Taking this analogy a little further, if one needle had to sew on a button (blocking I/O), the other needle could continue doing other useful work even if the other needle took 4 hours to sew on a single button.
Taking this analogy a little further, if one needle had to sew on a button (blocking I/O), the other needle could continue doing other useful work even if the other needle took 4 hours to sew on a single button.
把这个比方再扩展一下，如果一颗针要缝一个钮扣（I/O阻塞），即使这项工作要耗去4小时，另外一颗针也能同时做别的有用的工作。