Busy Waiting (忙等待)

  • Also known as Spinning
  • CPU is involved to keep check for the state
  • A Process (进程)/Thread repeatedly checks a condition without sleeping or giving up the processor until the condition is satisfied
  • This is in contrast to waiting for a condition using a mechanism such as a Semaphore (信号量) or a Mutex (互斥体), which releases the processor and allows other threads to run while waiting for the condition to be met


  • Simple and efficient synchronization mechanism
  • Shines when condition is expected to be met very quickly. Like Process (进程) waiting for input from the keyboard


  • Can waste CPU resources if the condition is not met quickly, especially on Multi-core Chip, generally considered to be a bad practice for most applications