Migrate channel to waitgroup for access the store in parallel (#16926)

* Migrate channel to waitgroup for access the store in parallel

* Addressing PR review comments

* Using a cleanest way of group errors

* Reverting go.mod change

go.mod

@@ -125,6 +125,7 @@ require (
 	golang.org/x/image v0.0.0-20201208152932-35266b937fa6
 	golang.org/x/mod v0.4.1 // indirect
 	golang.org/x/net v0.0.0-20210119194325-5f4716e94777
+	golang.org/x/sync v0.0.0-20201020160332-67f06af15bc9
 	golang.org/x/text v0.3.5
 	golang.org/x/tools v0.1.0
 	google.golang.org/genproto v0.0.0-20210119180700-e258113e47cc // indirect

store/sqlstore/user_store.go

@@ -14,6 +14,7 @@ import (
 	sq "github.com/Masterminds/squirrel"
 	"github.com/mattermost/gorp"
 	"github.com/pkg/errors"
+	"golang.org/x/sync/errgroup"
 
 	"github.com/mattermost/mattermost-server/v5/einterfaces"
 	"github.com/mattermost/mattermost-server/v5/model"
@@ -1942,35 +1943,25 @@ func (us SqlUserStore) DemoteUserToGuest(userID string) (*model.User, error) {
 }
 
 func (us SqlUserStore) AutocompleteUsersInChannel(teamId, channelId, term string, options *model.UserSearchOptions) (*model.UserAutocompleteInChannel, error) {
-	autocomplete := &model.UserAutocompleteInChannel{}
-	uchan := make(chan store.StoreResult, 1)
-	go func() {
-		users, err := us.SearchInChannel(channelId, term, options)
-		uchan <- store.StoreResult{Data: users, NErr: err}
-		close(uchan)
-	}()
-
-	nuchan := make(chan store.StoreResult, 1)
-	go func() {
-		users, err := us.SearchNotInChannel(teamId, channelId, term, options)
-		nuchan <- store.StoreResult{Data: users, NErr: err}
-		close(nuchan)
-	}()
-
-	result := <-uchan
-	if result.NErr != nil {
-		return nil, result.NErr
+	var usersInChannel, usersNotInChannel []*model.User
+	g := errgroup.Group{}
+	g.Go(func() (err error) {
+		usersInChannel, err = us.SearchInChannel(channelId, term, options)
+		return err
+	})
+	g.Go(func() (err error) {
+		usersNotInChannel, err = us.SearchNotInChannel(teamId, channelId, term, options)
+		return err
+	})
+	err := g.Wait()
+	if err != nil {
+		return nil, err
 	}
-	users := result.Data.([]*model.User)
-	autocomplete.InChannel = users
 
-	result = <-nuchan
-	if result.NErr != nil {
-		return nil, result.NErr
-	}
-	users = result.Data.([]*model.User)
-	autocomplete.OutOfChannel = users
-	return autocomplete, nil
+	return &model.UserAutocompleteInChannel{
+		InChannel:    usersInChannel,
+		OutOfChannel: usersNotInChannel,
+	}, nil
 }
 
 // GetKnownUsers returns the list of user ids of users with any direct

vendor/golang.org/x/sync/AUTHORS

@@ -0,0 +1,3 @@
+# This source code refers to The Go Authors for copyright purposes.
+# The master list of authors is in the main Go distribution,
+# visible at http://tip.golang.org/AUTHORS.

vendor/golang.org/x/sync/CONTRIBUTORS

@@ -0,0 +1,3 @@
+# This source code was written by the Go contributors.
+# The master list of contributors is in the main Go distribution,
+# visible at http://tip.golang.org/CONTRIBUTORS.

vendor/golang.org/x/sync/LICENSE

@@ -0,0 +1,27 @@
+Copyright (c) 2009 The Go Authors. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+   * Redistributions of source code must retain the above copyright
+notice, this list of conditions and the following disclaimer.
+   * Redistributions in binary form must reproduce the above
+copyright notice, this list of conditions and the following disclaimer
+in the documentation and/or other materials provided with the
+distribution.
+   * Neither the name of Google Inc. nor the names of its
+contributors may be used to endorse or promote products derived from
+this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

vendor/golang.org/x/sync/PATENTS

@@ -0,0 +1,22 @@
+Additional IP Rights Grant (Patents)
+
+"This implementation" means the copyrightable works distributed by
+Google as part of the Go project.
+
+Google hereby grants to You a perpetual, worldwide, non-exclusive,
+no-charge, royalty-free, irrevocable (except as stated in this section)
+patent license to make, have made, use, offer to sell, sell, import,
+transfer and otherwise run, modify and propagate the contents of this
+implementation of Go, where such license applies only to those patent
+claims, both currently owned or controlled by Google and acquired in
+the future, licensable by Google that are necessarily infringed by this
+implementation of Go.  This grant does not include claims that would be
+infringed only as a consequence of further modification of this
+implementation.  If you or your agent or exclusive licensee institute or
+order or agree to the institution of patent litigation against any
+entity (including a cross-claim or counterclaim in a lawsuit) alleging
+that this implementation of Go or any code incorporated within this
+implementation of Go constitutes direct or contributory patent
+infringement, or inducement of patent infringement, then any patent
+rights granted to you under this License for this implementation of Go
+shall terminate as of the date such litigation is filed.

vendor/golang.org/x/sync/errgroup/errgroup.go

@@ -0,0 +1,66 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package errgroup provides synchronization, error propagation, and Context
+// cancelation for groups of goroutines working on subtasks of a common task.
+package errgroup
+
+import (
+	"context"
+	"sync"
+)
+
+// A Group is a collection of goroutines working on subtasks that are part of
+// the same overall task.
+//
+// A zero Group is valid and does not cancel on error.
+type Group struct {
+	cancel func()
+
+	wg sync.WaitGroup
+
+	errOnce sync.Once
+	err     error
+}
+
+// WithContext returns a new Group and an associated Context derived from ctx.
+//
+// The derived Context is canceled the first time a function passed to Go
+// returns a non-nil error or the first time Wait returns, whichever occurs
+// first.
+func WithContext(ctx context.Context) (*Group, context.Context) {
+	ctx, cancel := context.WithCancel(ctx)
+	return &Group{cancel: cancel}, ctx
+}
+
+// Wait blocks until all function calls from the Go method have returned, then
+// returns the first non-nil error (if any) from them.
+func (g *Group) Wait() error {
+	g.wg.Wait()
+	if g.cancel != nil {
+		g.cancel()
+	}
+	return g.err
+}
+
+// Go calls the given function in a new goroutine.
+//
+// The first call to return a non-nil error cancels the group; its error will be
+// returned by Wait.
+func (g *Group) Go(f func() error) {
+	g.wg.Add(1)
+
+	go func() {
+		defer g.wg.Done()
+
+		if err := f(); err != nil {
+			g.errOnce.Do(func() {
+				g.err = err
+				if g.cancel != nil {
+					g.cancel()
+				}
+			})
+		}
+	}()
+}

vendor/modules.txt

@@ -764,6 +764,9 @@ golang.org/x/net/ipv4
 golang.org/x/net/ipv6
 golang.org/x/net/publicsuffix
 golang.org/x/net/trace
+# golang.org/x/sync v0.0.0-20201020160332-67f06af15bc9
+## explicit
+golang.org/x/sync/errgroup
 # golang.org/x/sys v0.0.0-20210119212857-b64e53b001e4
 golang.org/x/sys/cpu
 golang.org/x/sys/execabs