searcher: modify concurrent routine

Change the concurrent searchers init routine to simplify the
implementation and use only one common channel to return successfully
created searchers as well as errors. This way we also get rid of the go
routine collecting the results on the channel by making the main routine
collect the results by blocking the execution and listening on the
channel.

Author: sahildua2305

searcher/searcher.go

@@ -34,22 +34,13 @@ type Searcher struct {
 	doneCh            chan empty
 }
 
-// Wrapper around searcher - used for sending the searcher struct to channel once
-// successfully returned from `newSearcher` function.
-// We need this wrapper because we need to have the `name` of a repo which a
-// particular searcher belongs to.
-type searcherWrapper struct {
-	searcher *Searcher
+// Struct used to send the results from newSearcherConcurrent function.
+// This struct can either have a non-nil searcher or a non-nil error
+// depending on what newSearcher function returns.
+type searcherResult struct {
 	name     string
-}
-
-// Wrapper around error - used for sending error to channel once returned from
-// `newSearcher` function.
-// We need this wrapper because we need to have the `name` of a repo which a
-// particular error belongs to.
-type errorWrapper struct {
-	error error
-	name  string
+	searcher *Searcher
+	err      error
 }
 
 type empty struct{}
@@ -295,49 +286,30 @@ func MakeAll(cfg *config.Config) (map[string]*Searcher, map[string]error, error)
 
 	lim := makeLimiter(cfg.MaxConcurrentIndexers)
 
-	// Channel to receive the successfully created searchers.
-	searcherCh := make(chan searcherWrapper, 1)
-	// Channel to receive the errors in creation of searchers.
-	errorCh := make(chan errorWrapper, 1)
-	// Channel to quit the go routine listening for new successful searchers or errors.
-	quitCh := make(chan struct{}, 1)
-
-	// Create a wait group for total number of repos so that we can proceed once the
-	// go routines to create searchers for all repos have returned.
-	var wg sync.WaitGroup
-	wg.Add(len(cfg.Repos))
+	// Channel to receive the results from newSearcherConcurrent function.
+	resultCh := make(chan searcherResult, 1)
 
+	// Start new searchers for all repos in different go routines while
+	// respecting cfg.MaxConcurrentIndexers.
 	for name, repo := range cfg.Repos {
-		go newSearcherConcurrent(cfg.DbPath, name, repo, refs, lim, searcherCh, errorCh)
+		go newSearcherConcurrent(cfg.DbPath, name, repo, refs, lim, resultCh)
 	}
 
-	// Create a listener on searcherCh and errorCh.
-	// It also listens on quitCh to decide when to return.
-	go func() {
-		for {
-			select {
-			case sw := <-searcherCh:
-				searchers[sw.name] = sw.searcher
-				wg.Done()
-			case ew := <-errorCh:
-				log.Print(ew.error)
-				errs[ew.name] = ew.error
-				wg.Done()
-			case <-quitCh:
-				return
-			}
+	// Collect the results on resultCh channel for all repos.
+	for range cfg.Repos {
+		r := <-resultCh
+		if r.err != nil {
+			log.Print(r.err)
+			errs[r.name] = r.err
+			continue
 		}
-	}()
+		searchers[r.name] = r.searcher
+	}
 
 	if err := refs.removeUnclaimed(); err != nil {
 		return nil, nil, err
 	}
 
-	// Wait for all go routines to finish.
-	wg.Wait()
-	// Send close signal to quitCh to return the listening go routine.
-	close(quitCh)
-
 	// after all the repos are in good shape, we start their polling
 	for _, s := range searchers {
 		s.begin()
@@ -519,24 +491,25 @@ func newSearcherConcurrent(
 	repo *config.Repo,
 	refs *foundRefs,
 	lim limiter,
-	searcherCh chan searcherWrapper,
-	errorCh chan errorWrapper) {
+	resultCh chan searcherResult) {
 
 	// acquire a token from the rate limiter
 	lim.Acquire()
 	defer lim.Release()
 
 	s, err := newSearcher(dbpath, name, repo, refs, lim)
 	if err != nil {
-		errorCh <- errorWrapper{
-			error: err,
-			name: name,
+		resultCh <- searcherResult{
+			name:     name,
+			searcher: nil,
+			err:      err,
 		}
 		return
 	}
 
-	searcherCh <- searcherWrapper{
+	resultCh <- searcherResult{
+		name:     name,
 		searcher: s,
-		name: name,
+		err:      nil,
 	}
 }