Refactor the deadlock detector for testing. Add a test.

pkg/util/deadlock-detector.go

@@ -24,11 +24,6 @@ import (
 	"github.com/golang/glog"
 )
 
-type Lockable interface {
-	Lock()
-	Unlock()
-}
-
 type rwMutexToLockableAdapter struct {
 	rw *sync.RWMutex
 }
@@ -43,9 +38,12 @@ func (r *rwMutexToLockableAdapter) Unlock() {
 
 type deadlockDetector struct {
 	name          string
-	lock          Lockable
+	lock          sync.Locker
 	maxLockPeriod time.Duration
-	clock         Clock
+	exiter        exiter
+	exitChannelFn func() <-chan time.Time
+	// Really only useful for testing
+	stopChannel <-chan bool
 }
 
 // DeadlockWatchdogReadLock creates a watchdog on read/write mutex.  If the mutex can not be acquired
@@ -55,37 +53,68 @@ func DeadlockWatchdogReadLock(lock *sync.RWMutex, name string, maxLockPeriod tim
 	DeadlockWatchdog(&rwMutexToLockableAdapter{lock}, name, maxLockPeriod)
 }
 
-func DeadlockWatchdog(lock Lockable, name string, maxLockPeriod time.Duration) {
+func DeadlockWatchdog(lock sync.Locker, name string, maxLockPeriod time.Duration) {
+	if maxLockPeriod <= 0 {
+		panic("maxLockPeriod is <= 0, that can't be what you wanted")
+	}
 	detector := &deadlockDetector{
-		lock:  lock,
-		name:  name,
-		clock: RealClock{},
+		lock:          lock,
+		name:          name,
+		maxLockPeriod: maxLockPeriod,
+		exitChannelFn: func() <-chan time.Time { return time.After(maxLockPeriod) },
+		stopChannel:   make(chan bool),
 	}
 	go detector.run()
 }
 
-func (d *deadlockDetector) run() {
-	for {
-		ch := make(chan bool, 1)
-		go func() {
-			d.lock.Lock()
-			d.lock.Unlock()
+// Useful for injecting tests
+type exiter interface {
+	Exitf(format string, args ...interface{})
+}
 
-			ch <- true
+type realExiter struct{}
+
+func (realExiter) Exitf(format string, args ...interface{}) {
+	func() {
+		defer func() {
+			// Let's just be extra sure we die, even if Exitf panics
+			if r := recover(); r != nil {
+				glog.Errorf(format, args...)
+				os.Exit(2)
+			}
 		}()
-		select {
-		case <-time.After(d.maxLockPeriod):
-			go func() {
-				defer func() {
-					// Let's just be extra sure we die, even if Exitf panics
-					glog.Errorf("Failed to Exitf for %s, dying anyway", d.name)
-					os.Exit(2)
-				}()
-				glog.Exitf("Deadlock on %s, exiting", d.name)
-			}()
-		case <-ch:
-			glog.V(6).Infof("%s is not deadlocked", d.name)
+		glog.Exitf(format, args...)
+	}()
+}
+
+func (d *deadlockDetector) run() {
+	for {
+		if !d.runOnce() {
+			return
 		}
 		time.Sleep(d.maxLockPeriod / 2)
 	}
 }
+
+func (d *deadlockDetector) runOnce() bool {
+	ch := make(chan bool, 1)
+	go func() {
+		d.lock.Lock()
+		d.lock.Unlock()
+
+		ch <- true
+	}()
+	exitCh := d.exitChannelFn()
+	select {
+	case <-exitCh:
+		d.exiter.Exitf("Deadlock on %s, exiting", d.name)
+		// return is here for when we use a fake exiter in testing
+		return false
+	case <-ch:
+		glog.V(6).Infof("%s is not deadlocked", d.name)
+	case <-d.stopChannel:
+		glog.V(4).Infof("Stopping deadlock detector for %s", d.name)
+		return false
+	}
+	return true
+}

pkg/util/deadlock-detector_test.go

+/*
+Copyright 2015 The Kubernetes Authors All rights reserved.
+
+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 util
+
+import (
+	"sync"
+	"testing"
+	"time"
+)
+
+type fakeExiter struct {
+	format string
+	args   []interface{}
+	exited bool
+}
+
+func (f *fakeExiter) Exitf(format string, args ...interface{}) {
+	f.format = format
+	f.args = args
+	f.exited = true
+}
+
+func TestMaxLockPeriod(t *testing.T) {
+	lock := &sync.RWMutex{}
+	panicked := false
+	func() {
+		defer func() {
+			if r := recover(); r != nil {
+				panicked = true
+			}
+		}()
+		DeadlockWatchdogReadLock(lock, "test lock", 0)
+	}()
+	if !panicked {
+		t.Errorf("expected a panic for a zero max lock period")
+	}
+}
+
+func TestDeadlockWatchdogLocked(t *testing.T) {
+	lock := &sync.RWMutex{}
+	lock.Lock()
+
+	exitCh := make(chan time.Time, 1)
+	fake := fakeExiter{}
+
+	detector := &deadlockDetector{
+		lock:          &rwMutexToLockableAdapter{lock},
+		name:          "test deadlock",
+		exitChannelFn: func() <-chan time.Time { return exitCh },
+		exiter:        &fake,
+	}
+
+	exitCh <- time.Time{}
+
+	detector.run()
+
+	if !fake.exited {
+		t.Errorf("expected to have exited")
+	}
+
+	if len(fake.args) != 1 || fake.args[0].(string) != detector.name {
+		t.Errorf("unexpected args: %v", fake.args)
+	}
+}
+
+func TestDeadlockWatchdogUnlocked(t *testing.T) {
+	lock := &sync.RWMutex{}
+
+	fake := fakeExiter{}
+
+	detector := &deadlockDetector{
+		lock:          &rwMutexToLockableAdapter{lock},
+		name:          "test deadlock",
+		exitChannelFn: func() <-chan time.Time { return time.After(time.Second * 5) },
+		exiter:        &fake,
+	}
+
+	for i := 0; i < 100; i++ {
+		detector.runOnce()
+	}
+
+	if fake.exited {
+		t.Errorf("expected to have not exited")
+	}
+}
+
+func TestDeadlockWatchdogLocking(t *testing.T) {
+	lock := &sync.RWMutex{}
+
+	fake := fakeExiter{}
+
+	go func() {
+		for {
+			lock.Lock()
+			lock.Unlock()
+		}
+	}()
+
+	detector := &deadlockDetector{
+		lock:          &rwMutexToLockableAdapter{lock},
+		name:          "test deadlock",
+		exitChannelFn: func() <-chan time.Time { return time.After(time.Second * 5) },
+		exiter:        &fake,
+	}
+
+	for i := 0; i < 100; i++ {
+		detector.runOnce()
+	}
+
+	if fake.exited {
+		t.Errorf("expected to have not exited")
+	}
+}