com.rackspacecloud.blueflood.service.ZKBasedShardLockManager Maven / Gradle / Ivy
/*
* Copyright 2013 Rackspace
*
* 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 com.rackspacecloud.blueflood.service;
import com.rackspacecloud.blueflood.io.Constants;
import com.rackspacecloud.blueflood.utils.TimeValue;
import com.google.common.base.Ticker;
import com.netflix.curator.RetryPolicy;
import com.netflix.curator.framework.CuratorFramework;
import com.netflix.curator.framework.CuratorFrameworkFactory;
import com.netflix.curator.framework.imps.CuratorFrameworkState;
import com.netflix.curator.framework.recipes.locks.InterProcessMutex;
import com.netflix.curator.framework.state.ConnectionState;
import com.netflix.curator.framework.state.ConnectionStateListener;
import com.netflix.curator.retry.ExponentialBackoffRetry;
import com.yammer.metrics.Metrics;
import com.yammer.metrics.core.Gauge;
import com.yammer.metrics.core.Meter;
import com.yammer.metrics.core.Timer;
import com.yammer.metrics.core.TimerContext;
import com.yammer.metrics.util.JmxGauge;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import javax.management.MBeanServer;
import javax.management.ObjectName;
import java.lang.management.ManagementFactory;
import java.util.*;
import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicInteger;
class ZKBasedShardLockManager implements ConnectionStateListener, ShardLockManager, ZKBasedShardLockManagerMBean {
private Logger log = LoggerFactory.getLogger(ZKBasedShardLockManager.class);
private static AtomicInteger UNIQUE_IDENTIFIER = new AtomicInteger(0);
private final Random rand = new Random(System.currentTimeMillis());
private final int id = UNIQUE_IDENTIFIER.getAndIncrement();
private CuratorFramework client;
private final String ZK_NAMESPACE = "locks/blueflood";
private final String LOCK_QUALIFIER = "/shards";
private final long ZK_SESSION_TIMEOUT_MS = new TimeValue(120L, TimeUnit.SECONDS).toMillis();
private final long ZK_CONN_TIMEOUT_MS = new TimeValue(5L, TimeUnit.SECONDS).toMillis();
private final long ZK_RETRY_INTERVAL = new TimeValue(50L, TimeUnit.MILLISECONDS).toMillis();
private final int ZK_MAX_RETRIES = 2;
private final TimeValue ZK_LOCK_TIMEOUT = new TimeValue(1L, TimeUnit.SECONDS);
private final ConcurrentHashMap locks; // shard to lock objects
private boolean connected = false;
private final Ticker ticker = Ticker.systemTicker();
private TimeValue minLockHoldTime = new TimeValue(20, TimeUnit.MINUTES);
private TimeValue lockDisinterestedTime = new TimeValue(1, TimeUnit.MINUTES);
private TimeValue shardLockScavengeInterval = new TimeValue(2L, TimeUnit.MINUTES);
private java.util.Timer lockScavenger = null;
private long lastScavengedAt = System.currentTimeMillis();
private int maxLocksToAcquirePerCycle;
private int defaultMaxLocksToAcquirePerCycle;
private AtomicInteger locksAcquiredThisCycle = new AtomicInteger(0);
private Gauge lockDisinterestedTimeMillisGauge;
private Gauge minLockHoldTimeMillisGauge;
private Gauge secondsSinceLastScavengeGauge;
private Gauge zkConnectionStatusGauge;
private Gauge heldShardGauge;
private Gauge unheldShardGauge;
private Gauge errorShardGauge;
// thread that does the lock work.
