refactor coroutine lowering and tasks

24 files changed, 513 insertions, 417 deletions

diff --git a/src/internal/task/queue.go b/src/internal/task/queue.go
new file mode 100644
index 000000000..c86bc596c
--- /dev/null
+++ b/src/internal/task/queue.go
@@ -0,0 +1,98 @@
+package task
+
+const asserts = false
+
+// Queue is a FIFO container of tasks.
+// The zero value is an empty queue.
+type Queue struct {
+	head, tail *Task
+}
+
+// Push a task onto the queue.
+func (q *Queue) Push(t *Task) {
+	if asserts && t.Next != nil {
+		panic("runtime: pushing a task to a queue with a non-nil Next pointer")
+	}
+	if q.tail != nil {
+		q.tail.Next = t
+	}
+	q.tail = t
+	t.Next = nil
+	if q.head == nil {
+		q.head = t
+	}
+}
+
+// Pop a task off of the queue.
+func (q *Queue) Pop() *Task {
+	t := q.head
+	if t == nil {
+		return nil
+	}
+	q.head = t.Next
+	if q.tail == t {
+		q.tail = nil
+	}
+	t.Next = nil
+	return t
+}
+
+// Append pops the contents of another queue and pushes them onto the end of this queue.
+func (q *Queue) Append(other *Queue) {
+	if q.head == nil {
+		q.head = other.head
+	} else {
+		q.tail.Next = other.head
+	}
+	q.tail = other.tail
+	other.head, other.tail = nil, nil
+}
+
+// Stack is a LIFO container of tasks.
+// The zero value is an empty stack.
+// This is slightly cheaper than a queue, so it can be preferable when strict ordering is not necessary.
+type Stack struct {
+	top *Task
+}
+
+// Push a task onto the stack.
+func (s *Stack) Push(t *Task) {
+	if asserts && t.Next != nil {
+		panic("runtime: pushing a task to a stack with a non-nil Next pointer")
+	}
+	s.top, t.Next = t, s.top
+}
+
+// Pop a task off of the stack.
+func (s *Stack) Pop() *Task {
+	t := s.top
+	if t != nil {
+		s.top = t.Next
+	}
+	t.Next = nil
+	return t
+}
+
+// tail follows the chain of tasks.
+// If t is nil, returns nil.
+// Otherwise, returns the task in the chain where the Next field is nil.
+func (t *Task) tail() *Task {
+	if t == nil {
+		return nil
+	}
+	for t.Next != nil {
+		t = t.Next
+	}
+	return t
+}
+
+// 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 {
+	head := s.top
+	s.top = nil
+	return Queue{
+		head: head,
+		tail: head.tail(),
+	}
+}
diff --git a/src/internal/task/task.go b/src/internal/task/task.go
new file mode 100644
index 000000000..57b29eb39
--- /dev/null
+++ b/src/internal/task/task.go
@@ -0,0 +1,20 @@
+package task
+
+import (
+	"unsafe"
+)
+
+// Task is a state of goroutine for scheduling purposes.
+type Task struct {
+	// Next is a field which can be used to make a linked list of tasks.
+	Next *Task
+
+	// Ptr is a field which can be used for storing a pointer.
+	Ptr unsafe.Pointer
+
+	// Data is a field which can be used for storing state information.
+	Data uint
+
+	// state is the underlying running state of the task.
+	state state
+}
diff --git a/src/internal/task/task_coroutine.go b/src/internal/task/task_coroutine.go
new file mode 100644
index 000000000..374bfe11f
--- /dev/null
+++ b/src/internal/task/task_coroutine.go
@@ -0,0 +1,97 @@
+// +build scheduler.coroutines
+
+package task
+
+import (
+	"unsafe"
+)
+
+// rawState is an underlying coroutine state exposed by llvm.coro.
+// This matches *i8 in LLVM.
+type rawState uint8
+
+//go:export llvm.coro.resume
+func (s *rawState) resume()
+
+type state struct{ *rawState }
+
+//go:export llvm.coro.noop
+func noopState() *rawState
+
+// Resume the task until it pauses or completes.
+func (t *Task) Resume() {
+	t.state.resume()
+}
+
+// setState is used by the compiler to set the state of the function at the beginning of a function call.
+// Returns the state of the caller.
+func (t *Task) setState(s *rawState) *rawState {
+	caller := t.state
+	t.state = state{s}
+	return caller.rawState
+}
+
+// returnTo is used by the compiler to return to the state of the caller.
+func (t *Task) returnTo(parent *rawState) {
+	t.state = state{parent}
+	t.returnCurrent()
+}
+
+// returnCurrent is used by the compiler to return to the state of the caller in a case where the state is not replaced.
+func (t *Task) returnCurrent() {
+	scheduleTask(t)
+}
+
+//go:linkname scheduleTask runtime.runqueuePushBack
+func scheduleTask(*Task)
+
+// setReturnPtr is used by the compiler to store the return buffer into the task.
+// This buffer is where the return value of a function that is about to be called will be stored.
+func (t *Task) setReturnPtr(buf unsafe.Pointer) {
+	t.Ptr = buf
+}
+
+// getReturnPtr is used by the compiler to get the return buffer stored into the task.
+// This is called at the beginning of an async function, and the return is stored into this buffer immediately before resuming the caller.
+func (t *Task) getReturnPtr() unsafe.Pointer {
+	return t.Ptr
+}
+
+// createTask returns a new task struct initialized with a no-op state.
+func createTask() *Task {
+	return &Task{
+		state: state{noopState()},
+	}
+}
+
+// start invokes a function in a new goroutine. Calls to this are inserted by the compiler.
+// The created goroutine starts running immediately.
+// This is implemented inside the compiler.
+func start(fn uintptr, args unsafe.Pointer)
+
+// Current returns the current active task.
+// This is implemented inside the compiler.
+func Current() *Task
+
+// Pause suspends the current running task.
+// This is implemented inside the compiler.
+func Pause()
+
+type taskHolder interface {
+	setState(*rawState) *rawState
+	returnTo(*rawState)
+	returnCurrent()
+	setReturnPtr(unsafe.Pointer)
+	getReturnPtr() unsafe.Pointer
+}
+
+// If there are no direct references to the task methods, they will not be discovered by the compiler, and this will trigger a compiler error.
+// Instantiating this interface forces discovery of these methods.
+var _ = taskHolder((*Task)(nil))
+
+func fake() {
+	// Hack to ensure intrinsics are discovered.
+	Current()
+	go func() {}()
+	Pause()
+}
diff --git a/src/internal/task/task_none.go b/src/internal/task/task_none.go
new file mode 100644
index 000000000..31835892c
--- /dev/null
+++ b/src/internal/task/task_none.go
@@ -0,0 +1,29 @@
+// +build scheduler.none
+
+package task
+
+import "unsafe"
+
+//go:linkname runtimePanic runtime.runtimePanic
+func runtimePanic(str string)
+
+func Pause() {
+	runtimePanic("scheduler is disabled")
+}
+
