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all: add support for synchronous callbacks to js/wasm

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With this change, callbacks returned by syscall/js.NewCallback
get executed synchronously. This is necessary for the APIs of
many JavaScript libraries.

A callback triggered during a call from Go to JavaScript gets executed
on the same goroutine. A callback triggered by JavaScript's event loop
gets executed on an extra goroutine.

Fixes #26045
Fixes #27441

Change-Id: I591b9e85ab851cef0c746c18eba95fb02ea9e85b
Reviewed-on: https://go-review.googlesource.com/c/142004
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Richard Musiol 2018-10-11 12:46:14 +02:00 committed by Richard Musiol
parent e3e043bea4
commit 6dd70fc5e3
13 changed files with 268 additions and 251 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

84
misc/wasm/wasm_exec.js
View File

@ -79,6 +79,10 @@
console.warn("exit code:", code);
}
};
this._exitPromise = new Promise((resolve) => {
this._resolveExitPromise = resolve;
});
this._pendingCallback = null;
this._callbackTimeouts = new Map();
this._nextCallbackTimeoutID = 1;
@ -194,6 +198,11 @@
const timeOrigin = Date.now() - performance.now();
this.importObject = {
go: {
// Go's SP does not change as long as no Go code is running. Some operations (e.g. calls, getters and setters)
// may trigger a synchronous callback to Go. This makes Go code get executed in the middle of the imported
// function. A goroutine can switch to a new stack if the current stack is too small (see morestack function).
// This changes the SP, thus we have to update the SP used by the imported function.
// func wasmExit(code int32)
"runtime.wasmExit": (sp) => {
const code = mem().getInt32(sp + 8, true);
@ -229,7 +238,7 @@
const id = this._nextCallbackTimeoutID;
this._nextCallbackTimeoutID++;
this._callbackTimeouts.set(id, setTimeout(
() => { this._resolveCallbackPromise(); },
() => { this._resume(); },
getInt64(sp + 8) + 1, // setTimeout has been seen to fire up to 1 millisecond early
));
mem().setInt32(sp + 16, id, true);
@ -254,7 +263,9 @@
// func valueGet(v ref, p string) ref
"syscall/js.valueGet": (sp) => {
storeValue(sp + 32, Reflect.get(loadValue(sp + 8), loadString(sp + 16)));
const result = Reflect.get(loadValue(sp + 8), loadString(sp + 16));
sp = this._inst.exports.getsp(); // see comment above
storeValue(sp + 32, result);
},
// func valueSet(v ref, p string, x ref)
@ -278,7 +289,9 @@
const v = loadValue(sp + 8);
const m = Reflect.get(v, loadString(sp + 16));
const args = loadSliceOfValues(sp + 32);
storeValue(sp + 56, Reflect.apply(m, v, args));
const result = Reflect.apply(m, v, args);
sp = this._inst.exports.getsp(); // see comment above
storeValue(sp + 56, result);
mem().setUint8(sp + 64, 1);
} catch (err) {
storeValue(sp + 56, err);
@ -291,7 +304,9 @@
try {
const v = loadValue(sp + 8);
const args = loadSliceOfValues(sp + 16);
storeValue(sp + 40, Reflect.apply(v, undefined, args));
const result = Reflect.apply(v, undefined, args);
sp = this._inst.exports.getsp(); // see comment above
storeValue(sp + 40, result);
mem().setUint8(sp + 48, 1);
} catch (err) {
storeValue(sp + 40, err);
@ -304,7 +319,9 @@
try {
const v = loadValue(sp + 8);
const args = loadSliceOfValues(sp + 16);
storeValue(sp + 40, Reflect.construct(v, args));
const result = Reflect.construct(v, args);
sp = this._inst.exports.getsp(); // see comment above
storeValue(sp + 40, result);
mem().setUint8(sp + 48, 1);
} catch (err) {
storeValue(sp + 40, err);
@ -355,7 +372,6 @@
this,
];
this._refs = new Map();
this._callbackShutdown = false;
this.exited = false;
const mem = new DataView(this._inst.exports.mem.buffer)
@ -390,42 +406,30 @@
offset += 8;
});
while (true) {
const callbackPromise = new Promise((resolve) => {
this._resolveCallbackPromise = () => {
if (this.exited) {
throw new Error("bad callback: Go program has already exited");
}
setTimeout(resolve, 0); // make sure it is asynchronous
};
});
this._inst.exports.run(argc, argv);
if (this.exited) {
break;
}
await callbackPromise;
this._inst.exports.run(argc, argv);
if (this.exited) {
this._resolveExitPromise();
}
await this._exitPromise;
}
_resume() {
if (this.exited) {
throw new Error("bad callback: Go program has already exited");
}
this._inst.exports.resume();
if (this.exited) {
this._resolveExitPromise();
}
}
static _makeCallbackHelper(id, pendingCallbacks, go) {
_makeCallbackHelper(id) {
const go = this;
return function () {
pendingCallbacks.push({ id: id, args: arguments });
go._resolveCallbackPromise();
};
}
static _makeEventCallbackHelper(preventDefault, stopPropagation, stopImmediatePropagation, fn) {
return function (event) {
if (preventDefault) {
event.preventDefault();
}
if (stopPropagation) {
event.stopPropagation();
}
if (stopImmediatePropagation) {
event.stopImmediatePropagation();
}
fn(event);
const cb = { id: id, this: this, args: arguments };
go._pendingCallback = cb;
go._resume();
return cb.result;
};
}
}
@ -444,8 +448,8 @@
process.on("exit", (code) => { // Node.js exits if no callback is pending
if (code === 0 && !go.exited) {
// deadlock, make Go print error and stack traces
go._callbackShutdown = true;
go._inst.exports.run();
go._pendingCallback = { id: 0 };
go._resume();
}
});
return go.run(result.instance);

