syscall/js: rename js.Callback to js.Func

The name "Callback" does not fit to all use cases of js.Callback.
This commit changes its name to Func. Accordingly NewCallback
gets renamed to FuncOf, which matches ValueOf and TypedArrayOf.

The package syscall/js is currently exempt from Go's compatibility
promise and js.Callback is already affected by a breaking change in
this release cycle. See #28711 for details.

Fixes #28711

Change-Id: I2c380970c3822bed6a3893909672c15d0cbe9da3
Reviewed-on: https://go-review.googlesource.com/c/153559
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

misc/wasm/wasm_exec.js

@@ -87,8 +87,8 @@
 			this._exitPromise = new Promise((resolve) => {
 				this._resolveExitPromise = resolve;
 			});
-			this._pendingCallback = null;
+			this._pendingEvent = null;
-			this._callbackTimeouts = new Map();
+			this._scheduledTimeouts = new Map();
 			this._nextCallbackTimeoutID = 1;
 
 			const mem = () => {
@@ -204,7 +204,7 @@
 			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
+					// may synchronously trigger a Go event handler. 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.
 
@@ -238,22 +238,22 @@
 						mem().setInt32(sp + 16, (msec % 1000) * 1000000, true);
 					},
 
-					// func scheduleCallback(delay int64) int32
+					// func scheduleTimeoutEvent(delay int64) int32
-					"runtime.scheduleCallback": (sp) => {
+					"runtime.scheduleTimeoutEvent": (sp) => {
 						const id = this._nextCallbackTimeoutID;
 						this._nextCallbackTimeoutID++;
-						this._callbackTimeouts.set(id, setTimeout(
+						this._scheduledTimeouts.set(id, setTimeout(
 							() => { this._resume(); },
 							getInt64(sp + 8) + 1, // setTimeout has been seen to fire up to 1 millisecond early
 						));
 						mem().setInt32(sp + 16, id, true);
 					},
 
-					// func clearScheduledCallback(id int32)
+					// func clearTimeoutEvent(id int32)
-					"runtime.clearScheduledCallback": (sp) => {
+					"runtime.clearTimeoutEvent": (sp) => {
 						const id = mem().getInt32(sp + 8, true);
-						clearTimeout(this._callbackTimeouts.get(id));
+						clearTimeout(this._scheduledTimeouts.get(id));
-						this._callbackTimeouts.delete(id);
+						this._scheduledTimeouts.delete(id);
 					},
 
 					// func getRandomData(r []byte)
@@ -420,7 +420,7 @@
 
 		_resume() {
 			if (this.exited) {
-				throw new Error("bad callback: Go program has already exited");
+				throw new Error("Go program has already exited");
 			}
 			this._inst.exports.resume();
 			if (this.exited) {
@@ -428,13 +428,13 @@
 			}
 		}
 
-		_makeCallbackHelper(id) {
+		_makeFuncWrapper(id) {
 			const go = this;
 			return function () {
-				const cb = { id: id, this: this, args: arguments };
+				const event = { id: id, this: this, args: arguments };
-				go._pendingCallback = cb;
+				go._pendingEvent = event;
 				go._resume();
-				return cb.result;
+				return event.result;
 			};
 		}
 	}
@@ -450,10 +450,10 @@
 		go.env = Object.assign({ TMPDIR: require("os").tmpdir() }, process.env);
 		go.exit = process.exit;
 		WebAssembly.instantiate(fs.readFileSync(process.argv[2]), go.importObject).then((result) => {
-			process.on("exit", (code) => { // Node.js exits if no callback is pending
+			process.on("exit", (code) => { // Node.js exits if no event handler is pending
 				if (code === 0 && !go.exited) {
 					// deadlock, make Go print error and stack traces
-					go._pendingCallback = { id: 0 };
+					go._pendingEvent = { id: 0 };
 					go._resume();
 				}
 			});

src/cmd/vet/all/whitelist/wasm.txt

@@ -12,7 +12,7 @@ runtime/asm_wasm.s: [wasm] rt0_go: use of 8(SP) points beyond argument frame
 