+func Current() *Task {
+	runtimePanic("scheduler is disabled")
+	return nil
+}
+
+//go:noinline
+func start(fn uintptr, args unsafe.Pointer) {
+	// The compiler will error if this is reachable.
+	runtimePanic("scheduler is disabled")
+}
+
+type state struct{}
+
+func (t *Task) Resume() {
+	runtimePanic("scheduler is disabled")
+}
diff --git a/src/internal/task/task_stack.go b/src/internal/task/task_stack.go
new file mode 100644
index 000000000..0bd2f4c29
--- /dev/null
+++ b/src/internal/task/task_stack.go
@@ -0,0 +1,74 @@
+// +build scheduler.tasks
+
+package task
+
+import "unsafe"
+
+//go:linkname runtimePanic runtime.runtimePanic
+func runtimePanic(str string)
+
+// Stack canary, to detect a stack overflow. The number is a random number
+// generated by random.org. The bit fiddling dance is necessary because
+// otherwise Go wouldn't allow the cast to a smaller integer size.
+const stackCanary = uintptr(uint64(0x670c1333b83bf575) & uint64(^uintptr(0)))
+
+// state is a structure which holds a reference to the state of the task.
+// When the task is suspended, the registers are stored onto the stack and the stack pointer is stored into sp.
+type state struct {
+	// sp is the stack pointer of the saved state.
+	// When the task is inactive, the saved registers are stored at the top of the stack.
+	sp uintptr
+
+	// canaryPtr points to the top word of the stack (the lowest address).
+	// This is used to detect stack overflows.
+	// When initializing the goroutine, the stackCanary constant is stored there.
+	// If the stack overflowed, the word will likely no longer equal stackCanary.
+	canaryPtr *uintptr
+}
+
+// currentTask is the current running task, or nil if currently in the scheduler.
+var currentTask *Task
+
+// Current returns the current active task.
+func Current() *Task {
+	return currentTask
+}
+
+// Pause suspends the current task and returns to the scheduler.
+// This function may only be called when running on a goroutine stack, not when running on the system stack or in an interrupt.
+func Pause() {
+	// Check whether the canary (the lowest address of the stack) is still
+	// valid. If it is not, a stack overflow has occured.
+	if *currentTask.state.canaryPtr != stackCanary {
+		runtimePanic("goroutine stack overflow")
+	}
+	currentTask.state.pause()
+}
+
+// Resume the task until it pauses or completes.
+// This may only be called from the scheduler.
+func (t *Task) Resume() {
+	currentTask = t
+	t.state.resume()
+	currentTask = nil
+}
+
+// initialize the state and prepare to call the specified function with the specified argument bundle.
+func (s *state) initialize(fn uintptr, args unsafe.Pointer) {
+	// Create a stack.
+	stack := make([]uintptr, stackSize/unsafe.Sizeof(uintptr(0)))
+
+	// Invoke architecture-specific initialization.
+	s.archInit(stack, fn, args)
+}
+
+//go:linkname runqueuePushBack runtime.runqueuePushBack
+func runqueuePushBack(*Task)
+
+// start creates and starts a new goroutine with the given function and arguments.
+// The new goroutine is scheduled to run later.
+func start(fn uintptr, args unsafe.Pointer) {
+	t := &Task{}
+	t.state.initialize(fn, args)
+	runqueuePushBack(t)
+}
diff --git a/src/internal/task/task_stack_cortexm.go b/src/internal/task/task_stack_cortexm.go
new file mode 100644
index 000000000..b91e5f041
--- /dev/null
+++ b/src/internal/task/task_stack_cortexm.go
@@ -0,0 +1,83 @@
+// +build scheduler.tasks, cortexm
+
+package task
+
+import "unsafe"
+
+const stackSize = 1024
+
+// calleeSavedRegs is the list of registers that must be saved and restored when
+// switching between tasks. Also see scheduler_cortexm.S that relies on the
+// exact layout of this struct.
+type calleeSavedRegs struct {
+	r4  uintptr
+	r5  uintptr
+	r6  uintptr
+	r7  uintptr
+	r8  uintptr
+	r9  uintptr
+	r10 uintptr
+	r11 uintptr
+
+	pc uintptr
+}
+
+// registers gets a pointer to the registers stored at the top of the stack.
+func (s *state) registers() *calleeSavedRegs {
+	return (*calleeSavedRegs)(unsafe.Pointer(s.sp))
+}
+
+// startTask is a small wrapper function that sets up the first (and only)
+// argument to the new goroutine and makes sure it is exited when the goroutine
+// finishes.
+//go:extern tinygo_startTask
+var startTask [0]uint8
+
+// archInit runs architecture-specific setup for the goroutine startup.
+func (s *state) archInit(stack []uintptr, fn uintptr, args unsafe.Pointer) {
+	// Set up the stack canary, a random number that should be checked when
+	// switching from the task back to the scheduler. The stack canary pointer
+	// points to the first word of the stack. If it has changed between now and
+	// the next stack switch, there was a stack overflow.
+	s.canaryPtr = &stack[0]
+	*s.canaryPtr = stackCanary
+
+	// Store the initial sp for the startTask function (implemented in assembly).
+	s.sp = uintptr(unsafe.Pointer(&stack[uintptr(len(stack))-(unsafe.Sizeof(calleeSavedRegs{})/unsafe.Sizeof(uintptr(0)))]))
+
+	// Initialize the registers.
+	// These will be popped off of the stack on the first resume of the goroutine.
+	r := s.registers()
+
+	// Start the function at tinygo_startTask (defined in src/runtime/scheduler_cortexm.S).
+	// This assembly code calls a function (passed in r4) with a single argument (passed in r5).
+	// After the function returns, it calls Pause().
+	r.pc = uintptr(unsafe.Pointer(&startTask))
+
+	// Pass the function to call in r4.
+	// This function is a compiler-generated wrapper which loads arguments out of a struct pointer.
+	// See createGoroutineStartWrapper (defined in compiler/goroutine.go) for more information.
+	r.r4 = fn
+
+	// Pass the pointer to the arguments struct in r5.
+	r.r5 = uintptr(args)
+}
+
+func (s *state) resume() {
+	switchToTask(s.sp)
+}
+
+//export tinygo_switchToTask
+func switchToTask(uintptr)
+
+//export tinygo_switchToScheduler
+func switchToScheduler(*uintptr)
+
+func (s *state) pause() {
+	switchToScheduler(&s.sp)
+}
+
+//export tinygo_pause
+func pause() {
+	Pause()
+}
diff --git a/src/runtime/chan.go b/src/runtime/chan.go
index a4cb47484..95243136d 100644
--- a/src/runtime/chan.go
+++ b/src/runtime/chan.go
@@ -24,6 +24,7 @@ package runtime
 // element of the receiving coroutine and setting the 'comma-ok' value to false.
 
