在 GNU 中设置标准信号 SIGIO

Question

我发现 GNU 库中记录了 SIGIO 信号。据说只要我有输入（特别是在套接字中），系统就有可能发送信号。 根据创建此类信号的文档，我应该将 O_ASYNC 标志设置为相应的文件描述符。 我的问题是我的 GNU 版本（gcc 6.3.0）无法识别这样的关键字：

错误：'O_ASYNC' 未声明（在此函数中首次使用）

我使用以下块设置标志：

/* Set socket status async */
int status = fcntl(sockfd, F_SETFL, O_ASYNC);;
if (status < 0) error("Can't set async mode");
else printf("Async is set for signal %d\n", SIGIO); 

我使用 Cigwin GCC 6.3.0

代码如下：

static void OnTimer(int sig)
{
   /* write request to socket BIO */
}
static void OnTick(int sig)
{
   char read[BUFSIZE] = {};
   int received;

    received = SSL_read(ssl, read, sizeof(read));
    /* Handle errors here */
    /* print the server's reply */
    printf("%s\n\n", read);
}

void connectSSL()
{
    /* do all socket set-up and connection */

    /* Establish handler for I/O signal */
    saction.sa_flags = 0;
    saction.sa_handler = OnTick;
    sigemptyset(&saction.sa_mask);
    sigaddset(&saction.sa_mask, SIGALRM);
    if (sigaction(SIGIO, &saction, NULL) == -1) error("sigaction");
    else printf("OnTick handler created\n");

    /* Set socket status async */
    int status = fcntl(sockfd, F_SETFL, fcntl(sockfd, F_GETFL, 0) | FASYNC);
    if (status < 0) error("Can't set async mode");
    else printf("Async is set for signal %d\n", SIGIO);

    /* Select the process to receive the signal */
    int process = fcntl(sockfd, F_SETOWN, getpid());
    if (process < 0) error("Can't set address process");
    else printf("Process %d is set\n", getpid());

    /* do the rest SSL staff here */
}

int main(int argc, char argv[])
{
    sigset_t mask, oldmask;
    /* Wait for OnTimer event*/
    sigemptyset(&oldmask);
    sigaddset(&oldmask, SIGALRM);
    sigemptyset(&mask);
    sigaddset(&mask, SIGALRM);
    sigaddset(&mask, SIGIO);
    sigprocmask(SIG_BLOCK, &mask, &oldmask);
    connectSSL();
    createTimer(500000000);
    while(1)
    {
        printf("\nWaiting OnTimer %d\n", count + 1);
        sigsuspend(&oldmask);
    }

    return 0;
}

Answer 1

很可能您忘记包含sys/fcntl.h，无论是间接还是直接。这是定义标志的地方。

如果未定义O_ASYNC，您可以尝试使用该标志的功能等效前身FASYNC。

还要确保你已经执行了一个

int flags;

/* Install signal handler here... */

/* Set flags to receive SIGIO (and SIGURG) signals */
flags = fcntl (F_GETFL, 0);
flags = fcntl (F_SETFL, flags | FASYNC);

/* Bind our process as receiver of SIGIO signals */
flags = fcntl (F_SETOWN, getpid ());