timerfd

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http://blog.csdn.net/gdutliuyun827/article/details/8470777

看一下timerfd的例子，上代码：

[cpp] view plaincopy
#include <sys/timerfd.h>  
#include <sys/time.h>  
#include <time.h>  
#include <unistd.h>  
#include <stdlib.h>  
#include <stdio.h>  
#include <stdint.h>        /* Definition of uint64_t */  
  
#define handle_error(msg) \  
       do { perror(msg); exit(EXIT_FAILURE); } while (0)  
  
void printTime()  
{    
    struct timeval tv;    
    gettimeofday(&tv, NULL);    
    printf("printTime:  current time:%ld.%ld ", tv.tv_sec, tv.tv_usec);  
}  
  
int main(int argc, char *argv[])  
{  
   struct timespec now;  
   if (clock_gettime(CLOCK_REALTIME, &now) == -1)  
       handle_error("clock_gettime");  
  
   struct itimerspec new_value;  
   new_value.it_value.tv_sec = now.tv_sec + atoi(argv[1]);  
   new_value.it_value.tv_nsec = now.tv_nsec;  
   new_value.it_interval.tv_sec = atoi(argv[2]);  
   new_value.it_interval.tv_nsec = 0;  
  
   int fd = timerfd_create(CLOCK_REALTIME, 0);  
   if (fd == -1)  
       handle_error("timerfd_create");  
  
   if (timerfd_settime(fd, TFD_TIMER_ABSTIME, &new_value, NULL) == -1)  
       handle_error("timerfd_settime");  
  
   printTime();  
   printf("timer started\n");  
     
   for (uint64_t tot_exp = 0; tot_exp < atoi(argv[3]);)   
   {  
       uint64_t exp;  
       ssize_t s = read(fd, &exp, sizeof(uint64_t));  
       if (s != sizeof(uint64_t))  
           handle_error("read");  
  
       tot_exp += exp;  
       printTime();  
       printf("read: %llu; total=%llu\n",exp, tot_exp);  
   }  
  
   exit(EXIT_SUCCESS);  
}  

相关结构体如下：

[cpp] view plaincopy
struct timespec {  
   time_t tv_sec;                /* Seconds */  
   long   tv_nsec;               /* Nanoseconds */  
};  
  
struct itimerspec {  
   struct timespec it_interval;  /* Interval for periodic timer */  
   struct timespec it_value;     /* Initial expiration */  
};  

代码L25-L29：初始化定时器的参数，初始间隔与定时间隔。

L32：创建定时器fd，CLOCK_REALTIME：真实时间类型，修改时钟会影响定时器；CLOCK_MONOTONIC：相对时间类型，修改时钟不影响定时器。

L35：设置定时器的值。

L44：阻塞等待定时器到期。返回值是未处理的到期次数。比如定时间隔为2秒，但过了10秒才去读取，则读取的值是5。

编译运行：编译时要加rt库(g++ -lrt timerfd.cc -o timerfd)

[root@localhost appTest]# ./timerfd 5 2 10
printTime: current time:1357391736.146196 timer started
printTime: current time:1357391741.153430 read: 1; total=1
printTime: current time:1357391743.146550 read: 1; total=2
printTime: current time:1357391745.151483 read: 1; total=3
printTime: current time:1357391747.161155 read: 1; total=4
printTime: current time:1357391749.153934 read: 1; total=5
printTime: current time:1357391751.157309 read: 1; total=6
printTime: current time:1357391753.158384 read: 1; total=7
printTime: current time:1357391755.150470 read: 1; total=8
printTime: current time:1357391757.150253 read: 1; total=9
printTime: current time:1357391759.149954 read: 1; total=10
[root@localhost appTest]#

