refactor coroutine lowering and tasks

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(),
+	}
+}

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
+}

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()
+}

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")
+}

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)
+}

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()
+}