 import (
+	"internal/task"
 	"unsafe"
 )
 
@@ -46,7 +47,7 @@ type channelBlockedList struct {
 	// If this channel operation is not part of a select, then the pointer field of the state holds the data buffer.
 	// If this channel operation is part of a select, then the pointer field of the state holds the recieve buffer.
 	// If this channel operation is a receive, then the data field should be set to zero when resuming due to channel closure.
-	t *task
+	t *task.Task
 
 	// s is a pointer to the channel select state corresponding to this operation.
 	// This will be nil if and only if this channel operation is not part of a select statement.
@@ -141,24 +142,24 @@ func (ch *channel) resumeRX(ok bool) unsafe.Pointer {
 	b, ch.blocked = ch.blocked, ch.blocked.next
 
 	// get destination pointer
-	dst := b.t.state().ptr
+	dst := b.t.Ptr
 
 	if !ok {
 		// the result value is zero
 		memzero(dst, ch.elementSize)
-		b.t.state().data = 0
+		b.t.Data = 0
 	}
 
 	if b.s != nil {
 		// tell the select op which case resumed
-		b.t.state().ptr = unsafe.Pointer(b.s)
+		b.t.Ptr = unsafe.Pointer(b.s)
 
 		// detach associated operations
 		b.detach()
 	}
 
 	// push task onto runqueue
-	runqueuePushBack(b.t)
+	runqueue.Push(b.t)
 
 	return dst
 }
@@ -171,21 +172,21 @@ func (ch *channel) resumeTX() unsafe.Pointer {
 	b, ch.blocked = ch.blocked, ch.blocked.next
 
 	// get source pointer
-	src := b.t.state().ptr
+	src := b.t.Ptr
 
 	if b.s != nil {
 		// use state's source pointer
 		src = b.s.value
 
 		// tell the select op which case resumed
-		b.t.state().ptr = unsafe.Pointer(b.s)
+		b.t.Ptr = unsafe.Pointer(b.s)
 
 		// detach associated operations
 		b.detach()
 	}
 
 	// push task onto runqueue
-	runqueuePushBack(b.t)
+	runqueue.Push(b.t)
 
 	return src
 }
@@ -424,17 +425,16 @@ func chanSend(ch *channel, value unsafe.Pointer) {
 	}
 
 	// wait for reciever
-	sender := getCoroutine()
+	sender := task.Current()
 	ch.state = chanStateSend
-	senderState := sender.state()
-	senderState.ptr = value
+	sender.Ptr = value
 	ch.blocked = &channelBlockedList{
 		next: ch.blocked,
 		t:    sender,
 	}
 	chanDebug(ch)
-	yield()
-	senderState.ptr = nil
+	task.Pause()
+	sender.Ptr = nil
 }
 
 // chanRecv receives a single value over a channel.
@@ -454,18 +454,17 @@ func chanRecv(ch *channel, value unsafe.Pointer) bool {
 	}
 
