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//go:build go1.16
// +build go1.16
package pwalkdir
import (
"fmt"
"io/fs"
"path/filepath"
"runtime"
"sync"
)
// Walk is a wrapper for filepath.WalkDir which can call multiple walkFn
// in parallel, allowing to handle each item concurrently. A maximum of
// twice the runtime.NumCPU() walkFn will be called at any one time.
// If you want to change the maximum, use WalkN instead.
//
// The order of calls is non-deterministic.
//
// Note that this implementation only supports primitive error handling:
//
// - no errors are ever passed to walkFn;
//
// - once a walkFn returns any error, all further processing stops
// and the error is returned to the caller of Walk;
//
// - filepath.SkipDir is not supported;
//
// - if more than one walkFn instance will return an error, only one
// of such errors will be propagated and returned by Walk, others
// will be silently discarded.
func Walk(root string, walkFn fs.WalkDirFunc) error {
return WalkN(root, walkFn, runtime.NumCPU()*2)
}
// WalkN is a wrapper for filepath.WalkDir which can call multiple walkFn
// in parallel, allowing to handle each item concurrently. A maximum of
// num walkFn will be called at any one time.
//
// Please see Walk documentation for caveats of using this function.
func WalkN(root string, walkFn fs.WalkDirFunc, num int) error {
// make sure limit is sensible
if num < 1 {
return fmt.Errorf("walk(%q): num must be > 0", root)
}
files := make(chan *walkArgs, 2*num)
errCh := make(chan error, 1) // Get the first error, ignore others.
// Start walking a tree asap.
var (
err error
wg sync.WaitGroup
rootLen = len(root)
rootEntry *walkArgs
)
wg.Add(1)
go func() {
err = filepath.WalkDir(root, func(p string, entry fs.DirEntry, err error) error {
if err != nil {
close(files)
return err
}
if len(p) == rootLen {
// Root entry is processed separately below.
rootEntry = &walkArgs{path: p, entry: entry}
return nil
}
// Add a file to the queue unless a callback sent an error.
select {
case e := <-errCh:
close(files)
return e
default:
files <- &walkArgs{path: p, entry: entry}
return nil
}
})
if err == nil {
close(files)
}
wg.Done()
}()
wg.Add(num)
for i := 0; i < num; i++ {
go func() {
for file := range files {
if e := walkFn(file.path, file.entry, nil); e != nil {
select {
case errCh <- e: // sent ok
default: // buffer full
}
}
}
wg.Done()
}()
}
wg.Wait()
if err == nil {
err = walkFn(rootEntry.path, rootEntry.entry, nil)
}
return err
}
// walkArgs holds the arguments that were passed to the Walk or WalkN
// functions.
type walkArgs struct {
path string
entry fs.DirEntry
}
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