/
flatten.go
75 lines (62 loc) · 1.95 KB
/
flatten.go
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// Licensed to the Apache Software Foundation (ASF) under one or more
// contributor license agreements. See the NOTICE file distributed with
// this work for additional information regarding copyright ownership.
// The ASF licenses this file to You under the Apache License, Version 2.0
// (the "License"); you may not use this file except in compliance with
// the License. You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package exec
import (
"context"
"fmt"
)
// Flatten is a fan-in node. It ensures that Start/FinishBundle are only
// called once downstream.
type Flatten struct {
// UID is the unit identifier.
UID UnitID
// N is the number of incoming edges.
N int
// Out is the output node.
Out Node
active bool
seen int
}
func (m *Flatten) ID() UnitID {
return m.UID
}
func (m *Flatten) Up(ctx context.Context) error {
return nil
}
func (m *Flatten) StartBundle(ctx context.Context, id string, data DataContext) error {
if m.active {
return nil // ok: ignore multiple start bundles. We just want the first one.
}
m.active = true
m.seen = 0
return m.Out.StartBundle(ctx, id, data)
}
func (m *Flatten) ProcessElement(ctx context.Context, elm *FullValue, values ...ReStream) error {
return m.Out.ProcessElement(ctx, elm, values...)
}
func (m *Flatten) FinishBundle(ctx context.Context) error {
m.seen++
if m.seen < m.N {
return nil // ok: wait for last FinishBundle.
}
m.active = false
return m.Out.FinishBundle(ctx)
}
func (m *Flatten) Down(ctx context.Context) error {
return nil
}
func (m *Flatten) String() string {
return fmt.Sprintf("Flatten[%v]. Out:%v", m.N, m.Out)
}