searcher: make indexing of repos concurrent

searcher/searcher.go

@@ -34,6 +34,15 @@ type Searcher struct {
 	doneCh            chan empty
 }
 
+// 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
+	searcher *Searcher
+	err      error
+}
+
 type empty struct{}
 type limiter chan bool
 
@@ -277,15 +286,25 @@ func MakeAll(cfg *config.Config) (map[string]*Searcher, map[string]error, error)
 
 	lim := makeLimiter(cfg.MaxConcurrentIndexers)
 
+	n := len(cfg.Repos)
+	// Channel to receive the results from newSearcherConcurrent function.
+	resultCh := make(chan searcherResult, n)
+
+	// Start new searchers for all repos in different go routines while
+	// respecting cfg.MaxConcurrentIndexers.
 	for name, repo := range cfg.Repos {
-		s, err := newSearcher(cfg.DbPath, name, repo, refs, lim)
-		if err != nil {
-			log.Print(err)
-			errs[name] = err
+		go newSearcherConcurrent(cfg.DbPath, name, repo, refs, lim, resultCh)
+	}
+
+	// Collect the results on resultCh channel for all repos.
+	for i := 0; i < n; i++ {
+		r := <-resultCh
+		if r.err != nil {
+			log.Print(r.err)
+			errs[r.name] = r.err
 			continue
 		}
-
-		searchers[name] = s
+		searchers[r.name] = r.searcher
 	}
 
 	if err := refs.removeUnclaimed(); err != nil {
@@ -464,3 +483,32 @@ func newSearcher(
 
 	return s, nil
 }
+
+// This function is a wrapper around `newSearcher` function.
+// It respects the parameter `cfg.MaxConcurrentIndexers` while making the
+// creation of searchers for various repositories concurrent.
+func newSearcherConcurrent(
+	dbpath, name string,
+	repo *config.Repo,
+	refs *foundRefs,
+	lim limiter,
+	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 {
+		resultCh <- searcherResult{
+			name:     name,
+			err:      err,
+		}
+		return
+	}
+
+	resultCh <- searcherResult{
+		name:     name,
+		searcher: s,
+	}
+}