| 1 | package async |
| 2 | |
| 3 | import ( |
| 4 | "context" |
| 5 | "sync/atomic" |
| 6 | |
| 7 | "go.bigb.es/auxilia/fn" |
| 8 | "go.bigb.es/auxilia/goroutine" |
| 9 | ) |
| 10 | |
| 11 | var runningCount atomic.Int64 |
| 12 | |
| 13 | // RunningCount returns the number of currently executing async tasks. |
| 14 | func RunningCount() int { |
| 15 | return int(runningCount.Load()) |
| 16 | } |
| 17 | |
| 18 | // ErrFunc is a function that only returns an error. |
| 19 | type ErrFunc[T any] func(context.Context) error |
| 20 | |
| 21 | // Func is a function that returns a value and an error. |
| 22 | type Func[T any] func(context.Context) (T, error) |
| 23 | |
| 24 | // WrapErrFunc wraps an [ErrFunc] into a [Func] that returns the zero value of T. |
| 25 | func WrapErrFunc[T any](f ErrFunc[T]) Func[T] { |
| 26 | return func(ctx context.Context) (T, error) { return fn.Zero[T](), f(ctx) } |
| 27 | } |
| 28 | |
| 29 | // Task is a generic async task that runs a function in a goroutine |
| 30 | // and provides methods to wait for, poll, or cancel it. |
| 31 | type Task[T any] struct { |
| 32 | executor Func[T] |
| 33 | await chan struct{} |
| 34 | |
| 35 | val T |
| 36 | err error |
| 37 | cancel context.CancelFunc |
| 38 | |
| 39 | id uint64 |
| 40 | registry *Registry |
| 41 | } |
| 42 | |
| 43 | // Start creates and starts a new [Task] with the given executor. |
| 44 | // The task runs in a new goroutine with a derived cancellable context. |
| 45 | // Not thread-safe — do not call concurrently for the same Task instance. |
| 46 | func Start[T any](ctx context.Context, executor Func[T]) *Task[T] { |
| 47 | ctx, cancelFn := context.WithCancel(ctx) |
| 48 | return (&Task[T]{ |
| 49 | executor: executor, |
| 50 | cancel: cancelFn, |
| 51 | }).run(ctx) |
| 52 | } |
| 53 | |
| 54 | // StartWith creates and starts a new [Task], registering it in the given |
| 55 | // [Registry] with the provided tags for later investigation. |
| 56 | func StartWith[T any](ctx context.Context, registry *Registry, executor Func[T], tags ...string) *Task[T] { |
| 57 | ctx, cancelFn := context.WithCancel(ctx) |
| 58 | return (&Task[T]{ |
| 59 | executor: executor, |
| 60 | cancel: cancelFn, |
| 61 | registry: registry, |
| 62 | }).run(ctx, tags...) |
| 63 | } |
| 64 | |
| 65 | func (p *Task[T]) run(ctx context.Context, tags ...string) *Task[T] { |
| 66 | if p.await != nil { |
| 67 | panic("async: task already started") |
| 68 | } |
| 69 | p.await = make(chan struct{}) |
| 70 | |
| 71 | runningCount.Add(1) |
| 72 | |
| 73 | started := make(chan uint64, 1) |
| 74 | go func() { |
| 75 | defer runningCount.Add(-1) |
| 76 | defer close(p.await) |
| 77 | |
| 78 | if p.registry != nil { |
| 79 | goid := goroutine.ID() |
| 80 | p.id = p.registry.register(p.await, goid, tags) |
| 81 | started <- p.id |
| 82 | } else { |
| 83 | started <- 0 |
| 84 | } |
| 85 | |
| 86 | p.val, p.err = p.executor(ctx) |
| 87 | }() |
| 88 | |
| 89 | <-started |
| 90 | return p |
| 91 | } |
| 92 | |
| 93 | // ID returns the task's registry ID, or 0 if not registered. |
| 94 | func (p *Task[T]) ID() uint64 { |
| 95 | return p.id |
| 96 | } |
| 97 | |
| 98 | // IsDone reports whether the task has finished. |
| 99 | func (p *Task[T]) IsDone() bool { |
| 100 | if p.await == nil { |
| 101 | panic("async: task not started") |
| 102 | } |
| 103 | |
| 104 | select { |
| 105 | case <-p.await: |
| 106 | return true |
| 107 | default: |
| 108 | return false |
| 109 | } |
| 110 | } |
| 111 | |
| 112 | // C returns the channel that is closed when the task completes. |
| 113 | func (p *Task[T]) C() <-chan struct{} { |
| 114 | return p.await |
| 115 | } |
| 116 | |
| 117 | // Poll returns the task result without blocking. |
| 118 | // The second return value indicates whether the task has completed. |
| 119 | func (p *Task[T]) Poll() (T, bool, error) { |
| 120 | if p.await == nil { |
| 121 | panic("async: task not started") |
| 122 | } else if !p.IsDone() { |
| 123 | return p.val, false, p.err |
| 124 | } |
| 125 | |
| 126 | return p.val, true, p.err |
| 127 | } |
| 128 | |
| 129 | // Wait blocks until the task completes or ctx is cancelled. |
| 130 | // The second return value indicates whether the task completed (true) |
| 131 | // or the context was cancelled (false). |
| 132 | func (p *Task[T]) Wait(ctx context.Context) (T, bool, error) { |
| 133 | if p.await == nil { |
| 134 | panic("async: task not started") |
| 135 | } |
| 136 | |
| 137 | select { |
| 138 | case <-ctx.Done(): |
| 139 | return p.val, false, ctx.Err() |
| 140 | case <-p.await: |
| 141 | return p.val, true, p.err |
| 142 | } |
| 143 | } |
| 144 | |
| 145 | // Cancel cancels the task's internal context. |
| 146 | func (p *Task[T]) Cancel() { |
| 147 | if p.await == nil { |
| 148 | panic("async: task not started") |
| 149 | } |
| 150 | |
| 151 | p.cancel() |
| 152 | } |
| 153 | |
| 154 | // CancelAndWait cancels the task and waits for it to finish. |
| 155 | func (p *Task[T]) CancelAndWait(ctx context.Context) (T, bool, error) { |
| 156 | p.Cancel() |
| 157 | return p.Wait(ctx) |
| 158 | } |
| 159 | |
| 160 | // NewDummy creates a task that immediately completes with the zero value. |
| 161 | func NewDummy[T any](ctx context.Context) *Task[T] { |
| 162 | return Start[T](ctx, func(ctx context.Context) (T, error) { return fn.Zero[T](), nil }) |
| 163 | } |
| 164 | |