/
pipeline.go
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/
pipeline.go
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// Copyright 2020 Dolthub, Inc.
//
// Licensed 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 pipeline
import (
"context"
"errors"
"fmt"
"golang.org/x/sync/errgroup"
)
// ErrUnknownStageName is the error returned when an unknown stage name is referenced
var ErrUnknownStageName = errors.New("unknown stage name")
// ErrPipelidneAborted is the error returned from Pipeline.Wait when Pipeline.Abort is called.
var ErrPipelineAborted = errors.New("pipeline aborted")
// Pipeline is a batch processor which takes data in batches and transforms it in stages
type Pipeline struct {
nameToStage map[string]*Stage
stages []*Stage
waitCh <-chan []ItemWithProps
eg *errgroup.Group
ctx context.Context
}
// NewPipeline creates a new Pipeline from an ordered slice of stages. The first stage in the pipeline must produce data
// and each stage will pass data on to the next stage.
func NewPipeline(stages ...*Stage) *Pipeline {
var nextInStage chan []ItemWithProps
outBatchSize := -1
nameToStage := make(map[string]*Stage)
p := &Pipeline{waitCh: nextInStage}
for i := len(stages) - 1; i >= 0; i-- {
nextInStage = stages[i].init(outBatchSize, nextInStage, p)
outBatchSize = stages[i].inBatchSize
nameToStage[stages[i].name] = stages[i]
}
p.eg = nil
p.stages = stages
p.nameToStage = nameToStage
return p
}
// Start the pipeline
func (p *Pipeline) Start(ctx context.Context) {
if p.eg != nil {
panic("started multiple times")
}
p.eg, p.ctx = errgroup.WithContext(ctx)
for _, stage := range p.stages {
stage.start(p.eg, p.ctx)
}
}
// Wait waits for the pipeline to finish
func (p *Pipeline) Wait() error {
return p.eg.Wait()
}
// Abort aborts the pipeline. After abort is called the pipeline will continue running closing asynchronously
// Use Wait() if you want to wait for the pipeline to finish closing before continuing.
func (p *Pipeline) Abort() {
p.eg.Go(func() error {
return ErrPipelineAborted
})
}
// GetInputChannel gets the input channel for a pipeline stage
func (p *Pipeline) GetInputChannel(stageName string) (chan []ItemWithProps, error) {
stage, ok := p.nameToStage[stageName]
if !ok {
return nil, fmt.Errorf("%s: %w", stageName, ErrUnknownStageName)
}
return stage.inCh, nil
}