Linux Namespaces and Go Don't Mix
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Even though I am a big fan of go, I've personally built two container runtimes in other languages do to the namespace clumsiness.
Personally, I think rust is an excellent alternative for namespace utilities.
EDIT: there is more information and links in the issue in the netns library: https://github.com/vishvananda/netns/issues/17
Disclaimer: I am one of the original libnetwork authors and we have been aware of this issue with go for some time now.
Can you share any details on those other container runtimes?
At the moment I'm incredibly busy, but later this year I might be able to start working on that too.
The Linux syscall interface exposes certain functionalities that are much more easy to reason about at the process level such as namespaces, capabilities, seteuid and so on. However these syscalls all operate on the thread level (since the kernel treats threads pretty similarly to processes). Therefore in order to perform these operations safely you need some sort of process wide mechanism to apply the operation on every thread (and don't forget error handling!)
This is _not_ just a golang problem or an M:N threading problem as many comments suggest. The kernel really needs to provide new syscalls for these features that operate at the process / thread-group level. The current syscalls are extremely difficult to use correctly in any multithreaded context in any language. When you consider the security implications of these features it makes the problem even worse.
Check out https://ewontfix.com/17/ for a really good analysis of the difficulty musl libc has faced making a multi-thread safe seteuid on Linux. There are also many bugs in glibc related to this as well. Linux makes userspace responsible for patching up the leaks in the kernel's process abstraction and that's really not a job that userspace is in the right position to take on.
Or it could provide another clone flag that indicates that threads spawned that way should share privileges and similar things, then runtimes that need threads to all behave the same way can opt into that. I suspect that some tools do advanced privilege kung-fu that relies on those per-thread properties.
This is hardly a linux specific issue. Prominently for instance pthread_setugid_np exists on OS X, threads for different subsystems exist on Windows etc.
I've hit this exact problem with multithreading in C and setuid and just because it _can_ be managed in C doesn't make it easy or straightforward.
Therefore, I mirror the sentiment that there needs to be a way to operate on a process level, even if that has some interesting consequences.
(P.S.: In C, if you're using glibc, it DOES actually patch this issue up on its own using one hell of a nasty hack.)
I too love reading the code for nptl(7). It's a riot. :D
I mean, what's the better alternative to Go for this work? Maybe Rust? It is, at least more controllable at a lower level...but, not as easy to pick up for people coming from a C/Python/Perl/Ruby systems and ops background. I'm not saying one should use Go for containers/namespaces programming, but a lot of people are with some success (probably also banging into the namespaces issue now and then), I'm just saying it's not obvious to me what the better alternative would be.
This issue is one of the downsides of Go's M:N scheduling. The OS is simply not aware of what the Go runtime is doing, and as a result you get impedance mismatches like this.
It "raises a few eyebrows" because M:N scheduling is unpopular outside of Go and Erlang. It was tried early on in the Linux world and abandoned precisely because of issues like this. Go has repopularized M:N lately, and it's proof that such a system can work for lots of apps, but the downsides of that decision are every bit as real today as they were in the early days of NPTL.
It's not as easy as threads (M:N vs 1:1 is a red herring as far as this is concerned), but there's no free lunch.
I was pretty disappointed Rust didn't ship with async/await and some form of lightweight thread but it's understandable.
1. http://journal.stuffwithstuff.com/2015/02/01/what-color-is-y...
1. https://www.reddit.com/r/rust/comments/6enj5d/what_does_rust...
But, are you saying that to switch to a namespace in Go one must fork, whereas one wouldn't need to fork in C unless you need to switch namespace and you need concurrency (because you can determine when things will happen with precision in C)? I don't know. Again, this is beyond my understanding of Go right now.
I may just not be understanding the implications of this. The code to deal with it looks reasonable enough to me; it's a smallish function, easily isolated. I think the author did a great job explaining the problem, the troubleshooting, and the solution. I just didn't see the problem as being all that damning of Go...but, that may be a reflection of my shallow understanding of the problem, or of the implications of the cost spawning a new process (to me, I always think back to the old adage "fork is cheap on Linux").
Arguably it has been implemented with clone(2) which has flags.
> in fact, it's easier to reason about fork than something like POSIX threads, IMHO.