2
src/cmd/internal/obj/wasm/a.out.go
View File

@ -246,7 +246,7 @@ const (
REG_RET1
REG_RET2
REG_RET3
REG_RUN
REG_PAUSE
// locals
REG_R0

24
src/cmd/internal/obj/wasm/wasmobj.go
View File

@ -16,16 +16,16 @@ import (
)
var Register = map[string]int16{
"PC_F": REG_PC_F,
"PC_B": REG_PC_B,
"SP": REG_SP,
"CTXT": REG_CTXT,
"g": REG_g,
"RET0": REG_RET0,
"RET1": REG_RET1,
"RET2": REG_RET2,
"RET3": REG_RET3,
"RUN": REG_RUN,
"PC_F": REG_PC_F,
"PC_B": REG_PC_B,
"SP": REG_SP,
"CTXT": REG_CTXT,
"g": REG_g,
"RET0": REG_RET0,
"RET1": REG_RET1,
"RET2": REG_RET2,
"RET3": REG_RET3,
"PAUSE": REG_PAUSE,
"R0": REG_R0,
"R1": REG_R1,
@ -777,7 +777,7 @@ func assemble(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
}
reg := p.From.Reg
switch {
case reg >= REG_PC_F && reg <= REG_RUN:
case reg >= REG_PC_F && reg <= REG_PAUSE:
w.WriteByte(0x23) // get_global
writeUleb128(w, uint64(reg-REG_PC_F))
case reg >= REG_R0 && reg <= REG_R15:
@ -797,7 +797,7 @@ func assemble(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
}
reg := p.To.Reg
switch {
case reg >= REG_PC_F && reg <= REG_RUN:
case reg >= REG_PC_F && reg <= REG_PAUSE:
w.WriteByte(0x24) // set_global
writeUleb128(w, uint64(reg-REG_PC_F))
case reg >= REG_R0 && reg <= REG_F15:

