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Have Sockets Run Their Course?
ChelleChelle writes "This article examines the limitations of the sockets API. The Internet and the networking world in general have changed in very significant ways since the sockets API was first developed in 1982, but the API has had the effect of narrowing the ways in which developers think about and write networked applications. This article discusses the history as well as the future of the sockets API, focusing on how 'high bandwidth, low latency, and multihoming are driving the development of new alternatives.'"
I think sockets work fi.... *connection lost, host not routable*
is no sockets. some way to seamlessly connect LOCAL processes to each other without socket overhead by using the familiar socket interface. something simpler than shared memory.
and a better protocol method of opening sockets with the hard stuff taken care of by the OS. and with transparent buffer protection etc.
Been there, done that. Apple (once again) had a great implementation of an alternative technology, that it finally abandoned when it didn't feel like fighting any more.
Open Transport (the PPC stack used in the Classic Mac OS) was fast, efficient, and cool. And based on the STREAMS methodology, the only real competition to Berkeley Sockets.
Choice is good, mmmkay?
Hire a Linux system administrator, systems engineer,
This seems to dance a bit too close to Networking Truths 6a, 11, and possibly 12. I will reserve judgment until I see solid real-world evidence.
Ce n'est pas une signature automatique.
There has been an alternative all the time:
http://en.wikipedia.org/wiki/Transport_Layer_Interface
This guy's worried about "narrowing the ways in which developers think about and write networked applications" in a world where people are reinventing wall(1) as twitter, IRC as friendfeed, and other web 2.0 'innovations.' You want to widen developers' thinking about networking? Leave sockets alone and close off port 80.
REM Old programmers don't die. They just GOSUB without RETURN.
There are Berkeley sockets which are relatively portable, and then there are extremely platform-specific APIs for high performance and scalability. The old API might have run it's course, but most of the new ones are still relevant. Things like asio are helping to merge all the differences into one nice API.
Although the addition of a single system call to a loop would not seem to add much of a burden, this is not the case
Really? For a lot of networking code that's in use these days, I don't see that the system call overhead is the bottleneck. On clients you usually have network bandwidth as the limiting step (rather than system calls). On servers, it usually seems to be disk access or HLL interpreters.
Each system call requires arguments to be marshaled and copied into the kernel, as well as causing the system to block the calling process and schedule another.
That's easy to fix without changing the socket API: just add a system call that can return multiple packets from multiple streams simultaneously, a cross between select and readv. If there's a lot of data buffered in the kernel, it can then return that with a single system call.
Solving this problem requires inverting the communication model between an application and the operating system.
Not only does it not require that, inversion of control doesn't even solve it, since you still have the context switches.
BSD sockets have a limitation of only a single stream at a time (for example, if you are loading a website over HTTP and you get stuck loading a huge image, you have no choice but to open up another socket connection or else wait). They are also stuck around the paradigm of only supporting byte streams, which means that users are always forced to write the same code over and over to create packet headers or delimited messages.
I would highly recommend checking out Structured Stream Transport. I'm not from MIT and I wasn't entirely satisfied with their sample implementation, but the paper is really insightful and explains how you can develop basically a smarter version of TCP that is both more efficient and also more flexible. And I'm sure there are other systems being developed with similar ideas in mind.
We definitely need to keep bsd sockets, if not just because I'm a regular user of netcat :-p, and also because they are what allow the creation of more advanced protocols, but I don't think most applications should still be using such low-level protocols today.
he recently developed SCTP (Stream Control Transport Protocol)4 incorporates support for multihoming at the protocol level, but it is impossible to export this support through the sockets API
The word that bugs me there, is "impossible". The question is, why? If you have to do something with sockets under the hood, then so be it, but it would seem to me that you could just add a few more fields to socket address to take into account multiple homes.
We've already had alternative APIs to sockets and for quite some time. sockets won. There were named pipes, ipx/spx, and the seemingly stupid idea of treating a network resource as a file has trumped every time.
This is my sig.
I am developing SCTP applications and has contributed to the linux implementation, and I think that one of the advantages of the socket API is that it is usable with select()/ and poll(), ie. it is file descriptors you can pass around.
But for SCTP there are things that don't fit nicely into the socket API, especially when using one-to-many socket types. For instance for retrieving options for an association you have to piggyback data in a getsockopt() call by using the output buffer also for input. It works, but it is not nice. Also, for sending/receiving messages you have to use sendmsg/recvmsg with all the features including control data, and the ugly control data parsing.
In my experience the way the socket API can slow down a processor is having to monitor many thousands of socket descriptors using select() or poll(), like in a web server. For Linux epoll() was created for this scenario.
Macs used STREAMS from system 7.5.2 onwards. Was kind of sad to see that go away with the switch to OS X.
...that most of the things that this guy is talking about would be better implemented below the sockets API. As in, how the OS handles things. Making things transparent is a good thing.
