[#388] trace: make WithTaskGroup actually concurrent

daemon/logging/trace/trace_convenience_test.go

@@ -1,7 +1,10 @@
 package trace
 
 import (
+	"context"
+	"sync/atomic"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/assert"
 )
@@ -14,3 +17,46 @@ func TestGetCallerOrPanic(t *testing.T) {
 	// zrepl prefix is stripped
 	assert.Equal(t, "daemon/logging/trace.TestGetCallerOrPanic", ret)
 }
+
+func TestWithTaskGroupRunTasksConcurrently(t *testing.T) {
+
+	// spawn a task group where each task waits for the other to start
+	// => without concurrency, they would hang
+
+	rootCtx, endRoot := WithTaskFromStack(context.Background())
+	defer endRoot()
+
+	_, add, waitEnd := WithTaskGroup(rootCtx, "test-task-group")
+
+	schedulerTimeout := 2 * time.Second
+	timeout := time.After(schedulerTimeout)
+	var hadTimeout uint32
+	started0, started1 := make(chan struct{}), make(chan struct{})
+	for i := 0; i < 2; i++ {
+		i := i // capture by copy
+		add(func(ctx context.Context) {
+			switch i {
+			case 0:
+				close(started0)
+				select {
+				case <-started1:
+				case <-timeout:
+					atomic.AddUint32(&hadTimeout, 1)
+				}
+			case 1:
+				close(started1)
+				select {
+				case <-started0:
+				case <-timeout:
+					atomic.AddUint32(&hadTimeout, 1)
+				}
+			default:
+				panic("unreachable")
+			}
+		})
+	}
+
+	waitEnd()
+	assert.Zero(t, hadTimeout, "either bad impl or scheduler timeout (which is %v)", schedulerTimeout)
+
+}