Not if you call fork() in a multi-threaded program. That ends _exceptionally_ badly (let's just say there's a reason Go doesn't expose syscall.Fork and it has to do with horrific deadlocks).
> I just didn't see the problem as being all that damning of Go.
The problem is more subtle, and it comes down to maintainability and understandably. If you ever decide to read the runc codebase, I apologise. One of the reasons the codebase is so scattered is because of these sorts of hacks where you have to work around issues in the Go runtime (because it doesn't give you enough control). In the article, whenever you read the small function you have to keep in mind that it's actually spawning a subprocess (which then means you have to think about what namespaces had the process joined and so on). Go is an okay language, but it simply wasn't designed for stuff this low-level. We would be much better served with Rust in my opinion.
> But, are you saying that to switch to a namespace in Go one must fork, whereas one wouldn't need to fork in C unless you need to switch namespace and you need concurrency
In C you don't need to fork to switch namespaces, you just call setns(...). For the PID namespace you need to fork, but that's just a quirk of the interface.
In Go, you theoretically don't need to fork either (syscall.Setns is available). However, there is no real way to safely use it. First of all, the namespace interfaces in Linux are quite fragile when it comes to multi-threaded processes, but combine that with a runtime that will switch you between OS threads at random. And while the documentation on runtime.GOMAXPROC and runtime.LockOSThread might trick you into believing it's possible to stop the Go runtime from doing a clone(CLONE_THREAD|CLONE_PARENT), you can't.
The article is stating that to control the namespace that the threads execute in, that a separate process must be spawned so that the entire process can be forced into the correct namespace. Otherwise, the runtime can spawn new threads as it sees fit and you don't have control over which namespace they are in.
It might be possible to work around this from within the same process if it were possible to force the runtime to not spawn new threads in particular cases. If you could control when the runtime was allowed to spawn new threads, then you could organize the program / threads in a way that would keep the correct code operating in the correct namespace. Unfortunately, you can't.
Disclaimer: I don't know Go, but this is my understanding from reading the article.
When changing namespace happens often in a hot path, forking might not be fast enough.
I disagree with Walton that the blame is on the N:M threading. It's really on the Linux kernel that has never made a clean distinction between threads and processes, both in kernel and in the APIs.
If you have one thread in one namespace and another in another you now have to worry about what you can do in the context of a callback. This asymmetry just makes any multi-threaded program more complicated than it needs to be (and already is).
But there also are non-security applications of namespaces.
And it's not like namespaces are the only per-thread thing in linux. Capabilities, uid and signal handlers come to mind.
In addition fork() style concurrency was essentially nonexistent outside of Unix.
This is not a problem of M:N. This is a problem of Go being badly designed. Not new.
Due to the implicit M:N mapping, Go goroutines are extremely cheap. This allows you to spawn as many, as your algorithm naturally requires. The Go runtime will automatically map them to native threads - typically one per avaliable CPU. As a consequence, a Go program that heavily uses goroutines has a pretty clean code and scales without much overhead across a large variation of number of CPU cores.
Not for a long time, for all the reasons the parent mentioned (and then some).
Although they have their own set of issues, Windows fibers are also barely used.
Let me tell you how runc works. runc is written in Go, and we take an OCI configuration file. Because we can't just fork and set up all of the namespaces in Go, we have a C function called nsexec which is specified as __attribute__((constructor)). This ensures that our code will execute before the Go runtime boots. The parent process writes (using netlink as the wire protocol) to a pipe that the child has open and is parsed in C. Then, the child will have to do a series of forks, unshare, setns, {open,read,write} and so on (and the final PID needs to be sent back to the original parent) in order to set up and join all of the necessary namespaces.
In C, this code would be _immensely_ easier to read, write and maintain. Just look at LXC. Personally I really wish people had just gone with Rust earlier on rather than implementing everything in Go. I've had nothing but pain from Go.
Is it merely fear of C that keeps so much of the container infrastructure on Go? I've only spent a couple of weeks looking peripherally at Go, and I already like it better than C (which I've poked at peripherally for ~25 years), but I don't know it well enough to know its warts.
Sort of. Go binaries are statically linked by default which is a must in situations where you are e.g. unsure about what libs are available in the current environment. You have to go through a lot of hoops to make sure your C executable is really fully statically linked.