private final ThreadPoolExecutor worker = new ThreadPoolExecutor(1, 1, Long.MAX_VALUE, TimeUnit.DAYS, new ArrayBlockingQueue(1000), new ThreadFactory() {
public Thread newThread(Runnable r) {
return new Thread(r, "ZK Lock Worker " + id);
}
});
private final Meter lockAcquisitionFailure = Metrics.newMeter(ZKBasedShardLockManager.class, "Lock acquisition failures", "ZK", TimeUnit.MINUTES);
private final Timer lockAcquisitionTimer = Metrics.newTimer(ZKBasedShardLockManager.class, "Lock acquisition timer", TimeUnit.MILLISECONDS, TimeUnit.SECONDS);
private final Meter lockErrors = Metrics.newMeter(ZKBasedShardLockManager.class, "Lock errors", "ZK", TimeUnit.MINUTES);
ZKBasedShardLockManager(String zookeeperCluster, Set managedShards) {
try {
final MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();
final String name = String.format("com.rackspacecloud.blueflood.service:type=%s", getClass().getSimpleName() + (id == 0 ? "" : id));
final ObjectName nameObj = new ObjectName(name);
mbs.registerMBean(this, nameObj);
lockDisinterestedTimeMillisGauge = Metrics.newGauge(ZKBasedShardLockManager.class, "Lock Disinterested Time Millis",
new JmxGauge(nameObj, "LockDisinterestedTimeMillis"));
minLockHoldTimeMillisGauge = Metrics.newGauge(ZKBasedShardLockManager.class, "Min Lock Hold Time Millis",
new JmxGauge(nameObj, "MinLockHoldTimeMillis"));
secondsSinceLastScavengeGauge = Metrics.newGauge(ZKBasedShardLockManager.class, "Seconds Since Last Scavenge",
new JmxGauge(nameObj, "SecondsSinceLastScavenge"));
zkConnectionStatusGauge = Metrics.newGauge(ZKBasedShardLockManager.class, "Zk Connection Status",
new JmxGauge(nameObj, "ZkConnectionStatus") {
@Override
public Object value() {
Object val = super.value();
if (val.equals("connected")) {
return 1;
}
return 0;
}
});
heldShardGauge = Metrics.newGauge(ZKBasedShardLockManager.class, "Held Shards",
new Gauge() {
@Override
public Integer value() {
return getHeldShards().size();
}
});
unheldShardGauge = Metrics.newGauge(ZKBasedShardLockManager.class, "Unheld Shards",
new Gauge() {
@Override
public Integer value() {
return getUnheldShards().size();
}
});
errorShardGauge = Metrics.newGauge(ZKBasedShardLockManager.class, "Error Shards",
new Gauge() {
@Override
public Integer value() {
return getErrorShards().size();
}
});
} catch (Exception exc) {
log.error("Unable to register mbean for " + getClass().getSimpleName(), exc);
}
this.locks = new ConcurrentHashMap();
this.client = null;
RetryPolicy policy = new ExponentialBackoffRetry((int)ZK_RETRY_INTERVAL, ZK_MAX_RETRIES);
this.client = CuratorFrameworkFactory.
builder().namespace(ZK_NAMESPACE)
.connectString(zookeeperCluster)
.sessionTimeoutMs((int) ZK_SESSION_TIMEOUT_MS)
.connectionTimeoutMs((int) ZK_CONN_TIMEOUT_MS)
.retryPolicy(policy).build();
this.client.getConnectionStateListenable().addListener(this); // register our listener
for (int shard : managedShards)
addShard(shard);
this.client.start();
this.minLockHoldTime = new TimeValue(Configuration.getLongProperty("SHARD_LOCK_HOLD_PERIOD_MS"), TimeUnit.MILLISECONDS);
this.lockDisinterestedTime = new TimeValue(Configuration.getLongProperty("SHARD_LOCK_DISINTERESTED_PERIOD_MS"), TimeUnit.MILLISECONDS);
this.shardLockScavengeInterval = new TimeValue(Configuration.getLongProperty("SHARD_LOCK_SCAVENGE_INTERVAL_MS"),
TimeUnit.MILLISECONDS);
this.lockScavenger = new java.util.Timer("Lock scavenger " + (id != 0 ? id : ""), true);
this.defaultMaxLocksToAcquirePerCycle = Configuration.getIntegerProperty("MAX_ZK_LOCKS_TO_ACQUIRE_PER_CYCLE");
waitForZKConnections();
// attempt all locks. needs to be called before the scavenger is instantiated.
prefetchLocksAndScheduleLocksScavenging(managedShards);
}
private void waitForZKConnections() {
for (int i = 0; i < 5; i++) {
if (!connected) {
log.debug("Waiting for connect");
try { Thread.sleep(1000); } catch (Exception ex) {}
}
}
}
// Only called from the constructor; Iterates over shards trying to acquire locks.
private void prefetchLocksAndScheduleLocksScavenging(final Collection managedShards) {
// Try to achieve each lock. This will give us a good initial state where each lock is either held or unheld.
