被中断的系统调用

我们知道系统调用一旦阻塞，当信号到来是会中断此系统调用执行的，但是如下情况是不会对系统调用产生影响：

1.单个进程阻塞信号不会对后续系统调用产生中断行为。
2.线程中通过pthread_sigmask阻塞信号后，对该进程发送的信号是不影响该线程的系统调用的，会被发送到其他线程处理。

对于阻塞的信号，相当于是延后处理，改为unblock后，会立即触发信号行为。如果一直处于阻塞状态，那么相当于忽略。

多线程的示例如下：

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include "include/debug.h"


void *thr_fn(void *arg)
{
	int err, signo;
	sigset_t	mask;

	sigfillset(&mask);
	for (;;) {
		err = sigwait(&mask, &signo);
		if (err != 0) {
			err_exit("sigwait failed\n");
		}

		switch (signo) {
		case SIGTERM:
			pr_info("Catch SIGTERM; exiting\n");
			break;
		case SIGQUIT:
			pr_info("Catch SIGQUIT; exiting\n");
			exit(0);
			break;
		case SIGINT:
			pr_info("Catch SIGINT; exiting\n");
			break;

		default:
			pr_info("Unexpected signal %d\n", signo);
		}
	}
	return(0);
}

pthread_t setup_signal_thread(void)
{
	int err;
	struct sigaction	sa;
	sigset_t	mask;
	pthread_t	tid;

	/*
	 * Block all signals in main thread
	 */
	sigfillset(&mask);
	if ((err = pthread_sigmask(SIG_BLOCK, &mask, NULL)) != 0)
		err_exit("SIG_BLOCK error\n");

	/*
	 * Create a child thread to handle SIGHUP and SIGTERM.
	 */
	err = pthread_create(&tid, NULL, thr_fn, 0);
	if (err != 0)
		err_exit("can't create thread\n");
	return tid;
}

int main()
{
	char buf[10];
	pthread_t tid;
	void *tret;

	tid = setup_signal_thread();

	read(STDIN_FILENO, buf, 10);
	printf("read was interrupted!\n");
}

测试结果：

xiehaocheng@xiehaocheng:~/work/qemu/sdk/test/linuxc$ ./syscall_intr 
^C[604] INFO:  Catch SIGINT; exiting
^C[604] INFO:  Catch SIGINT; exiting
^C[604] INFO:  Catch SIGINT; exiting
^C[604] INFO:  Catch SIGINT; exiting
^C[604] INFO:  Catch SIGINT; exiting
^C[604] INFO:  Catch SIGINT; exiting
^C[604] INFO:  Catch SIGINT; exiting
^C[604] INFO:  Catch SIGINT; exiting
^C[604] INFO:  Catch SIGINT; exiting
^C[604] INFO:  Catch SIGINT; exiting
^C[604] INFO:  Catch SIGINT; exiting
^C[604] INFO:  Catch SIGINT; exiting