| 1 | package async |
| 2 | |
| 3 | import ( |
| 4 | "context" |
| 5 | "errors" |
| 6 | "sync" |
| 7 | ) |
| 8 | |
| 9 | // ErrNotStarted is returned when operating on a group that hasn't been started. |
| 10 | var ErrNotStarted = errors.New("async: group not started") |
| 11 | |
| 12 | type contextIDKey struct{} |
| 13 | |
| 14 | // WithContextID stores an integer ID in the context. |
| 15 | func WithContextID(ctx context.Context, id int) context.Context { |
| 16 | return context.WithValue(ctx, contextIDKey{}, id) |
| 17 | } |
| 18 | |
| 19 | // ContextID retrieves the integer ID from the context. Panics if absent. |
| 20 | func ContextID(ctx context.Context) int { |
| 21 | return ctx.Value(contextIDKey{}).(int) |
| 22 | } |
| 23 | |
| 24 | // Group manages a set of async tasks with collective start/stop/wait semantics. |
| 25 | type Group[T any] struct { |
| 26 | executors []Func[T] |
| 27 | cancelFn context.CancelFunc |
| 28 | |
| 29 | mu sync.Mutex |
| 30 | tasks []*Task[T] |
| 31 | } |
| 32 | |
| 33 | // NewGroup creates an empty [Group]. |
| 34 | func NewGroup[T any]() *Group[T] { |
| 35 | return &Group[T]{} |
| 36 | } |
| 37 | |
| 38 | // NewGroupFixed creates a [Group] pre-populated with the given executors. |
| 39 | func NewGroupFixed[T any](executors ...Func[T]) *Group[T] { |
| 40 | return &Group[T]{executors: executors} |
| 41 | } |
| 42 | |
| 43 | // NewGroupRepeated creates a [Group] with count copies of the same executor. |
| 44 | func NewGroupRepeated[T any](executor Func[T], count int) *Group[T] { |
| 45 | g := &Group[T]{} |
| 46 | for i := 0; i < count; i++ { |
| 47 | g.executors = append(g.executors, executor) |
| 48 | } |
| 49 | return g |
| 50 | } |
| 51 | |
| 52 | // AddExecutor adds an executor to the group. Panics if the group is already started. |
| 53 | func (g *Group[T]) AddExecutor(executor Func[T]) { |
| 54 | g.mu.Lock() |
| 55 | defer g.mu.Unlock() |
| 56 | |
| 57 | if g.tasks != nil { |
| 58 | panic("async: cannot add executor to started group") |
| 59 | } |
| 60 | |
| 61 | g.executors = append(g.executors, executor) |
| 62 | } |
| 63 | |
| 64 | // Start launches all executors concurrently. Each task receives a context |
| 65 | // with its index stored via [WithContextID]. Panics on double start. |
| 66 | func (g *Group[T]) Start(ctx context.Context) error { |
| 67 | g.mu.Lock() |
| 68 | defer g.mu.Unlock() |
| 69 | |
| 70 | if len(g.tasks) != 0 { |
| 71 | panic("async: group already started") |
| 72 | } |
| 73 | |
| 74 | ctx, g.cancelFn = context.WithCancel(ctx) |
| 75 | for id, executor := range g.executors { |
| 76 | g.tasks = append(g.tasks, Start[T](WithContextID(ctx, id), executor)) |
| 77 | } |
| 78 | return nil |
| 79 | } |
| 80 | |
| 81 | // Any blocks until any one task in the group completes or ctx is cancelled. |
| 82 | func (g *Group[T]) Any(ctx context.Context) error { |
| 83 | var chans []<-chan struct{} |
| 84 | |
| 85 | { |
| 86 | g.mu.Lock() |
| 87 | |
| 88 | if len(g.tasks) == 0 { |
| 89 | g.mu.Unlock() |
| 90 | return ErrNotStarted |
| 91 | } |
| 92 | |
| 93 | chans = make([]<-chan struct{}, 0, len(g.tasks)) |
| 94 | for _, t := range g.tasks { |
| 95 | chans = append(chans, t.C()) |
| 96 | } |
| 97 | |
| 98 | g.mu.Unlock() |
| 99 | } |
| 100 | |
| 101 | if pos, _, _ := SelectSlice(ctx, chans); pos == -1 { |
| 102 | return ctx.Err() |
| 103 | } |
| 104 | return nil |
| 105 | } |
| 106 | |
| 107 | // All blocks until all tasks in the group complete or ctx is cancelled. |
| 108 | func (g *Group[T]) All(ctx context.Context) error { |
| 109 | { |
| 110 | g.mu.Lock() |
| 111 | if g.tasks == nil { |
| 112 | g.mu.Unlock() |
| 113 | return ErrNotStarted |
| 114 | } |
| 115 | g.mu.Unlock() |
| 116 | } |
| 117 | |
| 118 | for _, t := range g.tasks { |
| 119 | _, ok, err := t.Wait(ctx) |
| 120 | if !ok { |
| 121 | return err |
| 122 | } |
| 123 | } |
| 124 | |
| 125 | return nil |
| 126 | } |
| 127 | |
| 128 | // FirstError polls all tasks and returns the first non-nil error found, or nil. |
| 129 | func (g *Group[T]) FirstError() error { |
| 130 | g.mu.Lock() |
| 131 | defer g.mu.Unlock() |
| 132 | |
| 133 | for _, t := range g.tasks { |
| 134 | _, ok, err := t.Poll() |
| 135 | if ok && err != nil { |
| 136 | return err |
| 137 | } |
| 138 | } |
| 139 | return nil |
| 140 | } |
| 141 | |
| 142 | // Stop cancels the group's shared context and waits for all tasks to finish. |
| 143 | func (g *Group[T]) Stop(ctx context.Context) error { |
| 144 | g.cancelFn() |
| 145 | return g.All(ctx) |
| 146 | } |
| 147 | |