Busy spin is a technique which concurrent programmers employ to make a thread wait on certain condition. Unlike traditional methods e.g. wait(), sleep() or yield() which all involves relinquishing CPU control, this method does not relinquish CPU, instead it just runs empty loop. Why would someone do that? to preserve CPU caches. In multi core system, its possible for a paused thread to resume on different core, which means rebuilding cache again. To avoid cost of rebuilding cache, programmer prefer to wait for much smaller time doing busy spin.
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