runtime: yield the thread in Gosched on the threads scheduler

src/internal/task/task_threads.go

@@ -202,6 +202,11 @@ func CoroExit(next *Task) {
 	tinygo_task_exit()
 }
 
+// Yield yields the current thread to the OS scheduler.
+func Yield() {
+	sched_yield()
+}
+
 // scanWaitGroup is used to wait on until all threads have finished the current state transition.
 var scanWaitGroup waitGroup
 
@@ -372,6 +377,9 @@ func tinygo_task_send_gc_signal(threadID)
 //export tinygo_task_current
 func tinygo_task_current() unsafe.Pointer
 
+//export sched_yield
+func sched_yield() int32
+
 func NumCPU() int {
 	return int(numCPU)
 }

src/runtime/runtime_unix.go

@@ -418,9 +418,6 @@ func signal_disable(s uint32) {
 func signal_waitUntilIdle() {
 	// Wait until signal_recv has processed all signals.
 	for receivedSignals.Load() != 0 {
-		// TODO: this becomes a busy loop when using threads.
-		// We might want to pause until signal_recv has no more incoming signals
-		// to process.
 		Gosched()
 	}
 }

src/runtime/scheduler_threads.go

@@ -61,9 +61,9 @@ func scheduleTaskNoWake(t *task.Task) {
 }
 
 func Gosched() {
-	// Each goroutine runs in a thread, so there's not much we can do here.
-	// There is sched_yield but it's only really intended for realtime
-	// operation, so is probably best not to use.
+	// Each goroutine runs in a thread, so yield the thread to let other
+	// goroutines make progress.
+	task.Yield()
 }
 
 // NumCPU returns the number of logical CPUs usable by the current process.