 	// wait for a value
-	receiver := getCoroutine()
+	receiver := task.Current()
 	ch.state = chanStateRecv
-	receiverState := receiver.state()
-	receiverState.ptr, receiverState.data = value, 1
+	receiver.Ptr, receiver.Data = value, 1
 	ch.blocked = &channelBlockedList{
 		next: ch.blocked,
 		t:    receiver,
 	}
 	chanDebug(ch)
-	yield()
-	ok := receiverState.data == 1
-	receiverState.ptr, receiverState.data = nil, 0
+	task.Pause()
+	ok := receiver.Data == 1
+	receiver.Ptr, receiver.Data = nil, 0
 	return ok
 }
 
@@ -515,7 +514,7 @@ func chanSelect(recvbuf unsafe.Pointer, states []chanSelectState, ops []channelB
 	for i, v := range states {
 		ops[i] = channelBlockedList{
 			next:         v.ch.blocked,
-			t:            getCoroutine(),
+			t:            task.Current(),
 			s:            &states[i],
 			allSelectOps: ops,
 		}
@@ -547,14 +546,15 @@ func chanSelect(recvbuf unsafe.Pointer, states []chanSelectState, ops []channelB
 	}
 
 	// expose rx buffer
-	getCoroutine().state().ptr = recvbuf
-	getCoroutine().state().data = 1
+	t := task.Current()
+	t.Ptr = recvbuf
+	t.Data = 1
 
 	// wait for one case to fire
-	yield()
+	task.Pause()
 
 	// figure out which one fired and return the ok value
-	return (uintptr(getCoroutine().state().ptr) - uintptr(unsafe.Pointer(&states[0]))) / unsafe.Sizeof(chanSelectState{}), getCoroutine().state().data != 0
+	return (uintptr(t.Ptr) - uintptr(unsafe.Pointer(&states[0]))) / unsafe.Sizeof(chanSelectState{}), t.Data != 0
 }
 
 // tryChanSelect is like chanSelect, but it does a non-blocking select operation.
diff --git a/src/runtime/runtime.go b/src/runtime/runtime.go
index 13f3ab3c9..ae9ab665f 100644
--- a/src/runtime/runtime.go
+++ b/src/runtime/runtime.go
@@ -10,17 +10,8 @@ const Compiler = "tinygo"
 // package.
 func initAll()
 
-// A function call to this function is replaced with one of the following,
-// depending on whether the scheduler is necessary:
-//
-// Without scheduler:
-//
-//     main.main()
-//
-// With scheduler:
-//
-//     main.main()
-//     scheduler()
+// callMain is a placeholder for the program main function.
+// All references to this are replaced with references to the program main function by the compiler.
 func callMain()
 
 func GOMAXPROCS(n int) int {
diff --git a/src/runtime/runtime_arm7tdmi.go b/src/runtime/runtime_arm7tdmi.go
index cff5bca36..cf2ff6818 100644
--- a/src/runtime/runtime_arm7tdmi.go
+++ b/src/runtime/runtime_arm7tdmi.go
@@ -40,7 +40,10 @@ func main() {
 	initAll()
 
 	// Compiler-generated call to main.main().
-	callMain()
+	go callMain()
+
+	// Run the scheduler.
+	scheduler()
 }
 
 func preinit() {
diff --git a/src/runtime/runtime_atsamd21.go b/src/runtime/runtime_atsamd21.go
index 440cd148e..a3aa6c973 100644
--- a/src/runtime/runtime_atsamd21.go
+++ b/src/runtime/runtime_atsamd21.go
@@ -17,7 +17,8 @@ type timeUnit int64
 func main() {
 	preinit()
 	initAll()
-	callMain()
+	go callMain()
+	scheduler()
 	abort()
 }
 
diff --git a/src/runtime/runtime_atsamd51.go b/src/runtime/runtime_atsamd51.go
index 7cbcad044..23d91109c 100644
--- a/src/runtime/runtime_atsamd51.go
+++ b/src/runtime/runtime_atsamd51.go
@@ -16,7 +16,8 @@ type timeUnit int64
 func main() {
 	preinit()
 	initAll()
-	callMain()
+	go callMain()
+	scheduler()
 	abort()
 }
 
diff --git a/src/runtime/runtime_cortexm.go b/src/runtime/runtime_cortexm.go
index 147a3b39f..04b34039a 100644
--- a/src/runtime/runtime_cortexm.go
+++ b/src/runtime/runtime_cortexm.go
@@ -40,29 +40,6 @@ func preinit() {
 	}
 }
 
-// calleeSavedRegs is the list of registers that must be saved and restored when
-// switching between tasks. Also see scheduler_cortexm.S that relies on the
-// exact layout of this struct.
-type calleeSavedRegs struct {
-	r4  uintptr
-	r5  uintptr
-	r6  uintptr
-	r7  uintptr
-	r8  uintptr
-	r9  uintptr
-	r10 uintptr
-	r11 uintptr
-}
-
-// prepareStartTask stores fn and args in some callee-saved registers that can
-// then be used by the startTask function (implemented in assembly) to set up
-// the initial stack pointer and initial argument with the pointer to the object
-// with the goroutine start arguments.
-func (r *calleeSavedRegs) prepareStartTask(fn, args uintptr) {
-	r.r4 = fn
-	r.r5 = args
-}
-
 func abort() {
 	// disable all interrupts
 	arm.DisableInterrupts()
diff --git a/src/runtime/runtime_cortexm_qemu.go b/src/runtime/runtime_cortexm_qemu.go
index f1f95caad..973c20ac2 100644
--- a/src/runtime/runtime_cortexm_qemu.go
+++ b/src/runtime/runtime_cortexm_qemu.go
@@ -21,7 +21,8 @@ var timestamp timeUnit
 func main() {
 	preinit()
 	initAll()
-	callMain()
+	go callMain()
+	scheduler()
 	arm.SemihostingCall(arm.SemihostingReportException, arm.SemihostingApplicationExit)
 	abort()
 }
diff --git a/src/runtime/runtime_fe310.go b/src/runtime/runtime_fe310.go
index 92cb9ad17..88295c9c0 100644
--- a/src/runtime/runtime_fe310.go
+++ b/src/runtime/runtime_fe310.go
@@ -52,7 +52,8 @@ func main() {
 	preinit()
 	initPeripherals()
 	initAll()
-	callMain()
+	go callMain()
+	scheduler()
 	abort()
 }
 
