Merge pull request #18196 from cpuguy83/18190_on_your_marks

Fix race in locker call to `dec()`

pkg/locker/locker.go

@@ -32,22 +32,23 @@ type Locker struct {
 type lockCtr struct {
 	mu sync.Mutex
 	// waiters is the number of waiters waiting to acquire the lock
-	waiters uint32
+	// this is int32 instead of uint32 so we can add `-1` in `dec()`
+	waiters int32
 }
 
 // inc increments the number of waiters waiting for the lock
 func (l *lockCtr) inc() {
-	atomic.AddUint32(&l.waiters, 1)
+	atomic.AddInt32(&l.waiters, 1)
 }
 
 // dec decrements the number of waiters wating on the lock
 func (l *lockCtr) dec() {
-	atomic.AddUint32(&l.waiters, ^uint32(l.waiters-1))
+	atomic.AddInt32(&l.waiters, -1)
 }
 
 // count gets the current number of waiters
-func (l *lockCtr) count() uint32 {
+func (l *lockCtr) count() int32 {
-	return atomic.LoadUint32(&l.waiters)
+	return atomic.LoadInt32(&l.waiters)
 }
 
 // Lock locks the mutex

pkg/locker/locker_test.go

@@ -1,6 +1,7 @@
 package locker
 
 import (
+	"sync"
 	"testing"
 	"time"
 )
@@ -89,3 +90,35 @@ func TestLockerUnlock(t *testing.T) {
 		t.Fatalf("lock should not be blocked")
 	}
 }
+
+func TestLockerConcurrency(t *testing.T) {
+	l := New()
+
+	var wg sync.WaitGroup
+	for i := 0; i <= 10000; i++ {
+		wg.Add(1)
+		go func() {
+			l.Lock("test")
+			// if there is a concurrency issue, will very likely panic here
+			l.Unlock("test")
+			wg.Done()
+		}()
+	}
+
+	chDone := make(chan struct{})
+	go func() {
+		wg.Wait()
+		close(chDone)
+	}()
+
+	select {
+	case <-chDone:
+	case <-time.After(10 * time.Second):
+		t.Fatal("timeout waiting for locks to complete")
+	}
+
+	// Since everything has unlocked this should not exist anymore
+	if ctr, exists := l.locks["test"]; exists {
+		t.Fatalf("lock should not exist: %v", ctr)
+	}
+}