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coroutine.go
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1393 lines (1255 loc) · 35.6 KB
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package async
import (
"context"
"fmt"
"iter"
"runtime/debug"
"slices"
"sync"
"time"
)
type action int
const (
_ action = iota
doYield
doSoftYield
doHardYield
doTransition
doTailTransition // Do transition and remove controller.
doEnd
doBreak
doContinue
doReturn
doRaise // Exit or panic.
)
const (
flagResumed = 1 << iota
flagEnqueued
flagCleanup
flagEnded
flagFreed
flagCanceled
flagSoftYield
flagHardYield
flagExiting
flagPanicking
flagInsideLoop
flagNonCancelable
flagNonRecyclable
)
type noCopy struct{}
func (*noCopy) Lock() {}
func (*noCopy) Unlock() {}
// A Coroutine is an execution of code, similar to a goroutine but cooperative
// and stackless.
//
// A coroutine is created with a function called [Task].
// A coroutine's job is to complete the task.
// When an [Executor] spawns a coroutine with a task, it runs the coroutine by
// calling the task function with the coroutine as the argument.
// The return value determines whether to end the coroutine or to yield it
// so that it could resume later.
//
// In order for a coroutine to resume, the coroutine must watch at least one
// [Event] (e.g. [Signal], [State], etc.), when calling the task function.
// A notification of such an event resumes the coroutine.
// When a coroutine is resumed, the executor runs the coroutine again.
//
// A coroutine can also make a transition to work on another task according to
// the return value of the task function.
// A coroutine can transition from one task to another until a task ends it.
type Coroutine struct {
_ noCopy
flag uint16
level uint16
childnum uint32
weight Weight
parent *Coroutine
executor *Executor
wg *sync.WaitGroup
ps panicstack
guard func() bool
task Task
deps map[Event]struct{}
cleanups []Cleanup
defers []Task
controllers []controller
}
type Weight int64
var coroutinePool = sync.Pool{
New: func() any { return new(Coroutine) },
}
func newCoroutine() *Coroutine {
return coroutinePool.Get().(*Coroutine)
}
func freeCoroutine(co *Coroutine) {
if co.flag&flagFreed != 0 {
panic("async: internal error: double free")
}
co.flag |= flagFreed
co.parent = nil
co.executor = nil
wg := co.wg
co.wg = nil
clear(co.ps)
co.ps = co.ps[:0]
co.task = nil
if co.flag&flagNonRecyclable == 0 {
coroutinePool.Put(co)
}
if wg != nil {
wg.Done()
}
}
func (co *Coroutine) init(l uint16, w Weight, e *Executor, t Task) *Coroutine {
co.flag = flagResumed
co.level = l
co.weight = w
co.executor = e
co.task = t
return co
}
func compare[Int intType](x, y Int) int {
if x < y {
return -1
}
if x > y {
return +1
}
return 0
}
func (co *Coroutine) less(other *Coroutine) bool {
if c := compare(co.weight, other.weight); c != 0 {
return c == +1
}
return co.level < other.level
}
// Resume resumes co.
func (co *Coroutine) Resume() {
co.executor.resumeCoroutine(co, true)
}
func (e *Executor) resumeCoroutine(co *Coroutine, lock bool) {
switch flag := co.flag; {
case flag&flagEnqueued != 0:
co.flag = flag | flagResumed
default:
co.flag = flag | flagResumed | flagEnqueued
if lock {
e.mu.Lock()
}
e.pq.Push(co)
if lock {
e.mu.Unlock()
}
}
}
func (e *Executor) runCoroutine(co *Coroutine) {
flag := co.flag
flag &^= flagEnqueued
co.flag = flag
switch {
case flag&flagEnded != 0:
freeCoroutine(co)
case flag&flagResumed != 0:
e.mu.Unlock()
co.run()
e.mu.Lock()
}
}
func (co *Coroutine) run() (suspended bool) {
var res Result
ps := &co.ps
guard := co.guard
for {
if guard != nil {
var ok bool
co.flag &^= flagResumed
if !ps.Try(func() { ok = guard() }) {
co.flag |= flagPanicking
co.task = (*Coroutine).raise
ok = true
}
if !ok {
return true
}
guard = nil
co.guard = nil
}
co.flag &^= flagResumed
co.flag |= flagCleanup
co.clearDeps()
co.clearCleanups()
if co.childnum != 0 {
return true
}
co.flag &^= flagResumed | flagCleanup | flagSoftYield
if !co.NonCancelable() {
co.flag &^= flagHardYield
}
if !ps.Try(func() { res = co.task(co) }) {
res = co.panic()
}
switch res.action {
case doYield:
if co.Canceled() && !co.NonCancelable() {
res = co.cancel()
}
case doSoftYield:
