sigsuspend

#include <signal.h>
int sigsuspend(const sigset_t *sigmask)

将进程的信号屏蔽字设置为sigmask的值。在捕捉到一个信号或是发生了一个信号终止该进程之前，该进程被挂起。如果捕捉到一个信号并从该信号处理程序返回，则sigsuspend返回，并将进程的信号屏蔽字设置为调用sigsuspend之前的值

#include "apue.h"
static void sig_int(int);

int
main(void)
{
    sigset_t newmask,oldmask,waitmask;
    pr_mask("program start:");

    if (signal(SIGINT,sig_int) == SIG_ERR)
        err_sys("signal(SIGINT) error");
    sigemptyset(&waitmask);
    sigaddset(&waitmask,SIGUSR1);
    sigemptyset(&newmask);
    sigaddset(&newmask,SIGINT);

    /*
     *block sigint and save current signal mask
     */
    if (sigprocmask(SIG_BLOCK,&newmask,&oldmask) < 0)
        err_sys("sig_block error");

    /*
     * critical region code
     */
    printf("this is critical region code \n");
    pr_mask("in critical region code");

    /*
     * Pause allowing all signals except sigusr1
     */
    if (sigsuspend(&waitmask) != -1)
        err_sys("sigsuspend error");
    pr_mask("after return from suspend");
    /*
     *
     * reset signal mask which unblocks sigint
     */

    if (sigprocmask(SIG_SETMASK,&oldmask,NULL) <0)
        err_sys("sig_setmask error");
    /*
     * and continue processing
     */
    pr_mask("program exit");
    exit(0);
}
static void
sig_int(int signo)
{
    pr_mask("\n in sig_int");
}

#include "apue.h"
#include <errno.h>

void pr_mask(const char *str)
{
    sigset_t sigset;
    int     errno_save;

    errno_save = errno ; /* we can be called by signal handles */
    if (sigprocmask(0,NULL,&sigset) <  0)
        err_sys("sigprocmask error");
    printf("%s",str);

    if (sigismember(&sigset,SIGINT)) printf("SIGINT");
    if (sigismember(&sigset,SIGQUIT)) printf("SIGQUIT");
    if (sigismember(&sigset,SIGUSR1)) printf("SIGUSR1");
    if (sigismember(&sigset,SIGALRM)) printf("SIGALRM");
    /* remaining signals can go here */
    printf("\n");
    errno  = errno_save;
}

#include "apue.h"
/* reliable version of signal() ,using posix signaction()*/
Sigfunc *
signal(int signo,Sigfunc * func)
{
    struct sigaction act,oact;

    act.sa_handler = func;
    sigemptyset(&act.sa_mask);
    act.sa_flags = 0;
    if ( signo  == SIGALRM){
    #ifdef SA_INTERRUPT
        act.sa_flags |=  SA_INTERRUPT;
    #endif
    } else{
    #ifdef  SA_RESTART
        act.sa_flags |= SA_RESTART;
    #endif
    }
    if (sigaction(signo,&act,&oact) < 0)
        return(SIG_ERR);
    return(oact.sa_handler);
}

program flow:

main()

block sig_int

critical code

sigprocmask    ------------ set sig_int 屏蔽字

pr_mask() -----------   sig_int

sigsuspend() ------------set sig_usr1  并使进程挂起

ctr+c

中断处理程序

pr_mask()-------------sig_int,sigusr1 

返回

exit（）

ubuntu@ubuntu-virtual-machine:~/Desktop/apue$ gcc -Wall -o c10-15 c10-15.c error
.c pr_mask.c c10-12.c

ubuntu@ubuntu-virtual-machine:~/Desktop/apue$ ./c10-15

program start:

this is critical region code

in critical region code
SIGINT

^C

 in sig_intSIGINTSIGUSR1

after return from suspend
SIGINT

program exit