made local image preparations use channels and go routines to speed it up and use all cpu cores to calculate the md5 sums

internal/pkg/localFileStructure/imageList.go

@@ -3,33 +3,105 @@ package localFileStructure
 import (
 	"github.com/sirupsen/logrus"
 	"path/filepath"
+	"runtime"
+	"sync"
 	"time"
 )
 
 func GetImageList(fileSystem map[string]*FilesystemNode) ([]*ImageNode, error) {
+	logrus.Debugln("Starting GetImageList to prepare local image metadata.")
+
 	imageFiles := make([]*ImageNode, 0, len(fileSystem))
 
-	for _, file := range fileSystem {
-		if file.IsDir {
-			continue
+	finished := make(chan bool, 1)
+	errChannel := make(chan error, 1)
+	queue := make(chan *FilesystemNode, 100)
+	results := make(chan *ImageNode, 200)
+	waitGroup := sync.WaitGroup{}
+
+	go resultCollector(results, &imageFiles)
+
+	waitGroup.Add(1)
+	go queueProducer(fileSystem, queue, &waitGroup)
+
+	numberOfCPUs := runtime.NumCPU()
+	for i := 0; i < numberOfCPUs; i++ {
+		logrus.Tracef("Starting getImageNodeWorker number %d", i)
+		waitGroup.Add(1)
+		go getImageNodeWorker(queue, results, errChannel, &waitGroup)
 	}
 
-		md5sum, err := calculateFileCheckSums(file.Path)
+	go func() {
+		waitGroup.Wait()
+
+		logrus.Debugln("All workers finished processing, closing channels.")
+
+		close(results)
+		close(finished)
+	}()
+
+	select {
+	case <-finished:
+	case err := <-errChannel:
 		if err != nil {
+			logrus.Errorf("Error during local image processing: %S", err)
 			return nil, err
 		}
-
-		logrus.Debugf("Local Image %s - %s - %s", md5sum, file.ModTime.Format(time.RFC3339), file.Path)
-
-		imageFiles = append(imageFiles, &ImageNode{
-			Path:         file.Path,
-			CategoryName: filepath.Dir(file.Key),
-			ModTime:      file.ModTime,
-			Md5Sum:       md5sum,
-		})
 	}
 
 	logrus.Infof("Found %d local images to process", len(imageFiles))
 
 	return imageFiles, nil
 }
+
+func queueProducer(fileSystem map[string]*FilesystemNode, queue chan *FilesystemNode, waitGroup *sync.WaitGroup) {
+	logrus.Debugln("Starting queueProducer to fill the queue of the files to check and calculate the checksum")
+	for _, file := range fileSystem {
+		if file.IsDir {
+			continue
+		}
+		queue <- file
+	}
+
+	// after the last item is in the queue, we close it as there will be no more and we like
+	// the workers to exit.
+	close(queue)
+
+	logrus.Debugln("Finished queueProducer")
+
+	waitGroup.Done()
+}
+
+func resultCollector(results chan *ImageNode, imageFiles *[]*ImageNode) {
+	logrus.Debugln("Starting image node result collector")
+	for imageNode := range results {
+		logrus.Debugf("Local Image prepared - %s - %s - %s", imageNode.Md5Sum, imageNode.ModTime.Format(time.RFC3339), imageNode.Path)
+		*imageFiles = append(*imageFiles, imageNode)
+	}
+	logrus.Debugln("Finished resultCollector")
+
+}
+
+func getImageNodeWorker(queue chan *FilesystemNode, results chan *ImageNode, errChannel chan error, waitGroup *sync.WaitGroup) {
+	logrus.Debugln("Starting image file worker to gather local image informations")
+	for file := range queue {
+		md5sum, err := calculateFileCheckSums(file.Path)
+		if err != nil {
+			errChannel <- err
+			// we try the next image in the queue, as this might be just one error
+			continue
+		}
+
+		imageNode := &ImageNode{
+			Path:         file.Path,
+			CategoryName: filepath.Dir(file.Key),
+			ModTime:      file.ModTime,
+			Md5Sum:       md5sum,
+		}
+
+		results <- imageNode
+	}
+
+	logrus.Debugln("Finished getImageNodeWorker")
+	waitGroup.Done()
+}