28
src/cmd/link/internal/wasm/asm.go
View File

@ -54,7 +54,11 @@ type wasmFuncType struct {
}
var wasmFuncTypes = map[string]*wasmFuncType{
"_rt0_wasm_js": &wasmFuncType{Params: []byte{I32, I32}}, // argc, argv
"_rt0_wasm_js": &wasmFuncType{Params: []byte{}}, //
"wasm_export_run": &wasmFuncType{Params: []byte{I32, I32}}, // argc, argv
"wasm_export_resume": &wasmFuncType{Params: []byte{}}, //
"wasm_export_getsp": &wasmFuncType{Results: []byte{I32}}, // sp
"wasm_pc_f_loop": &wasmFuncType{Params: []byte{}}, //
"runtime.wasmMove": &wasmFuncType{Params: []byte{I32, I32, I32}}, // dst, src, len
"runtime.wasmZero": &wasmFuncType{Params: []byte{I32, I32}}, // ptr, len
"runtime.wasmDiv": &wasmFuncType{Params: []byte{I64, I64}, Results: []byte{I64}}, // x, y -> x/y
@ -162,9 +166,6 @@ func asmb(ctxt *ld.Link) {
fns[i] = &wasmFunc{Name: name, Type: typ, Code: wfn.Bytes()}
}
// look up program entry point
rt0 := uint32(len(hostImports)) + uint32(ctxt.Syms.ROLookup("_rt0_wasm_js", 0).Value>>16) - funcValueOffset
ctxt.Out.Write([]byte{0x00, 0x61, 0x73, 0x6d}) // magic
ctxt.Out.Write([]byte{0x01, 0x00, 0x00, 0x00}) // version
@ -180,7 +181,7 @@ func asmb(ctxt *ld.Link) {
writeTableSec(ctxt, fns)
writeMemorySec(ctxt)
writeGlobalSec(ctxt)
writeExportSec(ctxt, rt0)
writeExportSec(ctxt, len(hostImports))
writeElementSec(ctxt, uint64(len(hostImports)), uint64(len(fns)))
writeCodeSec(ctxt, fns)
writeDataSec(ctxt)
@ -326,7 +327,7 @@ func writeGlobalSec(ctxt *ld.Link) {
I64, // 6: RET1
I64, // 7: RET2
I64, // 8: RET3
I32, // 9: RUN
I32, // 9: PAUSE
}
writeUleb128(ctxt.Out, uint64(len(globalRegs))) // number of globals
@ -348,15 +349,18 @@ func writeGlobalSec(ctxt *ld.Link) {
// writeExportSec writes the section that declares exports.
// Exports can be accessed by the WebAssembly host, usually JavaScript.
// Currently _rt0_wasm_js (program entry point) and the linear memory get exported.
func writeExportSec(ctxt *ld.Link, rt0 uint32) {
// The wasm_export_* functions and the linear memory get exported.
func writeExportSec(ctxt *ld.Link, lenHostImports int) {
sizeOffset := writeSecHeader(ctxt, sectionExport)
writeUleb128(ctxt.Out, 2) // number of exports
writeUleb128(ctxt.Out, 4) // number of exports
writeName(ctxt.Out, "run") // inst.exports.run in wasm_exec.js
ctxt.Out.WriteByte(0x00) // func export
writeUleb128(ctxt.Out, uint64(rt0)) // funcidx
for _, name := range []string{"run", "resume", "getsp"} {
idx := uint32(lenHostImports) + uint32(ctxt.Syms.ROLookup("wasm_export_"+name, 0).Value>>16) - funcValueOffset
writeName(ctxt.Out, name) // inst.exports.run/resume/getsp in wasm_exec.js
ctxt.Out.WriteByte(0x00) // func export
writeUleb128(ctxt.Out, uint64(idx)) // funcidx
}
writeName(ctxt.Out, "mem") // inst.exports.mem in wasm_exec.js
ctxt.Out.WriteByte(0x02) // mem export

