Sigaction将SIGINT传递给系统调用，但不传递信号

问题描述

我有一个处理accept(2)调用的循环。我希望在向程序发送SIGINT时能够执行一些清理。我的第一个想法是使用signal函数。

void signal_handler(int signal) {
    printf("Caught signal
");
}

int main() {
    signal(SIGINT, &signal_handler);
    // ...
    int accept_fd = accept(sock, NULL, NULL);
    if (accept_fd == -1) {
        close(sock);
        perror("accept");
        return 1;
    }
    // ...
}

但是，这只是打印"；捕获信号&，然后程序继续运行。

如果我将main修改为使用sigaction，程序将按预期运行。

int main() {
    struct sigaction sa;
    sa.sa_handler = &signal_handler;
    sa.sa_flags = 0;
    sigemptyset(&sa.sa_mask);
    sigaction(SIGINT, &sa, NULL);
    // ...
    int accept_fd = accept(sock, NULL, NULL);
    if (accept_fd == -1) {
        close(sock);
        perror("accept");
        return 1;
    }
    // ...
}

发送SIGINT后，我得到Caught Signal，然后是accept: Interrupted system call。从accept(2)

的手册页

我知道sigaction更现代，我应该比signal使用它，但我很好奇为什么它在功能上有这样的区别。

下面我为每种情况都包括了一个完整的可用的示例程序。

带信号(2)的示例

#include <netdb.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <unistd.h>

#define BUFFER_SIZE 32

void signal_handler(int signal) {
    printf("Caught signal
");
}

int main() {
    signal(SIGINT, &signal_handler);
    struct addrinfo hints;
    memset(&hints, 0, sizeof(struct addrinfo));
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    struct addrinfo *addr_info;
    int info_result = getaddrinfo("localhost", "8080", &hints, &addr_info);
    if (info_result != 0) {
        printf("Getting address failed
");
        return 1;
    }
    int sock = socket(addr_info->ai_family, addr_info->ai_socktype, addr_info->ai_protocol);
    if (sock == -1) {
        printf("Socket Failed
");
        return 1;
    }
    int bind_result = bind(sock, addr_info->ai_addr, addr_info->ai_addrlen);
    if (bind_result == -1) {
        close(sock);
        printf("Bind Failed
");
        return 1;
    }
    int listen_result = listen(sock, 8);
    if (listen_result == -1) {
        close(sock);
        printf("Listen Failed
");
        return 1;
    }
    printf("Waiting...
");
    int accept_fd = accept(sock, NULL, NULL);
    if (accept_fd == -1) {
        close(sock);
        perror("accept");
        return 1;
    }
    printf("Got fd %d
", accept_fd);
    char *buffer = malloc(BUFFER_SIZE * sizeof(char));
    int n;
    while ((n = read(accept_fd, buffer, BUFFER_SIZE)) > 0) {
        printf("%.*s
", n, buffer);
    }
    close(sock);
}

带sigaction(2)的示例

#include <netdb.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <unistd.h>

#define BUFFER_SIZE 32

void signal_handler(int signal) {
    printf("Caught signal
");
}

int main() {
    struct sigaction sa;
    sa.sa_handler = &signal_handler;
    sa.sa_flags = 0;
    sigemptyset(&sa.sa_mask);
    sigaction(SIGINT, &sa, NULL);
    struct addrinfo hints;
    memset(&hints, 0, sizeof(struct addrinfo));
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    struct addrinfo *addr_info;
    int info_result = getaddrinfo("localhost", "8080", &hints, &addr_info);
    if (info_result != 0) {
        printf("Getting address failed
");
        return 1;
    }
    int sock = socket(addr_info->ai_family, addr_info->ai_socktype, addr_info->ai_protocol);
    if (sock == -1) {
        printf("Socket Failed
");
        return 1;
    }
    int bind_result = bind(sock, addr_info->ai_addr, addr_info->ai_addrlen);
    if (bind_result == -1) {
        close(sock);
        printf("Bind Failed
");
        return 1;
    }
    int listen_result = listen(sock, 8);
    if (listen_result == -1) {
        close(sock);
        printf("Listen Failed
");
        return 1;
    }
    printf("Waiting...
");
    int accept_fd = accept(sock, NULL, NULL);
    if (accept_fd == -1) {
        close(sock);
        perror("accept");
        return 1;
    }
    printf("Got fd %d
", accept_fd);
    char *buffer = malloc(BUFFER_SIZE * sizeof(char));
    int n;
    while ((n = read(accept_fd, buffer, BUFFER_SIZE)) > 0) {
        printf("%.*s
", n, buffer);
    }
    close(sock);
}

推荐答案

在bsd和linux上，signal()相当于sigaction()，sa_flags设置为SA_RESTART。如果您在sigaction()代码中设置了该标志，它的行为将与您的代码相同。如果这不是您想要的，则只能使用sigaction()。

Linux man page(也适用于BSD和OS X)的说明：

       sa.sa_flags = SA_RESTART;

这篇关于Sigaction将SIGINT传递给系统调用，但不传递信号的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！