Note though that Go packages will be statically linked into your binary by default.
No, but there are more options than just Go and C. Rust is an option that I'm shilling at the moment (though I've only started learning it, so take that with a grain of salt). The main reason I would want to write it in C is because there's a lot of string parsing code you have to write in order to make container runtimes work -- and as we all know that's probably the #1 source of security vulnerabilities.
> Are there no advantages to Go for runc?
There are, mainly due to network effect (everything else is written in Go) and getting contributions from the community (Go is easy to pick up). Unfortunately there are also disadvantages, and quite a few of those disadvantages are present in Go but are not present in other memory-safe and low-level languages (Rust is a good example because to be quite honest it's the only player in this space that doesn't try to do more than necessary).
Go is a good language for it's designed for (Web servers and similar things), but from my experience it's not the best choice for low-level tasks. We've seen cases where long-running container daemons (not naming any names) will crash if you run more than 1000 containers on a single system. They don't crash because of the actual daemon code but because of issues with Go's GC (it doesn't actually free memory sanely, it uses MADV_DONTNEED which inflates RSS and causes OOM to kill your daemon).
> And, would it be possible for someone to write a somewhat standardized Go library for doing this grunt work?
Of course (and you could argue that we have done that in runc with github.com/opencontainers/runc/libcontainer/nsenter), but the thing to note is that in order to get around problems in the Go runtime you have to split out a single piece of code into separate processes and have to now redesign how a single function would work. So moving it to a separate library means that development is even more frustrating (you've created an API around the internal implementation of whatever thing you're working on).
> Is it merely fear of C that keeps so much of the container infrastructure on Go?
I think the network effect is the main reason. Most of the people I've worked with know quite a lot of C (we do kernel work sometimes) so writing a runtime in C would be frustrating but entirely doable. The problem is that you couldn't just import it into a Go project (and people don't like cgo because it makes binaries harder to build in certain cases).
> I've only spent a couple of weeks looking peripherally at Go, and I already like it better than C
Go definitely has it's uses, and I still use it for new projects. For example I recently wrote a tool for dealing with OCI container images in Go[1]. The standard library of Go is quite nice (though I found some bugs in archive/tar but let's not go there) and I'm always quite amazed just how much you can do before you have to import external libraries.
But I recently started learning Rust and I am _really_ enjoying being able to understand what my program will actually look like when compiled. If you've ever had to strace a Go program, you'll know exactly what I mean. Debugging Go programs is basically fucking impossible.
I've been tinkering with go, and the project I'm planning to use it for is container-oriented (building/using/distributing them for non-technical users, more than working with them at a very low level like runC or similar, but still, it's very useful to know). As an aside, umoci looks, at first glance, like one of the components I thought I'd need to build...so, that's cool.
I'm not gonna keep bugging you with questions; I'll go read the code. (I'm also finding rust really neat, conceptually, even if I'm not yet finding it easy to read or understand.)
Oh, and I haven't even mentioned the absolute shitfest that is the cgroup namespace and how you have to set up cgroups before you unshare it because its behaviour changes based on what cgroups you were in when you unshared it.
To avoid the authors' issue, you can write some functions in C. CGo has a very high level of integration (you can mix languages in the same source file) and would be quite simple for the case of a setns/execve wrapper.
No, no it doesn't. CGo is slow as balls to call into and return from.
Types can't fully be shared.
It's interacted with via comments.
You can't use cgo to control the threading of the Go runtime itself, which is the real problem here.
The behavior you want is to be able to call linux syscalls that operate on threads and not be utterly fucked. That behavior cannot be accomplished with go nor go+cgo easily.
Threads in cgo are also kinda fucked.
Go is deliberately opinionated about threading of the runtime. I think it's unlikely Go will offer much more control over these internals (beyond GOMAXPROCS), given the philosophy around e.g. GC tuning.
Cgo is a beefed-up runtime.LockOSThread() that could be used to avoid having the author resort to a helper process.
> CGo is slow as balls to call into and return from.
They're slower than Go function calls, but they still take only nanoseconds. This is negligible on the authors' scale of "launching an entire container".
For their case of "it is not possible to guarantee that a new OS process ... will run in a given namespace", you're not even returning from Cgo after exec.
