5 ms·

Excuse my ignorance, but could you use goroutines with different algorithms and pick the one that finishes first? Perhaps not in the case of MD5/SHA1, but for p

Excuse my ignorance, but could you use goroutines with different algorithms and pick the one that finishes first? Perhaps not in the case of MD5/SHA1, but for problems that have some algorithms that are very fast most of the time, but have a pathological worst case?

jgrahamc 14y ago
Yes, you could do that. It would be very simple to give the same channel to two goroutines. Each goroutine would transmit the solution on the channel. You would just wait around to get the first item off the channel. Toy example: http://play.golang.org/p/imM9nOwer_ http://play.golang.org/p/imM9nOwer_
numbernein 14y ago
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 14y 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 14y 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 14y 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 14y 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 14y 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 14y 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.
- jgrahamc 14y ago
  You can easily abort a goroutine using a channel: http://play.golang.org/p/OYnAdqnDLz http://play.golang.org/p/OYnAdqnDLz

jgrahamc 14y ago

Yes, you could do that. It would be very simple to give the same channel to two goroutines. Each goroutine would transmit the solution on the channel. You would just wait around to get the first item off the channel. Toy example: http://play.golang.org/p/imM9nOwer_ http://play.golang.org/p/imM9nOwer_

numbernein 14y ago

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 14y 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 14y 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 14y 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 14y 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 14y 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 14y 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.
jgrahamc 14y ago
You can easily abort a goroutine using a channel: http://play.golang.org/p/OYnAdqnDLz http://play.golang.org/p/OYnAdqnDLz