select和pselect的关于信号打断的实验

news2024/10/7 8:32:08

select和pslect的man手册

SELECT(2)                                                          Linux Programmer's Manual                                                         SELECT(2)

NAME
       select, pselect, FD_CLR, FD_ISSET, FD_SET, FD_ZERO - synchronous I/O multiplexing

SYNOPSIS
       /* According to POSIX.1-2001, POSIX.1-2008 */
       #include <sys/select.h>

       /* According to earlier standards */
       #include <sys/time.h>
       #include <sys/types.h>
       #include <unistd.h>

       int select(int nfds, fd_set *readfds, fd_set *writefds,
                  fd_set *exceptfds, struct timeval *timeout);

       void FD_CLR(int fd, fd_set *set);
       int  FD_ISSET(int fd, fd_set *set);
       void FD_SET(int fd, fd_set *set);
       void FD_ZERO(fd_set *set);

       #include <sys/select.h>

       int pselect(int nfds, fd_set *readfds, fd_set *writefds,
                   fd_set *exceptfds, const struct timespec *timeout,
                   const sigset_t *sigmask);

最大的区别在于pselect的最后一个参数const sigset_t *sigmask，看名字应该是信号屏蔽，现在分别写一个select和一个pselect对于信号的反应。

测试一：select测试代码

#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <sys/select.h>
#include <unistd.h>
#include <time.h>
#include <string.h>
#include <signal.h>
#include <errno.h>

#define _DEBUG_INFO
#ifdef _DEBUG_INFO
#define DEBUG_INFO(format, ...) printf("%s:%s:%d -- "format"\n" \
,__FILE__,__func__,__LINE__ \
, ##__VA_ARGS__)
#else
#define DEBUG_INFO(format, ...)
#endif

#define _DEBUG_PRINT
#ifdef _DEBUG_PRINT
#define DEBUG_PRINT(format,...)	printf(format,##__VA_ARGS__)	
#else
#define DEBUG_PRINT(format,...)
#endif

void sig_func(int sig){
    DEBUG_INFO(" sig = %d", sig);
}

int main(int argc, char *argv[])
{
    fd_set rfds;
    int retval;
    char buf[100];
    signal(SIGINT, sig_func);

    FD_ZERO(&rfds);
    FD_SET(0,&rfds);
select_pos:
    retval = select(1,&rfds,NULL,NULL,NULL);
    if(retval == -1){
        if(errno == EINTR){
            DEBUG_INFO("get a signal");
            exit(0);
        }
    }
    read(0,buf,sizeof(buf));
    goto select_pos;

    DEBUG_INFO("bye bye.");
    return 0;
}

测试：

实验解析：

当按下CTRL+C时，select返回-1，此时errno的值是EINTR，表示select被信号打断。

测试二：pselect的最后一个参数设置为NULL

#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <sys/select.h>
#include <unistd.h>
#include <time.h>
#include <string.h>
#include <signal.h>
#include <errno.h>

#define _DEBUG_INFO
#ifdef _DEBUG_INFO
#define DEBUG_INFO(format, ...) printf("%s:%s:%d -- "format"\n" \
,__FILE__,__func__,__LINE__ \
, ##__VA_ARGS__)
#else
#define DEBUG_INFO(format, ...)
#endif

#define _DEBUG_PRINT
#ifdef _DEBUG_PRINT
#define DEBUG_PRINT(format,...)	printf(format,##__VA_ARGS__)	
#else
#define DEBUG_PRINT(format,...)
#endif

void sig_func(int sig){
    DEBUG_INFO(" sig = %d", sig);
}

int main(int argc, char *argv[])
{
    fd_set rfds;
    int retval;
    char buf[100];
    signal(SIGINT, sig_func);

    FD_ZERO(&rfds);
    FD_SET(0,&rfds);
select_pos:
    retval = pselect(1,&rfds,NULL,NULL,NULL,NULL);
    if(retval == -1){
        if(errno == EINTR){
            DEBUG_INFO("get a signal");
            exit(0);
        }
    }
    read(0,buf,sizeof(buf));
    goto select_pos;

    DEBUG_INFO("bye bye.");
    return 0;
}

实验解析：

此时的pselect和测试一的select效果等价。

实验三： pselect的最后一个参数设置为有效值

#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <sys/select.h>
#include <unistd.h>
#include <time.h>
#include <string.h>
#include <signal.h>
#include <errno.h>

#define _DEBUG_INFO
#ifdef _DEBUG_INFO
#define DEBUG_INFO(format, ...) printf("%s:%s:%d -- "format"\n" \
,__FILE__,__func__,__LINE__ \
, ##__VA_ARGS__)
#else
#define DEBUG_INFO(format, ...)
#endif

#define _DEBUG_PRINT
#ifdef _DEBUG_PRINT
#define DEBUG_PRINT(format,...)	printf(format,##__VA_ARGS__)	
#else
#define DEBUG_PRINT(format,...)
#endif

void sig_func(int sig){
    DEBUG_INFO(" sig = %d", sig);
}

int main(int argc, char *argv[])
{
    fd_set rfds;
    int retval;
    char buf[100];
    sigset_t blockset;
    signal(SIGINT, sig_func);    

    FD_ZERO(&rfds);
    FD_SET(0,&rfds);
    sigemptyset(&blockset);
    sigaddset(&blockset,SIGINT);
select_pos:
    retval = pselect(1,&rfds,NULL,NULL,NULL,&blockset);
    if(retval == -1){
        if(errno == EINTR){
            DEBUG_INFO("get a signal");
            exit(0);
        }
        perror("pselect");
        return -1;
    }
    int len = read(0,buf,sizeof(buf));
    DEBUG_INFO("len = %d",len);
    for(int i = 0;i < len;i++){
        printf("%d,",buf[i]);
    }
    sigemptyset(&blockset);
    printf("\n");
    goto select_pos;

    DEBUG_INFO("bye bye.");
    return 0;
}

测试过程：