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runtime, sycall/js: add support for callbacks from JavaScript

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This commit adds support for JavaScript callbacks back into
WebAssembly. This is experimental API, just like the rest of the
syscall/js package. The time package now also uses this mechanism
to properly support timers without resorting to a busy loop.

JavaScript code can call into the same entry point multiple times.
The new RUN register is used to keep track of the program's
run state. Possible values are: starting, running, paused and exited.
If no goroutine is ready any more, the scheduler can put the
program into the "paused" state and the WebAssembly code will
stop running. When a callback occurs, the JavaScript code puts
the callback data into a queue and then calls into WebAssembly
to allow the Go code to continue running.

Updates #18892
Updates #25506

Change-Id: Ib8701cfa0536d10d69bd541c85b0e2a754eb54fb
Reviewed-on: https://go-review.googlesource.com/114197
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
This commit is contained in:
Richard Musiol 2018-05-20 00:56:36 +02:00 • committed by Austin Clements
parent 5fdacfa89f
commit e083dc6307
18 changed files with 482 additions and 49 deletions
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16
src/cmd/internal/obj/wasm/wasmobj.go
View file

@ -25,6 +25,7 @@ var Register = map[string]int16{
"RET1": REG_RET1,
"RET2": REG_RET2,
"RET3": REG_RET3,
"RUN": REG_RUN,
"R0": REG_R0,
"R1": REG_R1,
@ -487,7 +488,7 @@ func preprocess(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
p = appendp(p, AEnd) // end of Loop
}
case obj.ARET:
case obj.ARET, ARETUNWIND:
ret := *p
p.As = obj.ANOP
@ -528,7 +529,14 @@ func preprocess(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
p = appendp(p, AI32Add)
p = appendp(p, ASet, regAddr(REG_SP))
// not switching goroutine, return 0
if ret.As == ARETUNWIND {
// function needs to unwind the WebAssembly stack, return 1
p = appendp(p, AI32Const, constAddr(1))
p = appendp(p, AReturn)
break
}
// not unwinding the WebAssembly stack, return 0
p = appendp(p, AI32Const, constAddr(0))
p = appendp(p, AReturn)
}
@ -726,7 +734,7 @@ func assemble(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
}
reg := p.From.Reg
switch {
case reg >= REG_PC_F && reg <= REG_RET3:
case reg >= REG_PC_F && reg <= REG_RUN:
w.WriteByte(0x23) // get_global
writeUleb128(w, uint64(reg-REG_PC_F))
case reg >= REG_R0 && reg <= REG_F15:
@ -743,7 +751,7 @@ func assemble(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
}
reg := p.To.Reg
switch {
case reg >= REG_PC_F && reg <= REG_RET3:
case reg >= REG_PC_F && reg <= REG_RUN:
w.WriteByte(0x24) // set_global
writeUleb128(w, uint64(reg-REG_PC_F))
case reg >= REG_R0 && reg <= REG_F15: