remove demoting locks from sync package

sync/lock.go

@@ -18,8 +18,7 @@ type RWMutex struct {
 	callDepth   int
 	maxLockTime time.Duration
 
-	outer sync.Mutex
-	inner sync.RWMutex
+	mu sync.RWMutex
 }
 
 // lockInfo contains information about when and how a lock call was made.
@@ -67,10 +66,9 @@ func (rwm *RWMutex) threadedDeadlockFinder() {
 
 				// Undo the deadlock and delete the entry from the map.
 				if info.read {
-					rwm.inner.RUnlock()
+					rwm.mu.RUnlock()
 				} else {
-					rwm.inner.Unlock()
-					rwm.outer.Unlock()
+					rwm.mu.Unlock()
 				}
 				delete(rwm.openLocks, id)
 			}
@@ -95,10 +93,9 @@ func (rwm *RWMutex) safeLock(read bool) int {
 
 	// Lock the mutex.
 	if read {
-		rwm.inner.RLock()
+		rwm.mu.RLock()
 	} else {
-		rwm.outer.Lock()
-		rwm.inner.Lock()
+		rwm.mu.Lock()
 	}
 
 	// Safely register that a lock has been triggered.
@@ -137,29 +134,13 @@ func (rwm *RWMutex) safeUnlock(read bool, id int) {
 
 	// Remove the lock and delete the entry from the map.
 	if read {
-		rwm.inner.RUnlock()
+		rwm.mu.RUnlock()
 	} else {
-		rwm.inner.Unlock()
-		rwm.outer.Unlock()
+		rwm.mu.Unlock()
 	}
 	delete(rwm.openLocks, id)
 }
 
-// safeDemote demotes a safelock from a Lock to a RLock.
-func (rwm *RWMutex) safeDemote() {
-	rwm.openLocksMutex.Lock()
-	defer rwm.openLocksMutex.Unlock()
-
-	// Demote the lock. Ordering is important. First the inner lock is released
-	// and then regrabbed as a readlock. Then the outer lock is released.
-	// Because no safelock can grab the inner lock as a writelock until it has
-	// the outer lock, there is no risk of changes being made during the
-	// transition.
-	rwm.inner.Unlock()
-	rwm.inner.RLock()
-	rwm.outer.Unlock()
-}
-
 // RLock will read lock the RWMutex. The return value must be used as input
 // when calling RUnlock.
 func (rwm *RWMutex) RLock() int {
@@ -178,12 +159,6 @@ func (rwm *RWMutex) Lock() int {
 	return rwm.safeLock(false)
 }
 
-// Demote will demote the lock from a writelock to a readlock. Demote should
-// only be called on a writelocked safelock.
-func (rwm *RWMutex) Demote() {
-	rwm.safeDemote()
-}
-
 // Unlock will unlock the RWMutex. The return value of calling Lock must be
 // used as input.
 func (rwm *RWMutex) Unlock(id int) {

sync/lock_test.go

@@ -147,52 +147,3 @@ func TestLockSafety(t *testing.T) {
 		t.Error("test took too long to complete")
 	}
 }
-
-// TestDemote checks that lock demotion works correctly.
-func TestDemote(t *testing.T) {
-	if testing.Short() {
-		t.SkipNow()
-	}
-
-	startTime := time.Now().Unix()
-	value := 0
-	safeLock := New(time.Second, 1)
-	_ = safeLock.Lock()
-
-	readThreads := 100
-	var wg sync.WaitGroup
-	wg.Add(readThreads)
-	for i := 0; i < readThreads; i++ {
-		go func() {
-			readID := safeLock.RLock()
-			defer safeLock.RUnlock(readID)
-
-			if value != 1 {
-				t.Error("reading is not happening correctly")
-			}
-
-			// Sleep 250 milliseconds after grabbing the readlock. Because
-			// there are a bunch of threads, if the readlocks are not grabbing
-			// the lock in parallel the test will take a long time.
-			time.Sleep(time.Millisecond * 250)
-			wg.Done()
-		}()
-	}
-	value = 1
-
-	// A combination of sleep and gosched to give priority to the other
-	// threads.
-	time.Sleep(time.Millisecond * 100)
-	runtime.Gosched()
-	time.Sleep(time.Millisecond * 100)
-	safeLock.Demote()
-
-	// Wait for all of the threads to finish sleeping.
-	wg.Wait()
-	// Check that the whole test took under 3 seconds. If the readlocks were
-	// efficiently being grabbed in parallel, the test should be subtantially
-	// less than 3 seconds.
-	if time.Now().Unix()-startTime > 3 {
-		t.Error("test took too long to complete")
-	}
-}