Tweaks to dynamic locks (#10508)

* Fix cases where minimum timeout > default timeout.
* Add defensive code for too small/negative timeouts.
* Never set timeout below the maximum value of a request.
* Protect against (unlikely) int64 wraps.
* Decrease timeout slower.
* Don't re-lock before copying.

cmd/dynamic-timeouts.go

@@ -17,6 +17,7 @@
 package cmd
 
 import (
+	"math"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -26,7 +27,8 @@ const (
 	dynamicTimeoutIncreaseThresholdPct = 0.33 // Upper threshold for failures in order to increase timeout
 	dynamicTimeoutDecreaseThresholdPct = 0.10 // Lower threshold for failures in order to decrease timeout
 	dynamicTimeoutLogSize              = 16
-	maxDuration                        = 1<<63 - 1
+	maxDuration                        = math.MaxInt64
+	maxDynamicTimeout                  = 24 * time.Hour // Never set timeout bigger than this.
 )
 
 // timeouts that are dynamically adapted based on actual usage results
@@ -40,6 +42,12 @@ type dynamicTimeout struct {
 
 // newDynamicTimeout returns a new dynamic timeout initialized with timeout value
 func newDynamicTimeout(timeout, minimum time.Duration) *dynamicTimeout {
+	if timeout <= 0 || minimum <= 0 {
+		panic("newDynamicTimeout: negative or zero timeout")
+	}
+	if minimum > timeout {
+		minimum = timeout
+	}
 	return &dynamicTimeout{timeout: int64(timeout), minimum: int64(minimum)}
 }
 
@@ -61,60 +69,73 @@ func (dt *dynamicTimeout) LogFailure() {
 
 // logEntry stores a log entry
 func (dt *dynamicTimeout) logEntry(duration time.Duration) {
+	if duration < 0 {
+		return
+	}
 	entries := int(atomic.AddInt64(&dt.entries, 1))
 	index := entries - 1
 	if index < dynamicTimeoutLogSize {
 		dt.mutex.Lock()
 		dt.log[index] = duration
-		dt.mutex.Unlock()
-	}
-	if entries == dynamicTimeoutLogSize {
-		dt.mutex.Lock()
 
-		// Make copy on stack in order to call adjust()
-		logCopy := [dynamicTimeoutLogSize]time.Duration{}
-		copy(logCopy[:], dt.log[:])
+		// We leak entries while we copy
+		if entries == dynamicTimeoutLogSize {
 
-		// reset log entries
-		atomic.StoreInt64(&dt.entries, 0)
+			// Make copy on stack in order to call adjust()
+			logCopy := [dynamicTimeoutLogSize]time.Duration{}
+			copy(logCopy[:], dt.log[:])
 
-		dt.mutex.Unlock()
+			// reset log entries
+			atomic.StoreInt64(&dt.entries, 0)
+			dt.mutex.Unlock()
 
-		dt.adjust(logCopy)
+			dt.adjust(logCopy)
+			return
+		}
+		dt.mutex.Unlock()
 	}
 }
 
 // adjust changes the value of the dynamic timeout based on the
 // previous results
 func (dt *dynamicTimeout) adjust(entries [dynamicTimeoutLogSize]time.Duration) {
-
-	failures, average := 0, int64(0)
-	for i := 0; i < len(entries); i++ {
-		if entries[i] == maxDuration {
+	failures, max := 0, time.Duration(0)
+	for _, dur := range entries[:] {
+		if dur == maxDuration {
 			failures++
-		} else {
-			average += int64(entries[i])
+		} else if dur > max {
+			max = dur
 		}
 	}
-	if failures < len(entries) {
-		average /= int64(len(entries) - failures)
-	}
 
-	timeOutHitPct := float64(failures) / float64(len(entries))
+	failPct := float64(failures) / float64(len(entries))
 
-	if timeOutHitPct > dynamicTimeoutIncreaseThresholdPct {
+	if failPct > dynamicTimeoutIncreaseThresholdPct {
 		// We are hitting the timeout too often, so increase the timeout by 25%
 		timeout := atomic.LoadInt64(&dt.timeout) * 125 / 100
-		atomic.StoreInt64(&dt.timeout, timeout)
-	} else if timeOutHitPct < dynamicTimeoutDecreaseThresholdPct {
-		// We are hitting the timeout relatively few times, so decrease the timeout
-		average = average * 125 / 100 // Add buffer of 25% on top of average
 
