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copied!<h2>First of all</h2> <p>The usual disclaimer: concurrent programming, in any language, using any abstraction level, is <strong>hard</strong> and <strong>complicated</strong> and has many risks. Take into consideration:</p> <ul> <li>Concurrent programming complicates any application by magnitude</li> <li>Unit-testing critical sections is hard, and sometimes impossible</li> <li>Reproducing bugs originating in concurrent code is <strong>very hard</strong> and much dependent on architecture, OS flavor, version, etc...</li> </ul> <h2>Java Concurrent APIs</h2> <p>Java has gone a long way in making concurrent programming as easy as possible for developers. For most cases, you will see that <code>java.util.concurrent</code> has most of the abstractions you will need:</p> <ul> <li><strong><code>Runnable</code></strong> interface and <strong><code>Thread</code></strong> object you can extend. Just throw in your code and you have a thread ready to run</li> <li>A nice set of <strong><code>Executors</code></strong>: constant pool, dynamic pool, scheduled, or whatever. Just throw a <code>Runnable</code> at it and it does the rest.</li> <li><strong><code>Semaphore</code>s</strong> and <strong>locks</strong> of all sorts relieve you of needing to implement common locking techniques.</li> <li>A built-in <code>wait()</code> and <code>notify()</code> API for all objects.</li> </ul> <h2>Uses</h2> <p>The only thing left for you, as the software engineer, is to ensure you are writing <strong>correct</strong> code. Meaning you should be aware of the dangerous situations you might be exposing yourself to:</p> <ul> <li><strong>Deadlock</strong> - a situation in which two or more threads are waiting on unordered resources, rendering an infinite waiting loop.</li> <li><strong>Livelock</strong> - two or more threads which politely try to give way to the other on a shared resource but end up not taking it (consider two people in a corridor walking up to each other and constantly moving together from side to side)</li> <li><strong>Starvation</strong> - a single thread taking up most or all of a single shared resource, thus depriving other threads from access to it.</li> </ul> <h1>Main Point (or, when to use)</h1> <p><strong>Use threads only when concurrency will directly improve your applications behavior.</strong> </p> <p>If you are waiting on an IO/network/hardware-bound resource, <strong>DO</strong> spawn a thread on it so you can continue doing other stuff.</p> <p>If you are just trying to elegantly split CPU-bound computations, <strong>DO NOT</strong> use threads. You just might end up worsening your performance.</p> <p>If you do use threads, make sure you have thoroughly contemplated the risks, and triple-checked you did not miss any exceptional situations.</p> <h2>Useful (Online) Resources</h2> <p>Fastest way to get into things is to do the <a href="http://java.sun.com/docs/books/tutorial/essential/concurrency/" rel="nofollow noreferrer">Sun concurrency tutorial</a>. Other than that, get a good book.</p> <p>Good luck :)</p>

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