使用 TcpStream 强制非阻塞读取

Question

我有一个维护套接字列表的线程，我想遍历该列表，看看是否有任何要读取的内容，如果有 - 对其进行操作，如果没有 - 移动到下一个。问题是，一旦我遇到第一个节点，所有执行都会停止，直到读取完成。

我正在使用 std::io::Read::read(&mut self, buf: &mut [u8]) -> Result<usize>

来自doc

This function does not provide any guarantees about whether it blocks waiting for data, but if an object needs to block for a read but cannot it will typically signal this via an Err return value.

深入源码，TcpStream Read 实现是

impl Read for TcpStream {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> { self.0.read(buf) }
}

调用

pub fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> {
    let fd = self.fd();
    let dolock = || self.lock_nonblocking();
    let doread = |nb| unsafe {
        let flags = if nb {c::MSG_DONTWAIT} else {0};
        libc::recv(fd,
                   buf.as_mut_ptr() as *mut libc::c_void,
                   buf.len() as wrlen,
                   flags) as libc::c_int
    };
    read(fd, self.read_deadline, dolock, doread)
}

最后，调用 read<T, L, R>(fd: sock_t, deadline: u64, mut lock: L, mut read: R)

在检索数据或发生错误之前，我可以看到非阻塞读取循环。

有没有办法强制使用 TcpStream 进行非阻塞读取？

Answer 1

更新答案

需要注意的是，从 Rust 1.9.0 开始，std::net::TcpStream 增加了功能：

fn set_nonblocking(&self, nonblocking: bool) -> Result<()>

原答案

无法用TcpStream准确获取，又不想为IO操作拉入单独的lib，所以我决定在使用前将文件描述符设置为非阻塞，并执行系统调用至 read/write。绝对不是最安全的解决方案，但比实施新的 IO 库工作更少，即使 MIO 看起来不错。

extern "system" {
    fn read(fd: c_int, buffer: *mut c_void, count: size_t) -> ssize_t;
}

pub fn new(user: User, stream: TcpStream) -> Socket {

    // First we need to setup the socket as Non-blocking on POSIX
    let fd = stream.as_raw_fd();
    unsafe {
        let ret_value = libc::fcntl(fd,
            libc::consts::os::posix01::F_SETFL,
            libc::consts::os::extra::O_NONBLOCK);

        // Ensure we didnt get an error code
        if ret_value < 0 {
            panic!("Unable to set fd as non-blocking")
        }
    }

    Socket {
        user: user,
        stream: stream
    }
}

pub fn read(&mut self) {
    let count = 512 as size_t;
    let mut buffer = [0u8; 512];
    let fd = self.stream.as_raw_fd();

    let mut num_read = 0 as ssize_t;
    unsafe {
        let buf_ptr = buffer.as_mut_ptr();
        let void_buf_ptr: *mut c_void = mem::transmute(buf_ptr);
        num_read = read(fd, void_buf_ptr, count);
        if num_read > 0 {
            println!("Read: {}", num_read);
        }

        println!("test");
    }
}

使用 TcpStream 强制非阻塞读取

Force non blocking read with TcpStream

sockets

tcp

rust