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// Copyright 2017 Yahoo Inc. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.jdisc.core;
import com.google.inject.Inject;
import com.yahoo.jdisc.Metric;
import com.yahoo.jdisc.statistics.ActiveContainerMetrics;
import java.lang.ref.PhantomReference;
import java.lang.ref.ReferenceQueue;
import java.time.Clock;
import java.time.Duration;
import java.time.Instant;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.WeakHashMap;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.logging.Level;
import java.util.logging.Logger;
import static java.util.Comparator.comparing;
import static java.util.stream.Collectors.toList;
/**
* A watchdog that monitors all deactivated {@link ActiveContainer} instances with the purpose of detecting containers
* that are unable to be garbage collected by the JVM.
*
* @author bjorncs
*/
class ActiveContainerDeactivationWatchdog implements ActiveContainerMetrics, AutoCloseable {
static final Duration WATCHDOG_FREQUENCY = Duration.ofMinutes(20);
static final Duration ACTIVE_CONTAINER_GRACE_PERIOD = Duration.ofHours(1);
static final Duration GC_TRIGGER_FREQUENCY = ACTIVE_CONTAINER_GRACE_PERIOD.minusMinutes(5);
static final Duration ENFORCE_DESTRUCTION_GCED_CONTAINERS_FREQUENCY = Duration.ofMinutes(5);
private static final Logger log = Logger.getLogger(ActiveContainerDeactivationWatchdog.class.getName());
private final Object monitor = new Object();
private final WeakHashMap<ActiveContainer, LifecycleStats> deactivatedContainers = new WeakHashMap<>();
private final ReferenceQueue<ActiveContainer> garbageCollectedContainers = new ReferenceQueue<>();
@SuppressWarnings("MismatchedQueryAndUpdateOfCollection")
// Instances of the phantom references must be kept alive until they are polled from the reference queue
private final Set<ActiveContainerPhantomReference> destructorReferences = new HashSet<>();
private final ScheduledExecutorService scheduler;
private final Clock clock;
private ActiveContainer currentContainer;
private Instant currentContainerActivationTime;
@Inject
ActiveContainerDeactivationWatchdog() {
this(
Clock.systemUTC(),
new ScheduledThreadPoolExecutor(3, runnable -> {
Thread thread = new Thread(runnable, "active-container-deactivation-watchdog");
thread.setDaemon(true);
return thread;
}));
}
ActiveContainerDeactivationWatchdog(Clock clock, ScheduledExecutorService scheduler) {
this.clock = clock;
this.scheduler = scheduler;
this.scheduler.scheduleAtFixedRate(this::warnOnStaleContainers,
WATCHDOG_FREQUENCY.getSeconds(),
WATCHDOG_FREQUENCY.getSeconds(),
TimeUnit.SECONDS);
this.scheduler.scheduleAtFixedRate(System::gc,
GC_TRIGGER_FREQUENCY.getSeconds(),
GC_TRIGGER_FREQUENCY.getSeconds(),
TimeUnit.SECONDS);
this.scheduler.scheduleAtFixedRate(this::enforceDestructionOfGarbageCollectedContainers,
ENFORCE_DESTRUCTION_GCED_CONTAINERS_FREQUENCY.getSeconds(),
ENFORCE_DESTRUCTION_GCED_CONTAINERS_FREQUENCY.getSeconds(),
TimeUnit.SECONDS);
}
void onContainerActivation(ActiveContainer nextContainer) {
synchronized (monitor) {
Instant now = clock.instant();
ActiveContainer previousContainer = currentContainer;
currentContainer = nextContainer;
currentContainerActivationTime = now;
if (previousContainer != null) {
deactivatedContainers.put(previousContainer, new LifecycleStats(currentContainerActivationTime, now));
destructorReferences.add(new ActiveContainerPhantomReference(previousContainer, garbageCollectedContainers));
}
}
}
@Override
public void emitMetrics(Metric metric) {
List<DeactivatedContainer> snapshot = getDeactivatedContainersSnapshot();
