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pselect() 函数的原型是：int pselect(int nfds, fd_set *readfds, fd_set *writefds,

                   fd_set *exceptfds, const struct timespec *timeout, const sigset_t *sigmask); 它和 select() 函数基本相同，区别在于两个不同的参数，一个是 struct timespec *timeout，另一个是 sigset_t *sigmask 。

struct timespec 结构定义为：

  struct timespec {                long    tv_sec;                         long    tv_nsec;                    };

其中的时间表示秒和纳秒。和 select() 不同，每次超时后，pselect() 并不会去修改这个时间参数，也就是说，没有必要再次对这个时间参数进行初始化。 对于最后一个参数 sigmask 表示信号屏蔽掩码，设置掩码可以对相应的信号进行屏蔽，这样pselect就一直不会被屏蔽的信号所中断。

select等待期间不想被中断的方法有两个：

其一：pselect 代替select

#include "unp.h"

void sig_alarm(int signo) {         printf("%d\n",signo);         if(signo == SIGALRM)         {                 printf("SIGALRM\n");         }         else if(signo == SIGVTALRM)         {                 printf("SIGVTALRM\n");         } } int main() {         sigset_t sigmask;         fd_set rset;         ssize_t nread;         char buf[MAXLINE];         int maxfd;         struct itimerval value;         signal1(SIGALRM,sig_alarm);         value.it_interval.tv_sec = 3;         value.it_interval.tv_usec = 0;         value.it_value.tv_sec = 1;         value.it_value.tv_usec = 0;         if(setitimer(ITIMER_REAL,&value,NULL) == -1)         {                 printf("setitimer error.\n");                 return 0;

        }

        if(sigemptyset(&sigmask) ==  -1)

        {                 printf("sigemptyset error.\n");                 return 0;         }         if(sigaddset(&sigmask,SIGALRM) == -1)         {                 printf("sigaddset error.\n");                 return 0;         }         while(1)         {                 FD_ZERO(&rset);                 FD_SET(fileno(stdin),&rset);                 maxfd = fileno(stdin) + 1;                 int nready = pselect(maxfd,&rset,NULL,NULL,NULL,&sigmask);                 //printf("select called.%d\n",nready);                 if(nready < 0)                 {                         if(errno == EINTR)                         {                                 printf("interruped.\n");                         }                 }                 else                 {                         int nread = ReadLine(fileno(stdin),buf,MAXLINE);                         if(nread < 0)                         {                                 printf("读取失败!\n");                                 continue;                         }                 //      printf("nread: %d\n",nread);                         //Write(stdin,buf,nread);                         printf("%s",buf);                 }         } }

其二：运用sigprocmask函数

#include "unp.h"

void sig_alarm(int signo) {         printf("%d\n",signo);         if(signo == SIGALRM)         {                 printf("SIGALRM\n");         }         else if(signo == SIGVTALRM)         {                 printf("SIGVTALRM\n");         } } int main() {         sigset_t sigmask;         fd_set rset;         ssize_t nread;         char buf[MAXLINE];         int maxfd;         struct itimerval value;         signal1(SIGALRM,sig_alarm);         value.it_interval.tv_sec = 3;         value.it_interval.tv_usec = 0;         value.it_value.tv_sec = 1;         value.it_value.tv_usec = 0;         if(setitimer(ITIMER_REAL,&value,NULL) == -1)         {                 printf("setitimer error.\n");                 return 0;

        }

        if(sigemptyset(&sigmask) ==  -1)

        {                 printf("sigemptyset error.\n");                 return 0;         }         if(sigaddset(&sigmask,SIGALRM) == -1)         {                 printf("sigaddset error.\n");                 return 0;

        }

        sigprocmask(SIG_BLOCK,&sigmask,NULL);

        while(1)

        {                 FD_ZERO(&rset);                 FD_SET(fileno(stdin),&rset);                 maxfd = fileno(stdin) + 1;                 //int nready = pselect(maxfd,&rset,NULL,NULL,NULL,&sigmask);

                //printf("select called.%d\n",nready);

               int nready = select(maxfd,&rset,NULL,NULL,NULL);

                if(nready < 0)

                {                         if(errno == EINTR)                         {                                 printf("interruped.\n");                         }                 }                 else                 {                         int nread = ReadLine(fileno(stdin),buf,MAXLINE);                         if(nread < 0)                         {                                 printf("读取失败!\n");                                 continue;                         }                 //      printf("nread: %d\n",nread);                         //Write(stdin,buf,nread);                         printf("%s",buf);                 }         }

}

比较两种方法，都可以有效防止select被信号中断，经我测试，两者还是有区别的，第一种当你在终端输入数据时，时钟信号处理函数是会被执行的，而第二种则彻底屏蔽了时钟信号。

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