lock: Retry locking with an increasing random interval (#17200)

internal/dsync/drwmutex.go

@@ -34,23 +34,29 @@ import (
 // Indicator if logging is enabled.
 var dsyncLog bool
 
-// maximum time to sleep before retrying a failed blocking lock()
+// Retry unit interval
-var lockRetryInterval time.Duration
+var lockRetryMinInterval time.Duration
+
+var lockRetryBackOff func(*rand.Rand, uint) time.Duration
 
 func init() {
 	// Check for MINIO_DSYNC_TRACE env variable, if set logging will be enabled for failed REST operations.
 	dsyncLog = os.Getenv("_MINIO_DSYNC_TRACE") == "1"
 
-	// lockRetryInterval specifies the maximum time between retries for failed locks.
+	lockRetryMinInterval = 250 * time.Millisecond
-	// Average retry time will be value / 2.
-	lockRetryInterval = 250 * time.Millisecond
 	if lri := os.Getenv("_MINIO_LOCK_RETRY_INTERVAL"); lri != "" {
 		v, err := strconv.Atoi(lri)
 		if err != nil {
 			panic(err)
 		}
-		lockRetryInterval = time.Duration(v) * time.Millisecond
+		lockRetryMinInterval = time.Duration(v) * time.Millisecond
 	}
+
+	lockRetryBackOff = backoffWait(
+		lockRetryMinInterval,
+		100*time.Millisecond,
+		5*time.Second,
+	)
 }
 
 func log(format string, data ...interface{}) {
@@ -111,7 +117,7 @@ type DRWMutex struct {
 	clnt                 *Dsync
 	cancelRefresh        context.CancelFunc
 	refreshInterval      time.Duration
-	lockRetryInterval time.Duration
+	lockRetryMinInterval time.Duration
 }
 
 // Granted - represents a structure of a granted lock.
@@ -139,7 +145,7 @@ func NewDRWMutex(clnt *Dsync, names ...string) *DRWMutex {
 		clnt:                 clnt,
 		rng:                  rand.New(&lockedRandSource{src: rand.NewSource(time.Now().UTC().UnixNano())}),
 		refreshInterval:      drwMutexRefreshInterval,
-		lockRetryInterval: lockRetryInterval,
+		lockRetryMinInterval: lockRetryMinInterval,
 	}
 }
 
@@ -225,6 +231,7 @@ func (dm *DRWMutex) lockBlocking(ctx context.Context, lockLossCallback func(), i
 	log("lockBlocking %s/%s for %#v: lockType readLock(%t), additional opts: %#v, quorum: %d, tolerance: %d, lockClients: %d\n", id, source, dm.Names, isReadLock, opts, quorum, tolerance, len(restClnts))
 
 	tolerance = len(restClnts) - quorum
+	attempt := uint(0)
 
 	for {
 		select {
@@ -251,14 +258,15 @@ func (dm *DRWMutex) lockBlocking(ctx context.Context, lockLossCallback func(), i
 				return locked
 			}
 
-			lockRetryInterval := dm.lockRetryInterval
+			switch {
-			if opts.RetryInterval != 0 {
+			case opts.RetryInterval < 0:
-				lockRetryInterval = opts.RetryInterval
-			}
-			if lockRetryInterval < 0 {
 				return false
+			case opts.RetryInterval > 0:
+				time.Sleep(opts.RetryInterval)
+			default:
+				attempt++
+				time.Sleep(lockRetryBackOff(dm.rng, attempt))
 			}
-			time.Sleep(time.Duration(dm.rng.Float64() * float64(lockRetryInterval)))
 		}
 	}
 }
@@ -631,7 +639,7 @@ func (dm *DRWMutex) Unlock(ctx context.Context) {
 
 	isReadLock := false
 	for !releaseAll(ctx, dm.clnt, tolerance, owner, &locks, isReadLock, restClnts, dm.Names...) {
-		time.Sleep(time.Duration(dm.rng.Float64() * float64(dm.lockRetryInterval)))
+		time.Sleep(time.Duration(dm.rng.Float64() * float64(dm.lockRetryMinInterval)))
 	}
 }
 
@@ -672,7 +680,7 @@ func (dm *DRWMutex) RUnlock(ctx context.Context) {
 
 	isReadLock := true
 	for !releaseAll(ctx, dm.clnt, tolerance, owner, &locks, isReadLock, restClnts, dm.Names...) {
-		time.Sleep(time.Duration(dm.rng.Float64() * float64(dm.lockRetryInterval)))
+		time.Sleep(time.Duration(dm.rng.Float64() * float64(dm.lockRetryMinInterval)))
 	}
 }
 

internal/dsync/utils.go

@@ -0,0 +1,39 @@
+// Copyright (c) 2015-2021 MinIO, Inc.
+//
+// This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package dsync
+
+import (
+	"math/rand"
+	"time"
+)
+
+func backoffWait(min, unit, cap time.Duration) func(*rand.Rand, uint) time.Duration {
+	if unit > time.Hour {
+		// Protect against integer overflow
+		panic("unit cannot exceed one hour")
+	}
+	return func(r *rand.Rand, attempt uint) time.Duration {
+		sleep := min
+		sleep += unit * time.Duration(attempt)
+		if sleep > cap {
+			sleep = cap
+		}
+		sleep -= time.Duration(r.Float64() * float64(sleep))
+		return sleep
+	}
+}