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Go has no way to abort a goroutine so if you tried multiple algorithms you would use total CPU time for all algorithms. Unlike actual threads Go gives no assur

Go has no way to abort a goroutine so if you tried multiple algorithms you would use total CPU time for all algorithms. Unlike actual threads Go gives no assurance that goroutines are preemptively scheduled, so doing so might take worst case time anyway. Even worse, there is no guarantee that new goroutines run next so doing so could introduce a scheduling delay. So basically it would be a terrible idea to do this in Go. With C/pthreads it might have some use in some really exceptional case. These are all reasons of course why goroutines are a bad idea. They should have just used threads, but apparently they wanted to support 32-bit architectures or some archaic OSes where threads have a high unit cost.

enneff 13y ago
Gccgo did use threads for each goroutine for a while, and it was significantly slower than the gc "green thread" style implementation (used by both compilers today). Goroutines weigh in at about 4k each. OS threads are 64k minimum. That allows more than an order of magnitude more goroutines than threads, from a memory perspective. From an execution standpoint, goroutines managed by the Go runtime allow some nice scheduling optimisations, as the runtime is aware of the communication between goroutines. (some of these optimisations are in Go 1.1) Finally, there is no reason goroutines can't be preemptively scheduled. It is just an implementation detail, and work has already begun on this front.
- teenth 13y ago
  Gccgo didn't have a garbage collector for a while, around the same time it was using threads. Was it even using a pool? Did it run goroutines for a short time on the current thread before moving to its own thread? Certainly not. Thread overhead in Linux is 8k, only slightly more than goroutine. It's 24k for windows. You guys don't even know basic facts that should have guided the design.
  - enneff 13y ago
    Really? Can a Linux process spawn 1m threads? I didn't work on the design. If I made a mistake that's my fault. The people that did design Go and implement the runtime know what they're doing. You didn't respond to my other points, either.
    - teenth 13y ago
      Yes a Linux process can spawn 1m threads, and testlimit64.exe spawned 250k threads both with 64k user stack and 1 MiB user stack... because that is just reserved address space if it isn't actually used. Only the kernel overhead matters to how many threads. I'm not sure what point you want addressed... scheduling optimization? It's also a deoptimization in other ways, such as predictable latency and fairness. I agree the designers knew what they were doing: designing a 'modern' language for 32-bit computers. The question is why?
      - enneff 13y ago
        Even given that what you say is true, these are all implementation details and have nothing to do with the design of the language.
        teenth 13y ago
        An implementation is what you have to use, you can't use 'the language design'. When you have to use a special build system to generate Go -and- C stubs to call out, can't use a standard linker or partial compilation or shared libraries, have a massively large exe, can't embed in other programs (Go has to be 'main'), can't use with SELinux, has huge unpredictable latency spikes, etc it'll be cold comfort that those problems are 'just implementation details'. It's too bad they had NIH or thought 32-bit was the future and didn't stop at just creating a language.
        cmccabe 13y ago
        I don't understand any of your criticisms. What else would you expect to use to compile Go besides "a special build system"? A not-special build system? It's a compiled language. You can, however, use gccgo to link Go code with C/C++ code. Both gccgo and cgo already use partial compilation. You can invoke the 6l, 8l, etc. commands directly if you really want to. One of the design goals was build speed. Shared libraries are on the roadmap. See issue https://code.google.com/p/go/issues/detail?id=256 https://code.google.com/p/go/issues/detail?id=256. Go does not "have to be main". You can use gccgo to mix Go code into your existing C or C++ binary. See http://golang.org/doc/install/gccgo http://golang.org/doc/install/gccgo What the hell does "can't use with SELinux" mean? Are you talking about issue 871 that was fixed in 2010? You keep repeating over and over that Go is optimized for 32-bit systems. Repeating something doesn't make it true. In fact, exactly the opposite is true, however. Go uses a lot of address space, which is great on 64 bit, not so good on 32-bit. This has been discussed a lot years ago: http://lwn.net/Articles/428100/ http://lwn.net/Articles/428100/ is a good place to start. I've seen you repeat over and over in multiple discussion threads that having lots of kernel threads is no big deal. What you don't seem to realize is that in C/C++, thread overhead is somewhere between 1 MB and 2 MB a thread if you want to use pthreads and glibc and avoid random data corruption resulting from thread heap collisions (hint: you do). Linux also doesn't have an O(1) scheduler any more in mainline; it uses the completely fair scheduler (CFS), which has complexity O(log N). There are disadvantages to green threads, but to even start discussing this requires a lot more background than you have. Again, you can read about any of this on wikipedia, LWN.net, or even the replies that inevitably get made to all of your posts on HN. So learn already.
  - cmccabe 13y ago
    Thread overhead in Linux is 8k Those are weasel words. I assume your 8k figure is 4k kernel stack, and 4k userspace stack. First of all, your kernel may not even be compiled with 4k stacks. 8k kernel stacks are very common. But even if we assume that you do have a 4k kernel stack, you will never be able to do much useful with a 4k userspace stack. If you want to use pthreads, the default thread stack size is 2 MB, and the minimum is 16kb. Let me Google that for you. http://pubs.opengroup.org/onlinepubs/7908799/xsh/pthread_attr_setstacksize.html http://pubs.opengroup.org/onlinepubs/7908799/xsh/pthread_att... So the absolute mimimum for your normal C/C++ programmer, who doesn't want to do things like reimplement pthreads, is 20 kb. Even that figure seems suspicious to me because it doesn't take into account things like thread-local data in glibc and various other system libraries. You will quickly realize that if you want to do "luxurious" things like use standard glibc functions, call recursive functions, and so forth, you need more than 4k of userspace stack. For historical reasons, only the main thread has a growable stack-- all others have a fixed size stack. If you exceed the stack size on a thread, you will get undefined behavior, possibly a security vulnerability or a crash.
jgrahamc 13y ago
You can easily abort a goroutine using a channel: http://play.golang.org/p/OYnAdqnDLz http://play.golang.org/p/OYnAdqnDLz

