sigsuspend 函数疑问

pp25210 2015-01-06 10:04:53



// 这个程序是 apue10.16 节图10_22中的代码.



#include "apue.h"



static void	sig_int(int);

void pr_mask(const char*);



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 of code.

	 */

	pr_mask("in critical region: ");



	/*

	 * Pause, allowing all signals except SIGUSR1.

	 */

	if (sigsuspend(&waitmask) != -1)

		err_sys("sigsuspend error");



	pr_mask("after return from sigsuspend: ");



	/*

	 * 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("\nin sig_int: ");

}



void

pr_mask(const char *str)

{

	sigset_t	sigset;

	int			errno_save;



	errno_save = errno;		/* we can be called by signal handlers */

	if (sigprocmask(0, NULL, &sigset) < 0) {

		err_ret("sigprocmask error");

	} else {

		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;		/* restore errno */

}

执行

 if (sigsuspend(&waitmask) != -1)

语句之后进程会被挂起并且会屏蔽除 SIGUSR1 之外的所有信号,.
1. 此时为什么按 Ctrl+C 键入中断字符之后进程会被唤醒, 而通过 kill -USR1 PID 发送的SIGUSR1并不会使进程唤醒?
2. 将

 if (sigsuspend(&waitmask) != -1)

改为

 if (sigsuspend(&newmask) != -1)

之后, 进程应该会被挂起并且屏蔽除 SIGINT 之外的所有信号, 此时按Ctrl+C 键入中断字符为什么进程没有被唤醒?

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Cody2k3 2015-01-06

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引用楼主 qq252101792 的回复:


// 这个程序是 apue10.16 节图10_22中的代码.

#include "apue.h"

static void	sig_int(int);
void pr_mask(const char*);

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 of code.
	 */
	pr_mask("in critical region: ");

	/*
	 * Pause, allowing all signals except SIGUSR1.
	 */
	if (sigsuspend(&waitmask) != -1)
		err_sys("sigsuspend error");

	pr_mask("after return from sigsuspend: ");

	/*
	 * 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("\nin sig_int: ");
}

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

	errno_save = errno;		/* we can be called by signal handlers */
	if (sigprocmask(0, NULL, &sigset) < 0) {
		err_ret("sigprocmask error");
	} else {
		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;		/* restore errno */
}

执行