diff --git a/src/runtime/runtime_nrf.go b/src/runtime/runtime_nrf.go
index 50d3e5f2b..9b01ded70 100644
--- a/src/runtime/runtime_nrf.go
+++ b/src/runtime/runtime_nrf.go
@@ -22,7 +22,8 @@ func main() {
 	systemInit()
 	preinit()
 	initAll()
-	callMain()
+	go callMain()
+	scheduler()
 	abort()
 }
 
diff --git a/src/runtime/runtime_stm32.go b/src/runtime/runtime_stm32.go
index 0717e7cff..11e686f06 100644
--- a/src/runtime/runtime_stm32.go
+++ b/src/runtime/runtime_stm32.go
@@ -8,6 +8,7 @@ type timeUnit int64
 func main() {
 	preinit()
 	initAll()
-	callMain()
+	go callMain()
+	scheduler()
 	abort()
 }
diff --git a/src/runtime/runtime_unix.go b/src/runtime/runtime_unix.go
index 63d78917e..a88f243f7 100644
--- a/src/runtime/runtime_unix.go
+++ b/src/runtime/runtime_unix.go
@@ -52,7 +52,10 @@ func main() int {
 	initAll()
 
 	// Compiler-generated call to main.main().
-	callMain()
+	go callMain()
+
+	// Run scheduler.
+	scheduler()
 
 	// For libc compatibility.
 	return 0
diff --git a/src/runtime/runtime_wasm.go b/src/runtime/runtime_wasm.go
index 09216cc3f..c01fa9326 100644
--- a/src/runtime/runtime_wasm.go
+++ b/src/runtime/runtime_wasm.go
@@ -21,7 +21,8 @@ func fd_write(id uint32, iovs *wasiIOVec, iovs_len uint, nwritten *uint) (errno
 //export _start
 func _start() {
 	initAll()
-	callMain()
+	go callMain()
+	scheduler()
 }
 
 // Using global variables to avoid heap allocation.
@@ -50,7 +51,9 @@ func setEventHandler(fn func()) {
 
 //go:export resume
 func resume() {
-	handleEvent()
+	go func() {
+		handleEvent()
+	}()
 }
 
 //go:export go_scheduler
diff --git a/src/runtime/scheduler.go b/src/runtime/scheduler.go
index 7dc2b7906..49cf8e402 100644
--- a/src/runtime/scheduler.go
+++ b/src/runtime/scheduler.go
@@ -14,27 +14,16 @@ package runtime
 // of the coroutine-based scheduler, it is the coroutine pointer (a *i8 in
 // LLVM).
 
-import "unsafe"
+import (
+	"internal/task"
+)
 
 const schedulerDebug = false
 
-// State of a task. Internally represented as:
-//
-//     {i8* next, i8* ptr, i32/i64 data}
-type taskState struct {
-	next *task
-	ptr  unsafe.Pointer
-	data uint
-}
-
 // Queues used by the scheduler.
-//
-// TODO: runqueueFront can be removed by making the run queue a circular linked
-// list. The runqueueBack will simply refer to the front in the 'next' pointer.
 var (
-	runqueueFront      *task
-	runqueueBack       *task
-	sleepQueue         *task
+	runqueue           task.Queue
+	sleepQueue         *task.Task
 	sleepQueueBaseTime timeUnit
 )
 
@@ -46,14 +35,14 @@ func scheduleLog(msg string) {
 }
 
 // Simple logging with a task pointer, for debugging.
-func scheduleLogTask(msg string, t *task) {
+func scheduleLogTask(msg string, t *task.Task) {
 	if schedulerDebug {
 		println("---", msg, t)
 	}
 }
 
 // Simple logging with a channel and task pointer.
-func scheduleLogChan(msg string, ch *channel, t *task) {
+func scheduleLogChan(msg string, ch *channel, t *task.Task) {
 	if schedulerDebug {
 		println("---", msg, ch, t)
 	}
@@ -67,7 +56,7 @@ func scheduleLogChan(msg string, ch *channel, t *task) {
 //go:noinline
 func deadlock() {
 	// call yield without requesting a wakeup
-	yield()
+	task.Pause()
 	panic("unreachable")
 }
 
