4 files changed, 31 insertions, 4 deletions
diff --git a/src/runtime/lock_futex.go b/src/runtime/lock_futex.go
index d2828b138a..92873f2dac 100644
--- a/src/runtime/lock_futex.go
+++ b/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
 }
 
diff --git a/src/runtime/lock_js.go b/src/runtime/lock_js.go
index 23f17080f2..51cbe60607 100644
--- a/src/runtime/lock_js.go
+++ b/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)
diff --git a/src/runtime/lock_sema.go b/src/runtime/lock_sema.go
index 9507d46f41..af9517d744 100644
--- a/src/runtime/lock_sema.go
+++ b/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
 }
 
diff --git a/src/runtime/proc.go b/src/runtime/proc.go
index 71e756b991..fd93a3db5f 100644
--- a/src/runtime/proc.go
+++ b/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
 	}