-		timeout := (atomic.LoadInt64(&dt.timeout) + average) / 2 // Middle between current timeout and average success
+		// Set upper cap.
+		if timeout > int64(maxDynamicTimeout) {
+			timeout = int64(maxDynamicTimeout)
+		}
+		// Safety, shouldn't happen
+		if timeout < dt.minimum {
+			timeout = dt.minimum
+		}
+		atomic.StoreInt64(&dt.timeout, timeout)
+	} else if failPct < dynamicTimeoutDecreaseThresholdPct {
+		// We are hitting the timeout relatively few times,
+		// so decrease the timeout towards 25 % of maximum time spent.
+		max = max * 125 / 100
+
+		timeout := atomic.LoadInt64(&dt.timeout)
+		if max < time.Duration(timeout) {
+			// Move 50% toward the max.
+			timeout = (int64(max) + timeout) / 2
+		}
 		if timeout < dt.minimum {
 			timeout = dt.minimum
 		}
 		atomic.StoreInt64(&dt.timeout, timeout)
 	}
-
 }

cmd/dynamic-timeouts_test.go

@@ -18,6 +18,8 @@ package cmd
 
 import (
 	"math/rand"
+	"runtime"
+	"sync"
 	"testing"
 	"time"
 )
@@ -98,7 +100,7 @@ func TestDynamicTimeoutDualDecrease(t *testing.T) {
 	adjustedAgain := timeout.Timeout()
 
 	if initial <= adjusted || adjusted <= adjustedAgain {
-		t.Errorf("Failure to decrease timeout multiple times")
+		t.Errorf("Failure to decrease timeout multiple times, initial: %v, adjusted: %v, again: %v", initial, adjusted, adjustedAgain)
 	}
 }
 
@@ -123,6 +125,30 @@ func TestDynamicTimeoutManyDecreases(t *testing.T) {
 	}
 }
 
+func TestDynamicTimeoutConcurrent(t *testing.T) {
+	// Race test.
+	timeout := newDynamicTimeout(time.Second, time.Millisecond)
+	var wg sync.WaitGroup
+	for i := 0; i < runtime.GOMAXPROCS(0); i++ {
+		wg.Add(1)
+		rng := rand.New(rand.NewSource(int64(i)))
+		go func() {
+			defer wg.Done()
+			for i := 0; i < 100; i++ {
+				timeout.LogFailure()
+				for j := 0; j < 100; j++ {
+					timeout.LogSuccess(time.Duration(float64(time.Second) * rng.Float64()))
+				}
+				to := timeout.Timeout()
+				if to < time.Millisecond || to > time.Second {
+					panic(to)
+				}
+			}
+		}()
+	}
+	wg.Wait()
+}
+
 func TestDynamicTimeoutHitMinimum(t *testing.T) {
 
 	const minimum = 30 * time.Second
@@ -168,7 +194,7 @@ func TestDynamicTimeoutAdjustExponential(t *testing.T) {
 
 	timeout := newDynamicTimeout(time.Minute, time.Second)
 
-	rand.Seed(time.Now().UTC().UnixNano())
+	rand.Seed(0)
 
 	initial := timeout.Timeout()
 
@@ -188,7 +214,7 @@ func TestDynamicTimeoutAdjustNormalized(t *testing.T) {
 
 	timeout := newDynamicTimeout(time.Minute, time.Second)
 
-	rand.Seed(time.Now().UTC().UnixNano())
+	rand.Seed(0)
 
 	initial := timeout.Timeout()
 

cmd/global-heal.go

@@ -31,7 +31,7 @@ const (
 	leaderLockTimeoutSleepInterval = time.Hour
 )
 
-var leaderLockTimeout = newDynamicTimeout(30*time.Second, time.Minute)
+var leaderLockTimeout = newDynamicTimeout(1*time.Minute, 30*time.Second)
 
 // NewBgHealSequence creates a background healing sequence
 // operation which crawls all objects and heal them.

cmd/iam.go

@@ -450,7 +450,7 @@ func (sys *IAMSys) Init(ctx context.Context, objAPI ObjectLayer) {
 	wquorum := InsufficientWriteQuorum{}
 
 	// allocate dynamic timeout once before the loop
-	iamLockTimeout := newDynamicTimeout(3*time.Second, 5*time.Second)
+	iamLockTimeout := newDynamicTimeout(5*time.Second, 3*time.Second)
 
 	for range retry.NewTimerWithJitter(retryCtx, time.Second, 5*time.Second, retry.MaxJitter) {
 		// let one of the server acquire the lock, if not let them timeout.

cmd/server-main.go

@@ -231,7 +231,7 @@ func initSafeMode(ctx context.Context, newObject ObjectLayer) (err error) {
 	}
 
 	// allocate dynamic timeout once before the loop
-	configLockTimeout := newDynamicTimeout(3*time.Second, 5*time.Second)
+	configLockTimeout := newDynamicTimeout(5*time.Second, 3*time.Second)
 
 	// ****  WARNING ****
 	// Migrating to encrypted backend should happen before initialization of any