if co.Canceled() {
res = Result{action: doTransition, task: res.task}
} else {
co.flag |= flagSoftYield
res.action = doYield
}
case doHardYield:
co.flag |= flagHardYield
res.action = doYield
}
if res.action != doYield && res.action != doTransition {
co.flag &^= flagResumed
co.flag |= flagCleanup
co.clearDeps()
co.clearCleanups()
if co.childnum != 0 {
co.task = actionToTask(res.action)
return true
}
co.flag &^= flagResumed | flagCleanup
if co.Panicking() {
res = co.raise()
}
controllers := co.controllers
for len(controllers) != 0 {
i := len(controllers) - 1
c := &controllers[i]
if !ps.Try(func() { res = c.negotiate(co, res) }) {
res = c.negotiate(co, co.panic())
}
if res.action != doTransition {
if !ps.Try(c.cleanup) {
res = co.panic()
}
controllers[i] = controller{}
controllers = controllers[:i]
co.controllers = controllers
}
if res.action == doTransition || res.action == doTailTransition {
break
}
}
if res.action != doTransition && res.action != doTailTransition {
rootController := &controller{kind: funcController}
if !ps.Try(func() { res = rootController.negotiate(co, res) }) {
res = rootController.negotiate(co, co.panic())
}
}
if res.action == doTailTransition {
res.action = doTransition
}
}
if res.task != nil {
co.task = res.task
}
if res.guard != nil {
guard = res.guard
co.guard = guard
continue // For calling guard immediately.
}
if res.controller.kind != 0 {
addController := true
if res.controller.kind == funcController && res.controller.flag == 0 {
lastController := &controller{kind: funcController}
if n := len(co.controllers); n != 0 {
lastController = &co.controllers[n-1]
}
if lastController.kind == funcController && lastController.doff == res.controller.doff {
// Tail-call optimization:
// If the last controller is also a funcController, do not add another one.
// (doTailTransition also pays tribute to this optimization.)
addController = false
}
}
if addController {
co.controllers = append(co.controllers, res.controller)
if capSizeLimit := 1000000; cap(co.controllers) > capSizeLimit {
co.flag |= flagNonRecyclable
co.task = func(co *Coroutine) Result {
panic("async: too many controllers or recursions")
}
}
}
}
if res.action != doTransition {
break
}
}
if res.action == doYield {
return true
}
co.flag |= flagEnded
parent := co.parent
if parent != nil {
if i := slices.Index(parent.cleanups, Cleanup((*childCoroutineCleanup)(co))); i != -1 {
parent.cleanups = slices.Delete(parent.cleanups, i, i+1)
}
parent.childnum--
if parent.childnum == 0 && parent.flag&flagCleanup != 0 {
parent.Resume()
}
}
if co.Panicking() {
if parent != nil {
parent.flag |= flagPanicking
parent.guard = nil
parent.task = (*Coroutine).raise
parent.ps = append(parent.ps, co.ps...)
parent.Resume()
} else {
co.executor.ps = append(co.executor.ps, co.ps...)
}
}
if len(co.deps) != 0 {
panic("async: internal error: deps did not clear")
}
if len(co.cleanups) != 0 {
panic("async: internal error: cleanups did not clear")
}
if len(co.defers) != 0 {
panic("async: internal error: defers did not clear")
}
if len(co.controllers) != 0 {
panic("async: internal error: controllers did not clear")
}
if co.childnum != 0 {
panic("async: internal error: child coroutines did not clear")
}
if co.flag&flagEnqueued == 0 {
freeCoroutine(co)
}
return false
}
func (co *Coroutine) clearDeps() {
deps := co.deps
for d := range deps {
delete(deps, d)
d.removeListener(co)
}
}
func (co *Coroutine) clearCleanups() {
ok := true
cleanups := co.cleanups
for len(co.cleanups) != 0 {
cleanups := co.cleanups
co.cleanups = nil
for _, c := range slices.Backward(cleanups) {
ok = co.ps.Try(c.Cleanup) && ok
}
}
clear(cleanups)
co.cleanups = cleanups[:0]
if !ok {
co.flag |= flagPanicking
co.task = (*Coroutine).raise
}
}
type childCoroutineCleanup Coroutine
func (child *childCoroutineCleanup) Cleanup() {
co := (*Coroutine)(child)
co.flag |= flagCanceled
if co.flag&(flagSoftYield|flagHardYield) != flagHardYield {
co.guard = nil
if co.flag&flagSoftYield == 0 {
co.flag |= flagExiting
co.task = (*Coroutine).raise
}
co.run()
}
}
// Weight returns the weight of co.
func (co *Coroutine) Weight() Weight {
return co.weight
}
// Parent returns the parent coroutine of co.
