UNIX域流和数据报套接字之间的区别?-DifferencebetweenUNIXdomainSTREAMandDATAGRAMsockets?

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Just as the manual page says Unix sockets are always reliable. The difference between SOCK_STREAM and SOCK_DGRAM is in the semantics of consuming data out of the socket.

正如手册页所说，Unix套接字总是可靠的。SOCK_STREAM和SOCK_DGRAM之间的区别在于从套接字中使用数据的语义。

Stream socket allows for reading arbitrary number of bytes, but still preserving byte sequence. In other words, a sender might write 4K of data to the socket, and the receiver can consume that data byte by byte. The other way around is true too - sender can write several small messages to the socket that the receiver can consume in one read. Stream socket does not preserve message boundaries.

流套接字允许读取任意数量的字节，但仍然保留字节序列。换句话说，发送方可能向套接字写入4K数据，而接收方可以逐个字节地使用该数据。另一种方法也是正确的——发送方可以向套接字写入几个小消息，接收方可以在一次读取中使用这些消息。流套接字不保留消息边界。

Datagram socket, on the other hand, does preserve these boundaries - one write by the sender always corresponds to one read by the receiver (even if receiver's buffer given to read(2) or recv(2) is smaller then that message).

而另一方面，数据报套接字则保留了这些边界——发送方的写入总是对应于接收方的读取(即使接收方给读(2)或recv(2)的缓冲区小于该消息)。

So if your application protocol has small messages with known upper bound on message size you are better off with SOCK_DGRAM since that's easier to manage.

因此，如果您的应用程序协议具有消息大小已知上限的小消息，那么最好使用SOCK_DGRAM，因为这样更容易管理。

If your protocol calls for arbitrary long message payloads, or is just an unstructured stream (like raw audio or something), then pick SOCK_STREAM and do the required buffering.

如果您的协议调用任意长的消息有效负载，或者只是一个非结构化的流(如原始音频或其他)，那么选择SOCK_STREAM并进行所需的缓冲。

Performance should be the same since both types just go through local in-kernel memory, just the buffer management is different.

性能应该是相同的，因为这两种类型都只经过本地内核内存，只是缓冲区管理不同。

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The main difference is that one is connection based (STREAM) and the other is connection-less (DGRAM) - the difference between stream and packet oriented communication is usually much less important.

主要的区别是一个是基于连接的(流)，另一个是无连接的(DGRAM)——流和面向包的通信之间的区别通常不那么重要。

With SOCK_STREAM you still get all the connection handling, i.e. listen/accept and you can tell if a connection is closed by the other side.

使用SOCK_STREAM，您仍然可以获得所有的连接处理，例如监听/接收，并可以判断另一端是否关闭了连接。

Note that there is also a SEQPACKET socket type that's still connection oriented, but preserves message boundaries (which might save you from implementing a message-oriented layer on top of a STREAM socket).

注意，还有一个SEQPACKET套接字类型仍然是面向连接的，但是保留了消息边界(这可能会使您避免在流套接字之上实现面向消息的层)。

I would expect data transfer performance to be similar for all of these types, the main difference is just what semantics you want.

我希望所有这些类型的数据传输性能都是相似的，主要的区别在于您需要什么样的语义。

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1. One likely difference are message boundaries. Datagrams will be delivered as a whole with the datagrams being the natural message boundaries. With stream sockets you can read N bytes and the socket will block until N bytes are ready. But this means no obvious message boundaries.
2. 一个可能的区别是消息边界。数据报将作为一个整体交付，而数据报是自然的消息边界。使用流套接字，您可以读取N个字节，套接字将阻塞，直到N个字节就绪。但这意味着没有明显的信息界限。
3. Maybe. A stream socket with TCP at least needs the initial three way handshake to establish the connection. A UDP socket does not.
4. 也许吧。带有TCP的流套接字至少需要最初的三种方式握手来建立连接。UDP套接字没有。
5. All things being equal, if speed is a concern, instrument and measure. (I assume you already know that only a TCP stream socket provides built-in reliable in-order transport, and only datagram sockets can be used to send to multiple receivers).
6. 所有的事物都是平等的，如果速度是一个关注，工具和测量。(我假设您已经知道，只有TCP流套接字提供内置的可靠的按顺序传输，并且只有数据报套接字可以用于发送到多个接收器)。

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If the clients and servers will always be on the same machine and the goal is to have minimal latency and maximum bandwidth, use shared memory.

如果客户端和服务器总是在同一台机器上，并且目标是使延迟和最大带宽最小化，那么使用共享内存。