 // Calling WebAssembly import. No write from Go assembly.
 runtime/sys_wasm.s: [wasm] nanotime: RET without writing to 8-byte ret+0(FP)
-runtime/sys_wasm.s: [wasm] scheduleCallback: RET without writing to 4-byte ret+8(FP)
+runtime/sys_wasm.s: [wasm] scheduleTimeoutEvent: RET without writing to 4-byte ret+8(FP)
 syscall/js/js_js.s: [wasm] stringVal: RET without writing to 8-byte ret+16(FP)
 syscall/js/js_js.s: [wasm] valueGet: RET without writing to 8-byte ret+24(FP)
 syscall/js/js_js.s: [wasm] valueIndex: RET without writing to 8-byte ret+16(FP)

src/net/http/roundtrip_js.go

@@ -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(this js.Value, args []js.Value) interface{} {
+	success := js.FuncOf(func(this js.Value, args []js.Value) interface{} {
 		result := args[0]
 		header := Header{}
 		// https://developer.mozilla.org/en-US/docs/Web/API/Headers/entries
@@ -141,7 +141,7 @@ func (t *Transport) RoundTrip(req *Request) (*Response, error) {
 		return nil
 	})
 	defer success.Release()
-	failure := js.NewCallback(func(this js.Value, args []js.Value) interface{} {
+	failure := js.FuncOf(func(this js.Value, args []js.Value) interface{} {
 		err := fmt.Errorf("net/http: fetch() failed: %s", args[0].String())
 		select {
 		case errCh <- err:
@@ -190,7 +190,7 @@ func (r *streamReader) Read(p []byte) (n int, err error) {
 			bCh   = make(chan []byte, 1)
 			errCh = make(chan error, 1)
 		)
-		success := js.NewCallback(func(this js.Value, args []js.Value) interface{} {
+		success := js.FuncOf(func(this js.Value, args []js.Value) interface{} {
 			result := args[0]
 			if result.Get("done").Bool() {
 				errCh <- io.EOF
@@ -204,7 +204,7 @@ func (r *streamReader) Read(p []byte) (n int, err error) {
 			return nil
 		})
 		defer success.Release()
-		failure := js.NewCallback(func(this js.Value, args []js.Value) interface{} {
+		failure := js.FuncOf(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
@@ -258,7 +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(this js.Value, args []js.Value) interface{} {
+		success := js.FuncOf(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())
@@ -269,7 +269,7 @@ func (r *arrayReader) Read(p []byte) (n int, err error) {
 			return nil
 		})
 		defer success.Release()
-		failure := js.NewCallback(func(this js.Value, args []js.Value) interface{} {
+		failure := js.FuncOf(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.

src/runtime/lock_js.go

@@ -92,7 +92,7 @@ func notetsleepg(n *note, ns int64) bool {
 			delay = 1<<31 - 1 // cap to max int32
 		}
 
-		id := scheduleCallback(delay)
+		id := scheduleTimeoutEvent(delay)
 		mp := acquirem()
 		notes[n] = gp
 		notesWithTimeout[n] = noteWithTimeout{gp: gp, deadline: deadline}
@@ -100,7 +100,7 @@ func notetsleepg(n *note, ns int64) bool {
 
 		gopark(nil, nil, waitReasonSleep, traceEvNone, 1)
 
-		clearScheduledCallback(id) // note might have woken early, clear timeout
+		clearTimeoutEvent(id) // note might have woken early, clear timeout
 		mp = acquirem()
 		delete(notes, n)
 		delete(notesWithTimeout, n)
@@ -134,17 +134,17 @@ func checkTimeouts() {
 	}
 }
 
-var returnedCallback *g
+var returnedEventHandler *g
 
 func init() {
-	// At the toplevel we need an extra goroutine that handles asynchronous callbacks.
+	// At the toplevel we need an extra goroutine that handles asynchronous events.
 	initg := getg()
 	go func() {
-		returnedCallback = getg()
+		returnedEventHandler = getg()
 		goready(initg, 1)
 
 		gopark(nil, nil, waitReasonZero, traceEvNone, 1)
-		returnedCallback = nil
+		returnedEventHandler = nil
 
 		pause(getcallersp() - 16)
 	}()
@@ -152,44 +152,43 @@ func init() {
 }
 
 // beforeIdle gets called by the scheduler if no goroutine is awake.
-// If a callback has returned, then we resume the callback handler which
+// We resume the event handler (if available) which will pause the execution.
-// will pause the execution.
 func beforeIdle() bool {
-	if returnedCallback != nil {
+	if returnedEventHandler != nil {
-		goready(returnedCallback, 1)
+		goready(returnedEventHandler, 1)
 		return true
 	}
 	return false
 }
 
-// pause sets SP to newsp and pauses the execution of Go's WebAssembly code until a callback is triggered.
+// pause sets SP to newsp and pauses the execution of Go's WebAssembly code until an event is triggered.
 func pause(newsp uintptr)
 