> It's interacted with via comments.
Do you use build tags? Or go:generate? Like it or not, it's idiomatic.
I'm with you on the types, though! `go tool cgo -godefs` helps, but it would be great to see improvements especially in the reverse case of exporting Go buildmode=c-shared for C consumption. Still, a little marshaling seems tidier than a whole helper process.
GOMAXPROCS is actually a lie. If you set it to 1, the runtime will still create threads.
It's not a lie. The variable is GOMAXPROCS, not GOMAXTHREADS. "procs" is specific jargon of the G:M:P scheduler design.
Separate processes, like the post suggests?
I have no idea why someone would expect user-level pseudothreads to execute across system-level primitive boundaries.. seems fairly obvious to me.
I don't expect a chrooted daemon (e.g. apache, etc) to have access to parent thread contexts.. etc.
Fork & pipe IPC shouldn't be too difficult for anyone to understand, beyond that, if you don't understand these things, you probably shouldn't be writing code that complex..
runtime.LockOSThread() does exactly that [1].
Trust me, we've been trying to get Go to co-operate with containers for quite a few years. It's not as simple as just reading the standard library docs. ;)
That sounds like an implementation issue, why not assume the documentation is the intended behavior and this side effect is a bug? I'd support a CL to fix this behavior or add a block-clone-from-here runtime call (but the end result of that is you want the thread to exit when you're done with it, and not to go back into the pool... which is also new behavior). At the minimum, this behavior of new threads spawning from LockOSThread could be documented.
As a workaround, what about CGO -> pthreads -> spawn a control thread free from the Go scheduler -> call back into Golang to run a control loop function? You can do this in init() to ensure it has full control over itself. Or will Golang call clone() from unscheduled code?
Because after discussion with the Go devs they've concluded it's not a bug. To be fair, it's their decision to make a language runtime hostile to user's being able to mess with the process model, it just makes programs hard to write.
> At the minimum, this behavior of new threads spawning from LockOSThread could be documented.
The thing is it is documented[1], it's just very subtle:
> LockOSThread wires the calling goroutine to its current operating system thread. Until the calling goroutine exits or calls UnlockOSThread, it will always execute in that thread, and no other goroutine can.
An implication of the emphasised part is that if you use 'go' (or a function you call uses 'go') inside a locked goroutine, you are guaranteed that goroutine will be scheduled on another thread. Which is not what you might want or expect (personally I would expect goroutines created from a locked goroutine to act as normal coroutines). The problem is made much worse because a lot of the Go standard library uses 'go' internally and there's no way for you to know what functions use it and what functions don't (and what functions might use it in future versions). Not to mention that there are even more edge cases where functions you call could end up on separate OS threads.
> As a workaround, what about CGO -> pthreads -> spawn a control thread free from the Go scheduler -> call back into Golang to run a control loop function?
At that point you're really just massively hacking around the Go runtime. I would not be confident that such hacks would be a good idea in the long run. Remember that Go doesn't have any real forking model in its standard library or language, so the language provides no guarantees that it has to "play nice" with foreign threads.
Also, calling from foreign C code into Go is quite difficult (especially if you're calling into an _already running Go program_ which might reschedule your code at any time and would require hooking into core runtime internals).
> You can do this in init() to ensure it has full control over itself.
init() runs after the Go runtime starts up, you would want to do it as an __attribute__((constructor)) in C code so it is started before the Go runtime.
I hope it continues to play nice, as I have a project depending on this behavior (bindings for a CPU emulator which spawns a thread for the CPU main loop, and calls back into my Go code on some events).
Thanks for the info. I guess the biggest problem is making sure `go` in a locked goroutine doesn't release threads to the scheduler from the locked goroutine? That's a weird thing to reason about. I initially guessed you'd need a separate feeder thread, but you want `go` from a locked thread to keep the uid and namespace of the locked thread.
So I guess there are two potential solutions:
- goroutines spawned from locked threads are pure coroutines and will not be scheduled on another thread
- goroutines spawned from locked threads can only execute on the locked thread, or on threads spawned from the locked thread that don't predate the goroutine. Child threads can also only be used for matching child goroutines, and will be more aggressively collected. This would converge closer to an oldschool threading model than green threads, but should hopefully prevent bugs like UID/namespace hopping.
