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copied!<blockquote> <p>In getInstance function (un-commented), static object's reference is returned. Does it requires thread-safe mechanism?</p> </blockquote> <p>As long as you don't access it outside the lifetime of the <code>main</code> function, or modify it when other threads might have unsynchronised access, then it's safe to access from any thread.</p> <p>If you do access before <code>main</code> starts or after it ends (e.g. from the constructor or destructor of another static object), then there is a danger that it won't have been initialised, or will already have been destroyed, at that point. That is the motivation for "lazy initialisation" such as your second version.</p> <blockquote> <p>In second getInstance (commented), we create the object if singleObject is null. So, it requires a locking mechanism and needs to be synchronized, right?</p> </blockquote> <p>Yes, that requires a locking mechanism. For compilers that support the C++11 (or similar) threading model, a simpler way to get lazy initialisation like this is to use a function-static variable, which will be initialised in a thread-safe way the first time it comes into scope:</p> <pre><code>S& getInstance () { static S singleObject; return singleObject; } </code></pre> <p>This will also avoid the memory leak of your version, but introduces a danger that it might be destroyed before other static objects; therefore, it's not safe to access from a static object's destructor.</p> <p>In general, static objects in C++ are a minefield of such deathtraps (whether or not you try to wrap them up in some kind of singleton anti-pattern) and are best avoided.</p>

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