//
// Note that a coroutine must not escape to a non-child coroutine or another
// goroutine because, a coroutine may be put into pool for later reuse when
// it completes.
func (co *Coroutine) Parent() *Coroutine {
return co.parent
}
// Executor returns the executor that spawned co.
func (co *Coroutine) Executor() *Executor {
return co.executor
}
// Resumed reports whether co has been resumed.
func (co *Coroutine) Resumed() bool {
return co.flag&flagResumed != 0
}
// Exiting reports whether co is exiting.
//
// When exiting, entering a [Func], in a deferred task, would temporarily
// reset Exiting to false until that [Func] ends or exits again.
func (co *Coroutine) Exiting() bool {
return co.flag&flagExiting != 0
}
// Panicking reports whether co is panicking.
//
// When panicking, entering a [Func], in a deferred task, would temporarily
// reset Panicking to false until that [Func] ends or panics again.
func (co *Coroutine) Panicking() bool {
return co.flag&flagPanicking != 0
}
// Canceled reports whether co has been canceled.
func (co *Coroutine) Canceled() bool {
return co.flag&flagCanceled != 0
}
// NonCancelable reports whether co is currently running a [NonCancelable] task.
func (co *Coroutine) NonCancelable() bool {
return co.flag&flagNonCancelable != 0
}
// Watch watches some events so that, when any of them notifies, co resumes.
func (co *Coroutine) Watch(ev ...Event) {
if co.flag&flagCleanup != 0 {
panic("async: watch during cleanup")
}
var deps map[Event]struct{}
for _, d := range ev {
if deps == nil {
deps = co.deps
if deps == nil {
deps = make(map[Event]struct{})
co.deps = deps
}
}
deps[d] = struct{}{}
d.addListener(co)
}
}
// Cleanup represents any type that carries a Cleanup method.
// A Cleanup can be added to a coroutine in a [Task] function for making
// an effect some time later when the coroutine resumes or finishes a [Task].
type Cleanup interface {
Cleanup()
}
// A CleanupFunc is a func() that implements the [Cleanup] interface.
type CleanupFunc func()
// Cleanup implements the [Cleanup] interface.
func (f CleanupFunc) Cleanup() { f() }
// Cleanup adds something to clean up when co resumes or finishes a [Task].
func (co *Coroutine) Cleanup(c Cleanup) {
if c == nil {
return
}
co.cleanups = append(co.cleanups, c)
}
// CleanupFunc adds a function call when co resumes or finishes a [Task].
func (co *Coroutine) CleanupFunc(f func()) {
if f == nil {
return
}
co.cleanups = append(co.cleanups, CleanupFunc(f))
}
// Defer adds a [Task] for execution when returning from a [Func].
// Deferred tasks are executed in last-in-first-out (LIFO) order.
func (co *Coroutine) Defer(t Task) {
if t == nil {
return
}
co.defers = append(co.defers, t)
}
// Recover returns the latest value in the panic stack and stops co from
// panicking.
// If co isn't panicking, Recover returns nil.
//
// One might be tempted to use the built-in panic function and this method to
// mimic the power of try-catch statement in some other programming languages,
// but there's a cost.
// In order to be able to continue running, when there's a panic, a coroutine
// immediately recovers it and puts it into the panic stack, along with a stack
// trace returned by [runtime/debug.Stack], which might take thousands of bytes.
//
// Instead of using the built-in panic function to trigger a panic, one could
// consider use [Coroutine.Panic] to mimic one, which leaves no stack trace
// behind.
func (co *Coroutine) Recover() (v any) {
switch flag := co.flag; {
case flag&flagCleanup != 0:
panic("async: recover during cleanup")
case flag&flagPanicking == 0:
return nil
}
p := &co.ps[len(co.ps)-1]
p.recovered = true
co.flag &^= flagPanicking
return p.value
}
// RecoverFunc is like [Coroutine.Recover] but only recovers the recent panic
// that satisfies a condition.
func (co *Coroutine) RecoverFunc(f func(v any) bool) (v any) {
switch flag := co.flag; {
case flag&flagCleanup != 0:
panic("async: recover during cleanup")
case flag&flagPanicking == 0:
return nil
}
p := &co.ps[len(co.ps)-1]
if f(p.value) {
p.recovered = true
co.flag &^= flagPanicking
v = p.value
}
return v
}
// Spawn creates a child coroutine with the same weight as co to work on t.
