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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行程管理
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則會產生一個包含三個行程的行程群組。於是，shell 可以同時通知這三個行程。因為用
戶在控制台（console）之上鍵入這道命令的時候，並未加上結尾的「&」符號，所以我
們也可以說此行程群組位於前景。圖 5-1 可以看到期程、行程群組、行程與控制終端機
之間的關係。
圖 5-1 期程、行程群組、行程與控制終端機之間的關係
Linux 提供了若干介面，可用於設定與取得「與所指定之行程有關的」期程及行程群
組。這些介面主要是供 shell 所使用，不過也可以用在想要擺脫期程與行程群組之事務
的行程，例如監控程式（daemon）。
期程系統呼叫
shell 會在登入的時候建立新的期程。它們完成此事的方式係透過一個特殊的系統呼叫，
以簡化新期程的建立：
#include <unistd.h>
pid_t setsid (void);
在行程尚不是一個行程群組的帶頭者時，叫用
setsid()
將可建立一個新的期程。進行叫
用之行程，將會成為新期程的帶頭者，以及此期程的唯一成員；此期程並未具有控制終
端機。此呼叫還會在此期程中建立一個新的行程群組，並且讓進行叫用之行程成為行程
群組的帶頭者以及此行程群組的唯一成員。新期程與行程群組之識別碼會被設定成進行
叫用之行程的 pid。
期程
行程群組
行程
控制終端機
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