This is the kind of thing you could possibly do with a small patch to the Go runtime. Go makes it so easy to build the compiler/runtime, perhaps forking Go for this is reasonable until there's an official solution.
There's also the issue of what to do with the primary thread that has been marked unsafe when it returns. Instead of LockOSThread, you probably want "give this OS thread and its children magic sandbox scheduling behavior, which includes collecting the thread when it returns, because we're going to call stuff like setuid".
I think C++ may just be too rich a language to be a part-time thing. I think Rust might have the same problem (though I'm finding it easier to read than C++, it doesn't seem to be afraid to require a lot of learning time from its developers). But, I'm willing to entertain other theories.
For whatever reason, Go seems to have very quickly entered that category of language that systems and ops people are comfortable with.
In contrast, one of the reasons I'm a big fan of go is it is extremely easy to read for almost anyone. People pick it up very quickly.
C let's me focus on the underlying system and it is what Linux is written in, Python is quick to write and has great libraries, and Go is amazingly easy to pick up/read.
C++ always felt like it was more so a language designed for programmers who love code than something that lets me focus on what I love (systems).
But, building new things in C? Nah. I don't see any reason for that. Since C was designed, we've ("we" as in our industry, not specifically me and you) learned a lot and our systems have grown massively in all dimensions. It would be optimistic to assume we don't need different tools 40+ years on.
C++ looks good on paper. It has containers and types and generics. You come to find out that it's all based on meta-programming which is an interesting idea: Basically you're writing code to write code, and that code writes code. The whole system is macros all the way down. There's no native language support for anything but macros and the macros implement everything.
The student's experience is that he can quickly solve a problem using a list of stacks of strings (vector<stack<string> > > in the parlance.) Which is fine, almost like typed-python until you make a mistake. Then, the compiler, who knows nothing about those types which were all built by expanding macros, is not your friend.
Miss a minor `*` and a single line of code will fully expand its underlying macros giving a 10-page, indecipherable error message.
Should you make it to runtime, no debugger can tell you the contents of a vector, string or stack. They're just blobs of buffers and pointers with mangled (and yeah, that's the word that they chose: mangled) names to make them extra unreadable.
This is when most people ask if they can just have C back.
It is entirely possible to write C-style programs in C++ (very few classes, globals all over the place) and so on, and at least for me, C-style software in C++ are much safer/easier to debug than C-style software in C .
But I'm like you, if I know that I'm going to need "advanced" data structures I'll pick C++ over C (or these days more likely Rust).
You know, it's interesting. I've been programming with Python for about 6 years now. I've also picked up Javascript, SQL, bash, and PHP along the way. I'm always gaining a little bit of C knowledge here and there when writing C extensions for my Python applications. I'm a fairly experienced programmer at this point. To the point:
I tried picking up Go one day because I was hearing so much about how it could replace Python as network glue code with better performance and reliable concurrency. I can't really validate or invalidate those claims. That said, I found Go to be sort of difficult. The syntax is really simple. Compiling is really simple. Concurrency is even simple. However, need to do something in a different way than Go decides is correct? Well, you can't. It won't even compile. The difficulty in Go is in learning about what the compiler thinks is OK. I don't really like that. You don't really know if your code will work until you compile. Basically, I just think Go isn't really flexible enough for modern programming. I find that Nim can do Go's job better than Go can for my use cases anyways.
I think this is similar to what people think about the type system in Haskell or the borrow checker in Rust. With every higher level language comes new things to learn and obey.
I want to mix C++11/14 into that also. Now that the typesystem is used by the standard library to describe resource ownership in code whole categories of errors can be found at compile time. If you are new this it can seem like you are fighting the compiler, but once you learn that the compiler just won't let you make certain kinds of mistakes you get access to every level of abstraction with C++11/14 and Rust. You can code in terms of passing database bindings betweens threads in threadpools or you can twiddle individual bits in specific registers and everything in between.
I don't know Go well, but it seems really limited. You can't write certain classes of bugs, but you also can't write many design patterns.
Whether or not I choose Go is almost always comes down to whether I want to solve a problem quickly and with decent performance/readability/etc or if I want to take a lot longer for a solution that is more aesthetically pleasing or with a smaller risk of error.