//
// Spawn runs t immediately. If t panics immediately, Spawn panics, too.
//
// Child coroutines, if not yet ended, are canceled when the parent one resumes
// or finishes a [Task].
// When a coroutine is canceled, it runs to completion with all yield points
// treated like exit points.
//
// However, within a [NonCancelable] context, a canceled coroutine is allowed
// to yield, which would correspondingly cause its parent coroutine to yield,
// too. In such case, the parent coroutine stays suspended until all its child
// coroutines complete.
func (co *Coroutine) Spawn(t Task) {
level := co.level + 1
if level == 0 {
panic("async: too many levels")
}
if co.childnum+1 == 0 {
panic("async: too many child coroutines")
}
child := newCoroutine().init(level, co.weight, co.executor, t)
child.parent = co
co.childnum++
switch suspended := child.run(); {
case suspended:
co.cleanups = append(co.cleanups, (*childCoroutineCleanup)(child))
case co.Panicking():
// child panics.
panic(dummy{}) // Stop current task.
}
}
// Result is the type of the return value of a [Task] function.
// A Result determines what next for a coroutine to do after running a task.
//
// A Result can be created by calling one of the following methods:
// - [Coroutine.Await], [Coroutine.SoftAwait] or [Coroutine.HardAwait]:
// for creating a [PendingResult] that can be transformed into a [Result]
// with one of its methods, which will then cause the running coroutine to
// yield;
// - [Coroutine.Yield], [Coroutine.SoftYield] or [Coroutine.HardYield]:
// for yielding a coroutine with additional events to watch and, when
// resumed, reiterating the running task;
// - [Coroutine.Transition]: for making a transition to work on another task;
// - [Coroutine.End]: for ending the running task of a coroutine;
// - [Coroutine.Break]: for breaking a [Loop] (or [LoopN]);
// - [Coroutine.Continue]: for continuing a [Loop] (or [LoopN]);
// - [Coroutine.Return]: for returning from a [Func];
// - [Coroutine.Exit]: for exiting a coroutine;
// - [Coroutine.Panic]: for simulating a panic;
// - [Coroutine.PanicWithStackTrace]: for simulating a panic with a stack
// trace.
//
// These methods may have side effects. One should never store a Result in
// a variable and overwrite it with another, before returning it. Instead,
// one should just return a Result right after it is created.
type Result struct {
action action
guard func() bool // used by do(Soft|Hard)Yield only
task Task // used by do(Soft|Hard)Yield and do(Tail)Transition
controller controller // used by doTransition only
}
// PendingResult is the return type of the [Coroutine.Await] method.
// A PendingResult is an intermediate value that must be transformed into
// a [Result] with one of its methods before returning from a [Task].
type PendingResult struct {
res Result
}
// Reiterate returns a [Result] that will cause the running coroutine to yield
// and, when resumed, reiterate the running task.
func (pr PendingResult) Reiterate() Result {
return pr.res
}
// Then returns a [Result] that will cause the running coroutine to yield and,
// when resumed, make a transition to work on another [Task].
func (pr PendingResult) Then(t Task) Result {
pr.res.task = must(t)
return pr.res
}
// End returns a [Result] that will cause the running coroutine to yield and,
// when resumed, end the running task.
func (pr PendingResult) End() Result {
return pr.Then(End())
}
// Break returns a [Result] that will cause the running coroutine to yield and,
// when resumed, break a [Loop] (or [LoopN]).
func (pr PendingResult) Break() Result {
return pr.Then(Break())
}
// Continue returns a [Result] that will cause the running coroutine to yield
// and, when resumed, continue a [Loop] (or [LoopN]).
func (pr PendingResult) Continue() Result {
return pr.Then(Continue())
}
// Return returns a [Result] that will cause the running coroutine to yield and,
// when resumed, return from a [Func].
func (pr PendingResult) Return() Result {
return pr.Then(Return())
}
// Exit returns a [Result] that will cause the running coroutine to yield and,
// when resumed, cause the running coroutine to exit.
func (pr PendingResult) Exit() Result {
return pr.Then(Exit())
}
// Panic returns a [Result] that will cause the running coroutine to yield and,
// when resumed, cause the running coroutine to behave like there's a panic.