// The purpose is to avoid a situation at startup where a node assumes it can schedule anything (until a lock
// is held).
if (!connected) {
log.warn("Cannot connect to Zookeeper; will not perform initial lock acquisition");
for (Lock lock : locks.values())
lock.connectionLost();
} else {
log.info("Pre-fetching zookeeper locks for shards");
boolean isManagingAllShards = managedShards.size() >= Constants.NUMBER_OF_SHARDS;
int maxLocksToPrefetch = managedShards.size()/2 + 1;
if (isManagingAllShards) {
maxLocksToPrefetch = managedShards.size();
}
List shards = new ArrayList(managedShards);
Collections.shuffle(shards);
int locksObtained = 0;
for (int shard : shards) {
try {
log.debug("Initial lock attempt for " + shard);
final Lock lock = locks.get(shard);
worker.submit(lock.acquirer()).get();
if (lock.isHeld() && ++locksObtained >= maxLocksToPrefetch) {
break;
}
} catch (InterruptedException ex) {
log.warn("Thread exception while acquiring initial locks: " + ex.getMessage(), ex);
} catch (ExecutionException ex) {
log.error("Problem acquiring lock " + shard + " " + ex.getCause().getMessage(), ex.getCause());
}
}
log.info("Finished pre-fetching zookeeper locks");
}
// initial locks are set. safe to start the scavenger now.
this.lockScavenger.schedule(new TimerTask() {
@Override
public void run() {
scavengeLocks();
}
}, 120000, this.shardLockScavengeInterval.toMillis()); // wait 2 min, then check every shardLockScavengeInterval.
}
public boolean canWork(int shard) {
return locks.containsKey(shard) && locks.get(shard).canWork();
}
private String getLockId(int shard) {
return LOCK_QUALIFIER + "/" + shard;
}
// This is called when connection to zookeeper is lost
private void handleZookeeperConnectionFailed() {
// It is okay for us to proceed with the work we already scheduled (either running or in scheduled queue)
// for slots. We would duplicate work just for those slots which is fine.
log.info("Force release all locks as zookeeper connection is lost");
for (Lock lock : locks.values())
lock.connectionLost();
}
private void scavengeLocks() {
locksAcquiredThisCycle.set(0);
maxLocksToAcquirePerCycle = defaultMaxLocksToAcquirePerCycle;
final Integer[] shards = locks.keySet().toArray(new Integer[]{});
// Linear scan to figure out how many locks are held.
int locksHeld = 0;
for (int shard : shards) {
if (locks.get(shard).isHeld()) {
locksHeld++;
}
}
// if the number of locks held is less than 50% of the number of managed shards,
// be aggressive and acquire more locks
if (locksHeld <= locks.size()/2 + 1) {
maxLocksToAcquirePerCycle = locks.size()/2 + 1;
}
for (int shard : shards) {
locks.get(shard).performMaintenance();
}
lastScavengedAt = nowMillis();
}
public void stateChanged(CuratorFramework curatorFramework, ConnectionState connectionState) {
log.info("Connection to Zookeeper toggled to state " + connectionState.toString());
connected = connectionState == ConnectionState.CONNECTED || connectionState == ConnectionState.RECONNECTED;
if (connectionState == ConnectionState.LOST) {
log.error("Connection to Zookeeper toggled to state " + connectionState.toString());
this.handleZookeeperConnectionFailed();
} else if (connectionState == ConnectionState.RECONNECTED) {
log.info("Reconnected to zookeeper, forcing lock scavenge");
forceLockScavenge();
} else {
log.info("Connection to Zookeeper toggled to state " + connectionState.toString());
}
}
public synchronized void addShard(int shard) {
if (locks.containsKey(shard))
return;
this.locks.put(shard, new Lock(shard));
}
public synchronized void removeShard(int shard) {
Lock lock = locks.remove(shard);
if (lock != null)
lock.release();
}
public boolean isConnected() {
return connected && client != null && isCuratorStarted() && client.getZookeeperClient().isConnected();
}
private boolean isCuratorStarted() {
return client.getState() == CuratorFrameworkState.STARTED;
}
//
// unsafe methods for testing.
