c++ - posix 管道作为消息队列 : What happens on blocked write + signal

Question

我想使用管道作为内部消息队列，如下所述:posix pipe as a work queue

根据 glibc 的文档，如果数据小于 PIPE_BUF，则写入管道是原子的。 https://www.gnu.org/software/libc/manual/html_node/Pipe-Atomicity.html#Pipe-Atomicity

但是:如果出现信号，写入可能会被中断。假设 write 被阻塞是因为管道快满了。现在出现了一个信号。数据会自动写入管道吗？

template <typename T>
ssize_t put(const T& data)
{       
    static_assert(sizeof(T) < PIPE_BUF, "We use the atomic property of the pipe write. So sizeof(T) MUST be smaller than PIPE_BUF");

    int written;
    const size_t id = T::value;
    written = write(m_fds[write_fd], &id, sizeof(size_t));
    assert(written == sizeof(size_t));

    const size_t sT = sizeof(T);
    write(m_fds[write_fd], &sT, sizeof(size_t));
    assert(written == sizeof(size_t));

    write(m_fds[write_fd], &data, sizeof(T)); // * this blocks in example
    assert(written == sizeof(T));

    return sizeof(T);
}

Answer 1

Atomic 只是意味着 "the whole amount written in one operation is not interleaved with data from any other process."

信号中断略有不同。根据the man page of signal ，管道是一种“慢设备”。因此，除非设置了SA_RESTART，否则write 操作将返回成功并返回写入的数据数。因此，最好经常检查write的返回值，以确保所有数据都已写入。或者，您可以屏蔽可能的信号。