// Unlike the built-in panic function, Panic leaves no stack trace behind.
// Please use with caution.
func (pr PendingResult) Panic(v any) Result {
return pr.Then(Panic(v))
}
// Until transforms pr into one with a condition.
// Affected coroutines remain suspended until the condition is met.
func (pr PendingResult) Until(f func() bool) PendingResult {
pr.res.guard = f
return pr
}
// Await returns a [PendingResult] that can be transformed into a [Result]
// with one of its methods, which will then cause co to yield.
// Await also accepts additional events to watch.
func (co *Coroutine) Await(ev ...Event) PendingResult {
if len(ev) != 0 {
co.Watch(ev...)
}
return PendingResult{res: Result{action: doYield}}
}
// SoftAwait is like [Coroutine.Await], but cancelable.
// Upon cancellation, where [Coroutine.Await] would unwind and exit,
// SoftAwait would just resume and continue running.
func (co *Coroutine) SoftAwait(ev ...Event) PendingResult {
if len(ev) != 0 {
co.Watch(ev...)
}
return PendingResult{res: Result{action: doSoftYield}}
}
// HardAwait is like [Coroutine.Await], but non-cancelable.
// Upon cancellation, where [Coroutine.Await] would unwind and exit,
// HardAwait would just do nothing and remain suspended.
func (co *Coroutine) HardAwait(ev ...Event) PendingResult {
if len(ev) != 0 {
co.Watch(ev...)
}
return PendingResult{res: Result{action: doHardYield}}
}
// Yield returns a [Result] that will cause co to yield and, when co is resumed,
// reiterate the running task.
// Yield also accepts additional events to watch.
func (co *Coroutine) Yield(ev ...Event) Result {
return co.Await(ev...).Reiterate()
}
// SoftYield is like [Coroutine.Yield], but cancelable.
// Upon cancellation, where [Coroutine.Yield] would unwind and exit,
// SoftYield would just resume and continue running.
func (co *Coroutine) SoftYield(ev ...Event) Result {
return co.SoftAwait(ev...).Reiterate()
}
// HardYield is like [Coroutine.Yield], but non-cancelable.
// Upon cancellation, where [Coroutine.Yield] would unwind and exit,
// HardYield would just do nothing and remain suspended.
func (co *Coroutine) HardYield(ev ...Event) Result {
return co.HardAwait(ev...).Reiterate()
}
// Transition returns a [Result] that will cause co to make a transition to
// work on t.
func (co *Coroutine) Transition(t Task) Result {
return Result{action: doTransition, task: must(t)}
}
// End returns a [Result] that will cause co to end its current running task.
func (co *Coroutine) End() Result {
return Result{action: doEnd}
}
// Break returns a [Result] that will cause co to break a [Loop] (or [LoopN]).
func (co *Coroutine) Break() Result {
if co.flag&flagInsideLoop == 0 {
panic("async: break without a loop")
}
return Result{action: doBreak}
}
// Continue returns a [Result] that will cause co to continue a [Loop]
// (or [LoopN]).
func (co *Coroutine) Continue() Result {
if co.flag&flagInsideLoop == 0 {
panic("async: continue without a loop")
}
return Result{action: doContinue}
}
// Return returns a [Result] that will cause co to return from a [Func].
func (co *Coroutine) Return() Result {
return Result{action: doReturn}
}
// Exit returns a [Result] that will cause co to exit.
// All deferred tasks will be run before co exits.
func (co *Coroutine) Exit() Result {
co.flag |= flagExiting
return Result{action: doRaise}
}
func (co *Coroutine) cancel() Result {
co.flag |= flagExiting | flagCanceled
return Result{action: doRaise}
}
func (co *Coroutine) panic() Result {
co.flag |= flagPanicking
return Result{action: doRaise}
}
func (co *Coroutine) raise() Result {
return Result{action: doRaise}
}
// Panic returns a [Result] that will cause co to behave as there's a panic.
// Unlike the built-in panic function, Panic leaves no stack trace behind.
// Please use with caution.
func (co *Coroutine) Panic(v any) Result {
if v == nil {
panic("async: Panic called with nil argument")
}
co.ps.Push(v, nil)
co.flag |= flagPanicking
return Result{action: doRaise}
}
// PanicWithStackTrace returns a [Result] that will cause co to behave as
// there's a panic.
