Merge pull request #2299 from dmage/regulator

Fix signalling Wait in regulator.enter

registry/storage/driver/base/regulator.go

@@ -38,11 +38,7 @@ func (r *regulator) enter() {
 
 func (r *regulator) exit() {
 	r.L.Lock()
-	// We only need to signal to a waiting FS operation if we're already at the
-	// limit of threads used
-	if r.available == 0 {
-		r.Signal()
-	}
+	r.Signal()
 	r.available++
 	r.L.Unlock()
 }

registry/storage/driver/base/regulator_test.go

@@ -0,0 +1,67 @@
+package base
+
+import (
+	"sync"
+	"testing"
+	"time"
+)
+
+func TestRegulatorEnterExit(t *testing.T) {
+	const limit = 500
+
+	r := NewRegulator(nil, limit).(*regulator)
+
+	for try := 0; try < 50; try++ {
+		run := make(chan struct{})
+
+		var firstGroupReady sync.WaitGroup
+		var firstGroupDone sync.WaitGroup
+		firstGroupReady.Add(limit)
+		firstGroupDone.Add(limit)
+		for i := 0; i < limit; i++ {
+			go func() {
+				r.enter()
+				firstGroupReady.Done()
+				<-run
+				r.exit()
+				firstGroupDone.Done()
+			}()
+		}
+		firstGroupReady.Wait()
+
+		// now we exhausted all the limit, let's run a little bit more
+		var secondGroupReady sync.WaitGroup
+		var secondGroupDone sync.WaitGroup
+		for i := 0; i < 50; i++ {
+			secondGroupReady.Add(1)
+			secondGroupDone.Add(1)
+			go func() {
+				secondGroupReady.Done()
+				r.enter()
+				r.exit()
+				secondGroupDone.Done()
+			}()
+		}
+		secondGroupReady.Wait()
+
+		// allow the first group to return resources
+		close(run)
+
+		done := make(chan struct{})
+		go func() {
+			secondGroupDone.Wait()
+			close(done)
+		}()
+		select {
+		case <-done:
+		case <-time.After(5 * time.Second):
+			t.Fatal("some r.enter() are still locked")
+		}
+
+		firstGroupDone.Wait()
+
+		if r.available != limit {
+			t.Fatalf("r.available: got %d, want %d", r.available, limit)
+		}
+	}
+}