@@ -80,122 +69,20 @@ func Goexit() {
 	deadlock()
 }
 
-// unblock unblocks a task and returns the next value
-func unblock(t *task) *task {
-	state := t.state()
-	next := state.next
-	state.next = nil
-	activateTask(t)
-	return next
-}
-
-// unblockChain unblocks the next task on the stack/queue, returning it
-// also updates the chain, putting the next element into the chain pointer
-// if the chain is used as a queue, tail is used as a pointer to the final insertion point
-// if the chain is used as a stack, tail should be nil
-func unblockChain(chain **task, tail ***task) *task {
-	t := *chain
-	if t == nil {
-		return nil
-	}
-	*chain = unblock(t)
-	if tail != nil && *chain == nil {
-		*tail = chain
-	}
-	return t
-}
-
-// dropChain drops a task from the given stack or queue
-// if the chain is used as a queue, tail is used as a pointer to the field containing a pointer to the next insertion point
-// if the chain is used as a stack, tail should be nil
-func dropChain(t *task, chain **task, tail ***task) {
-	for c := chain; *c != nil; c = &((*c).state().next) {
-		if *c == t {
-			next := (*c).state().next
-			if next == nil && tail != nil {
-				*tail = c
-			}
-			*c = next
-			return
-		}
-	}
-	panic("runtime: task not in chain")
-}
-
-// Pause the current task for a given time.
-//go:linkname sleep time.Sleep
-func sleep(duration int64) {
-	addSleepTask(getCoroutine(), duration)
-	yield()
-}
-
-func avrSleep(duration int64) {
-	sleepTicks(timeUnit(duration / tickMicros))
-}
-
-// Add a non-queued task to the run queue.
-//
-// This is a compiler intrinsic, and is called from a callee to reactivate the
-// caller.
-func activateTask(t *task) {
-	if t == nil {
-		return
-	}
-	scheduleLogTask("  set runnable:", t)
-	runqueuePushBack(t)
-}
-
-// getTaskStateData is a helper function to get the current .data field of the
-// goroutine state.
-//go:inline
-func getTaskStateData(t *task) uint {
-	return t.state().data
-}
-
-// Add this task to the end of the run queue. May also destroy the task if it's
-// done.
-func runqueuePushBack(t *task) {
-	if schedulerDebug {
-		scheduleLogTask("  pushing back:", t)
-		if t.state().next != nil {
-			panic("runtime: runqueuePushBack: expected next task to be nil")
-		}
-	}
-	if runqueueBack == nil { // empty runqueue
-		runqueueBack = t
-		runqueueFront = t
-	} else {
-		lastTaskState := runqueueBack.state()
-		lastTaskState.next = t
-		runqueueBack = t
-	}
-}
-
-// Get a task from the front of the run queue. Returns nil if there is none.
-func runqueuePopFront() *task {
-	t := runqueueFront
-	if t == nil {
-		return nil
-	}
-	state := t.state()
-	runqueueFront = state.next
-	if runqueueFront == nil {
-		// Runqueue is empty now.
-		runqueueBack = nil
-	}
-	state.next = nil
-	return t
+// Add this task to the end of the run queue.
+func runqueuePushBack(t *task.Task) {
+	runqueue.Push(t)
 }
 
 // Add this task to the sleep queue, assuming its state is set to sleeping.
-func addSleepTask(t *task, duration int64) {
+func addSleepTask(t *task.Task, duration int64) {
 	if schedulerDebug {
 		println("  set sleep:", t, uint(duration/tickMicros))
-		if t.state().next != nil {
+		if t.Next != nil {
 			panic("runtime: addSleepTask: expected next task to be nil")
 		}
 	}
-	t.state().data = uint(duration / tickMicros) // TODO: longer durations
+	t.Data = uint(duration / tickMicros) // TODO: longer durations
 	now := ticks()
 	if sleepQueue == nil {
 		scheduleLog("  -> sleep new queue")
@@ -206,20 +93,20 @@ func addSleepTask(t *task, duration int64) {
 
 	// Add to sleep queue.
 	q := &sleepQueue
-	for ; *q != nil; q = &((*q).state()).next {
-		if t.state().data < (*q).state().data {
+	for ; *q != nil; q = &(*q).Next {
+		if t.Data < (*q).Data {
 			// this will finish earlier than the next - insert here
 			break
 		} else {
 			// this will finish later - adjust delay
-			t.state().data -= (*q).state().data
+			t.Data -= (*q).Data
 		}
 	}
 	if *q != nil {
 		// cut delay time between this sleep task and the next
-		(*q).state().data -= t.state().data
+		(*q).Data -= t.Data
 	}
-	t.state().next = *q
+	t.Next = *q
 	*q = t
 }
 
@@ -236,17 +123,16 @@ func scheduler() {
 
 		// Add tasks that are done sleeping to the end of the runqueue so they
 		// will be executed soon.
-		if sleepQueue != nil && now-sleepQueueBaseTime >= timeUnit(sleepQueue.state().data) {
+		if sleepQueue != nil && now-sleepQueueBaseTime >= timeUnit(sleepQueue.Data) {
 			t := sleepQueue
 			scheduleLogTask("  awake:", t)
-			state := t.state()
-			sleepQueueBaseTime += timeUnit(state.data)
-			sleepQueue = state.next
-			state.next = nil
-			runqueuePushBack(t)
+			sleepQueueBaseTime += timeUnit(t.Data)
+			sleepQueue = t.Next
+			t.Next = nil
+			runqueue.Push(t)
 		}
 
-		t := runqueuePopFront()
+		t := runqueue.Pop()
 		if t == nil {
 			if sleepQueue == nil {
 				// No more tasks to execute.
@@ -256,11 +142,11 @@ func scheduler() {
 				scheduleLog("  no tasks left!")
 				return
 			}
-			timeLeft := timeUnit(sleepQueue.state().data) - (now - sleepQueueBaseTime)
+			timeLeft := timeUnit(sleepQueue.Data) - (now - sleepQueueBaseTime)
 			if schedulerDebug {
 				println("  sleeping...", sleepQueue, uint(timeLeft))
-				for t := sleepQueue; t != nil; t = t.state().next {
-					println("    task sleeping:", t, timeUnit(t.state().data))
+				for t := sleepQueue; t != nil; t = t.Next {
+					println("    task sleeping:", t, timeUnit(t.Data))
 				}
 			}
 			sleepTicks(timeLeft)
@@ -275,11 +161,11 @@ func scheduler() {
 
