我们倾向于把主线程叫做在前台运行（running in the foreground），把额外的线程叫做在后台运行（running in the background）。他们其实在状态上是平等的，交替在使用设备CPU上执行，但是从用户的观点来看，主线程是在前台因为它与UI交互。
基于24个网页-相关网页
The server is running in the background.
服务端在后台运行。
youdao
Signals can also be caught, when a script is running in the background.
在后台运行脚本时，仍然可以捕获信号。
Websites like this have Web 2.0 concepts like Mashups, forums and blogs running in the background.
这类网站都在后台运行 Web 2.0 概念，比如 Mashups、论坛和 blog。
The multiplatform project is tentatively titled Running in the Background: The True Story of John McAfee.
FORBES: John McAfee Sells Rights To Life Story In Latest Display Of Narcissism
This means that synergys has been launched and is running in the background.
ENGADGET: How-To: Share your keyboard and mouse in realtime with Synergy
This means that synergyc has been launched and is running in the background.
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