《Operating System Concepts》学习第 18 天，p177-p178 总结，总计 2 页。
一、技术总结
1.implicit thread
A programming model that transfers the creation and management of threading from application developers to compilers and run-time libraries.
2.thread pool
Unlimited threads could exhaust system resources, such as CPU time or memory. One solution to this problem is to use a thread pool.
thread pool 是一种解决方案(solution)：A thread pool is a solution where a number of threads are created at process startup and placed in a pool, waiting for work.
二、英语总结(生词：3)
1.trivial
(1)trivial: ("three") + via("road")
adj. Trivial is from trivialis("a place three roads meet"), over time, trivial means "havingf little value and importance(微不足道的)"。
(2)示例
Designing such applications is not a trivial undertaking: programmers must address not only the challenges outlined in Section 4.2 but additional difficulties as well(《Operating System Concepts》第 177 页)。
2.discard
(1)discard: dis("away") + card
vt. Historically, "discard" meant "remove a card from one's hand" in a card game. Over time, discard means "to throw away sth(抛弃，丢弃)", "to get rid of sth(摆脱)" when sth is no longer useful or needed(这是 discard 的使用语境)。
(2)示例
he first issue concerns the amount of time required to create the thread, together with the fact that the thread will be discarded once it has completed its work(《Operating System Concepts》第 177 页)。
在这个例子中， "discard the thread" 意思是 "terminate the thread, destroy the thread"。
3.resume
(1)resume: re-("again") + sumere("to take")
vi/vt. Resume literally means "to take again", over time, it envolve to mean "continue doing sth after a pause"。
(2)示例
When a server receives a request, rather than creating a thread, it instead submits the request to the thread pool and resumes waiting for additional requests(《Operating System Concepts》第 177 页)。
在上面这个句子中，resume 也是"continue doing sth after a pause"的意思。当然，英语中有时候为了简洁，往往会省略一些内容，为了更好的理解，这里句子可以改成：
When a server receives a request, rather than creating a thread, it instead stop waiting to submit the request to the thread pool. After submitting the request, server resumes waiting for additional requests.
总之，要理解resume的在具体上下文中的含义，就要把握住"continue doing sth after a pause"的思想。如果句子不全不好理解，就先把句子补全去理解。
关于英语的注解同步更新汇总到 https://github.com/codists/English-In-CS-Books 仓库。
三、其它
今天没有什么想说的。
四、参考资料
1. 编程
(1) Abraham Silberschatz，Peter Baer Galvin，Greg Gagne《Operating System Concepts》：https://book.douban.com/subject/30272539/
2. 英语
(1) Etymology Dictionary：https://www.etymonline.com
(2) Cambridge Dictionary：https://dictionary.cambridge.org
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