runtime: add wasm support for timers on P's

When we put timers on P's, the wasm code will not be able to rely on
the timer goroutine. Use the beforeIdle hook to schedule a wakeup.

Updates #6239
Updates #27707

Change-Id: Idf6309944778b8c3d7178f5d09431940843ea233
Reviewed-on: https://go-review.googlesource.com/c/go/+/171827
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

Author: ianlancetaylor

src/runtime/lock_futex.go

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

src/runtime/lock_js.go

@@ -111,6 +111,8 @@ func notetsleepg(n *note, ns int64) bool {
 		gopark(nil, nil, waitReasonSleep, traceEvNone, 1)
 
 		clearTimeoutEvent(id) // note might have woken early, clear timeout
+		clearIdleID()
+
 		mp = acquirem()
 		delete(notes, n)
 		delete(notesWithTimeout, n)
@@ -148,10 +150,25 @@ var isHandlingEvent = false
 var nextEventIsAsync = false
 var returnedEventHandler *g
 
+// The timeout event started by beforeIdle.
+var idleID int32
+
 // beforeIdle gets called by the scheduler if no goroutine is awake.
 // If we are not already handling an event, then we pause for an async event.
 // If an event handler returned, we resume it and it will pause the execution.
-func beforeIdle() bool {
+func beforeIdle(delay int64) bool {
+	if delay > 0 {
+		if delay < 1e6 {
+			delay = 1
+		} else if delay < 1e15 {
+			delay = delay / 1e6
+		} else {
+			// An arbitrary cap on how long to wait for a timer.
+			// 1e9 ms == ~11.5 days.
+			delay = 1e9
+		}
+		idleID = scheduleTimeoutEvent(delay)
+	}
 	if !isHandlingEvent {
 		nextEventIsAsync = true
 		pause(getcallersp() - 16)
@@ -164,6 +181,14 @@ func beforeIdle() bool {
 	return false
 }
 
+// clearIdleID clears our record of the timeout started by beforeIdle.
+func clearIdleID() {
+	if idleID != 0 {
+		clearTimeoutEvent(idleID)
+		idleID = 0
+	}
+}
+
 // pause sets SP to newsp and pauses the execution of Go's WebAssembly code until an event is triggered.
 func pause(newsp uintptr)
 
@@ -189,6 +214,8 @@ func handleEvent() {
 
 	eventHandler()
 
+	clearIdleID()
+
 	// wait until all goroutines are idle
 	returnedEventHandler = getg()
 	gopark(nil, nil, waitReasonZero, traceEvNone, 1)

src/runtime/lock_sema.go

@@ -289,7 +289,7 @@ func notetsleepg(n *note, ns int64) bool {
 	return ok
 }
 
-func beforeIdle() bool {
+func beforeIdle(int64) bool {
 	return false
 }
 

src/runtime/proc.go

@@ -2355,7 +2355,7 @@ stop:
 	// wasm only:
 	// If a callback returned and no other goroutine is awake,
 	// then pause execution until a callback was triggered.
-	if beforeIdle() {
+	if beforeIdle(delta) {
 		// At least one goroutine got woken.
 		goto top
 	}