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copied!<p>Firstly, threading is tricky ;-p</p> <p>Yes, despite all the rumours to the contrary, it <strong>is</strong> required to <em>either</em> use <code>lock</code> <em>or</em> <code>volatile</code> (but not both) when accessing a <code>bool</code> from multiple threads.</p> <p>For simple types and access such as an exit flag (<code>bool</code>), then <code>volatile</code> is sufficient - this ensures that threads don't cache the value in their registers (meaning: one of the threads never sees updates).</p> <p>For larger values (where atomicity is an issue), or where you want to synchronize a <em>sequence</em> of operations (a typical example being "if not exists and add" dictionary access), a <code>lock</code> is more versatile. This acts as a memory-barrier, so still gives you the thread safety, but provides other features such as pulse/wait. Note that you shouldn't use a <code>lock</code> on a value-type or a <code>string</code>; nor <code>Type</code> or <code>this</code>; the best option is to have your own locking object as a field (<code>readonly object syncLock = new object();</code>) and lock on this.</p> <p>For an example of how badly it breaks (i.e. looping forever) if you don't synchronize - <a href="https://stackoverflow.com/questions/458173/can-a-c-thread-really-cache-a-value-and-ignore-changes-to-that-value-on-other-th/458193#458193">see here</a>.</p> <p>To span multiple programs, an OS primitive like a <code>Mutex</code> or <code>*ResetEvent</code> may also be useful, but this is overkill for a single exe.</p>

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