21
src/net/http/roundtrip_js.go
View File

@ -93,7 +93,7 @@ func (t *Transport) RoundTrip(req *Request) (*Response, error) {
respCh = make(chan *Response, 1)
errCh = make(chan error, 1)
)
success := js.NewCallback(func(args []js.Value) {
success := js.NewCallback(func(this js.Value, args []js.Value) interface{} {
result := args[0]
header := Header{}
// https://developer.mozilla.org/en-US/docs/Web/API/Headers/entries
@ -137,14 +137,17 @@ func (t *Transport) RoundTrip(req *Request) (*Response, error) {
}:
case <-req.Context().Done():
}
return nil
})
defer success.Release()
failure := js.NewCallback(func(args []js.Value) {
failure := js.NewCallback(func(this js.Value, args []js.Value) interface{} {
err := fmt.Errorf("net/http: fetch() failed: %s", args[0].String())
select {
case errCh <- err:
case <-req.Context().Done():
}
return nil
})
defer failure.Release()
respPromise.Call("then", success, failure)
@ -187,26 +190,28 @@ func (r *streamReader) Read(p []byte) (n int, err error) {
bCh = make(chan []byte, 1)
errCh = make(chan error, 1)
)
success := js.NewCallback(func(args []js.Value) {
success := js.NewCallback(func(this js.Value, args []js.Value) interface{} {
result := args[0]
if result.Get("done").Bool() {
errCh <- io.EOF
return
return nil
}
value := make([]byte, result.Get("value").Get("byteLength").Int())
a := js.TypedArrayOf(value)
a.Call("set", result.Get("value"))
a.Release()
bCh <- value
return nil
})
defer success.Release()
failure := js.NewCallback(func(args []js.Value) {
failure := js.NewCallback(func(this js.Value, args []js.Value) interface{} {
// Assumes it's a TypeError. See
// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypeError
// for more information on this type. See
// https://streams.spec.whatwg.org/#byob-reader-read for the spec on
// the read method.
errCh <- errors.New(args[0].Get("message").String())
return nil
})
defer failure.Release()
r.stream.Call("read").Call("then", success, failure)
@ -253,7 +258,7 @@ func (r *arrayReader) Read(p []byte) (n int, err error) {
bCh = make(chan []byte, 1)
errCh = make(chan error, 1)
)
success := js.NewCallback(func(args []js.Value) {
success := js.NewCallback(func(this js.Value, args []js.Value) interface{} {
// Wrap the input ArrayBuffer with a Uint8Array
uint8arrayWrapper := js.Global().Get("Uint8Array").New(args[0])
value := make([]byte, uint8arrayWrapper.Get("byteLength").Int())
@ -261,14 +266,16 @@ func (r *arrayReader) Read(p []byte) (n int, err error) {
a.Call("set", uint8arrayWrapper)
a.Release()
bCh <- value
return nil
})
defer success.Release()
failure := js.NewCallback(func(args []js.Value) {
failure := js.NewCallback(func(this js.Value, args []js.Value) interface{} {
// Assumes it's a TypeError. See
// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypeError
// for more information on this type.
// See https://fetch.spec.whatwg.org/#concept-body-consume-body for reasons this might error.
errCh <- errors.New(args[0].Get("message").String())
return nil
})
defer failure.Release()
r.arrayPromise.Call("then", success, failure)

2
src/runtime/lock_futex.go
View File

@ -230,7 +230,7 @@ func notetsleepg(n *note, ns int64) bool {
return ok
}
func pauseSchedulerUntilCallback() bool {
func beforeIdle() bool {
return false
}

67
src/runtime/lock_js.go
View File

@ -134,35 +134,36 @@ func checkTimeouts() {
}
}
var waitingForCallback *g
var returnedCallback *g
// sleepUntilCallback puts the current goroutine to sleep until a callback is triggered.
// It is currently only used by the callback routine of the syscall/js package.
//go:linkname sleepUntilCallback syscall/js.sleepUntilCallback
func sleepUntilCallback() {
waitingForCallback = getg()
func init() {
// At the toplevel we need an extra goroutine that handles asynchronous callbacks.
initg := getg()
go func() {
returnedCallback = getg()
goready(initg, 1)
gopark(nil, nil, waitReasonZero, traceEvNone, 1)
returnedCallback = nil
pause(getcallersp() - 16)
}()
gopark(nil, nil, waitReasonZero, traceEvNone, 1)
waitingForCallback = nil
}
// pauseSchedulerUntilCallback gets called from the scheduler and pauses the execution
// of Go's WebAssembly code until a callback is triggered. Then it checks for note timeouts
// and resumes goroutines that are waiting for a callback.
func pauseSchedulerUntilCallback() bool {
if waitingForCallback == nil && len(notesWithTimeout) == 0 {
return false
// beforeIdle gets called by the scheduler if no goroutine is awake.
// If a callback has returned, then we resume the callback handler which
// will pause the execution.
func beforeIdle() bool {
if returnedCallback != nil {
goready(returnedCallback, 1)
return true
}
pause()
checkTimeouts()
if waitingForCallback != nil {
goready(waitingForCallback, 1)
}
return true
return false
}
// pause pauses the execution of Go's WebAssembly code until a callback is triggered.
func pause()
// pause sets SP to newsp and pauses the execution of Go's WebAssembly code until a callback is triggered.
func pause(newsp uintptr)
// scheduleCallback tells the WebAssembly environment to trigger a callback after ms milliseconds.
// It returns a timer id that can be used with clearScheduledCallback.
@ -170,3 +171,25 @@ func scheduleCallback(ms int64) int32
// clearScheduledCallback clears a callback scheduled by scheduleCallback.
func clearScheduledCallback(id int32)
func handleCallback() {
prevReturnedCallback := returnedCallback
returnedCallback = nil
checkTimeouts()
callbackHandler()
returnedCallback = getg()
gopark(nil, nil, waitReasonZero, traceEvNone, 1)
returnedCallback = prevReturnedCallback
pause(getcallersp() - 16)
}
var callbackHandler func()
//go:linkname setCallbackHandler syscall/js.setCallbackHandler
func setCallbackHandler(fn func()) {
callbackHandler = fn
}

