runtime: make channels work in interrupts

src/examples/systick/systick.go

@@ -5,6 +5,8 @@ import (
 	"machine"
 )
 
+var timerCh = make(chan struct{}, 1)
+
 func main() {
 	machine.LED.Configure(machine.PinConfig{Mode: machine.PinOutput})
 
@@ -12,17 +14,18 @@ func main() {
 	arm.SetupSystemTimer(machine.CPUFrequency() / 10)
 
 	for {
+		machine.LED.Low()
+		<-timerCh
+		machine.LED.High()
+		<-timerCh
 	}
 }
 
-var led_state bool
-
 //export SysTick_Handler
 func timer_isr() {
-	if led_state {
-		machine.LED.Low()
-	} else {
-		machine.LED.High()
+	select {
+	case timerCh <- struct{}{}:
+	default:
+		// The consumer is running behind.
 	}
-	led_state = !led_state
 }

src/internal/task/queue.go

@@ -1,5 +1,7 @@
 package task
 
+import "runtime/interrupt"
+
 const asserts = false
 
 // Queue is a FIFO container of tasks.
@@ -10,7 +12,9 @@ type Queue struct {
 
 // Push a task onto the queue.
 func (q *Queue) Push(t *Task) {
+	i := interrupt.Disable()
 	if asserts && t.Next != nil {
+		interrupt.Restore(i)
 		panic("runtime: pushing a task to a queue with a non-nil Next pointer")
 	}
 	if q.tail != nil {
@@ -21,12 +25,15 @@ func (q *Queue) Push(t *Task) {
 	if q.head == nil {
 		q.head = t
 	}
+	interrupt.Restore(i)
 }
 
 // Pop a task off of the queue.
 func (q *Queue) Pop() *Task {
+	i := interrupt.Disable()
 	t := q.head
 	if t == nil {
+		interrupt.Restore(i)
 		return nil
 	}
 	q.head = t.Next
@@ -34,11 +41,13 @@ func (q *Queue) Pop() *Task {
 		q.tail = nil
 	}
 	t.Next = nil
+	interrupt.Restore(i)
 	return t
 }
 
 // Append pops the contents of another queue and pushes them onto the end of this queue.
 func (q *Queue) Append(other *Queue) {
+	i := interrupt.Disable()
 	if q.head == nil {
 		q.head = other.head
 	} else {
@@ -46,6 +55,15 @@ func (q *Queue) Append(other *Queue) {
 	}
 	q.tail = other.tail
 	other.head, other.tail = nil, nil
+	interrupt.Restore(i)
+}
+
+// Empty checks if the queue is empty.
+func (q *Queue) Empty() bool {
+	i := interrupt.Disable()
+	empty := q.head == nil
+	interrupt.Restore(i)
+	return empty
 }
 
 // Stack is a LIFO container of tasks.
@@ -57,19 +75,24 @@ type Stack struct {
 
 // Push a task onto the stack.
 func (s *Stack) Push(t *Task) {
+	i := interrupt.Disable()
 	if asserts && t.Next != nil {
+		interrupt.Restore(i)
 		panic("runtime: pushing a task to a stack with a non-nil Next pointer")
 	}
 	s.top, t.Next = t, s.top
+	interrupt.Restore(i)
 }
 
 // Pop a task off of the stack.
 func (s *Stack) Pop() *Task {
+	i := interrupt.Disable()
 	t := s.top
 	if t != nil {
 		s.top = t.Next
 		t.Next = nil
 	}
+	interrupt.Restore(i)
 	return t
 }
 
@@ -89,10 +112,13 @@ func (t *Task) tail() *Task {
 // Queue moves the contents of the stack into a queue.
 // Elements can be popped from the queue in the same order that they would be popped from the stack.
 func (s *Stack) Queue() Queue {
+	i := interrupt.Disable()
 	head := s.top
 	s.top = nil
-	return Queue{
+	q := Queue{
 		head: head,
 		tail: head.tail(),
 	}
+	interrupt.Restore(i)
+	return q
 }

src/runtime/arch_cortexm.go

@@ -102,3 +102,7 @@ func procPin() {
 func procUnpin() {
 	arm.EnableInterrupts(procPinnedMask)
 }
+
+func waitForEvents() {
+	arm.Asm("wfe")
+}

src/runtime/arch_tinygoriscv.go

@@ -90,3 +90,11 @@ func procPin() {
 func procUnpin() {
 	riscv.EnableInterrupts(procPinnedMask)
 }
+
+func waitForEvents() {
+	mask := riscv.DisableInterrupts()
+	if !runqueue.Empty() {
+		riscv.Asm("wfi")
+	}
+	riscv.EnableInterrupts(mask)
+}

src/runtime/chan.go

@@ -25,6 +25,7 @@ package runtime
 
 import (
 	"internal/task"
+	"runtime/interrupt"
 	"unsafe"
 )
 