I'm sure lots of people will argue that their language is faster to develop in, but apart from toy programs or those requiring libraries unavailable in Go, this has never been my experience. In particular, even after two years with Rust, I still have trouble reasoning around memory management, lifetimes, how to pass around functions, how to do anything asynchronously, etc. Go isn't perfect for anything, but it strikes a good balance for the kind of work I tend to do.
YMMV.
That was my experience, too. Vaguely interesting in a couple of ways, but definitely a bondage and discipline language and nowhere near compelling enough to make me want to put up with that.
This is true in every text-based programming language. s/compile/execute/ for interpreted or repl-based languages.
My favorite was the Comair christmas failure back in 2004 or 2005. I tried googling the root cause, but I think it was an Integer overflow in the 16 bit integer they used for storing the flight number. The system was designed in the mid 80s and 65535 flights was an insane amount, but but when the software failed on Christmas it interupted more than 1,100 flights.
No one disagreed with this comment and it is one of the least controversial thing I have said on HN. I think I have a downvote fairy, someone who just downvotes everything I say. If so, why bother? If I don't have one then when you downvoted me, why didn't you respond?
Go hijacks control flow and makes it more difficult to reason about how your code will be compiled and executed. At least that is true in my personal experience.
https://gobyexample.com/channel-buffering
As far as my understanding is concerned, channels are a way for goroutines to pass data between one another, correct? Yet in this particular case, the channel `messages` is operating in the same manner as a generator or array. So, am I creating goroutines by passing messages to the channel or am I just using the channel as a simple buffer?
This example helps as well: https://gobyexample.com/channel-directions
Am I implicitly creating goroutines by using channels or am I simply creating a buffer?
Sorry I don't have any of my own code to share as I deleted all of my Go practice stuff.
The flow of data through channels can be confusing until the concept becomes familiar, but the behavior is well-defined, so the behavior is as easy or difficult to predict as of any program of the given complexity.
Pid ! {self(), 42}
receive
{From, Data} when is_pid(From) ->
handle_data(From, Data)
end
Too bad we can't use Erlang for systems programming, but you can't have everything!
A channel is just a thread-safe queue. An unbuffered channel blocks until something else receives the sent value. A buffered channel allows n sends until it blocks. Using a channel will never create a new goroutine, its just a way send data. You can use a select statment to wait on sending or reciving from multiple channels or to send or get without being blocked by a full or empty channel.
In C you could put together a RW mutex, condition and a linked list or array and have the same thing pretty much.... If you want to create a goroutine you need to invoke "go X".
Out of curiosity, do you know C/C++ or Java?
Will Nim be as versatile and solid as Go in the future? Hard to predict but i would say no. You need a solid financial backing and certain amount of adoption where people actually write software that makes them money.
Agreed, that's why I don't use it for anything super important yet. Nim is approaching a 1.0 release soon. Go has a similar problem in that it is maintained almost entirely by Google who has a history of dropping projects without warning.
> Go is more versatile and at the same time more mature than anything out there.
This is objectively incorrect. In fact, Go aims precisely to be non-versatile for the sake of simplicity. That is why Go does not have generics for instance.
> It is a different design and it excels in what it does (considering all tradeoffs now)
I don't think it's design is all that different. It looks like a stripped down version of C and it's definitely not the first PL focused on concurrency.
> Will Nim be as versatile and solid as Go in the future?
Nim is already leagues above Go in the versatility(I assume you mean flexibility?) department. As far Nim being as "solid" as Go, I'm not entirely sure what you mean. If you're asking about stability, I believe that Nim can reach a similar level of stability as Go, yes.
> You need a solid financial backing and certain amount of adoption where people actually write software that makes them money.
I agree with this. However, it's not always a quick process. The only reason Go is as popular as it is is because of Google's size and reputation(edited). Every programmer on Earth heard of Go within a few days of it's official release. Nim is taking a slow roll approach. Look at Python. It took almost 15 years before it started getting really popular.
All that said, I didn't come into this thread to argue about Go vs Nim. I've been accused of shilling Nim in the past. I'm sorry that I like talking about PLs I enjoy using.
