本文介绍了轮询（Polling）的概念及其在并发程序中的应用。轮询是一种不断检查资源是否可用的方法，通常通过非阻塞调用实现。然而，轮询会浪费处理器时间，更好的方法是设置事件并等待资源可用时触发。文章还讨论了如何选择阻塞或立即返回的选项以适应不同的编程需求。
Polling (see also
spin-waiting) is testing for the availability of a
resource by repeatedly requesting the resource via a
non-blocking call, until the resource becomes available. Polling is wasteful of processor time that could be used by another
thread of control in a
concurrent program. Unless the resource is likely to become available almost instantaneously, a better approach is to have the resource set an
event when it becomes available, and block awaiting the event.
The is-resource-available function for many common resources has an option either to block or to return immediately. The first option is used in simple programs that are typically single threads of control. The second option facilitates polling, but it also supports blocking on a binary semaphore, then accessing the resource multiple times until the resource is exhausted.
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