//
public void waitForQuiesceUnsafe() {
while (worker.getActiveCount() != 0 || worker.getQueue().size() != 0) {
if (log.isTraceEnabled())
log.trace("Waiting for quiesce");
try { Thread.sleep(100); } catch (InterruptedException ignore) {}
}
// this time out nees to be longer than ZK_LOCK_TIMEOUT for valid tests.
try { Thread.sleep(1500); } catch (InterruptedException ignore) {}
}
public boolean holdsLockUnsafe(int shard) {
return locks.containsKey(shard) && locks.get(shard).isHeldZk();
}
public boolean releaseLockUnsafe(int shard) throws Exception {
return worker.submit(locks.get(shard).releaser()).get();
}
public void shutdownUnsafe() throws Exception {
for (Lock lock : locks.values())
worker.submit(lock.releaser()).get();
client.close();
}
private long nowMillis() { return ticker.read() / 1000000; }
//
// JMX
//
public synchronized Collection getHeldShards() {
SortedSet held = new TreeSet();
for (Lock lock : locks.values()) {
if (lock.isHeld()) {
held.add(lock.getShard());
}
}
return held;
}
public synchronized Collection getUnheldShards() {
SortedSet unheld = new TreeSet();
for (Lock lock : locks.values()) {
if (lock.isUnheld()) {
unheld.add(lock.getShard());
}
}
return unheld;
}
public synchronized Collection getErrorShards() {
SortedSet errorShards = new TreeSet();
for (Lock lock : locks.values()) {
if (lock.getLockState() == LockState.ERROR) {
errorShards.add(lock.getShard());
}
}
return errorShards;
}
public synchronized void forceLockScavenge() {
scavengeLocks();
}
public synchronized String getZkConnectionStatus() {
if (client == null)
return "null";
else if (!isCuratorStarted())
return "not started";
else if (client.getZookeeperClient().isConnected())
return "connected";
else
return "not connected";
}
public synchronized boolean release(int shard) {
if (locks.containsKey(shard)) {
try {
return worker.submit(locks.get(shard).releaser()).get();
} catch (InterruptedException ex) {
log.error("Thread error: "+ ex.getMessage(), ex);
return false;
} catch (ExecutionException ex) {
log.error("Release error: " + ex.getCause().getMessage(), ex.getCause());
return false;
}
}
return false;
}
public synchronized boolean acquire(int shard) {
if (locks.containsKey(shard)) {
try {
return worker.submit(locks.get(shard).acquirer()).get();
} catch (InterruptedException ex) {
log.error("Thread error: "+ ex.getMessage(), ex);
return false;
} catch (ExecutionException ex) {
log.error("Release error: " + ex.getCause().getMessage(), ex.getCause());
return false;
}
}
return false;
}
public synchronized long getMinLockHoldTimeMillis() { return minLockHoldTime.toMillis(); }
public synchronized void setMinLockHoldTimeMillis(long millis) { minLockHoldTime = new TimeValue(millis, TimeUnit.MILLISECONDS); }
public synchronized long getLockDisinterestedTimeMillis() { return lockDisinterestedTime.toMillis(); }
public synchronized void setLockDisinterestedTimeMillis(long millis) { lockDisinterestedTime = new TimeValue(millis, TimeUnit.MILLISECONDS); }
public synchronized long getSecondsSinceLastScavenge() { return ((nowMillis() - lastScavengedAt) / 1000); }
//
// Helper classes
//
enum LockState {
UNKNOWN,
ACQUIRED,
ACQUIRE_FAILED,
ERROR,
DISINTERESTED;
}
class Lock {
private final int shard;
private LockState state = LockState.UNKNOWN;
private InterProcessMutex mutex = null;
private long stateChanged = ticker.read() / 1000000;
private boolean isAcquiring = false;
private boolean isReleasing = false;
Lock(int shard) {
this.shard = shard;
checkMutex();
}
synchronized void checkMutex() {
if (client == null) {
state = LockState.ERROR;
stateChanged = nowMillis();
} else if (mutex == null) {
mutex = new InterProcessMutex(client, getLockId(shard));
}
}
int getShard() { return shard; }
boolean isHeld() { return mutex != null && state == LockState.ACQUIRED; }
boolean isUnheld() { return mutex != null && state == LockState.ACQUIRE_FAILED; }
boolean isHeldZk() {
return mutex != null && mutex.isAcquiredInThisProcess();
}
void performMaintenance() {
updateLockState();
long now = nowMillis();
// determine if we should acquire or release.
if (state == LockState.UNKNOWN && locksAcquiredThisCycle.get() < maxLocksToAcquirePerCycle) {
acquire();
if (isHeld()) {
locksAcquiredThisCycle.incrementAndGet();
}
} else if (state == LockState.ACQUIRED && now - stateChanged > minLockHoldTime.toMillis()) {
// maybe release.