@@ -308,13 +309,17 @@ func (ch *channel) trySend(value unsafe.Pointer) bool {
 		return false
 	}
 
+	i := interrupt.Disable()
+
 	switch ch.state {
 	case chanStateEmpty, chanStateBuf:
 		// try to dump the value directly into the buffer
 		if ch.push(value) {
 			ch.state = chanStateBuf
+			interrupt.Restore(i)
 			return true
 		}
+		interrupt.Restore(i)
 		return false
 	case chanStateRecv:
 		// unblock reciever
@@ -328,16 +333,21 @@ func (ch *channel) trySend(value unsafe.Pointer) bool {
 			ch.state = chanStateEmpty
 		}
 
+		interrupt.Restore(i)
 		return true
 	case chanStateSend:
 		// something else is already waiting to send
+		interrupt.Restore(i)
 		return false
 	case chanStateClosed:
+		interrupt.Restore(i)
 		runtimePanic("send on closed channel")
 	default:
+		interrupt.Restore(i)
 		runtimePanic("invalid channel state")
 	}
 
+	interrupt.Restore(i)
 	return false
 }
 
@@ -351,6 +361,8 @@ func (ch *channel) tryRecv(value unsafe.Pointer) (bool, bool) {
 		return false, false
 	}
 
+	i := interrupt.Disable()
+
 	switch ch.state {
 	case chanStateBuf, chanStateSend:
 		// try to pop the value directly from the buffer
@@ -373,6 +385,7 @@ func (ch *channel) tryRecv(value unsafe.Pointer) (bool, bool) {
 				ch.state = chanStateEmpty
 			}
 
+			interrupt.Restore(i)
 			return true, true
 		} else if ch.blocked != nil {
 			// unblock next sender if applicable
@@ -386,19 +399,24 @@ func (ch *channel) tryRecv(value unsafe.Pointer) (bool, bool) {
 				ch.state = chanStateEmpty
 			}
 
+			interrupt.Restore(i)
 			return true, true
 		}
+		interrupt.Restore(i)
 		return false, false
 	case chanStateRecv, chanStateEmpty:
 		// something else is already waiting to recieve
+		interrupt.Restore(i)
 		return false, false
 	case chanStateClosed:
 		if ch.pop(value) {
+			interrupt.Restore(i)
 			return true, true
 		}
 
 		// channel closed - nothing to recieve
 		memzero(value, ch.elementSize)
+		interrupt.Restore(i)
 		return true, false
 	default:
 		runtimePanic("invalid channel state")
@@ -447,14 +465,18 @@ type chanSelectState struct {
 // This operation will block unless a value is immediately available.
 // May panic if the channel is closed.
 func chanSend(ch *channel, value unsafe.Pointer, blockedlist *channelBlockedList) {
+	i := interrupt.Disable()
+
 	if ch.trySend(value) {
 		// value immediately sent
 		chanDebug(ch)
+		interrupt.Restore(i)
 		return
 	}
 
 	if ch == nil {
 		// A nil channel blocks forever. Do not schedule this goroutine again.
+		interrupt.Restore(i)
 		deadlock()
 	}
 
@@ -468,6 +490,7 @@ func chanSend(ch *channel, value unsafe.Pointer, blockedlist *channelBlockedList
 	}
 	ch.blocked = blockedlist
 	chanDebug(ch)
+	interrupt.Restore(i)
 	task.Pause()
 	sender.Ptr = nil
 }
@@ -477,14 +500,18 @@ func chanSend(ch *channel, value unsafe.Pointer, blockedlist *channelBlockedList
 // The recieved value is copied into the value pointer.
 // Returns the comma-ok value.
 func chanRecv(ch *channel, value unsafe.Pointer, blockedlist *channelBlockedList) bool {
+	i := interrupt.Disable()
+
 	if rx, ok := ch.tryRecv(value); rx {
 		// value immediately available
 		chanDebug(ch)
+		interrupt.Restore(i)
 		return ok
 	}
 
 	if ch == nil {
 		// A nil channel blocks forever. Do not schedule this goroutine again.
+		interrupt.Restore(i)
 		deadlock()
 	}
 