// PanicWithStackTrace takes an extra stacktrace argument, which makes it
// very much like the built-in panic function.
// Useful when one wants to propagate panics from goroutines.
func (co *Coroutine) PanicWithStackTrace(v any, stacktrace []byte) Result {
if v == nil {
panic("async: PanicWithStackTrace called with nil argument")
}
co.ps.Push(v, stacktrace)
co.flag |= flagPanicking
return Result{action: doRaise}
}
type controllerKind int8
const (
_ controllerKind = iota
funcController
thenController
blockController
loopController
seqController
ncController
)
type controller struct {
kind controllerKind
flag uint16 // used by funcController and loopController
poff int // used by funcController only
doff int // used by funcController only
task Task // used by thenController and loopController
tasks []Task // used by blockController only
next func() (Task, bool) // used by seqController only
stop func() // used by seqController only
}
func (c *controller) negotiate(co *Coroutine, res Result) Result {
switch c.kind {
case funcController:
switch res.action {
case doEnd, doReturn, doRaise:
if !co.Panicking() && len(co.ps) > c.poff {
// Discard recovered panic values.
clear(co.ps[c.poff:])
co.ps = co.ps[:c.poff]
}
if len(co.defers) > c.doff {
i := len(co.defers) - 1
t := co.defers[i]
co.defers[i] = nil
co.defers = co.defers[:i]
return co.Transition(t)
}
raise := co.flag&(flagExiting|flagPanicking) != 0
co.flag |= c.flag
if raise {
return co.raise()
}
return co.End()
case doBreak, doContinue:
panic("async: internal error: unhandled break/continue action")
default:
panic(fmt.Sprintf("async: unknown action: %v", res.action))
}
case thenController:
if res.action != doEnd {
return res
}
return Result{action: doTailTransition, task: c.task}
case blockController:
if res.action != doEnd || len(c.tasks) == 0 {
return res
}
t := c.tasks[0]
c.tasks = c.tasks[1:]
action := doTransition
if len(c.tasks) == 0 {
action = doTailTransition
}
return Result{action: action, task: must(t)}
case loopController:
switch res.action {
case doEnd, doContinue:
return co.Transition(c.task)
}
if c.flag == 0 {
co.flag &^= flagInsideLoop
}
if res.action == doBreak {
return co.End()
}
return res
case seqController:
if res.action == doEnd {
if t, ok := c.next(); ok {
return co.Transition(t)
}
}
return res
case ncController:
co.flag &^= flagHardYield | flagNonCancelable
return res
default:
panic("async: internal error: unknown controller")
}
}
func (c *controller) cleanup() {
switch c.kind {
case seqController:
c.stop()
}
}
// A Task is a piece of work that a coroutine is given to do when it is spawned.
// The return value of a task, a [Result], determines what next for a coroutine
// to do.
//
// The argument co must not escape to a non-child coroutine or another goroutine
// because, co may be put into pool for later reuse when co completes.
type Task func(co *Coroutine) Result
// Then returns a [Task] that first works on t, then next after t ends.
//
// To chain multiple tasks, use [Block] function.
func (t Task) Then(next Task) Task {
return func(co *Coroutine) Result {
return Result{
action: doTransition,
task: must(t),
controller: controller{kind: thenController, task: must(next)},
}
}
}
// Do returns a [Task] that calls f, and then ends.
func Do(f func()) Task {
return func(co *Coroutine) Result {
f()
return co.End()
}
}
// End returns a [Task] that ends without doing anything.
func End() Task {
return (*Coroutine).End
}
// Await returns a [Task] that awaits some events until any of them notifies,
// and then ends.
// If ev is empty, Await returns a [Task] that never ends.
func Await(ev ...Event) Task {
if len(ev) == 0 {
// Return a pure function instead.
return func(co *Coroutine) Result {
return co.Await().End()
}
}
return func(co *Coroutine) Result {
return co.Await(ev...).End()
}
}
// SoftAwait is like [Await], but cancelable.
// Upon cancellation, where [Await] would unwind and exit, SoftAwait would
// just resume and continue running.
func SoftAwait(ev ...Event) Task {
if len(ev) == 0 {
// Return a pure function instead.
return func(co *Coroutine) Result {
return co.SoftAwait().End()
}
}
return func(co *Coroutine) Result {
return co.SoftAwait(ev...).End()
}