add NewBatchFuture API

internal/batch/batch_future.go

@@ -0,0 +1,138 @@
+package batch
+
+import (
+	"fmt"
+	"reflect"
+
+	"go.uber.org/multierr"
+
+	"go.uber.org/cadence/internal"
+)
+
+// BatchFuture is an implementation of public BatchFuture interface.
+type BatchFuture struct {
+	futures   []internal.Future
+	settables []internal.Settable
+	factories []func(ctx internal.Context) internal.Future
+	batchSize int
+
+	// state
+	wg internal.WaitGroup
+}
+
+func NewBatchFuture(ctx internal.Context, batchSize int, factories []func(ctx internal.Context) internal.Future) (*BatchFuture, error) {
+	var futures []internal.Future
+	var settables []internal.Settable
+	for range factories {
+		future, settable := internal.NewFuture(ctx)
+		futures = append(futures, future)
+		settables = append(settables, settable)
+	}
+
+	batchFuture := &BatchFuture{
+		futures:   futures,
+		settables: settables,
+		factories: factories,
+		batchSize: batchSize,
+
+		wg: internal.NewWaitGroup(ctx),
+	}
+	batchFuture.start(ctx)
+	return batchFuture, nil
+}
+
+func (b *BatchFuture) GetFutures() []internal.Future {
+	return b.futures
+}
+
+func (b *BatchFuture) start(ctx internal.Context) {
+
+	buffered := internal.NewBufferedChannel(ctx, b.batchSize) // buffered channel to limit the number of concurrent futures
+	channel := internal.NewNamedChannel(ctx, "batch-future-channel")
+	b.wg.Add(1)
+	internal.GoNamed(ctx, "batch-future-submitter", func(ctx internal.Context) {
+		defer b.wg.Done()
+
+		for i := range b.factories {
+			buffered.Send(ctx, nil)
+			channel.Send(ctx, i)
+		}
+		channel.Close()
+	})
+
+	b.wg.Add(1)
+	internal.GoNamed(ctx, "batch-future-processor", func(ctx internal.Context) {
+		defer b.wg.Done()
+
+		wgForFutures := internal.NewWaitGroup(ctx)
+
+		var idx int
+		for channel.Receive(ctx, &idx) {
+			idx := idx
+
+			wgForFutures.Add(1)
+			internal.GoNamed(ctx, fmt.Sprintf("batch-future-processor-one-future-%d", idx), func(ctx internal.Context) {
+				defer wgForFutures.Done()
+
+				// fork a future and chain it to the processed future for user to get the result
+				f := b.factories[idx](ctx)
+				b.settables[idx].Chain(f)
+
+				// error handling is not needed here because the result is chained to the settable
+				f.Get(ctx, nil)
+				buffered.Receive(ctx, nil)
+			})
+		}
+		wgForFutures.Wait(ctx)
+	})
+}
+
+func (b *BatchFuture) IsReady() bool {
+	for _, future := range b.futures {
+		if !future.IsReady() {
+			return false
+		}
+	}
+	return true
+}
+
+// Get assigns the result of the futures to the valuePtr.
+// NOTE: valuePtr must be a pointer to a slice, or nil.
+// If valuePtr is a pointer to a slice, the slice will be resized to the length of the futures. Each element of the slice will be assigned with the underlying Future.Get() and thus behaves the same way.
+// If valuePtr is nil, no assignment will be made.
+// If error occurs, values will be set on successful futures and the errors of failed futures will be returned.
+func (b *BatchFuture) Get(ctx internal.Context, valuePtr interface{}) error {
+	// No assignment if valuePtr is nil
+	if valuePtr == nil {
+		b.wg.Wait(ctx)
+		var errs error
+		for i := range b.futures {
+			errs = multierr.Append(errs, b.futures[i].Get(ctx, nil))
+		}
+		return errs
+	}
+
+	v := reflect.ValueOf(valuePtr)
+	if v.Kind() != reflect.Ptr || v.Elem().Kind() != reflect.Slice {
+		return fmt.Errorf("valuePtr must be a pointer to a slice, got %v", v.Kind())
+	}
+
+	// resize the slice to the length of the futures
+	slice := v.Elem()
+	if slice.Cap() < len(b.futures) {
+		slice.Grow(len(b.futures) - slice.Cap())
+	}
+	slice.SetLen(len(b.futures))
+
+	// wait for all futures to be ready
+	b.wg.Wait(ctx)
+
+	// loop through all elements of valuePtr
+	var errs error
+	for i := range b.futures {
+		e := b.futures[i].Get(ctx, slice.Index(i).Addr().Interface())
+		errs = multierr.Append(errs, e)
+	}
+
+	return errs
+}