@@ -498,6 +525,7 @@ func chanRecv(ch *channel, value unsafe.Pointer, blockedlist *channelBlockedList
 	}
 	ch.blocked = blockedlist
 	chanDebug(ch)
+	interrupt.Restore(i)
 	task.Pause()
 	ok := receiver.Data == 1
 	receiver.Ptr, receiver.Data = nil, 0
@@ -511,15 +539,18 @@ func chanClose(ch *channel) {
 		// Not allowed by the language spec.
 		runtimePanic("close of nil channel")
 	}
+	i := interrupt.Disable()
 	switch ch.state {
 	case chanStateClosed:
 		// Not allowed by the language spec.
+		interrupt.Restore(i)
 		runtimePanic("close of closed channel")
 	case chanStateSend:
 		// This panic should ideally on the sending side, not in this goroutine.
 		// But when a goroutine tries to send while the channel is being closed,
 		// that is clearly invalid: the send should have been completed already
 		// before the close.
+		interrupt.Restore(i)
 		runtimePanic("close channel during send")
 	case chanStateRecv:
 		// unblock all receivers with the zero value
@@ -531,6 +562,7 @@ func chanClose(ch *channel) {
 		// Easy case. No available sender or receiver.
 	}
 	ch.state = chanStateClosed
+	interrupt.Restore(i)
 	chanDebug(ch)
 }
 
@@ -541,8 +573,11 @@ func chanClose(ch *channel) {
 // TODO: do this in a round-robin fashion (as specified in the Go spec) instead
 // of picking the first one that can proceed.
 func chanSelect(recvbuf unsafe.Pointer, states []chanSelectState, ops []channelBlockedList) (uintptr, bool) {
+	istate := interrupt.Disable()
+
 	if selected, ok := tryChanSelect(recvbuf, states); selected != ^uintptr(0) {
 		// one channel was immediately ready
+		interrupt.Restore(istate)
 		return selected, ok
 	}
 
@@ -570,6 +605,7 @@ func chanSelect(recvbuf unsafe.Pointer, states []chanSelectState, ops []channelB
 			case chanStateRecv:
 				// already in correct state
 			default:
+				interrupt.Restore(istate)
 				runtimePanic("invalid channel state")
 			}
 		} else {
@@ -582,6 +618,7 @@ func chanSelect(recvbuf unsafe.Pointer, states []chanSelectState, ops []channelB
 			case chanStateBuf:
 				// already in correct state
 			default:
+				interrupt.Restore(istate)
 				runtimePanic("invalid channel state")
 			}
 		}
@@ -594,6 +631,7 @@ func chanSelect(recvbuf unsafe.Pointer, states []chanSelectState, ops []channelB
 	t.Data = 1
 
 	// wait for one case to fire
+	interrupt.Restore(istate)
 	task.Pause()
 
 	// figure out which one fired and return the ok value
@@ -602,22 +640,27 @@ func chanSelect(recvbuf unsafe.Pointer, states []chanSelectState, ops []channelB
 
 // tryChanSelect is like chanSelect, but it does a non-blocking select operation.
 func tryChanSelect(recvbuf unsafe.Pointer, states []chanSelectState) (uintptr, bool) {
+	istate := interrupt.Disable()
+
 	// See whether we can receive from one of the channels.
 	for i, state := range states {
 		if state.value == nil {
 			// A receive operation.
 			if rx, ok := state.ch.tryRecv(recvbuf); rx {
 				chanDebug(state.ch)
+				interrupt.Restore(istate)
 				return uintptr(i), ok
 			}
 		} else {
 			// A send operation: state.value is not nil.
 			if state.ch.trySend(state.value) {
 				chanDebug(state.ch)
+				interrupt.Restore(istate)
 				return uintptr(i), true
 			}
 		}
 	}
 
+	interrupt.Restore(istate)
 	return ^uintptr(0), false
 }

src/runtime/gc_conservative.go

@@ -29,6 +29,8 @@ package runtime
 // Moss.
 
 import (
+	"internal/task"
+	"runtime/interrupt"
 	"unsafe"
 )
 
@@ -292,10 +294,36 @@ func GC() {
 	}
 
 	// Mark phase: mark all reachable objects, recursively.
-	markGlobals()
 	markStack()
+	markGlobals()
+
+	// Channel operations in interrupts may move task pointers around while we are marking.
+	// Therefore we need to scan the runqueue seperately.
+	var markedTaskQueue task.Queue
+runqueueScan:
+	for !runqueue.Empty() {
+		// Pop the next task off of the runqueue.
+		t := runqueue.Pop()
+
+		// Mark the task if it has not already been marked.
+		markRoot(uintptr(unsafe.Pointer(&runqueue)), uintptr(unsafe.Pointer(t)))
+
+		// Push the task onto our temporary queue.
+		markedTaskQueue.Push(t)
+	}
+
 	finishMark()
 
