Linux高级文件操作 -6

比较poll()和epoll()

poll()已经很好地标准化，但是不具有很好的扩展性，但是epoll仅仅在Linux上扩展得比较好。

当有少量的文件描述符，并且移植性重要的时候，应该使用poll()。

当有大量的文件描述符，epoll是更好的选择。

/* poll-vs-epoll.c - Compares the performance of \codefn{poll()} and \codefn{epoll} */

#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <sys/epoll.h>
#include <sys/poll.h>
#include <sys/signal.h>
#include <unistd.h>
#include <sys/resource.h>
#include <string.h>
#include <stdlib.h>

#include <sys/select.h>

int gotAlarm;

void catch(int sig) {
gotAlarm = 1;
}

#define OFFSET 10

int main(int argc, const char ** argv) {
int pipeFds[2];
int count;
int numFds;
struct pollfd * pollFds;
struct epoll_event event;
int epfd;
int i;
struct rlimit lim;
char * end;

if (!argv[1]) {
fprintf(stderr, "number expected\n");
return 1;
}

numFds = strtol(argv[1], &end, 0);
if (*end) {
fprintf(stderr, "number expected\n");
return 1;
}

printf("Running test on %d file descriptors.\n", numFds);

lim.rlim_cur = numFds + OFFSET;
lim.rlim_max = numFds + OFFSET;
if (setrlimit(RLIMIT_NOFILE, &lim)) {
perror("setrlimit");
exit(1);
}

pipe(pipeFds);

pollFds = malloc(sizeof(*pollFds) * numFds);

epfd = epoll_create(numFds);
event.events = EPOLLIN;

for (i = OFFSET; i < OFFSET + numFds; i++) {
if (dup2(pipeFds[0], i) != i) {
printf("failed at %d: %s\n", i, strerror(errno));
exit(1);
}

pollFds[i - OFFSET].fd = i;
pollFds[i - OFFSET].events = POLLIN;

event.data.fd = i;
epoll_ctl(epfd, EPOLL_CTL_ADD, i, &event);
}

/* use a signal to know when time's up */
signal(SIGALRM, catch);

count = 0;
gotAlarm = 0;
alarm(1);
while (!gotAlarm) {
poll(pollFds, numFds, 0);
count++;
}

printf("poll() calls per second: %d\n", count);

alarm(1);

count = 0;
gotAlarm = 0;
alarm(1);
while (!gotAlarm) {
epoll_wait(epfd, &event, 1, 0);
count++;
}

printf("epoll() calls per second: %d\n", count);

return 0;
}