5 ms·

You could build an erlang/OTP style supervision tree using recover at the top level to restart panic'd goroutines.

by lgas 12y ago

jacquesm 12y ago
You're going to have a hard time maintaining consistent state but if you manage your bookkeeping very well that might work in a long lived process. If not you might end up leaking resources. Go routines and erlang processes are not mapping 1:1 with each other and I (maybe naively) assume that resources such as file descriptors and other subtle state modifications could easily survive a naive implementation of such a scheme causing eventual resource depletion. Erlang is bulletproof in this respect.
- lgas 12y ago
  That is true, and I suppose the fact that third party go libraries won't be written with this philosophy in mind means that you would have to audit all third party library use pretty carefully, which would make using this approach on projects of significant size untenable.
- pushrax 12y ago
  Defers are still called when the stack is unwound due to a panic. It's standard practise to clean up resources with a defer, so maybe it wouldn't be too unreasonable if you're mainly dealing with the standard libraries.
  - jacquesm 12y ago
    Would you bet your phone switchboard, nuclear plant or assembly line to that strategy? Go is very much a work in development, it is a vast improvement over C but I highly doubt that this strategy will get you out of every corner case. It might get you from 'crash now' to 'crash a (little) while later' but I think you will still end up having an unpredictable element in there. It all depends on how ugly the crash is and once things become unpredictable leakage (even between go-routines) is not to be ruled out categorically. Think of erlang processes to be about as well isolated as unix processes and think of go processes to be a bit more isolated than unix threads but not much more. The trick here is that erlang is essentially an OS inside a process and that go-routines are co-operative multi-tasking inside a process aided by one or more cpu threads. That's a lot closer to the C multi-threading model than erlang and that implies there are some risks.
    - troutwine 12y ago
      It's worth noting that Erlang is only a soft-realtime language. I wouldn't bet my nuclear plant and only some assembly lines on it. (There's plenty I do bet on Erlang, though.)
      - jacquesm 12y ago
        That's valid, hard real time problems require guarantees that erlang can't give, that was an unwarranted exaggeration on my part. But anything that needs to be very long running (years or more) will need ironclad guarantees that it won't be leaking resources and I can't prove but suspect that erlang will do a lot better than go for those applications. Let's leave the nuclear plants and the assembly lines to RTos and QnX then :).
        peerst 12y ago
        "require guarantees that erlang can't give" ... at the moment, working on it. In the meantime note that the percentage of stuff that really needs hard realtime in many systems is quite low. What I do at the moment is run Erlang on RTEMS (see my other posts) keep the hard realtime parts as simple as possible (always a good idea), write them in C and run them on a higher prio than the Erlang runtime which handles all the complicated things. Works like a breeze in practice
      - phamilton 12y ago
        I wonder whether Erlang insome form could provide hard realtime guarantees. Something along the lines of LING.
        troutwine 12y ago
        It's an interesting question. I think you'd need at least: * a way to define scheduling requirements on a process level (beyond current, coarse, priority settings), * bounded process message queues (this would be handy in soft-realtime Erlang), * deadline accurate receives, * accurate control over resource allocation I've been meaning to sit down with some theory and think through this more analytically, but the above are my BART thinking-time derived set of requirements. I'm sure there are cases--some which would be obvious, in retrospect--that are not covered by the above.

You could build an erlang/OTP style supervision tree using recover at the top level to restart panic'd goroutines.

by lgas 12y ago

You could build an erlang/OTP style supervision tree using recover at the top level to restart panic'd goroutines.

You're going to have a hard time maintaining consistent state but if you manage your bookkeeping very well that might work in a long lived process. If not you might end up leaking resources. Go routines and erlang processes are not mapping 1:1 with each other and I (maybe naively) assume that resources such as file descriptors and other subtle state modifications could easily survive a naive implementation of such a scheme causing eventual resource depletion. Erlang is bulletproof in this respect.

lgas 12y ago
That is true, and I suppose the fact that third party go libraries won't be written with this philosophy in mind means that you would have to audit all third party library use pretty carefully, which would make using this approach on projects of significant size untenable.
pushrax 12y ago
Defers are still called when the stack is unwound due to a panic. It's standard practise to clean up resources with a defer, so maybe it wouldn't be too unreasonable if you're mainly dealing with the standard libraries.
- jacquesm 12y ago
  Would you bet your phone switchboard, nuclear plant or assembly line to that strategy? Go is very much a work in development, it is a vast improvement over C but I highly doubt that this strategy will get you out of every corner case. It might get you from 'crash now' to 'crash a (little) while later' but I think you will still end up having an unpredictable element in there. It all depends on how ugly the crash is and once things become unpredictable leakage (even between go-routines) is not to be ruled out categorically. Think of erlang processes to be about as well isolated as unix processes and think of go processes to be a bit more isolated than unix threads but not much more. The trick here is that erlang is essentially an OS inside a process and that go-routines are co-operative multi-tasking inside a process aided by one or more cpu threads. That's a lot closer to the C multi-threading model than erlang and that implies there are some risks.
  - troutwine 12y ago
    It's worth noting that Erlang is only a soft-realtime language. I wouldn't bet my nuclear plant and only some assembly lines on it. (There's plenty I do bet on Erlang, though.)
    - jacquesm 12y ago
      That's valid, hard real time problems require guarantees that erlang can't give, that was an unwarranted exaggeration on my part. But anything that needs to be very long running (years or more) will need ironclad guarantees that it won't be leaking resources and I can't prove but suspect that erlang will do a lot better than go for those applications. Let's leave the nuclear plants and the assembly lines to RTos and QnX then :).
      - peerst 12y ago
        "require guarantees that erlang can't give" ... at the moment, working on it. In the meantime note that the percentage of stuff that really needs hard realtime in many systems is quite low. What I do at the moment is run Erlang on RTEMS (see my other posts) keep the hard realtime parts as simple as possible (always a good idea), write them in C and run them on a higher prio than the Erlang runtime which handles all the complicated things. Works like a breeze in practice
    - phamilton 12y ago
      I wonder whether Erlang insome form could provide hard realtime guarantees. Something along the lines of LING.
      - troutwine 12y ago
        It's an interesting question. I think you'd need at least: * a way to define scheduling requirements on a process level (beyond current, coarse, priority settings), * bounded process message queues (this would be handy in soft-realtime Erlang), * deadline accurate receives, * accurate control over resource allocation I've been meaning to sit down with some theory and think through this more analytically, but the above are my BART thinking-time derived set of requirements. I'm sure there are cases--some which would be obvious, in retrospect--that are not covered by the above.