Hey Chris! Thanks for your informative reply! I did not remember, that the parallel forms are already that clever. It might be the case, that I only need to use futures or parallel forms then. I have a question regarding futures though.
In Racket the futures have some limitations, where one needs to use a different number type to enable them in some cases to run in parallel – wait, I am looking for the link … here: https://docs.racket-lang.org/guide/parallelism.html – Is there any similar restriction for futures in Guile? Regards, Zelphir On 1/5/20 10:45 PM, Chris Vine wrote: > On Sun, 5 Jan 2020 19:22:14 +0100 > Zelphir Kaltstahl <zelphirkaltst...@posteo.de> wrote: >> I think the decision tree calculations, which I want to parallelize, are >> not I/O related. However, I am not quite sure I understand the whole >> suspendable port thing, but here is what I think it is: >> >> When some I/O happens in a fiber, the fiber is still able to pause >> (suspend, yield, …) at that point, because the suspendable ports work in >> such a way, that no harm is done in doing so. Later the I/O work can be >> resumed (woken up from suspension). This quality had to be built into >> Guile first, before fibers were able to take advantage of it. >> >> Is this correct? > Yes, suspendable ports were first implemented in guile-2.2. They are > used by 8-sync (https://www.gnu.org/software/8sync/), guile-a-sync2 > (https://github.com/ChrisVine/guile-a-sync2/wiki) and fibers, and > possibly by other libraries. > > The basic arrangement is that if a port's file descriptor is not ready, > then its continuation is saved, and is resumed by the scheduler when it > becomes ready. fibers use epoll rather than POSIX select or poll for > this. > >> But I do not understand, why this is not the case with normal OS >> threads. Maybe it can be done but is not convenient or difficult to get >> right, to work with suspendable ports, when not using the fibers library? >> >> And why is simple-format not "suspendable-port-safe"? (What does a >> procedure need to do, in order to be "suspendable-port-safe"?) > simple-format does not suspend as it is implemented in C in libguile and > its continuation is not available to scheme code. There is a > list of those of guile's i/o procedures which do (and which do not) > suspend here, in the second and third paragraphs, although it does not > mention format/simple-format: > https://github.com/ChrisVine/guile-a-sync2/wiki/await-ports > (That library has nothing to do with fibers, but as mentioned above it > happens to use suspendable ports for similar purposes): > > None of this is likely to be relevant to your use case. > > [snip] >> With the parallel forms, isn't it the case, that at each call of such a >> form, new OS threads are created? In this case it might be a good idea >> to create a fibers scheduler and reuse it, if that is possible, so that >> I do not need to create my own process pool kind of thingy. > guile's parallel forms are implemented using futures, which use an > internal thread pool according to this: > https://www.gnu.org/software/guile/docs/master/guile.html/Futures.html#Futures > > "Internally, a fixed-size pool of threads is used to evaluate futures, > such that offloading the evaluation of an expression to another thread > doesn’t incur thread creation costs. By default, the pool contains one > thread per available CPU core, minus one, to account for the main > thread." > > Chris