 		// Run the given task.
 		scheduleLogTask("  run:", t)
-		t.resume()
+		t.Resume()
 	}
 }
 
 func Gosched() {
-	runqueuePushBack(getCoroutine())
-	yield()
+	runqueue.Push(task.Current())
+	task.Pause()
 }
diff --git a/src/runtime/scheduler_any.go b/src/runtime/scheduler_any.go
new file mode 100644
index 000000000..d541dc6a3
--- /dev/null
+++ b/src/runtime/scheduler_any.go
@@ -0,0 +1,12 @@
+// +build !scheduler.none
+
+package runtime
+
+import "internal/task"
+
+// Pause the current task for a given time.
+//go:linkname sleep time.Sleep
+func sleep(duration int64) {
+	addSleepTask(task.Current(), duration)
+	task.Pause()
+}
diff --git a/src/runtime/scheduler_coroutines.go b/src/runtime/scheduler_coroutines.go
index 1d0996d94..5e871a64a 100644
--- a/src/runtime/scheduler_coroutines.go
+++ b/src/runtime/scheduler_coroutines.go
@@ -2,103 +2,8 @@
 
 package runtime
 
-// This file implements the Go scheduler using coroutines.
-// A goroutine contains a whole stack. A coroutine is just a single function.
-// How do we use coroutines for goroutines, then?
-//   * Every function that contains a blocking call (like sleep) is marked
-//     blocking, and all it's parents (callers) are marked blocking as well
-//     transitively until the root (main.main or a go statement).
-//   * A blocking function that calls a non-blocking function is called as
-//     usual.
-//   * A blocking function that calls a blocking function passes its own
-//     coroutine handle as a parameter to the subroutine. When the subroutine
-//     returns, it will re-insert the parent into the scheduler.
-// Note that we use the type 'task' to refer to a coroutine, for compatibility
-// with the task-based scheduler. A task type here does not represent the whole
-// task, but just the topmost coroutine. For most of the scheduler, this
-// difference doesn't matter.
-//
-// For more background on coroutines in LLVM:
-// https://llvm.org/docs/Coroutines.html
-
-import "unsafe"
-
-// A coroutine instance, wrapped here to provide some type safety. The value
-// must not be used directly, it is meant to be used as an opaque *i8 in LLVM.
-type task uint8
-
-//go:export llvm.coro.resume
-func (t *task) resume()
-
-//go:export llvm.coro.destroy
-func (t *task) destroy()
-
-//go:export llvm.coro.done
-func (t *task) done() bool
-
-//go:export llvm.coro.promise
-func (t *task) _promise(alignment int32, from bool) unsafe.Pointer
-
-// Get the state belonging to a task.
-func (t *task) state() *taskState {
-	return (*taskState)(t._promise(int32(unsafe.Alignof(taskState{})), false))
-}
-
-func makeGoroutine(uintptr) uintptr
-
-// Compiler stub to get the current goroutine. Calls to this function are
-// removed in the goroutine lowering pass.
-func getCoroutine() *task
-
-// setTaskStatePtr is a helper function to set the current .ptr field of a
-// coroutine promise.
-func setTaskStatePtr(t *task, value unsafe.Pointer) {
-	t.state().ptr = value
-}
-
-// getTaskStatePtr is a helper function to get the current .ptr field from a
-// coroutine promise.
-func getTaskStatePtr(t *task) unsafe.Pointer {
-	if t == nil {
-		blockingPanic()
-	}
-	return t.state().ptr
-}
-
-// yield suspends execution of the current goroutine
-// any wakeups must be configured before calling yield
-func yield()
-
 // getSystemStackPointer returns the current stack pointer of the system stack.
 // This is always the current stack pointer.
 func getSystemStackPointer() uintptr {
 	return getCurrentStackPointer()
 }
-
-func fakeCoroutine(dst **task) {
-	*dst = getCoroutine()
-	for {
-		yield()
-	}
-}
-
-func getFakeCoroutine() *task {
-	// this isnt defined behavior, but this is what our implementation does
-	// this is really a horrible hack
-	var t *task
-	go fakeCoroutine(&t)
-
-	// the first line of fakeCoroutine will have completed by now
-	return t
-}
-
-// noret is a placeholder that can be used to indicate that an async function is not going to directly return here
-func noret()
-
-func getParentHandle() *task
-
-func llvmCoroRefHolder() {
-	noret()
-	getParentHandle()
-	getCoroutine()
-}
diff --git a/src/runtime/scheduler_cortexm.S b/src/runtime/scheduler_cortexm.S
index 6d83ba4f3..121992e7d 100644
--- a/src/runtime/scheduler_cortexm.S
+++ b/src/runtime/scheduler_cortexm.S
@@ -17,7 +17,7 @@ tinygo_startTask:
     blx   r4
 
     // After return, exit this goroutine. This is a tail call.
-    bl    runtime.yield
+    bl    	tinygo_pause
 
 .section .text.tinygo_getSystemStackPointer
 .global  tinygo_getSystemStackPointer
@@ -35,24 +35,23 @@ tinygo_getSystemStackPointer:
 .global  tinygo_switchToScheduler
 .type    tinygo_switchToScheduler, %function
 tinygo_switchToScheduler:
-    // r0 = oldTask *task
+    // r0 = sp *uintptr
 