enneff 13y ago

Gccgo did use threads for each goroutine for a while, and it was significantly slower than the gc "green thread" style implementation (used by both compilers today). Goroutines weigh in at about 4k each. OS threads are 64k minimum. That allows more than an order of magnitude more goroutines than threads, from a memory perspective. From an execution standpoint, goroutines managed by the Go runtime allow some nice scheduling optimisations, as the runtime is aware of the communication between goroutines. (some of these optimisations are in Go 1.1) Finally, there is no reason goroutines can't be preemptively scheduled. It is just an implementation detail, and work has already begun on this front.

teenth 13y ago
Gccgo didn't have a garbage collector for a while, around the same time it was using threads. Was it even using a pool? Did it run goroutines for a short time on the current thread before moving to its own thread? Certainly not. Thread overhead in Linux is 8k, only slightly more than goroutine. It's 24k for windows. You guys don't even know basic facts that should have guided the design.
- enneff 13y ago
  Really? Can a Linux process spawn 1m threads? I didn't work on the design. If I made a mistake that's my fault. The people that did design Go and implement the runtime know what they're doing. You didn't respond to my other points, either.
  - teenth 13y ago
    Yes a Linux process can spawn 1m threads, and testlimit64.exe spawned 250k threads both with 64k user stack and 1 MiB user stack... because that is just reserved address space if it isn't actually used. Only the kernel overhead matters to how many threads. I'm not sure what point you want addressed... scheduling optimization? It's also a deoptimization in other ways, such as predictable latency and fairness. I agree the designers knew what they were doing: designing a 'modern' language for 32-bit computers. The question is why?
    - enneff 13y ago
      Even given that what you say is true, these are all implementation details and have nothing to do with the design of the language.
      - teenth 13y ago
        An implementation is what you have to use, you can't use 'the language design'. When you have to use a special build system to generate Go -and- C stubs to call out, can't use a standard linker or partial compilation or shared libraries, have a massively large exe, can't embed in other programs (Go has to be 'main'), can't use with SELinux, has huge unpredictable latency spikes, etc it'll be cold comfort that those problems are 'just implementation details'. It's too bad they had NIH or thought 32-bit was the future and didn't stop at just creating a language.
        cmccabe 13y ago
        I don't understand any of your criticisms. What else would you expect to use to compile Go besides "a special build system"? A not-special build system? It's a compiled language. You can, however, use gccgo to link Go code with C/C++ code. Both gccgo and cgo already use partial compilation. You can invoke the 6l, 8l, etc. commands directly if you really want to. One of the design goals was build speed. Shared libraries are on the roadmap. See issue https://code.google.com/p/go/issues/detail?id=256 https://code.google.com/p/go/issues/detail?id=256. Go does not "have to be main". You can use gccgo to mix Go code into your existing C or C++ binary. See http://golang.org/doc/install/gccgo http://golang.org/doc/install/gccgo What the hell does "can't use with SELinux" mean? Are you talking about issue 871 that was fixed in 2010? You keep repeating over and over that Go is optimized for 32-bit systems. Repeating something doesn't make it true. In fact, exactly the opposite is true, however. Go uses a lot of address space, which is great on 64 bit, not so good on 32-bit. This has been discussed a lot years ago: http://lwn.net/Articles/428100/ http://lwn.net/Articles/428100/ is a good place to start. I've seen you repeat over and over in multiple discussion threads that having lots of kernel threads is no big deal. What you don't seem to realize is that in C/C++, thread overhead is somewhere between 1 MB and 2 MB a thread if you want to use pthreads and glibc and avoid random data corruption resulting from thread heap collisions (hint: you do). Linux also doesn't have an O(1) scheduler any more in mainline; it uses the completely fair scheduler (CFS), which has complexity O(log N). There are disadvantages to green threads, but to even start discussing this requires a lot more background than you have. Again, you can read about any of this on wikipedia, LWN.net, or even the replies that inevitably get made to all of your posts on HN. So learn already.
- cmccabe 13y ago
  Thread overhead in Linux is 8k Those are weasel words. I assume your 8k figure is 4k kernel stack, and 4k userspace stack. First of all, your kernel may not even be compiled with 4k stacks. 8k kernel stacks are very common. But even if we assume that you do have a 4k kernel stack, you will never be able to do much useful with a 4k userspace stack. If you want to use pthreads, the default thread stack size is 2 MB, and the minimum is 16kb. Let me Google that for you. http://pubs.opengroup.org/onlinepubs/7908799/xsh/pthread_attr_setstacksize.html http://pubs.opengroup.org/onlinepubs/7908799/xsh/pthread_att... So the absolute mimimum for your normal C/C++ programmer, who doesn't want to do things like reimplement pthreads, is 20 kb. Even that figure seems suspicious to me because it doesn't take into account things like thread-local data in glibc and various other system libraries. You will quickly realize that if you want to do "luxurious" things like use standard glibc functions, call recursive functions, and so forth, you need more than 4k of userspace stack. For historical reasons, only the main thread has a growable stack-- all others have a fixed size stack. If you exceed the stack size on a thread, you will get undefined behavior, possibly a security vulnerability or a crash.

jgrahamc 13y ago

You can easily abort a goroutine using a channel: http://play.golang.org/p/OYnAdqnDLz http://play.golang.org/p/OYnAdqnDLz