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Pre-proposal: Interrupt handling #1446
Description
This might sound rather strange, and possibly ill-suited to WebAssembly, but I could imagine certain embedders actually wanting to support it. Browsers probably wouldn’t.
The basic idea is to provide a way to handle a callback from an embedder that may happen at any CPU (not WebAssembly!) instruction boundary. The classic examples of this are hardware interrupts and Unix signals.
Activity
sbc100 commentedon Mar 25, 2022
This came up recently on an issue in the WASI repo it was mentioned that linux has signalfd(): https://man7.org/linux/man-pages/man2/signalfd.2.html. How many of the use cases you have in mind do you think could be handled adding something like that at the WASI level? It avoids the whole preemption issue, and allows application to effectively poll/wait for signal events.
DemiMarie commentedon Mar 25, 2022
signalfd()on Linux, andEVFILT_SIGNALon the BSDs, are a much better solution for Unix signals. I suspect illumos event ports also have a mechanism for this, and if nothing else the self-pipe trick works on all Unix systems. That isn’t sufficient for preemption, though, and there are actually applications that want that (usually for context switching). Go, for example, switched from cooperative to preemptive goroutine scheduling.sbc100 commentedon Mar 25, 2022
Also maybe if interest: https://github.com/WebAssembly/stack-switching
frank-dspeed commentedon Aug 15, 2022
@sbc100 good point and i agree and Fuchsia OS as a whole does also use that with good results. in Fuchsia there are Only Jobs/Tasks and Processes. Overall my experience with that scheduling is well
RossTate commentedon Dec 12, 2022
There's some discussion related to this issue in #1459 (comment) and preceding comments.
DemiMarie commentedon Dec 13, 2022
@RossTate I am not sure if those approaches would be sufficient for this pre-proposal, which is mostly aimed at OS kernels and embedded systems. In this case it may be necessary to do something in the interrupt, such as acknowledge it so that the hardware deasserts the interrupt line (assuming level-triggered interrupts).
RossTate commentedon Dec 13, 2022
Sorry, didn't mean to imply they solved the problem! Just pointing to some challenges on both specifying and implementing a related problem, in case it offered some shortcuts.
frank-dspeed commentedon Dec 15, 2022
the gc linear memory root marking is interesting for wasm i already run net wide memory grids in the browser based on concept of persistent loaded memory and throwing away like gc what is not loaded i designed a new kind of ffi to make that hapen where i do not do ffi i throw in a empty context and use it like shared memory let the function do its thing on the context directly so like working with handels and do not transfer data that leads to a net wide in memory grid program able via import export operators in ECMAScript i call that web 4.0 as it does not need html
frank-dspeed commentedon Dec 16, 2022
My final conclusion is this should not get added we should use Streams over a file handle if we want to link directly from linux or a posix compatible signal i did check the current state of posix signals in a variation of kernel implementations mainly the compat between linux bsd mach(macos) (iridium win11) it makes no sense to take the signals as given by default wasm does not run on a posix environment by default.
Streams do solve efficient wait locking mutex futex stuff in a nice way you do not even need code any logic for that.
DemiMarie commentedon Dec 16, 2022
@frank-dspeed: I agree when it comes to signal handling, but this does not work for preemptive context switching.