     // Currently on the task stack (SP=PSP). We need to store the position on
     // the stack where the in-use registers will be stored.
     mov r1, sp
     subs r1, #36
-    str r1, [r0, #36]
+    str r1, [r0]
 
     b tinygo_swapTask
 
 .global  tinygo_switchToTask
 .type    tinygo_switchToTask, %function
 tinygo_switchToTask:
-    // r0 = newTask *task
+    // r0 = sp uintptr
 
     // Currently on the scheduler stack (SP=MSP). We'll have to update the PSP,
     // and then we can invoke swapTask.
-    ldr r0, [r0, #36]
     msr PSP, r0
 
     // Continue executing in the swapTask function, which swaps the stack
diff --git a/src/runtime/scheduler_none.go b/src/runtime/scheduler_none.go
new file mode 100644
index 000000000..222867dd0
--- /dev/null
+++ b/src/runtime/scheduler_none.go
@@ -0,0 +1,14 @@
+// +build scheduler.none
+
+package runtime
+
+//go:linkname sleep time.Sleep
+func sleep(duration int64) {
+	sleepTicks(timeUnit(duration / tickMicros))
+}
+
+// getSystemStackPointer returns the current stack pointer of the system stack.
+// This is always the current stack pointer.
+func getSystemStackPointer() uintptr {
+	return getCurrentStackPointer()
+}
diff --git a/src/runtime/scheduler_tasks.go b/src/runtime/scheduler_tasks.go
index b2142892e..9be63d5d5 100644
--- a/src/runtime/scheduler_tasks.go
+++ b/src/runtime/scheduler_tasks.go
@@ -2,110 +2,6 @@
 
 package runtime
 
-import "unsafe"
-
-const stackSize = 1024
-
-// Stack canary, to detect a stack overflow. The number is a random number
-// generated by random.org. The bit fiddling dance is necessary because
-// otherwise Go wouldn't allow the cast to a smaller integer size.
-const stackCanary = uintptr(uint64(0x670c1333b83bf575) & uint64(^uintptr(0)))
-
-var (
-	currentTask *task // currently running goroutine, or nil
-)
-
-// This type points to the bottom of the goroutine stack and contains some state
-// that must be kept with the task. The last field is a canary, which is
-// necessary to make sure that no stack overflow occured when switching tasks.
-type task struct {
-	// The order of fields in this structs must be kept in sync with assembly!
-	calleeSavedRegs
-	pc uintptr
-	sp uintptr
-	taskState
-	canaryPtr *uintptr // used to detect stack overflows
-}
-
-// getCoroutine returns the currently executing goroutine. It is used as an
-// intrinsic when compiling channel operations, but is not necessary with the
-// task-based scheduler.
-//go:inline
-func getCoroutine() *task {
-	return currentTask
-}
-
-// state is a small helper that returns the task state, and is provided for
-// compatibility with the coroutine implementation.
-//go:inline
-func (t *task) state() *taskState {
-	return &t.taskState
-}
-
-// resume is a small helper that resumes this task until this task switches back
-// to the scheduler.
-func (t *task) resume() {
-	currentTask = t
-	switchToTask(t)
-	currentTask = nil
-}
-
-// switchToScheduler saves the current state on the stack, saves the current
-// stack pointer in the task, and switches to the scheduler. It must only be
-// called when actually running on this task.
-// When it returns, the scheduler has switched back to this task (for example,
-// after a blocking operation completed).
-//export tinygo_switchToScheduler
-func switchToScheduler(t *task)
-
-// switchToTask switches from the scheduler to the task. It must only be called
-// from the scheduler.
-// When this function returns, the task just yielded control back to the
-// scheduler.
-//export tinygo_switchToTask
-func switchToTask(t *task)
-
-// startTask is a small wrapper function that sets up the first (and only)
-// argument to the new goroutine and makes sure it is exited when the goroutine
-// finishes.
-//go:extern tinygo_startTask
-var startTask [0]uint8
-
-// startGoroutine starts a new goroutine with the given function pointer and
-// argument. It creates a new goroutine stack, prepares it for execution, and
-// adds it to the runqueue.
-func startGoroutine(fn, args uintptr) {
-	stack := alloc(stackSize)
-	t := (*task)(unsafe.Pointer(uintptr(stack) + stackSize - unsafe.Sizeof(task{})))
-
-	// Set up the stack canary, a random number that should be checked when
-	// switching from the task back to the scheduler. The stack canary pointer
-	// points to the first word of the stack. If it has changed between now and
-	// the next stack switch, there was a stack overflow.
-	t.canaryPtr = (*uintptr)(unsafe.Pointer(stack))
-	*t.canaryPtr = stackCanary
-
-	// Store the initial sp/pc for the startTask function (implemented in
-	// assembly).
-	t.sp = uintptr(stack) + stackSize - unsafe.Sizeof(task{})
-	t.pc = uintptr(unsafe.Pointer(&startTask))
-	t.prepareStartTask(fn, args)
-	scheduleLogTask("  start goroutine:", t)
-	runqueuePushBack(t)
-}
-
-// yield suspends execution of the current goroutine
-// any wakeups must be configured before calling yield
-//export runtime.yield
-func yield() {
-	// Check whether the canary (the lowest address of the stack) is still
-	// valid. If it is not, a stack overflow has occured.
-	if *currentTask.canaryPtr != stackCanary {
-		runtimePanic("goroutine stack overflow")
-	}
-	switchToScheduler(currentTask)
-}
-
 // getSystemStackPointer returns the current stack pointer of the system stack.
 // This is not necessarily the same as the current stack pointer.
 //export tinygo_getSystemStackPointer