command/expand: fix data race for concurrent writes

atomic/bool.go

@@ -0,0 +1,21 @@
+package atomic
+
+import "sync/atomic"
+
+// Bool is an atomic Boolean.
+type Bool int32
+
+// Set sets the Boolean to value.
+func (b *Bool) Set(value bool) {
+	var i int32 = 0
+	if value {
+		i = 1
+	}
+
+	atomic.StoreInt32((*int32)(b), int32(i))
+}
+
+// Get gets the Boolean value.
+func (b *Bool) Get() bool {
+	return atomic.LoadInt32((*int32)(b)) != 0
+}

atomic/bool_test.go

@@ -0,0 +1,32 @@
+package atomic
+
+import (
+	"sync"
+	"testing"
+)
+
+func TestRace(t *testing.T) {
+	t.Parallel()
+
+	var wg sync.WaitGroup
+	var atomicBool Bool
+	repeat := 10000
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		for i := 0; i < repeat; i++ {
+			atomicBool.Set(true)
+		}
+	}()
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		for i := 0; i < repeat; i++ {
+			_ = atomicBool.Get()
+		}
+	}()
+
+	wg.Wait()
+}

command/expand.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"sync"
 
+	"github.com/peak/s5cmd/atomic"
 	"github.com/peak/s5cmd/storage"
 	"github.com/peak/s5cmd/storage/url"
 )
@@ -58,7 +59,7 @@ func expandSources(
 		defer close(ch)
 
 		var wg sync.WaitGroup
-		var objFound bool
+		var objFound atomic.Bool
 
 		for _, origSrc := range srcurls {
 			wg.Add(1)
@@ -76,13 +77,13 @@ func expandSources(
 						continue
 					}
 					ch <- object
-					objFound = true
+					objFound.Set(true)
 				}
 			}(origSrc)
 		}
 
 		wg.Wait()
-		if !objFound {
+		if !objFound.Get() {
 			ch <- &storage.Object{Err: storage.ErrNoObjectFound}
 		}
 	}()