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redo context #4

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17 changes: 11 additions & 6 deletions first.go
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Original file line number Diff line number Diff line change
Expand Up @@ -46,6 +46,10 @@ type First[T any] struct {
cancel context.CancelFunc
}

// WithContext initializes an instance of First with the given context.
// It also returns the context that the instance of First will use.
// After Wait() completes, the returned context will be canceled.
// The parent context (passed in to this function) will NOT be canceled.
func WithContext[T any](ctx context.Context) (*First[T], context.Context) {
var f First[T]

Expand Down Expand Up @@ -104,17 +108,18 @@ func (f *First[T]) Do(fn func() (T, error)) {
}()
}

// DoContext works like Do, except it accepts and provides a context.
// The FIRST context provided to DoContext will be used. The rest will be ignored.
// DoContext works like Do, except it provides a context.
// After the first Do or DoContext call completes, the ctx provided to all DoContext callbacks will be canceled.
// This is useful for canceling long-running tasks that should short-circuit when the first operation completes.
// You are allowed to mix DoContext and Do with a single call to Wait.
//
// If you want to provide a context, use first.WithContext(ctx)
//
// Example:
//
// var f first.First
// f, ctx := first.WithContext(ctx)
//
// f.DoContext(ctx, func(ctx context.Context) (*example, error) {
// f.DoContext(func(ctx context.Context) (*example, error) {
// // do some long-running task that requires context
// data, err := getFromDatabase(ctx)
// if err != nil {
Expand All @@ -124,8 +129,8 @@ func (f *First[T]) Do(fn func() (T, error)) {
// })
//
// data, err := f.Wait()
func (f *First[T]) DoContext(ctx context.Context, fn func(context.Context) (T, error)) {
f.init(ctx)
func (f *First[T]) DoContext(fn func(context.Context) (T, error)) {
f.init(context.Background())

go func() {
res, err := fn(f.context)
Expand Down
42 changes: 21 additions & 21 deletions first_context_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -17,9 +17,9 @@ func TestContextFirstSecond(t *testing.T) {

ctx := context.Background()

var f first.First[*example]
f, _ := first.WithContext[*example](ctx)

f.DoContext(ctx, func(ctx context.Context) (*example, error) {
f.DoContext(func(ctx context.Context) (*example, error) {
defer wg.Done()

time.Sleep(10 * time.Millisecond)
Expand All @@ -31,7 +31,7 @@ func TestContextFirstSecond(t *testing.T) {
return &example{name: "one"}, nil
})

f.DoContext(ctx, func(ctx context.Context) (*example, error) {
f.DoContext(func(ctx context.Context) (*example, error) {
defer wg.Done()

if ctx.Err() != nil {
Expand Down Expand Up @@ -64,9 +64,9 @@ func TestContextFirstFirst(t *testing.T) {

ctx := context.Background()

var f first.First[*example]
f, _ := first.WithContext[*example](ctx)

f.DoContext(ctx, func(ctx context.Context) (*example, error) {
f.DoContext(func(ctx context.Context) (*example, error) {
defer wg.Done()

if ctx.Err() != nil {
Expand All @@ -76,7 +76,7 @@ func TestContextFirstFirst(t *testing.T) {
return &example{name: "one"}, nil
})

f.DoContext(ctx, func(ctx context.Context) (*example, error) {
f.DoContext(func(ctx context.Context) (*example, error) {
defer wg.Done()

time.Sleep(10 * time.Millisecond)
Expand Down Expand Up @@ -111,9 +111,9 @@ func TestContextFirstError(t *testing.T) {

ctx := context.Background()

var f first.First[*example]
f, _ := first.WithContext[*example](ctx)

f.DoContext(ctx, func(ctx context.Context) (*example, error) {
f.DoContext(func(ctx context.Context) (*example, error) {
defer wg.Done()

time.Sleep(10 * time.Millisecond)
Expand All @@ -125,7 +125,7 @@ func TestContextFirstError(t *testing.T) {
return &example{name: "one"}, nil
})