I'll also point out that having a fail over interface so that the client doesn't lose the connection has already been done in OpenBSD's pf called CARP. It is a free alternative to VRRP and HSRP. In other words, this doesn't have to be implemented in the API when another avenue already exists that does it.
My socks are fine for now. When they do run their course I go to walmart and get new socks its $5 for 6 pair!
This is hardly news and partly mistaken.
The statement that sockets limit throughput by copying between kernel and application processes is a bit simplistic. The copy of Rx data to an application usually primes the cache. If data isn't touched and loaded into the cache at this point, it will have to be loaded shortly, anyway. Granted, for Tx this trick does not hold.
Second, the interface is not the implementation. Just because sockets are traditionally implemented as system calls does not state that they have to. User level networking is a well known alternative to OS services for high-bandwidth and low-latency communication (e.g., U-net developed around '96). I know, because I myself built a network stack with large shared buffers that implements the socket API through local function calls (blatant plug, but on topic. The implementation is still shoddy, but good enough for UDP benchmarking).
User level networking can also offers low latency. My implementation doesn't, but U-net does.
This leaves the third point of the article, on multihoming. As sockets abstract away IP addresses and network interfaces, I don't see why they cannot support multihoming behind the socket interface. Note that IP addresses do not have to mapped 1:1 onto NICs. Operating systems generally support load-balancing or fail-over behind the interface through virtual interfaces (in IRIX) or some other means (Netfilter in Linux).
Not need to replace sockets just yet.
The word that bugs me there, is "impossible". The question is, why? If you have to do something with sockets under the hood, then so be it, but it would seem to me that you could just add a few more fields to socket address to take into account multiple homes.
Especially since SCTP actually does use the sockets API. You have to use recvmsg() instead of recv() if you want to do multi-homing, but in using SCTP I was actually impressed by how flexible the BSD socket API actually is. I can't say I particularly like it, and everyone who uses it ends up writing a wrapper around most of the send and recv calls, but flexibility is definitely it's strong point. If we ever do get routing by carrier pigeon, the BSD socket API will be able to adapt to it.
Qxe4
"damn punk kids"
Ro-ro..
Let's get outta here Scooby!
And did you exchange a walk on part in the war for a lead role in a cage? - Pink Floyd.
The socket API... or rather the UNIX file descriptor API... has been extended many times. Sockets are already one such extension, and there's no reason you couldn't do something like mmap() a socket to map the buffers into user space directly. Heck, udp sockets already diverge from the read/write paradigm.
The problem with sockets is at a higher level. They're not mapped into the file system name space. You should be able to open a socket by calling open() on something like "/dev/tcp/address-or-name/port-or-name" and completely hide the details of gethostbyname(), bind(), and so on from the application layer. If they'd done that we'd already be using IPv6 for everything because applications wouldn't have to know about the details of addresses because they'd just be arbitrary strings like file names already are.
You mean, like pipes?
Already does that.
That explains why - fortunately - it wasn't widely adopted.
All hope abandon ye who enter here.
It seems to me that all the issues the author mentions could be solved with some library written over the top of sockets (and potentially other primitives like threads). Sockets are meant to be a low level interface, not to solve every problem.
The multi-home problem is real, but could be fixed with a relatively minor extension to the API, like IPV6 has been added in.
Having RTFA, I have to ask: "What in Cthulu's name have APIs got to do with all this?".
The author broadly complains of the current status of networking at the OS level (copying bytes, connecting to/from multihomed hosts, etc.). APIs don't get into it.
The title of the article appears to be an attention grabbing device, it could well have been titled "Does Britney Spears carry my baby?".
(The incipit would be "No. Now, in a world of low latency and high bandwidth...")
Cheers,
alf
Comment removed based on user account deletion
Sockets are very annoying when you have a lot of clients being served by one server. Consider, for instance, a chat server, with 25000 clients connected. You have 25000 sockets, one per client (plus a listen socket for new clients to connect to).
Whenever data arrives, the system has to somehow notify you that one of your sockets is ready to read. That generally involves some kind of polling, with select or poll, or some kind of interrupt mechanism, such as a signal. I'm leaving out some options, but regardless of how you get notified, you then read the data from the appropriate socket.
Then guess what happens? Most likely you take that data, wrap it in a data structure that tells you which client it was for, and stick it on a work queue, where the main thread or threads pull things to process.
Step back and look at what happened here:
That's just insane! The kernel demultiplexed the incoming data, and the server just remultiplexed it when it put it onto the work queue. Demultiplexing belongs in the server application, not the kernel.
What I want is a single stream between my code and the kernel that delivers all the data for all 25000 clients. Whenever any client has data, I want to be able to read from that, and get back a message, that identifies which client it is from, and gives me that data.
The kernel should just be parsing the incoming TCP stream enough to recognize what port a given packet is for, and what client it came from, and then should queue it up into a single stream for the server handling that port. (The kernel has enough information from that to keep track, on a per client basis, of how much data is pending in the queue for the server app, so has what it needs to manage flow control).