December 2013
Intermediate to advanced
496 pages
8h 57m
Chinese
Content preview from LINUX系統程式設計 第二版
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進階的行程管理
|
203
車系統
（
anti-lock braking system
，常簡寫成
ABS
）。在此系統中，當煞車被踩下時，電
腦會調控煞車壓力，通常是每秒施加和釋放最大煞車壓力許多次。這可以防止因為車輪
「被鎖死」而降低煞車的性能，或甚至讓汽車進入無法控制的滑行狀態。在這樣的系統
中，操作期限就是指：系統回應車輪遭鎖死之情況的速度有多快，以及系統施加煞車壓
力的速度有多快。
多數現代的作業系統，包括 Linux，都會對即時功能提供某種程度的支援。
硬性與軟性即時系統
即時系統分成兩類：硬性及軟性。
硬性即時系統
（
hard real-time system
）需要嚴格遵守
操作期限。超過期限便構成失敗，而且是一個重大的錯誤。另一方面，
軟性即時系統
（
soft real-time system
）並不認為逾越期限是一個重要的失敗。
硬性即時應用程式很容易區分，例如：防鎖死煞車系統、軍事武器系統、醫療裝置以及
信號的處理。軟性即時應用程式往往不容易區分。其中一個比較明顯的例子是視訊處理
應用程式：如果錯過了期限，用戶會注意到品質變差，然而只是漏掉幾幀畫面是可以被
忍受的。
許多其他的應用程式具有時間限制，如果沒有得到滿足，將不利於用戶的使用經驗，例
如：多媒體應用程式、遊戲以及網路程式。然而，文字編輯器呢？如果程式無法快速回
應按鍵，這是一個糟糕的使用經驗，會讓用戶感到不悅或挫敗。這是軟性即時應用程式
嗎？沒錯，開發者在撰寫應用程式當時，已經意識到他們需要及時回應按鍵。但這可以
視為操作期限嗎？儘管軟性即時應用程式的定義不一而足，但是相當明確。 ...
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.