFX Application Thread.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> </p><p>Most network servers and frameworks such as Node.js are also event-driven.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> </p> <h2 id="interrupt-and-exception-handling">Interrupt and exception handling</h2> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Autonomous_peripheral_operation/GPktp5d0">Autonomous peripheral operation</a></li> <li><a href="/facts/Dataflow_programming/60IdWpE1">Dataflow programming</a></li> <li><a href="/facts/DOM_events/1KoczpWr">DOM events</a></li> <li><a href="/facts/Event-driven_architecture/THC25H6E">Event-driven architecture</a></li> <li><a href="/facts/Event_stream_processing/0808WCf0">Event stream processing</a> (a similar concept)</li> <li><a href="/facts/Hardware_description_language/g19KvKCu">Hardware description language</a></li> <li><a href="/facts/Interrupt/Mm6C4rpc">Interrupt</a></li> <li><a href="/facts/Inversion_of_control/CYWDbFlM">Inversion of control</a></li> <li><a href="/facts/Message-oriented_middleware/jI3NVb5b">Message-oriented middleware</a></li> <li><a href="/facts/Programming_paradigm/7LwgRpB3">Programming paradigm</a></li> <li><a href="/facts/Publish%E2%80%93subscribe_pattern/d2aH1etM">Publish–subscribe pattern</a></li> <li><a href="/facts/Reactor_pattern/svHjSFHw">Reactor pattern</a></li> <li><a href="/facts/Signal_programming/Roh7dNuN">Signal programming</a> (a similar concept)</li> <li><a href="/facts/Staged_event-driven_architecture/dcjyaHMS">Staged event-driven architecture</a> (SEDA)</li> <li><a href="/facts/Time-triggered_system/jo0gf4LM">Time-triggered system</a> (an alternative architecture for computer systems)</li> <li><a href="/facts/Virtual_synchrony/URHHI2Hw">Virtual synchrony</a>, a distributed execution model for event-driven programming</li></ul> <h2 id="external-links">External links</h2> <ul><li><a href="http://shairosenfeld.com/concurrency.html">Concurrency patterns presentation</a> given at <a href="http://scaleconf.org">scaleconf</a></li> <li><a href="http://eventdrivenpgm.sourceforge.net/">Event-Driven Programming: Introduction, Tutorial, History</a>, tutorial by Stephen Ferg</li> <li><a href="http://www.alan-g.me.uk/l2p/tutevent.htm">Event-Driven Programming</a>, tutorial by Alan Gauld</li> <li><a href="http://www.martinfowler.com/eaaDev/EventCollaboration.html">Event Collaboration</a>, article by Martin Fowler</li> <li><a href="https://web.archive.org/web/20150919021358/https://today.java.net/pub/a/today/2003/10/24/swing.html">Rethinking Swing Threading</a>, article by Jonathan Simon</li> <li><a href="http://www.csse.uwa.edu.au/cnet/eventdriven.html">The event-driven programming style</a> <a href="https://web.archive.org/web/20050220142724/http://www.csse.uwa.edu.au/cnet/eventdriven.html">Archived</a> 2005-02-20 at the <a href="/facts/Wayback_Machine/nmQ3a6JC">Wayback Machine</a>, article by Chris McDonald</li> <li><a href="https://web.archive.org/web/20050207025012/http://www.codeproject.com/cpp/static-callbacks.asp">Event Driven Programming using Template Specialization</a>, article by Christopher Diggins</li> <li>Schiffer, S.; Frohlich, J.H. (1994). "Concepts and architecture of Vista-a multiparadigm programming environment". <i>Proceedings of 1994 IEEE Symposium on Visual Languages</i>. pp. 40–47. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.1109%2FVL.1994.363642">10.1109/VL.1994.363642</a>. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 0-8186-6660-9. <a href="/facts/S2CID_(identifier)/ldJsHa2Y">S2CID</a> <a href="https://api.semanticscholar.org/CorpusID:15927869">15927869</a>.</li> <li><a href="http://docs.eiffel.com/book/method/8-event-driven-programming-and-agents">Event-Driven Programming and Agents</a>, chapter</li> <li><a href="https://archive.today/20121208205239/http://zone.ni.com/devzone/devzone.nsf/webcategories/FCE7EA7ECA51169C862567A9005878EA">LabWindows/CVI Resources</a></li> <li><a href="http://www.codeplex.com/pubsub">Distributed Publish/Subscribe Event System</a>, an open-source example which is in production on MSN.com and Microsoft.com</li> <li><a href="https://techboxweb.com/javasript-event-loop/">Javascript Event loop</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Chandrasekaran, Premanand; Krishnan, Karthik; Ford, Neal; Byars, Brandon; Buijze, Allard (2022). Domain-Driven Design with Java - A Practitioner's Guide. Packt Publishing. ISBN 9781800564763. <a href="9781800564763" target="_blank">9781800564763</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Samek, Miro (April 1, 2013). "Who Moved My State?". Dr. Dobb's. Retrieved 2018-01-28. <a href="http://www.ddj.com/cpp/184401643" target="_blank">http://www.ddj.com/cpp/184401643</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Fedortsova, Irina (June 2012). "Concurrency in JavaFX". JavaFX Documentation Home. Oracle. Retrieved 4 January 2018. The JavaFX scene graph, which represents the graphical user interface of a JavaFX application, is not thread-safe and can only be accessed and modified from the UI thread also known as the JavaFX Application thread. <a href="https://docs.oracle.com/javafx/2/threads/jfxpub-threads.htm" target="_blank">https://docs.oracle.com/javafx/2/threads/jfxpub-threads.htm</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Event-Driven Programming in Node.js. <a href="https://www.digitalocean.com/community/tutorials/nodejs-event-driven-programming/" target="_blank">https://www.digitalocean.com/community/tutorials/nodejs-event-driven-programming/</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> </ol>