Add support for timeouts for locks (#4377)

cmd/dynamic-timeouts.go

@@ -0,0 +1,120 @@
+/*
+ * Minio Cloud Storage, (C) 2017 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package cmd
+
+import (
+	"sync"
+	"sync/atomic"
+	"time"
+)
+
+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                        = time.Duration(1<<63 - 1)
+)
+
+// timeouts that are dynamically adapted based on actual usage results
+type dynamicTimeout struct {
+	timeout int64
+	minimum int64
+	entries int64
+	log     [dynamicTimeoutLogSize]time.Duration
+	mutex   sync.Mutex
+}
+
+// newDynamicTimeout returns a new dynamic timeout initialized with timeout value
+func newDynamicTimeout(timeout, minimum time.Duration) *dynamicTimeout {
+	return &dynamicTimeout{timeout: int64(timeout), minimum: int64(minimum)}
+}
+
+// Timeout returns the current timeout value
+func (dt *dynamicTimeout) Timeout() time.Duration {
+	return time.Duration(atomic.LoadInt64(&dt.timeout))
+}
+
+// LogSuccess logs the duration of a successful action that
+// did not hit the timeout
+func (dt *dynamicTimeout) LogSuccess(duration time.Duration) {
+	dt.logEntry(duration)
+}
+
+// LogFailure logs an action that hit the timeout
+func (dt *dynamicTimeout) LogFailure() {
+	dt.logEntry(maxDuration)
+}
+
+// logEntry stores a log entry
+func (dt *dynamicTimeout) logEntry(duration time.Duration) {
+	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[:])
+
+		// reset log entries
+		atomic.StoreInt64(&dt.entries, 0)
+
+		dt.mutex.Unlock()
+
+		dt.adjust(logCopy)
+	}
+}
+
+// adjust changes the value of the dynamic timeout based on the
+// previous results
+func (dt *dynamicTimeout) adjust(entries [dynamicTimeoutLogSize]time.Duration) {
+
+	failures, average := 0, 0
+	for i := 0; i < len(entries); i++ {
+		if entries[i] == maxDuration {
+			failures++
+		} else {
+			average += int(entries[i])
+		}
+	}
+	if failures < len(entries) {
+		average /= len(entries) - failures
+	}
+
+	timeOutHitPct := float64(failures) / float64(len(entries))
+
+	if timeOutHitPct > 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) + int64(average)) / 2 // Middle between current timeout and average success
+		if timeout < dt.minimum {
+			timeout = dt.minimum
+		}
+		atomic.StoreInt64(&dt.timeout, timeout)
+	}
+
+}