2
src/runtime/lock_sema.go
View File

@ -283,7 +283,7 @@ func notetsleepg(n *note, ns int64) bool {
return ok
}
func pauseSchedulerUntilCallback() bool {
func beforeIdle() bool {
return false
}

8
src/runtime/proc.go
View File

@ -2280,10 +2280,10 @@ stop:
}
// wasm only:
// Check if a goroutine is waiting for a callback from the WebAssembly host.
// If yes, pause the execution until a callback was triggered.
if pauseSchedulerUntilCallback() {
// A callback was triggered and caused at least one goroutine to wake up.
// If a callback returned and no other goroutine is awake,
// then pause execution until a callback was triggered.
if beforeIdle() {
// At least one goroutine got woken.
goto top
}

112
src/runtime/rt0_js_wasm.s
View File

@ -5,53 +5,61 @@
#include "go_asm.h"
#include "textflag.h"
// The register RUN indicates the current run state of the program.
// Possible values are:
#define RUN_STARTING 0
#define RUN_RUNNING 1
#define RUN_PAUSED 2
#define RUN_EXITED 3
// _rt0_wasm_js is not used itself. It only exists to mark the exported functions as alive.
TEXT _rt0_wasm_js(SB),NOSPLIT,$0
I32Const $wasm_export_run(SB)
Drop
I32Const $wasm_export_resume(SB)
Drop
I32Const $wasm_export_getsp(SB)
Drop
// _rt0_wasm_js does NOT follow the Go ABI. It has two WebAssembly parameters:
// wasm_export_run gets called from JavaScript. It initializes the Go runtime and executes Go code until it needs
// to wait for a callback. It does NOT follow the Go ABI. It has two WebAssembly parameters:
// R0: argc (i32)
// R1: argv (i32)
TEXT _rt0_wasm_js(SB),NOSPLIT,$0
Get RUN
I32Const $RUN_STARTING
I32Eq
If
MOVD $runtime·wasmStack+m0Stack__size(SB), SP
TEXT wasm_export_run(SB),NOSPLIT,$0
MOVD $runtime·wasmStack+m0Stack__size(SB), SP
Get SP
Get R0 // argc
I64ExtendUI32
I64Store $0
Get SP
Get R0 // argc
I64ExtendUI32
I64Store $0
Get SP
Get R1 // argv
I64ExtendUI32
I64Store $8
Get SP
Get R1 // argv
I64ExtendUI32
I64Store $8
I32Const $runtime·rt0_go(SB)
I32Const $16
I32ShrU
Set PC_F
I32Const $runtime·rt0_go(SB)
I32Const $16
I32ShrU
Set PC_F
I32Const $RUN_RUNNING
Set RUN
Else
Get RUN
I32Const $RUN_PAUSED
I32Eq
If
I32Const $RUN_RUNNING
Set RUN
Else
Unreachable
End
End
I32Const $0
Set PC_B
// Call the function for the current PC_F. Repeat until RUN != 0 indicates pause or exit.
Call wasm_pc_f_loop(SB)
Return
// wasm_export_resume gets called from JavaScript. It resumes the execution of Go code until it needs to wait for
// a callback.
TEXT wasm_export_resume(SB),NOSPLIT,$0
I32Const $runtime·handleCallback(SB)
I32Const $16
I32ShrU
Set PC_F
I32Const $0
Set PC_B
Call wasm_pc_f_loop(SB)
Return
TEXT wasm_pc_f_loop(SB),NOSPLIT,$0
// Call the function for the current PC_F. Repeat until PAUSE != 0 indicates pause or exit.
// The WebAssembly stack may unwind, e.g. when switching goroutines.
// The Go stack on the linear memory is then used to jump to the correct functions
// with this loop, without having to restore the full WebAssembly stack.
@ -61,25 +69,33 @@ loop:
CallIndirect $0
Drop
Get RUN
I32Const $RUN_RUNNING
I32Eq
Get PAUSE
I32Eqz
BrIf loop
End
I32Const $0
Set PAUSE
Return
TEXT runtime·pause(SB), NOSPLIT, $0
I32Const $RUN_PAUSED
Set RUN
// wasm_export_getsp gets called from JavaScript to retrieve the SP.
TEXT wasm_export_getsp(SB),NOSPLIT,$0
Get SP
Return
TEXT runtime·pause(SB), NOSPLIT, $0-8
MOVD newsp+0(FP), SP
I32Const $1
Set PAUSE
RETUNWIND
TEXT runtime·exit(SB), NOSPLIT, $0-4
Call runtime·wasmExit(SB)
Drop
I32Const $RUN_EXITED
Set RUN
I32Const $1
Set PAUSE
RETUNWIND
TEXT _rt0_wasm_js_lib(SB),NOSPLIT,$0
TEXT wasm_export_lib(SB),NOSPLIT,$0
UNDEF

