Busy waiting

In computer science and software engineering, busy-waiting, busy-looping or spinning is a technique in which a process repeatedly checks to see if a condition is true, such as whether keyboard input or a lock is available. Spinning can also be used to generate an arbitrary time delay, a technique that was necessary on systems that lacked a method of waiting a specific length of time. Processor speeds vary greatly from computer to computer, especially as some processors are designed to dynamically adjust speed based on current workload.^[1] Consequently, spinning as a time-delay technique can produce inconsistent or even unpredictable results on different systems unless code is included to determine the time a processor takes to execute a "do nothing" loop, or the looping code explicitly checks a real-time clock.

In most cases spinning is considered an anti-pattern and should be avoided,^[2] as processor time that could be used to execute a different task is instead wasted on useless activity. Spinning can be a valid strategy in certain circumstances, most notably in the implementation of spinlocks within operating systems designed to run on SMP systems.