float chance = (float)(now - stateChanged - minLockHoldTime.toMillis()) / (float)(Math.max(1, minLockHoldTime.toMillis()));
float r = rand.nextFloat();
if (log.isTraceEnabled())
log.trace(String.format("Will release %s if, %f < %f", shard, r, chance));
if (r < chance)
release();
} else if (state == LockState.ERROR && now - stateChanged > minLockHoldTime.toMillis()) {
log.error("Lock state hasn't toggled from ERROR for " + minLockHoldTime.toString()
+ "; Client connection status: " + connected);
}
}
synchronized void updateLockState() {
boolean toUnk = false;
long now = nowMillis();
if (state == LockState.DISINTERESTED && now - stateChanged > lockDisinterestedTime.toMillis())
toUnk = true;
else if (state == LockState.ERROR && connected)
toUnk = true;
else if (state == LockState.ACQUIRE_FAILED && now - stateChanged > lockDisinterestedTime.toMillis())
toUnk = true;
if (toUnk) {
state = LockState.UNKNOWN;
stateChanged = now;
}
}
synchronized LockState getLockState() {
return state;
}
synchronized boolean canWork() {
return state == LockState.ACQUIRED || state == LockState.ERROR;
}
synchronized void connectionLost() {
// assume client = null.
state = LockState.ERROR;
stateChanged = nowMillis();
mutex = null;
}
synchronized void acquire() {
if (isAcquiring || isReleasing) return;
isAcquiring = true;
try {
log.debug("Acquiring lock for " + shard);
worker.execute(new FutureTask(acquirer()));
} catch (RejectedExecutionException ex) {
log.warn(String.format("Rejected lock execution: active:%d queue:%d shard:%d", worker.getActiveCount(), worker.getQueue().size(), shard));
}
}
synchronized void release() {
if (isAcquiring || isReleasing) return;
isReleasing = true;
try {
log.debug("Releasing lock for " + shard);
worker.execute(new FutureTask(releaser()));
} catch (RejectedExecutionException ex) {
log.warn(String.format("Rejected lock execution: active:%d queue:%d shard:%d", worker.getActiveCount(), worker.getQueue().size(), shard));
}
}
synchronized Callable acquirer() {
return new Callable() {
public Boolean call() throws Exception {
checkMutex();
if (client == null || !connected || mutex == null) {
state = LockState.ERROR;
stateChanged = nowMillis();
return false;
} else if (state == LockState.ACQUIRED)
return true;
else if (state == LockState.ACQUIRE_FAILED)
return false;
else {
log.debug("Trying ZK lock for " + shard);
TimerContext ctx = lockAcquisitionTimer.time();
if (mutex.isAcquiredInThisProcess()) {
if (log.isTraceEnabled())
log.trace("Lock already acquired for " + shard);
ctx.stop();
return true;
} else {
try {
boolean acquired = mutex.acquire(ZK_LOCK_TIMEOUT.getValue(), ZK_LOCK_TIMEOUT.getUnit());
if (acquired) {
state = LockState.ACQUIRED;
stateChanged = nowMillis();
log.debug("Acquired ZK lock for " + shard);
} else {
state = LockState.ACQUIRE_FAILED;
stateChanged = nowMillis();
lockAcquisitionFailure.mark();
log.debug("Acquire ZK failed for " + shard);
}
return acquired;
} catch (Exception ex) {
log.debug("Exception on ZK acquire for " + shard);
log.warn(ex.getMessage(), ex);
lockErrors.mark();
state = LockState.ERROR;
return true;
} finally {
isAcquiring = false;
ctx.stop();
}
}
}
}
};
}
synchronized Callable releaser() {
return new Callable() {
public Boolean call() throws Exception {
checkMutex();
boolean result = false;
if (client == null || !connected || mutex == null) {
state = LockState.ERROR;
stateChanged = nowMillis();
result = true;
} else if (state != LockState.ACQUIRED)
result = false;
else if (mutex.isAcquiredInThisProcess()) {
log.debug("Releasing lock for shard " + shard);
mutex.release();
state = LockState.DISINTERESTED;
stateChanged = nowMillis();
result = true;
} else {
log.error("Held lock not held by this process? " + shard);
state = LockState.UNKNOWN;
stateChanged = nowMillis();
result = true;
}
isReleasing = false;
return result;
}
};
}
}
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