-// scheduleCallback tells the WebAssembly environment to trigger a callback after ms milliseconds.
+// scheduleTimeoutEvent tells the WebAssembly environment to trigger an event after ms milliseconds.
-// It returns a timer id that can be used with clearScheduledCallback.
+// It returns a timer id that can be used with clearTimeoutEvent.
-func scheduleCallback(ms int64) int32
+func scheduleTimeoutEvent(ms int64) int32
 
-// clearScheduledCallback clears a callback scheduled by scheduleCallback.
+// clearTimeoutEvent clears a timeout event scheduled by scheduleTimeoutEvent.
-func clearScheduledCallback(id int32)
+func clearTimeoutEvent(id int32)
 
-func handleCallback() {
+func handleEvent() {
-	prevReturnedCallback := returnedCallback
+	prevReturnedEventHandler := returnedEventHandler
-	returnedCallback = nil
+	returnedEventHandler = nil
 
 	checkTimeouts()
-	callbackHandler()
+	eventHandler()
 
-	returnedCallback = getg()
+	returnedEventHandler = getg()
 	gopark(nil, nil, waitReasonZero, traceEvNone, 1)
 
-	returnedCallback = prevReturnedCallback
+	returnedEventHandler = prevReturnedEventHandler
 
 	pause(getcallersp() - 16)
 }
 
-var callbackHandler func()
+var eventHandler func()
 
-//go:linkname setCallbackHandler syscall/js.setCallbackHandler
+//go:linkname setEventHandler syscall/js.setEventHandler
-func setCallbackHandler(fn func()) {
+func setEventHandler(fn func()) {
-	callbackHandler = fn
+	eventHandler = fn
 }

src/runtime/rt0_js_wasm.s

@@ -15,7 +15,7 @@ TEXT _rt0_wasm_js(SB),NOSPLIT,$0
 	Drop
 
 // 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:
+// to wait for an event. It does NOT follow the Go ABI. It has two WebAssembly parameters:
 // R0: argc (i32)
 // R1: argv (i32)
 TEXT wasm_export_run(SB),NOSPLIT,$0
@@ -44,9 +44,9 @@ TEXT wasm_export_run(SB),NOSPLIT,$0
 	Return
 
 // wasm_export_resume gets called from JavaScript. It resumes the execution of Go code until it needs to wait for
-// a callback.
+// an event.
 TEXT wasm_export_resume(SB),NOSPLIT,$0
-	I32Const $runtime·handleCallback(SB)
+	I32Const $runtime·handleEvent(SB)
 	I32Const $16
 	I32ShrU
 	Set PC_F

src/runtime/sys_wasm.s

@@ -187,11 +187,11 @@ TEXT ·walltime(SB), NOSPLIT, $0
 	CallImport
 	RET
 
-TEXT ·scheduleCallback(SB), NOSPLIT, $0
+TEXT ·scheduleTimeoutEvent(SB), NOSPLIT, $0
 	CallImport
 	RET
 
-TEXT ·clearScheduledCallback(SB), NOSPLIT, $0
+TEXT ·clearTimeoutEvent(SB), NOSPLIT, $0
 	CallImport
 	RET
 

src/syscall/fs_js.go

@@ -474,7 +474,7 @@ func fsCall(name string, args ...interface{}) (js.Value, error) {
 	}
 
 	c := make(chan callResult, 1)
-	jsFS.Call(name, append(args, js.NewCallback(func(this js.Value, args []js.Value) interface{} {
+	jsFS.Call(name, append(args, js.FuncOf(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

src/syscall/js/callback.go

@@ -1,92 +0,0 @@
-// Copyright 2018 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// +build js,wasm
-
-package js
-
-import "sync"
-
-var (
-	callbacksMu    sync.Mutex
-	callbacks             = make(map[uint32]func(Value, []Value) interface{})
-	nextCallbackID uint32 = 1
-)
-
-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 invokes the Go function
-	id    uint32
-}
-
-// NewCallback returns a wrapped callback function.
-//
-// 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(this Value, args []Value) interface{}) Callback {
-	callbacksMu.Lock()
-	id := nextCallbackID
-	nextCallbackID++
-	callbacks[id] = fn
-	callbacksMu.Unlock()
-	return Callback{
-		id:    id,
-		Value: jsGo.Call("_makeCallbackHelper", id),
-	}
-}
-
-// Release frees up resources allocated for the callback.
-// The callback must not be invoked after calling Release.
-func (c Callback) Release() {
-	callbacksMu.Lock()
-	delete(callbacks, c.id)
-	callbacksMu.Unlock()
-}
-
-// setCallbackHandler is defined in the runtime package.
-func setCallbackHandler(fn func())
-
-func init() {
-	setCallbackHandler(handleCallback)
-}
-
-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)
-}