5
src/syscall/fs_js.go
View File

@ -473,8 +473,8 @@ func fsCall(name string, args ...interface{}) (js.Value, error) {
err error
}
c := make(chan callResult)
jsFS.Call(name, append(args, js.NewCallback(func(args []js.Value) {
c := make(chan callResult, 1)
jsFS.Call(name, append(args, js.NewCallback(func(this js.Value, args []js.Value) interface{} {
var res callResult
if len(args) >= 1 { // on Node.js 8, fs.utimes calls the callback without any arguments
@ -489,6 +489,7 @@ func fsCall(name string, args ...interface{}) (js.Value, error) {
}
c <- res
return nil
}))...)
res := <-c
return res.val, res.err

120
src/syscall/js/callback.go
View File

@ -8,15 +8,9 @@ package js
import "sync"
var (
pendingCallbacks = Global().Get("Array").New()
makeCallbackHelper = Global().Get("Go").Get("_makeCallbackHelper")
makeEventCallbackHelper = Global().Get("Go").Get("_makeEventCallbackHelper")
)
var (
callbacksMu sync.Mutex
callbacks = make(map[uint32]func([]Value))
callbacks = make(map[uint32]func(Value, []Value) interface{})
nextCallbackID uint32 = 1
)
@ -24,61 +18,32 @@ var _ Wrapper = Callback{} // Callback must implement Wrapper
// Callback is a Go function that got wrapped for use as a JavaScript callback.
type Callback struct {
Value // the JavaScript function that queues the callback for execution
Value // the JavaScript function that invokes the Go function
id uint32
}
// NewCallback returns a wrapped callback function.
//
// Invoking the callback in JavaScript will queue the Go function fn for execution.
// This execution happens asynchronously on a special goroutine that handles all callbacks and preserves
// the order in which the callbacks got called.
// As a consequence, if one callback blocks this goroutine, other callbacks will not be processed.
// Invoking the callback in JavaScript will synchronously call the Go function fn with the value of JavaScript's
// "this" keyword and the arguments of the invocation.
// The return value of the invocation is the result of the Go function mapped back to JavaScript according to ValueOf.
//
// A callback triggered during a call from Go to JavaScript gets executed on the same goroutine.
// A callback triggered by JavaScript's event loop gets executed on an extra goroutine.
// Blocking operations in the callback will block the event loop.
// As a consequence, if one callback blocks, other callbacks will not be processed.
// A blocking callback should therefore explicitly start a new goroutine.
//
// Callback.Release must be called to free up resources when the callback will not be used any more.
func NewCallback(fn func(args []Value)) Callback {
callbackLoopOnce.Do(func() {
go callbackLoop()
})
func NewCallback(fn func(this Value, args []Value) interface{}) Callback {
callbacksMu.Lock()
id := nextCallbackID
nextCallbackID++
callbacks[id] = fn
callbacksMu.Unlock()
return Callback{
Value: makeCallbackHelper.Invoke(id, pendingCallbacks, jsGo),
id: id,
}
}
type EventCallbackFlag int
const (
// PreventDefault can be used with NewEventCallback to call event.preventDefault synchronously.
PreventDefault EventCallbackFlag = 1 << iota
// StopPropagation can be used with NewEventCallback to call event.stopPropagation synchronously.
StopPropagation
// StopImmediatePropagation can be used with NewEventCallback to call event.stopImmediatePropagation synchronously.
StopImmediatePropagation
)
// NewEventCallback returns a wrapped callback function, just like NewCallback, but the callback expects to have
// exactly one argument, the event. Depending on flags, it will synchronously call event.preventDefault,
// event.stopPropagation and/or event.stopImmediatePropagation before queuing the Go function fn for execution.
func NewEventCallback(flags EventCallbackFlag, fn func(event Value)) Callback {
c := NewCallback(func(args []Value) {
fn(args[0])
})
return Callback{
Value: makeEventCallbackHelper.Invoke(
flags&PreventDefault != 0,
flags&StopPropagation != 0,
flags&StopImmediatePropagation != 0,
c,
),
id: c.id,
Value: jsGo.Call("_makeCallbackHelper", id),
}
}
@ -90,35 +55,38 @@ func (c Callback) Release() {
callbacksMu.Unlock()
}
var callbackLoopOnce sync.Once
// setCallbackHandler is defined in the runtime package.
func setCallbackHandler(fn func())
func callbackLoop() {
for !jsGo.Get("_callbackShutdown").Bool() {
sleepUntilCallback()
for {
cb := pendingCallbacks.Call("shift")
if cb == Undefined() {
break
}
id := uint32(cb.Get("id").Int())
callbacksMu.Lock()
f, ok := callbacks[id]
callbacksMu.Unlock()
if !ok {
Global().Get("console").Call("error", "call to closed callback")
continue
}
argsObj := cb.Get("args")
args := make([]Value, argsObj.Length())
for i := range args {
args[i] = argsObj.Index(i)
}
f(args)
}
}
func init() {
setCallbackHandler(handleCallback)
}
// sleepUntilCallback is defined in the runtime package
func sleepUntilCallback()
func handleCallback() {
cb := jsGo.Get("_pendingCallback")
if cb == Null() {
return
}
jsGo.Set("_pendingCallback", Null())
id := uint32(cb.Get("id").Int())
if id == 0 { // zero indicates deadlock
select {}
}
callbacksMu.Lock()
f, ok := callbacks[id]
callbacksMu.Unlock()
if !ok {
Global().Get("console").Call("error", "call to closed callback")
return
}
this := cb.Get("this")
argsObj := cb.Get("args")
args := make([]Value, argsObj.Length())
for i := range args {
args[i] = argsObj.Index(i)
}
result := f(this, args)
cb.Set("result", result)
}

