使用longjmp，带超时限制调用read

//Set max timeout when block reading
// by Jay Zhang

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>
#include <setjmp.h>

static void sig_alarm(int);
static jmp_buf env_alarm;

#define MAXLINE	1024

int main(void)
{
	int n;
	char line[MAXLINE];

	if(signal(SIGALRM, sig_alarm) == SIG_ERR) {
		printf("signal SIGALARM error\n");
		return -1;
	}
	if(setjmp(env_alarm) != 0) {
		printf("read timeout\n");
		return 0;
	}

	alarm(10);
	if((n = read(STDIN_FILENO, line, MAXLINE)) < 0) {
		printf("read error\n");
	}
	alarm(0);

	write(STDOUT_FILENO, line, n);
	return 0;
}

static void
sig_alarm(int signo)
{
	longjmp(env_alarm, 1);
}