Parallelise Bulk Import. (#6267)

* Parallelise Bulk Import.

* Set worker count through command line flag.

app/import.go

@@ -11,6 +11,7 @@ import (
 	"net/http"
 	"regexp"
 	"strings"
+	"sync"
 	"unicode/utf8"
 
 	l4g "github.com/alecthomas/log4go"
@@ -95,15 +96,40 @@ type PostImportData struct {
 	CreateAt *int64  `json:"create_at"`
 }
 
+type LineImportWorkerData struct {
+	LineImportData
+	LineNumber int
+}
+
+type LineImportWorkerError struct {
+	Error      *model.AppError
+	LineNumber int
+}
+
 //
 // -- Bulk Import Functions --
 // These functions import data directly into the database. Security and permission checks are bypassed but validity is
 // still enforced.
 //
 
-func BulkImport(fileReader io.Reader, dryRun bool) (*model.AppError, int) {
+func bulkImportWorker(dryRun bool, wg *sync.WaitGroup, lines <-chan LineImportWorkerData, errors chan<- LineImportWorkerError) {
+	for line := range lines {
+		if err := ImportLine(line.LineImportData, dryRun); err != nil {
+			errors <- LineImportWorkerError{err, line.LineNumber}
+		}
+	}
+	wg.Done()
+}
+
+func BulkImport(fileReader io.Reader, dryRun bool, workers int) (*model.AppError, int) {
 	scanner := bufio.NewScanner(fileReader)
 	lineNumber := 0
+
+	errorsChan := make(chan LineImportWorkerError, (2*workers)+1) // size chosen to ensure it never gets filled up completely.
+	var wg sync.WaitGroup
+	var linesChan chan LineImportWorkerData
+	lastLineType := ""
+
 	for scanner.Scan() {
 		decoder := json.NewDecoder(strings.NewReader(scanner.Text()))
 		lineNumber++
@@ -121,12 +147,50 @@ func BulkImport(fileReader io.Reader, dryRun bool) (*model.AppError, int) {
 				if importDataFileVersion != 1 {
 					return model.NewAppError("BulkImport", "app.import.bulk_import.unsupported_version.error", nil, "", http.StatusBadRequest), lineNumber
 				}
-			} else if err := ImportLine(line, dryRun); err != nil {
-				return err, lineNumber
+			} else {
+				if line.Type != lastLineType {
+					if lastLineType != "" {
+						// Changing type. Clear out the worker queue before continuing.
+						close(linesChan)
+						wg.Wait()
+
+						// Check no errors occurred while waiting for the queue to empty.
+						if len(errorsChan) != 0 {
+							err := <-errorsChan
+							return err.Error, err.LineNumber
+						}
+					}
+
+					// Set up the workers and channel for this type.
+					lastLineType = line.Type
+					linesChan = make(chan LineImportWorkerData, workers)
+					for i := 0; i < workers; i++ {
+						wg.Add(1)
+						go bulkImportWorker(dryRun, &wg, linesChan, errorsChan)
+					}
+				}
+
+				select {
+				case linesChan <- LineImportWorkerData{line, lineNumber}:
+				case err := <-errorsChan:
+					close(linesChan)
+					wg.Wait()
+					return err.Error, err.LineNumber
+				}
 			}
 		}
 	}
 
+	// No more lines. Clear out the worker queue before continuing.
+	close(linesChan)
+	wg.Wait()
+
+	// Check no errors occurred while waiting for the queue to empty.
+	if len(errorsChan) != 0 {
+		err := <-errorsChan
+		return err.Error, err.LineNumber
+	}
+
 	if err := scanner.Err(); err != nil {
 		return model.NewLocAppError("BulkImport", "app.import.bulk_import.file_scan.error", nil, err.Error()), 0
 	}