+	// Restore the runqueue.
+	i := interrupt.Disable()
+	if !runqueue.Empty() {
+		// Something new came in while finishing the mark.
+		interrupt.Restore(i)
+		goto runqueueScan
+	}
+	runqueue = markedTaskQueue
+	interrupt.Restore(i)
+
 	// Sweep phase: free all non-marked objects and unmark marked objects for
 	// the next collection cycle.
 	sweep()

src/runtime/gc_extalloc.go

@@ -2,7 +2,11 @@
 
 package runtime
 
-import "unsafe"
+import (
+	"internal/task"
+	"runtime/interrupt"
+	"unsafe"
+)
 
 // This garbage collector implementation allows TinyGo to use an external memory allocator.
 // It appends a header to the end of every allocation which the garbage collector uses for tracking purposes.
@@ -417,9 +421,9 @@ func (t *memTreap) destroy() {
 // This is used to detect if the collector is invoking itself or trying to allocate memory.
 var gcrunning bool
 
-// activeMem is a treap used to store marked allocations which have already been scanned.
+// activeMem is a queue used to store marked allocations which have already been scanned.
 // This is only used when the garbage collector is running.
-var activeMem memTreap
+var activeMem memScanQueue
 
 func GC() {
 	if gcDebug {
@@ -449,10 +453,27 @@ func GC() {
 	// These can be quickly compared against to eliminate most false positives.
 	firstPtr, lastPtr = allocations.minAddr(), allocations.maxAddr()
 
-	// Start by scanning all of the global variables and the stack.
-	markGlobals()
+	// Start by scanning the stack.
 	markStack()
 
+	// Scan all globals.
+	markGlobals()
+
+	// Channel operations in interrupts may move task pointers around while we are marking.
+	// Therefore we need to scan the runqueue seperately.
+	var markedTaskQueue task.Queue
+runqueueScan:
+	for !runqueue.Empty() {
+		// Pop the next task off of the runqueue.
+		t := runqueue.Pop()
+
+		// Mark the task if it has not already been marked.
+		markRoot(uintptr(unsafe.Pointer(&runqueue)), uintptr(unsafe.Pointer(t)))
+
+		// Push the task onto our temporary queue.
+		markedTaskQueue.Push(t)
+	}
+
 	// Scan all referenced allocations, building a new treap with marked allocations.
 	// The marking process deletes the allocations from the old allocations treap, so they are only queued once.
 	for !scanQueue.empty() {
@@ -462,19 +483,29 @@ func GC() {
 		// Scan and mark all nodes that this references.
 		n.scan()
 
-		// Insert this node into the new treap.
-		activeMem.insert(n)
+		// Insert this node into the active memory queue.
+		activeMem.push(n)
 	}
 
+	i := interrupt.Disable()
+	if !runqueue.Empty() {
+		// Something new came in while finishing the mark.
+		interrupt.Restore(i)
+		goto runqueueScan
+	}
+	runqueue = markedTaskQueue
+	interrupt.Restore(i)
+
 	// The allocations treap now only contains unreferenced nodes. Destroy them all.
 	allocations.destroy()
 	if gcAsserts && !allocations.empty() {
 		runtimePanic("failed to fully destroy allocations")
 	}
 
-	// Replace the allocations treap with the new treap.
-	allocations = activeMem
-	activeMem = memTreap{}
+	// Treapify the active memory queue.
+	for !activeMem.empty() {
+		allocations.insert(activeMem.pop())
+	}
 
 	if gcDebug {
 		println("GC finished")

src/runtime/interrupt/interrupt_none.go

@@ -0,0 +1,25 @@
+// +build !baremetal
+
+package interrupt
+
+// State represents the previous global interrupt state.
+type State uintptr
+
+// Disable disables all interrupts and returns the previous interrupt state. It
+// can be used in a critical section like this:
+//
+//     state := interrupt.Disable()
+//     // critical section
+//     interrupt.Restore(state)
+//
+// Critical sections can be nested. Make sure to call Restore in the same order
+// as you called Disable (this happens naturally with the pattern above).
+func Disable() (state State) {
+	return 0
+}
+
+// Restore restores interrupts to what they were before. Give the previous state
+// returned by Disable as a parameter. If interrupts were disabled before
+// calling Disable, this will not re-enable interrupts, allowing for nested
+// cricital sections.
+func Restore(state State) {}

src/runtime/runtime_atsamd21.go

@@ -216,14 +216,14 @@ func initRTC() {
 	sam.RTC_MODE0.CTRL.SetBits(sam.RTC_MODE0_CTRL_ENABLE)
 	waitForSync()
 
