wasi sdk and runtime (wasmtime)

[pmp-p]

when using wasi reactor ( ideal for calling gameloop repeatdly instead of being stuck in main() )

_start vanishes

globals init go into (should be added) to _initializer() actually go in main() but that's just Nim compiler begin funny with reactor model ( should be harmless according to nim lang-dev channel )

wasmtime automatically call _initializer, and then invoke is used to call any exported function

problem:
if not calling main(), gc is probably not active and modules globals are not setup. There is possible undefined behaviour.

• setup can be done manually ( think PyInit_ )
  but that may not starting GC and complete NiMain routines
  => but bamboo sample works

---

when defined(wasi):
    proc initialize(argc: cint, args: ptr UncheckedArray[cstring], env: ptr UncheckedArray[cstring]): int {.importc: "main".}
proc setup() : void {.exportC:"setup".} =
    when defined(wasi):
        discard initialize(0, nil,nil)
        echo "_initialized"
        discard
    # bamboo sample code here

• when calling manually main() to complete _initializer job, with gc inactive
  => bamboo sample works

• when calling manually main() to complete _initializer job, with gc( arc/orc ) active.
  => bamboo sample crashes.

• normal expected way does not work when GC is active after main was called that line does not pass, usually with cryptic traces : it was hard to locate.
  

  nim-panda3d/direct/showbase/Messenger.nim

  Line 15 in ac908ca

  var acceptorDict = addr this.callbacks.mgetOrPut(event, Table[int, proc (args: openArray[EventParameter])]())

neither taskMgr.add later because same model.

• actual less worse option :
  removing calls to .accept or .add makes a running sample with a GC and stepping like that

proc step*(this: ShowBase) =
    eventMgr.doEvents()
    discard hold_base.dataLoop()
    discard hold_base.igLoop()
    #discard hold_base.audioLoop()
    AsyncTaskManager.getGlobalPtr().poll()

[pmp-p]

seems placement and lifecycle of "elem" is critical for GC in tables. locals declarations when dynamic also have side effects that is why re-ordering showbase open window init was giving different errors.

import std/os # getEnv
import std/tables

when defined(wasi):
    proc initialize(argc: cint, args: ptr UncheckedArray[cstring], env: ptr UncheckedArray[cstring]): int {.importc: "main".}

type
    t_callback = proc (args: openArray[string]) : void {.gcsafe.}
    t_slot = Table[int, t_callback]
    t_callbacks = Table[string, t_slot]


proc proc_cb(args: openArray[string]) : void =
    echo "cb"

var cb = initTable[string, t_slot]()

when defined(nobug):
    var elem : t_slot


proc setup() : void {.exportC:"setup".} =
    when defined(wasi):
        discard initialize(0, nil,nil)
        echo "_initialized"
        discard

    # alloc something dynamic
    var cwd = getEnv("PWD","./")

    when not defined(nobug):
        var elem = initTable[int, t_callback]()
    else:
        elem = initTable[int, t_callback]()

    var fnptr = elem.mgetOrPut( 1 , proc_cb )

    discard cb.mgetOrPut("string", elem )

    echo "setup:end"

when not defined(wasi):
    setup()
# else call with "wasmtime --dir / --invoke setup a.out.wasm"

will crash in nimDecRefIsLastCyclicDyn until adding --define:nobug to change life scope

[pmp-p]

fixed thank to Nim-lang discord folks.
calling main() is not enough as it is chained in fact from NimMain and should be all toplevel ie chained with __wasm_call_ctors so proper sample init is

import std/strformat
import std/tables
var some_global =  "global_value"

when not defined(wasi):
    echo "native"
    while true:
        renderAnimationFrame()
else:
    echo "wasi"
    proc NimMain(): void {.cdecl, importc.}
    {.pragma: constructor, codegenDecl: "__attribute__((constructor)) $# $#$#", exportc.}
    proc wasm_call_ctors() {.exportc, constructor, cdecl.} = NimMain()

proc renderAnimationFrame() : void {.exportC.} =
    echo "begin"
    echo fmt"{some_global=}"
    echo "end"

with proper constructor call, no more funky gc side effects (well almost).