signal(SIGALRM,...)为什么执行不起来？

[uuussseeennn]

#define ALARM_SLEEP 1

void my_sigalarm(int sig) {
printf("sigalarm!\n");
alarm(ALARM_SLEEP);
signal(SIGALRM, my_sigalarm);
}

int main(int argc, char* argv[]) {
signal(SIGALRM, my_sigalarm);
alarm(ALARM_SLEEP);
sleep(3000);

return 0;
}

上面的代码在ARM板子上面一跑，只输出一行：
sigalarm!
程序接着就退出了，不提示任何信息。

请问这是为什么？谢谢！

[mymtom]

[/code]
这么复杂，还是改用sigaction和setitimer好了。
[code=C/C++]
#include <sys/time.h>
#include <signal.h>
#include <unistd.h>

#include <stdio.h>

/* ARGSUSED */
static void catch_sigalrm(int sig)
{
(void)printf("%s\n", "SIGALRM received.");
}

static void (*Signal (int sig, void (*handler)(int)))(int)
{
struct sigaction act, oact;

act.sa_handler = handler;
act.sa_flags = 0;
#ifdef SA_INTERRUPT
act.sa_flags |= SA_INTERRUPT;
#endif
if (sigaction(sig, &act, &oact))
return SIG_ERR;

return oact.sa_handler;
}

int main(void)
{
struct itimerval it;

(void)Signal(SIGALRM, &catch_sigalrm);
it.it_interval.tv_sec = 1;
it.it_interval.tv_usec = 0;
it.it_value.tv_sec = 1;
it.it_value.tv_usec = 0;
(void)setitimer(ITIMER_REAL, &it, NULL);

/* CONSTCOND */
for (;;)
(void)pause();

/* NOTREACHED */
return 0;
}

[mymtom]

[/code]

#include <sys/time.h>
#include <signal.h>
#include <unistd.h>

#include <stdio.h>

/* ARGSUSED */
static void catch_sigalrm(int sig)
{
        (void)printf("%s\n", "SIGALRM received.");
}

static void (*Signal (int sig, void (*handler)(int)))(int)
{
        struct sigaction act, oact;

        act.sa_handler = handler;
        act.sa_flags = 0;
#ifdef SA_INTERRUPT
        act.sa_flags |= SA_INTERRUPT;
#endif
        if (sigaction(sig, &act, &oact))
                return SIG_ERR;

        return oact.sa_handler;
}

int main(void)
{
        struct itimerval it;

        (void)Signal(SIGALRM, &catch_sigalrm);
        it.it_interval.tv_sec = 1;
        it.it_interval.tv_usec = 0;
        it.it_value.tv_sec = 1;
        it.it_value.tv_usec = 0;
        (void)setitimer(ITIMER_REAL, &it, NULL);
        
        /* CONSTCOND */
        for (;;)
                (void)pause();

        /* NOTREACHED */
        return 0;
}

[once_and_again]

[Quote=引用 4 楼 mymtom 的回复:]

[/code]
C/C++ code

#include <sys/time.h>
#include <signal.h>
#include <unistd.h>

#include <stdio.h>

/* ARGSUSED */
static void catch_sigalrm(int sig)
{
(void)printf("%s\n", "SIGALRM rece……
[/Quote]

学习

[howema]

楼上说的没错！

[sabflying]

[Quote=引用楼主 uuussseeennn 的回复:]
#define ALARM_SLEEP 1

void my_sigalarm(int sig) {
printf("sigalarm!\n");
alarm(ALARM_SLEEP);
signal(SIGALRM, my_sigalarm);
}

int main(int argc, char* argv[]) {
signal(SIGALRM, my_si……
[/Quote]


第一次被唤醒后就退出了，当然只执行一次

[yanjinbin0]

当然只了,你只设置了执行一次时钟信号,所以只会执行一次.
sleep会被信号中断,所以也不会等待3000s,
所以你的程序现在就是不会等待的只执行一次my_sigalarm().
所以你不用惊讶 :)

[激情的头发]

接收到信号以后，SLEEP会被中断。所以，在信号处理程序执行完后，程序从SLEEP被中断后开始执行。程序就此退出了。如果想要不使程序退出的话，应该将alarm放到死循环中。

/* Install signal handler */
signal( SIGALRM, handler );

/* Suspend signal SIGSEGV */
sigset_t mask;
sigemptyset( &mask );
sigaddset( &mask, SIGSEGV );

while ( 1 )
{
        alarm( 1 );
        sigsuspend( &mask );
}