The reasons Go doesn't (yet) have generics are practical rather than philosophical. And well-documented.
I also don't believe Google's marketing budget contributed much if anything to supporting Go. The _reputation_ of Google and the Go authors was far more important. (Personally, when I saw people like Brad Fitzpatrick try Go and rave about it making programming fun again, I decided to try it.)
You can happily accuse me of shilling Go if you like :-)
> The reasons Go doesn't (yet) have generics are practical rather than philosophical. And well-documented.
Can you give an example? I guess I fail to understand why a statically typed language would choose to forgo all of the advantages generics provide. Does it have something to do with Goroutines?
> I also don't believe Google's marketing budget contributed much if anything to supporting Go.
I didn't necessarily mean their marketing budget. I should probably edit that. I meant that anything they do is news.
Like I said, the objections are practical, not philosophical:
They published four past design docs for generics in Go that simply didn't pass technical muster (https://github.com/golang/proposal/blob/master/design/15292-...)
Also, rsc stated he plans to understand generics better in 2017: https://research.swtch.com/go2017#generics
Also, bradfitz said recently on the GoTimeFM podcast that doing Generics and Go2 together makes sense.
> I didn't necessarily mean their marketing budget. I should probably edit that. I meant that anything they do is news.
I feel like the comments from others about Dart give the lie to this one. Go is fantastically, dramatically, massively more popular than Dart, which is also from Google.
Russ Cox and Rob Pike keep repeating this mantra, but I don't buy it. No, I don't believe they object the idea of generics itself. And yes, generics pose practical complexities and a plethora of issues that have to be resolved.
But so does every other language feature. The features you choose to add reflect your philosophical values and priorities.
Go chose to bake some hitherto very niche features that could have been as libraries into the language. Channels in particular, are a language construct only because Go doesn't allow operator overloading and generics for user types. But channels get them, because channels are demonstratively important for Rob Pike[1].
There's nothing wrong with that of course, but that's a philosophical decision. Why channels can avoid the vagaries of interface{} boxing, but not sets, linked lists or queues?
The reality is that every modern statically typed language except Go has generics, and they all implemented them very well. The ML languages and Ada were already doing it in the 80s, and OCaml and Eiffel managed to combine generics and polymorphism back in the 90s.
It seems to me that when originally designing Go, Pike, Griesemer and Thompson just didn't think generics are worthwhile enough for the effort it takes to properly research them.
When Go was started, its authors mostly looked to languages which implemented generics later in their lifecycle (namely Java and C++) and their implementations suffered from problems due to other, rather obvious, design defects: https://research.swtch.com/generic
I'm happy to see that this attitude is changing, and other languages are looked at.
> It seems to me that when originally designing Go, Pike, Griesemer and Thompson just didn't think generics are worthwhile enough for the effort it takes to properly research them.
Are you arguing that it's easy, and they just haven't done it? Or are you arguing that it wasn't important enough at first, and so the implementation developed in directions that preclude straightforward implementations now? I can believe the latter, but after reading the multiple, detailed proposals from Ian Lance Taylor, I don't believe the former.
I think Google put lot of marketing budget for Dart. But I don't see it ever comes in discussion regarding popularity or lack of it.
It is fine a lot of people do not like Go but claiming its popular just because of Google seems baseless.
It is fair to say that without those names attached I would have likely passed it by. Google is boring, but those three names, for me at least, I had to take a look.
Let's see if Flutter and Fuschia teams manage to push adoption for Dart.
> Google & adoption
I think it helped get around the initial cycle of drawing in the curious. An argument counter to claims regarding the importance of the people involved would point out Plan9 etc. that are hardly widely known, much less adopted.
In sum, I think the role of Google in one becoming a Go programmer depends entirely on when it happened. Today, of course Go has its own brand name. 8 years ago, it was Google that eased the debutante phase of the language.
This doesn't seem like a very credible statement on the face of it. Is Go more mature and more versatile than Python? Than Java? Than...Scala? Go does seem to share a lot of use cases (and limitations) with Java; and it would be hard to call it more mature.
It was the same for Linux, Python, Ruby. Being community-driven can be a bug or a feature.
> Go is more versatile
Nim has macros, templates, overloading and compiles to C, JS, Objective-C. Runs on more architectures than Go including arduino microcontrollers.
