linux应用程序中的延时和定时器
笔记:
在linux应用程序中延时有sleep()、msleep()和usleep()函数之类的延时,也有如下形式的延时:
struct timeval delay; delay.tv_sec = sleepSecond; delay.tv_usec = 0; select( 0, NULL, NULL, NULL, &delay );
但是基本上都是基于进程休眠的,好像没有循环等待的延时,有待证实,目前没发现。
考虑到一个问题,如果定时发送信号,执行相应一个信号处理函数时,该函数还么有执行完成,另一个信号又来了,怎么处理呢?答案是等待前面一个信号处理完成。
定时器配合kill函数一起使用,可以满足某些想立即执行又要有周期执行相应函数的特殊要求,如下:
/********************************************************************************* * Copyright: (C) 2014 EAST * All rights reserved. * * Filename: setitimer.c * Description: This file * * Version: 1.0.0(08/08/2014) * Author: fulinux <[email protected]> * ChangeLog: 1, Release initial version on "08/08/2014 12:58:48 PM" * ********************************************************************************/ #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <signal.h> #include <time.h> #include <sys/time.h> static int switch_val = 0; void sigroutine(int signo){ switch (signo){ case SIGALRM: printf("Catch a signal -- SIGALRM \n"); break; case SIGVTALRM: printf("Catch a signal -- SIGVTALRM \n"); switch(switch_val){ case 0: printf ("switch_val = 0\n"); break; case 1: printf ("switch_val = 1\n"); break; case 2: printf ("switch_val = 2\n"); break; case 3: printf ("switch_val = 3\n"); break; default: return; } break; } return; } int main() { struct itimerval value, ovalue, value2; //(1) printf("process id is %d\n", getpid()); signal(SIGALRM, sigroutine); signal(SIGVTALRM, sigroutine); value.it_value.tv_sec = 1; value.it_value.tv_usec = 0; value.it_interval.tv_sec = 1; value.it_interval.tv_usec = 0; setitimer(ITIMER_REAL, &value, &ovalue); //(2) value2.it_value.tv_sec = 0; value2.it_value.tv_usec = 1; value2.it_interval.tv_sec = 0; value2.it_interval.tv_usec = 500000; setitimer(ITIMER_VIRTUAL, &value2, &ovalue); #if 0 struct timeval delay; delay.tv_sec = 0; delay.tv_usec = 500000; select(0, NULL, NULL, NULL, &delay); #endif switch_val = 1; kill(getpid(), SIGVTALRM); printf ("fulinux 1\n"); switch_val = 2; kill(getpid(), SIGVTALRM); printf ("fulinux 2\n"); switch_val = 3; kill(getpid(), SIGVTALRM); printf ("fulinux 3\n"); for(;;) ; }
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