f.DoContext(ctx, func(ctx context.Context) (*example, error) {
f.DoContext(func(ctx context.Context) (*example, error) {
defer wg.Done()

if ctx.Err() != nil {
Expand Down Expand Up @@ -158,9 +158,9 @@ func TestContextErrors(t *testing.T) {

ctx := context.Background()

var f first.First[*example]
f, _ := first.WithContext[*example](ctx)

f.DoContext(ctx, func(ctx context.Context) (*example, error) {
f.DoContext(func(ctx context.Context) (*example, error) {
defer wg.Done()

time.Sleep(10 * time.Millisecond)
Expand All @@ -172,7 +172,7 @@ func TestContextErrors(t *testing.T) {
return nil, errOne
})

f.DoContext(ctx, func(ctx context.Context) (*example, error) {
f.DoContext(func(ctx context.Context) (*example, error) {
defer wg.Done()

if ctx.Err() != nil {
Expand Down Expand Up @@ -225,10 +225,10 @@ func TestContextFirstNone(t *testing.T) {
func TestContextFirstRoutines(t *testing.T) {
ctx := context.Background()

var f first.First[*example]
f, _ := first.WithContext[*example](ctx)

// Go ahead and set up one func to avoid the ErrNothingToWaitOn error.
f.DoContext(ctx, func(ctx context.Context) (*example, error) {
f.DoContext(func(ctx context.Context) (*example, error) {
if ctx.Err() != nil {
t.Fatalf("Unexpected context error: %s", ctx.Err())
}
Expand All @@ -243,7 +243,7 @@ func TestContextFirstRoutines(t *testing.T) {
go func() {
defer wg.Done()

f.DoContext(ctx, func(ctx context.Context) (*example, error) {
f.DoContext(func(ctx context.Context) (*example, error) {
time.Sleep(10 * time.Millisecond)

return &example{name: "two"}, nil
Expand Down Expand Up @@ -281,17 +281,17 @@ func TestRespectsCancel(t *testing.T) {

ctx, cancel := context.WithCancel(context.Background())

var f first.First[*example]
f, _ := first.WithContext[*example](ctx)

f.DoContext(ctx, func(ctx context.Context) (*example, error) {
f.DoContext(func(ctx context.Context) (*example, error) {
defer wg.Done()

wg.Wait()

return &example{name: "one"}, nil
})

f.DoContext(ctx, func(ctx context.Context) (*example, error) {
f.DoContext(func(ctx context.Context) (*example, error) {
defer wg.Done()

wg.Wait()
Expand All @@ -317,17 +317,17 @@ func TestRespectsWithContextCancel(t *testing.T) {

ctx, cancel := context.WithCancel(context.Background())

f, ctx := first.WithContext[*example](ctx)
f, _ := first.WithContext[*example](ctx)

f.DoContext(ctx, func(ctx context.Context) (*example, error) {
f.DoContext(func(ctx context.Context) (*example, error) {
defer wg.Done()

wg.Wait()

return &example{name: "one"}, nil
})

f.DoContext(ctx, func(ctx context.Context) (*example, error) {
f.DoContext(func(ctx context.Context) (*example, error) {
defer wg.Done()

wg.Wait()
Expand Down
6 changes: 3 additions & 3 deletions first_example_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -87,16 +87,16 @@ func ExampleFirst_DoContext() {

wg.Add(2)

var f first.First[*example]
f, _ := first.WithContext[*example](ctx)

f.DoContext(ctx, func(ctx context.Context) (*example, error) {
f.DoContext(func(ctx context.Context) (*example, error) {
defer wg.Done()
time.Sleep(1 * time.Millisecond)
fmt.Printf("2 ctx=%s\n", ctx.Err())
return nil, errors.New("oops 2")
})

f.DoContext(ctx, func(ctx context.Context) (*example, error) {
f.DoContext(func(ctx context.Context) (*example, error) {
defer wg.Done()
fmt.Printf("1 ctx=%s\n", ctx.Err())
return &example{name: "one"}, nil
Expand Down