第一个参数5为第一次定时器到期间隔，第二个参数2为定时器的间隔，第三个参数为定时器到期10次则退出。程序运行(5+2*10)S退出。

详细信息可以：man timerfd_create

#include <sys/timerfd.h>#include <sys/time.h>#include <time.h>#include <unistd.h>#include <stdlib.h>#include <stdio.h>#include <stdint.h>        /* Definition of uint64_t */#define handle_error(msg) \   do { perror(msg); exit(EXIT_FAILURE); } while (0)void printTime(){  struct timeval tv;  gettimeofday(&tv, NULL);  printf("printTime:  current time:%ld.%ld ", tv.tv_sec, tv.tv_usec);}int main(int argc, char *argv[]){   struct timespec now;   if (clock_gettime(/*CLOCK_REALTIME*/CLOCK_MONOTONIC, &now) == -1)   handle_error("clock_gettime");   struct itimerspec new_value;   new_value.it_value.tv_sec = /*now.tv_sec +*/ atoi(argv[1]);   new_value.it_value.tv_nsec =/*now.tv_nsec*/0;   new_value.it_interval.tv_sec = atoi(argv[2]);   new_value.it_interval.tv_nsec = 0;   int fd = timerfd_create(/*CLOCK_REALTIME*/CLOCK_MONOTONIC, 0);   if (fd == -1)   handle_error("timerfd_create");   if (timerfd_settime(fd, /*TFD_TIMER_ABSTIME*/0, &new_value, NULL) == -1)   handle_error("timerfd_settime");   printTime();   printf("timer started\n");      for (uint64_t tot_exp = 0; tot_exp < atoi(argv[3]);)    {       uint64_t exp;   ssize_t s = read(fd, &exp, sizeof(uint64_t));   if (s != sizeof(uint64_t))   handle_error("read");   tot_exp += exp;   printTime();   printf("read: %llu; total=%llu\n",exp, tot_exp);   }   exit(EXIT_SUCCESS);}

#include <iostream>#include <sys/socket.h>#include <sys/epoll.h>#include <netinet/in.h>#include <arpa/inet.h>#include <fcntl.h>#include <unistd.h>#include <stdio.h>#include <errno.h>using namespace std;int filedes[2];int main( void ){    char buf[80];    pid_t pid;        pipe( filedes );    fcntl(filedes[0], F_SETFL, O_NONBLOCK);    fcntl(filedes[1], F_SETFL, O_NONBLOCK);    int epoll_fd = epoll_create(20);    if (epoll_fd!= -1)fcntl(epoll_fd, F_SETFD, FD_CLOEXEC);     epoll_event ev = { 0, { 0 } };    ev.events = EPOLLIN | EPOLLERR | EPOLLET;    ev.data.fd = filedes[0];    epoll_ctl(epoll_fd, EPOLL_CTL_ADD, filedes[0], &ev);    pid=fork();            if (pid > 0)    {        printf( "This is in the father process,here write a string to the pipe.\n" );        char s[] = "Hello world , this is write by pipe.\n";        write( filedes[1], s, sizeof(s) );while(1){sleep(10);epoll_event ev = { 0, { 0 } };  ev.events = EPOLLIN | EPOLLERR | EPOLLET;  ev.data.fd = filedes[0];  epoll_ctl(epoll_fd, EPOLL_CTL_MOD, filedes[0], &ev);printf( "interrupt send\n" );}    }    else if(pid == 0)    {        printf( "This is in the child process,here read a string from the pipe.\n" );while(1){epoll_event events[128];int num_events = epoll_wait(epoll_fd, events, 20, 10000);for (int i = 0; i < num_events; ++i){int  fd = events[i].data.fd;if (fd == filedes[0]){printf("interrupt recv\n");}}}           }     close( filedes[0] );     close( filedes[1] );      close(epoll_fd);    //waitpid( pid, NULL, 0 );        return 0;}

timerfd简单的性能测试：

申请1000个定时器，超时间定位1s，每秒超时一次，发现cpu占用率在3.0G的cpu上大概为1%，10000个定时器的话再7%左右，而且不会出现同时超时两个的情况，如果有printf到前台，则一般会出现定时器超时多次（3-5）才回调。

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