December 2013
Intermediate to advanced
496 pages
8h 57m
Chinese
Content preview from LINUX系統程式設計 第二版
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.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.I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.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.
時間
|
415
計時器之所以有用，基於若干理由。例子包括：每秒刷新螢幕 60 次，以及如果 500 毫
秒之後仍然持續下去就取消未決的交易。
簡單的警報信號
alarm()
是最簡單的計時器介面：
#include <unistd.h>
unsigned int alarm (unsigned int seconds);
叫用此函式，我們可以安排，在真實的時間已過去
seconds
秒後，把一個
SIGALRM
信號遞
送給進行調用的行程。如果有一個之前所安排的信號懸而未決，此呼叫會取消該警報信
號，把它代換成剛才所要求的警報信號，以及傳回之前的警報信號所剩下的秒數。如果
seconds
的值為
0
，則之前的警報信號（如果有的話）會被取消，但是不會安排新的警報
信號。
要成功使用此函式，還需要替
SIGALRM
信號註冊一個信號處理程序。（信號與信號處理程
序可參考前一章所做的說明。）下面的程式碼片段會註冊一個
SIGALRM
處理程序
alarm_
handler()
以及替五秒設定一個警報信號：
void alarm_handler (int signum)
{
printf ("Five seconds passed!\n");
}
void func (void)
{
signal (SIGALRM, alarm_handler);
alarm (5);
pause ();
}
時間間隔計時器
時間間隔計時器
（
interval timer
）系統呼叫，自從被 POSIX 標準化後，首次出現於
4.2BSD，能夠提供的控制比
alarm() ...
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Read now
Unlock full access
More than 5,000 organizations count on O’Reilly
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
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.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
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.