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executor.go
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executor.go
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package main
import (
"io"
"sync"
)
// Executor executes an ordered sequence of commands
type Executor struct {
commands []Command
wg sync.WaitGroup
// Channels between goroutines in the command pipeline
chans []chan Range
input io.ReaderAt
inputLength int64
Output io.Writer
Sep string
}
func NewExecutor(commands []Command) *Executor {
return &Executor{commands: commands}
}
// Idea: have two pipelines that are connected:
// filtering pipeline -> action pipeline
//
// filtering pipeline is connected using a series of channels that pass successively more restrictive ranges
//
// action pipeline is connected using a series of channels that pass byte buffers for more manipulation
//
// Between the two is a connector that reads a range and converts it to a buffer.
func (ex *Executor) Go(input io.ReaderAt) error {
err := ex.prepareToGo(input)
if err != nil {
return err
}
dbg("%d commands\n", len(ex.commands))
ex.wg.Add(len(ex.commands))
for stage := 1; stage < len(ex.commands); stage++ {
go ex.doCommandForStage(stage)
}
ex.doCommandForStage(0)
ex.wg.Wait()
return nil
}
func (ex *Executor) prepareToGo(input io.ReaderAt) error {
var err error
ex.inputLength, err = lengthOfReaderAt(input)
if err != nil {
return err
}
ex.commands = ex.addPrintCommandIfNeeded(ex.commands)
ex.input = input
// Setup a pipeline for the commands
ex.makeChans(len(ex.commands) - 1)
return nil
}
func (ex *Executor) doCommandForStage(stage int) {
defer ex.wg.Done()
dbg("Starting stage %d\n", stage)
if stage == 0 {
// First stage reads from the reader directly
dbg("Stage %d is reading range %d-%d\n", stage, 0, ex.inputLength)
ex.commands[stage].Do(ex.input, 0, ex.inputLength, ex.writeRangeToChan(ex.firstChan()))
} else {
// Later stages read from a pipe
for rnge := range ex.chans[stage-1] {
dbg("Stage %d is reading range %d-%d\n", stage, rnge.Start, rnge.End)
fn := nop
if stage < len(ex.commands)-1 {
fn = ex.writeRangeToChan(ex.chans[stage])
}
ex.commands[stage].Do(ex.input, rnge.Start, rnge.End, fn)
}
}
if doner, ok := ex.commands[stage].(Doner); ok {
doner.Done()
}
if stage < len(ex.chans) {
close(ex.chans[stage])
}
}
func (ex *Executor) firstChan() chan Range {
if len(ex.chans) > 0 {
return ex.chans[0]
}
return nil
}
func (ex *Executor) makeChans(count int) {
// Setup a pipeline for the commands
ex.chans = make([]chan Range, count)
for i := range ex.chans {
ex.chans[i] = make(chan Range)
}
}
func (ex Executor) writeRangeToChan(c chan Range) func(start, end int64) {
if c == nil {
return nop
}
return func(start, end int64) {
dbg("Stage is sending range %d-%d\n", start, end)
c <- Range{start, end}
}
}
func nop(start, end int64) {
}
func (ex Executor) addPrintCommandIfNeeded(commands []Command) (result []Command) {
add := false
if len(commands) == 0 {
add = true
} else {
switch commands[len(commands)-1].(type) {
case *PrintCommand, *PrintLineCommand:
add = false
default:
add = true
}
}
result = commands
if add {
result = append(commands, NewPrintCommand(ex.Output, ex.Sep))
}
return
}