> mature than anything out there
Go is not more mature than C, C++, Java, Python, Perl...
> You need a solid financial backing
See Linux, Python, Ruby... many projects had no big company or funding behind them.
Pardon me and no offense, but it sounds like you are hitting the 'statically typed language' boundary.. all of the others you mention are fairly loose and dynamic. Go & C, not so much. It sounds like your use of C has been library code, which presumably is more 'data processing' oriented and so doesn't require much structure or control of process/runtime/etc.. which is where you will run into this stuff on the c side..
This is why I moved from c/c++ into dynamic languages to start with.. that said, as I grow more sophisticated and can 'deal' with the typing/lower 'machine' level control, the more I can understand other tools.. even C++! ..
i mention this because each layer of abstraction is there for a reason.. best to view with a fresh pair of eyes imho
You are supposed to "compile on save".
The namespace issues are unfortunately a lot tougher to address.
Also: please don't spawn goroutines during init(). There's generally a better time and place, and in the event that you justifiably need a package-level background routine you can spawn it on demand with a sync.Once.
I get the feeling that the Go runtime doesn't do the same.
Note that you'd run into this bug within any multithreaded process, whether the code was written in go, Java, c, or whatever.
I really don't think this is a language design issue but clearly if you want absolute control you can't get that with the Go run-time.
It's true the Go runtime could give users more control over goroutine and thread scheduling but that would kind of defeat the purpose of not needing to know about it and having Goroutines as the only flexible unit of concurrency.
I think the kludge here is on the Linux side. Having some magic properties bestowed upon threads doesn't make sense. The property should be accessible via a handle that can be shared amongst all threads.
This isn't true in Linux or Windows so I don't see why Go would make this assumption other than poor design.
>The property should be accessible via a handle that can be shared amongst all threads.
It literally is. The namespace information is shared with all threads in a PID group globally available in the /proc fs.
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What OP is doing is effectively having 1 program run part of itself in 1 container, and another part outside of that container.
Go isn't a systems programming language so this level of fine grain control isn't possible. Hell its pretty difficult in a C/Rust/C++ environment.
I think it's mostly true in Linux and the situations where it isn't true are subtle and require expert knowledge in some specific areas. It's not like there's a big sticker on Linux that says threads are generally not symmetric.
I get the bit of half the process being in one space and half in another. I just find it odd. Can half the process run as root and half the process run as another user? Maybe yes? Can a file be open in half the process and not open in the other?
At any rate, I think it's not black and white. Green threads do make sense in general and introducing different thread types and more granular control makes things more complicated.
I think you're missing my point about APIs and handles:
handle = open_namespace("test")
syscall(handle, "yes")
(EDIT: thread local storage I guess is an example of asymmetry between threads but it's intentional/clear asymmetry designed for specific purposes and something you don't need to access in Go e.g. because you don't use threads directly).
Any of the data stored in the TIB. For instance each thread can be bound to a different subsystem.
More prominently the locale is stored there.
In Linux you can unset CLONE_FS when creating a thread, but the Go runtime does not do this.
I note the Windows docs[1] say "Multithreaded applications and shared library code should not use the SetCurrentDirectory function" (which Go's Chdir() calls)
[1] https://msdn.microsoft.com/en-us/library/windows/desktop/aa3...
I've never needed to have half my process in one namespace and half in another. It's a niche application. Green threads/goroutines is something I use extensively and I wouldn't give it up for the ability to have half my process in another namespace. There's probably some middle ground there in giving Go users more control over which thread pools run which goroutines...
Someone should file a Go bug and see what the response is...
From memory, several people working on Docker have done so over the years. It's still a problem because the only "real" solutions are:
1. Do what glibc does and implement nptl(7) (effectively a way to make Linux threads look like POSIX threads by synchronising certain operations on all threads). This would require making first-class library APIs for Linux features (outside of the wild-west that is syscall).
2. Give programs far more control over threading, which would require making runtime.LockOSThread and GOMAXPROCS actually do what their documentation says. However, that would restrict their ability to be opinionated about threading (and would almost certainly cause deadlocks in some programs) so I understand why they don't want to do this either.
It's not exactly the same issue, but the themes are all the same.