long containersWithRetainedRefsCount = snapshot.stream()
.filter(c -> c.activeContainer.retainCount() > 0)
.count();
metric.set(TOTAL_DEACTIVATED_CONTAINERS, snapshot.size(), null);
metric.set(DEACTIVATED_CONTAINERS_WITH_RETAINED_REFERENCES, containersWithRetainedRefsCount, null);
}
@Override
public void close() {
synchronized (monitor) {
scheduler.shutdown();
deactivatedContainers.clear();
destructorReferences.clear();
currentContainer = null;
currentContainerActivationTime = null;
}
}
private void warnOnStaleContainers() {
try {
List<DeactivatedContainer> snapshot = getDeactivatedContainersSnapshot();
if (snapshot.isEmpty()) return;
logWarning(snapshot);
} catch (Throwable t) {
log.log(Level.WARNING, "Watchdog task died!", t);
}
}
private void enforceDestructionOfGarbageCollectedContainers() {
ActiveContainerPhantomReference reference;
while ((reference = (ActiveContainerPhantomReference) garbageCollectedContainers.poll()) != null) {
try {
reference.enforceDestruction();
} catch (Throwable t) {
log.log(Level.SEVERE, "Failed to do post-GC destruction of " + reference.containerName, t);
} finally {
destructorReferences.remove(reference);
reference.clear();
}
}
}
private List<DeactivatedContainer> getDeactivatedContainersSnapshot() {
Instant now = clock.instant();
synchronized (monitor) {
return deactivatedContainers.entrySet().stream()
.filter(e -> e.getValue().isPastGracePeriod(now))
.map(e -> new DeactivatedContainer(e.getKey(), e.getValue()))
.sorted(comparing(e -> e.lifecycleStats.timeActivated))
.collect(toList());
}
}
private static void logWarning(List<DeactivatedContainer> snapshot) {
log.warning(String.format("%s instances of deactivated containers are still alive.", snapshot.size()));
for (DeactivatedContainer deactivatedContainer : snapshot) {
log.warning(" - " + deactivatedContainer.toSummaryString());
}
}
private static class LifecycleStats {
public final Instant timeActivated;
public final Instant timeDeactivated;
public LifecycleStats(Instant timeActivated, Instant timeDeactivated) {
this.timeActivated = timeActivated;
this.timeDeactivated = timeDeactivated;
}
public boolean isPastGracePeriod(Instant instant) {
return timeDeactivated.plus(ACTIVE_CONTAINER_GRACE_PERIOD).isBefore(instant);
}
}
private static class DeactivatedContainer {
public final ActiveContainer activeContainer;
public final LifecycleStats lifecycleStats;
public DeactivatedContainer(ActiveContainer activeContainer, LifecycleStats lifecycleStats) {
this.activeContainer = activeContainer;
this.lifecycleStats = lifecycleStats;
}
public String toSummaryString() {
return String.format("%s: time activated = %s, time deactivated = %s, reference count = %d",
activeContainer.toString(),
lifecycleStats.timeActivated.toString(),
lifecycleStats.timeDeactivated.toString(),
activeContainer.retainCount());
}
}
private static class ActiveContainerPhantomReference extends PhantomReference<ActiveContainer> {
public final String containerName;
private final ActiveContainer.Destructor destructor;
public ActiveContainerPhantomReference(ActiveContainer activeContainer,
ReferenceQueue<? super ActiveContainer> q) {
super(activeContainer, q);
this.containerName = activeContainer.toString();
this.destructor = activeContainer.destructor;
}
public void enforceDestruction() {
boolean alreadyCompleted = destructor.destruct();
if (!alreadyCompleted) {
log.severe(containerName + " was not correctly cleaned up " +
"because of a resource leak or invalid use of reference counting.");
}
}
}
}
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