src/syscall/js/func.go

@@ -0,0 +1,92 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build js,wasm
+
+package js
+
+import "sync"
+
+var (
+	funcsMu    sync.Mutex
+	funcs             = make(map[uint32]func(Value, []Value) interface{})
+	nextFuncID uint32 = 1
+)
+
+var _ Wrapper = Func{} // Func must implement Wrapper
+
+// Func is a wrapped Go function to be called by JavaScript.
+type Func struct {
+	Value // the JavaScript function that invokes the Go function
+	id    uint32
+}
+
+// FuncOf returns a wrapped function.
+//
+// Invoking the JavaScript function 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 wrapped function triggered during a call from Go to JavaScript gets executed on the same goroutine.
+// A wrapped function triggered by JavaScript's event loop gets executed on an extra goroutine.
+// Blocking operations in the wrapped function will block the event loop.
+// As a consequence, if one wrapped function blocks, other wrapped funcs will not be processed.
+// A blocking function should therefore explicitly start a new goroutine.
+//
+// Func.Release must be called to free up resources when the function will not be used any more.
+func FuncOf(fn func(this Value, args []Value) interface{}) Func {
+	funcsMu.Lock()
+	id := nextFuncID
+	nextFuncID++
+	funcs[id] = fn
+	funcsMu.Unlock()
+	return Func{
+		id:    id,
+		Value: jsGo.Call("_makeFuncWrapper", id),
+	}
+}
+
+// Release frees up resources allocated for the function.
+// The function must not be invoked after calling Release.
+func (c Func) Release() {
+	funcsMu.Lock()
+	delete(funcs, c.id)
+	funcsMu.Unlock()
+}
+
+// setEventHandler is defined in the runtime package.
+func setEventHandler(fn func())
+
+func init() {
+	setEventHandler(handleEvent)
+}
+
+func handleEvent() {
+	cb := jsGo.Get("_pendingEvent")
+	if cb == Null() {
+		return
+	}
+	jsGo.Set("_pendingEvent", Null())
+
+	id := uint32(cb.Get("id").Int())
+	if id == 0 { // zero indicates deadlock
+		select {}
+	}
+	funcsMu.Lock()
+	f, ok := funcs[id]
+	funcsMu.Unlock()
+	if !ok {
+		Global().Get("console").Call("error", "call to released function")
+		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)
+}

src/syscall/js/js.go

@@ -107,7 +107,7 @@ func Global() Value {
 //  | ---------------------- | ---------------------- |
 //  | js.Value               | [its value]            |
 //  | js.TypedArray          | typed array            |
-//  | js.Callback            | function               |
+//  | js.Func                | function               |
 //  | nil                    | null                   |
 //  | bool                   | boolean                |
 //  | integers and floats    | number                 |

src/syscall/js/js_test.go

@@ -300,9 +300,9 @@ func TestZeroValue(t *testing.T) {
 	}
 }
 
-func TestCallback(t *testing.T) {
+func TestFuncOf(t *testing.T) {
 	c := make(chan struct{})
-	cb := js.NewCallback(func(this js.Value, args []js.Value) interface{} {
+	cb := js.FuncOf(func(this js.Value, args []js.Value) interface{} {
 		if got := args[0].Int(); got != 42 {
 			t.Errorf("got %#v, want %#v", got, 42)
 		}
@@ -314,10 +314,10 @@ func TestCallback(t *testing.T) {
 	<-c
 }
 
-func TestInvokeCallback(t *testing.T) {
+func TestInvokeFunction(t *testing.T) {
 	called := false
-	cb := js.NewCallback(func(this js.Value, args []js.Value) interface{} {
+	cb := js.FuncOf(func(this js.Value, args []js.Value) interface{} {
-		cb2 := js.NewCallback(func(this js.Value, args []js.Value) interface{} {
+		cb2 := js.FuncOf(func(this js.Value, args []js.Value) interface{} {
 			called = true
 			return 42
 		})
@@ -329,15 +329,15 @@ func TestInvokeCallback(t *testing.T) {
 		t.Errorf("got %#v, want %#v", got, 42)
 	}
 	if !called {
-		t.Error("callback not called")
+		t.Error("function not called")
 	}
 }
 
-func ExampleNewCallback() {
+func ExampleFuncOf() {
-	var cb js.Callback
+	var cb js.Func
-	cb = js.NewCallback(func(this js.Value, args []js.Value) interface{} {
+	cb = js.FuncOf(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
+		cb.Release() // release the function if the button will not be clicked again
 		return nil
 	})
 	js.Global().Get("document").Call("getElementById", "myButton").Call("addEventListener", "click", cb)