-	intr := interrupt.New(sam.IRQ_RTC, func(intr interrupt.Interrupt) {
+	rtcInterrupt := interrupt.New(sam.IRQ_RTC, func(intr interrupt.Interrupt) {
 		// disable IRQ for CMP0 compare
 		sam.RTC_MODE0.INTFLAG.Set(sam.RTC_MODE0_INTENSET_CMP0)
 
 		timerWakeup.Set(1)
 	})
-	intr.SetPriority(0xc0)
-	intr.Enable()
+	rtcInterrupt.SetPriority(0xc0)
+	rtcInterrupt.Enable()
 }
 
 func waitForSync() {
@@ -261,7 +261,10 @@ func sleepTicks(d timeUnit) {
 	for d != 0 {
 		ticks() // update timestamp
 		ticks := uint32(d)
-		timerSleep(ticks)
+		if !timerSleep(ticks) {
+			// Bail out early to handle a non-time interrupt.
+			return
+		}
 		d -= timeUnit(ticks)
 	}
 }
@@ -280,7 +283,9 @@ func ticks() timeUnit {
 }
 
 // ticks are in microseconds
-func timerSleep(ticks uint32) {
+// Returns true if the timer completed.
+// Returns false if another interrupt occured which requires an early return to scheduler.
+func timerSleep(ticks uint32) bool {
 	timerWakeup.Set(0)
 	if ticks < 7 {
 		// Due to around 6 clock ticks delay waiting for the register value to
@@ -302,8 +307,20 @@ func timerSleep(ticks uint32) {
 	// enable IRQ for CMP0 compare
 	sam.RTC_MODE0.INTENSET.SetBits(sam.RTC_MODE0_INTENSET_CMP0)
 
-	for timerWakeup.Get() == 0 {
-		arm.Asm("wfi")
+wait:
+	arm.Asm("wfe")
+	if timerWakeup.Get() != 0 {
+		return true
+	}
+	if hasScheduler {
+		// The interurpt may have awoken a goroutine, so bail out early.
+		// Disable IRQ for CMP0 compare.
+		sam.RTC_MODE0.INTENCLR.SetBits(sam.RTC_MODE0_INTENSET_CMP0)
+		return false
+	} else {
+		// This is running without a scheduler.
+		// The application expects this to sleep the whole time.
+		goto wait
 	}
 }
 

src/runtime/scheduler.go

@@ -20,6 +20,8 @@ import (
 
 const schedulerDebug = false
 
+var schedulerDone bool
+
 // Queues used by the scheduler.
 var (
 	runqueue           task.Queue
@@ -114,7 +116,7 @@ func addSleepTask(t *task.Task, duration timeUnit) {
 func scheduler() {
 	// Main scheduler loop.
 	var now timeUnit
-	for {
+	for !schedulerDone {
 		scheduleLog("")
 		scheduleLog("  schedule")
 		if sleepQueue != nil {
@@ -135,12 +137,11 @@ func scheduler() {
 		t := runqueue.Pop()
 		if t == nil {
 			if sleepQueue == nil {
-				// No more tasks to execute.
-				// It would be nice if we could detect deadlocks here, because
-				// there might still be functions waiting on each other in a
-				// deadlock.
-				scheduleLog("  no tasks left!")
-				return
+				if asyncScheduler {
+					return
+				}
+				waitForEvents()
+				continue
 			}
 			timeLeft := timeUnit(sleepQueue.Data) - (now - sleepQueueBaseTime)
 			if schedulerDebug {

src/runtime/scheduler_any.go

@@ -19,6 +19,9 @@ func run() {
 		initAll()
 		postinit()
 		callMain()
+		schedulerDone = true
 	}()
 	scheduler()
 }
+
+const hasScheduler = true

src/runtime/scheduler_none.go

@@ -21,3 +21,5 @@ func run() {
 	postinit()
 	callMain()
 }
+
+const hasScheduler = false

src/runtime/wait_other.go

@@ -0,0 +1,8 @@
+// +build !tinygo.riscv
+// +build !cortexm
+
+package runtime
+
+func waitForEvents() {
+	runtimePanic("deadlocked: no event source")
+}