44
src/syscall/js/js_test.go
View File

@ -302,49 +302,43 @@ func TestZeroValue(t *testing.T) {
func TestCallback(t *testing.T) {
c := make(chan struct{})
cb := js.NewCallback(func(args []js.Value) {
cb := js.NewCallback(func(this js.Value, args []js.Value) interface{} {
if got := args[0].Int(); got != 42 {
t.Errorf("got %#v, want %#v", got, 42)
}
c <- struct{}{}
return nil
})
defer cb.Release()
js.Global().Call("setTimeout", cb, 0, 42)
<-c
}
func TestEventCallback(t *testing.T) {
for _, name := range []string{"preventDefault", "stopPropagation", "stopImmediatePropagation"} {
c := make(chan struct{})
var flags js.EventCallbackFlag
switch name {
case "preventDefault":
flags = js.PreventDefault
case "stopPropagation":
flags = js.StopPropagation
case "stopImmediatePropagation":
flags = js.StopImmediatePropagation
}
cb := js.NewEventCallback(flags, func(event js.Value) {
c <- struct{}{}
func TestInvokeCallback(t *testing.T) {
called := false
cb := js.NewCallback(func(this js.Value, args []js.Value) interface{} {
cb2 := js.NewCallback(func(this js.Value, args []js.Value) interface{} {
called = true
return 42
})
defer cb.Release()
event := js.Global().Call("eval", fmt.Sprintf("({ called: false, %s: function() { this.called = true; } })", name))
cb.Invoke(event)
if !event.Get("called").Bool() {
t.Errorf("%s not called", name)
}
<-c
defer cb2.Release()
return cb2.Invoke()
})
defer cb.Release()
if got := cb.Invoke().Int(); got != 42 {
t.Errorf("got %#v, want %#v", got, 42)
}
if !called {
t.Error("callback not called")
}
}
func ExampleNewCallback() {
var cb js.Callback
cb = js.NewCallback(func(args []js.Value) {
cb = js.NewCallback(func(this js.Value, args []js.Value) interface{} {
fmt.Println("button clicked")
cb.Release() // release the callback if the button will not be clicked again
return nil
})
js.Global().Get("document").Call("getElementById", "myButton").Call("addEventListener", "click", cb)
}