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Apache Geode provides a database-like consistency model, reliable transaction processing and a shared-nothing architecture to maintain very low latency performance with high concurrency processing
/*
* Licensed to the Apache Software Foundation (ASF) under one or more contributor license
* agreements. See the NOTICE file distributed with this work for additional information regarding
* copyright ownership. The ASF licenses this file to You 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 org.apache.geode.distributed.internal;
import org.apache.geode.distributed.DistributedMember;
import org.apache.geode.internal.SystemTimer;
import org.apache.geode.internal.SystemTimer.SystemTimerTask;
import org.apache.geode.internal.cache.GemFireCacheImpl;
import org.apache.geode.internal.i18n.LocalizedStrings;
import org.apache.geode.internal.logging.DateFormatter;
import org.apache.geode.internal.logging.LogService;
import org.apache.geode.internal.logging.log4j.LocalizedMessage;
import org.apache.logging.log4j.Logger;
import java.util.Date;
import java.util.concurrent.atomic.AtomicLong;
/**
* DSClock tracks the system time. The most useful method is cacheTimeMillis(). The rest are for
* clock adjustments.
*
* Clock adjustments can be turned off with gemfire.disable-distributed-clock
*
*/
public class DSClock implements CacheTime {
private static final Logger logger = LogService.getLogger();
private final int MAX_TIME_OFFSET_DIFF = 100; /* in milliseconds */
private final long MAX_CACHE_TIME_MILLIS = 0x00FFFFFFFFFFFFFFL;
/**
* Time shift received from server must be at least this far off in order for the cacheTimeMillis
* clock to be changed. Servers are much more aggressive about it.
*/
private final static long MINIMUM_TIME_DIFF = 5000;
/**
* cacheTimeMillis offset from System.currentTimeMillis
*/
private volatile long cacheTimeDelta;
/**
* a task to slow down the clock if cacheTimeDelta decreases in value
*/
private SystemTimerTask cacheTimeTask = null; // task to slow down the clock
/**
* State variable used by the cacheTimeTask
*/
private final AtomicLong suspendedTime = new AtomicLong(0L);
/**
* Is this a client "distributed system"
*/
private final boolean isLoner;
/** GemFire internal test hook for unit testing */
private DSClockTestHook testHook;
protected DSClock(boolean lonerDS) {
this.isLoner = lonerDS;
}
@Override
public long cacheTimeMillis() {
long result;
final long offset = getCacheTimeOffset();
final long st = getStopTime();
if (st != 0) {
result = st + offset;
if (result < 0 || result > MAX_CACHE_TIME_MILLIS) {
throw new IllegalStateException("Expected cacheTimeMillis " + result + " to be >= 0 and <= "
+ MAX_CACHE_TIME_MILLIS + " stopTime=" + st + " offset=" + offset);
}
} else {
long ct = System.currentTimeMillis();
result = ct + offset;
if (result < 0 || result > MAX_CACHE_TIME_MILLIS) {
throw new IllegalStateException("Expected cacheTimeMillis " + result + " to be >= 0 and <= "
+ MAX_CACHE_TIME_MILLIS + " curTime=" + ct + " offset=" + offset);
}
}
return result;
}
/**
* @return Offset for system time, calculated by distributed system coordinator.
* @since GemFire 8.0
*/
public long getCacheTimeOffset() {
return this.cacheTimeDelta;
}
/**
* Sets the deviation of this process's local time from the rest of the GemFire distributed
* system.
*
* @since GemFire 8.0
*/
public void setCacheTimeOffset(DistributedMember coord, long offset, boolean isJoin) {
if (Boolean.getBoolean(DistributionConfig.GEMFIRE_PREFIX + "disable-distributed-clock")) {
return;
}
if (isLoner) {
setLonerCacheTimeOffset(offset);
} else {
setServerCacheTimeOffset(coord, offset, isJoin);
}
}
// set the time offset in a client cache
private void setLonerCacheTimeOffset(long offset) {
if (offset > (this.cacheTimeDelta + MINIMUM_TIME_DIFF)) {
long theTime = System.currentTimeMillis();
this.cacheTimeDelta = offset;
String cacheTime = DateFormatter.formatDate(new Date(theTime + offset));
logger.info(LocalizedMessage.create(LocalizedStrings.LonerDistributionManager_Cache_Time,
new Object[] {cacheTime, this.cacheTimeDelta}));
} else if (offset < (this.cacheTimeDelta - MINIMUM_TIME_DIFF)) {
// We don't issue a warning for client caches
// if ((this.cacheTimeDelta - offset) >= MAX_TIME_OFFSET_DIFF /* Max offset difference allowed
// */) {
// this.logger.warning(LocalizedStrings.DistributionManager_Cache_Time_Offset_Skew_Warning,
// (this.cacheTimeDelta - offset));
// }
this.cacheTimeDelta = offset;
// We need to suspend the cacheTimeMillis for (cacheTimeDelta - offset) ms.
cancelAndScheduleNewCacheTimerTask(offset);
}
}
private void setServerCacheTimeOffset(DistributedMember coord, long offset, boolean isJoin) {
if (isJoin || offset > this.cacheTimeDelta) {
long theTime = System.currentTimeMillis();
this.cacheTimeDelta = offset;
if (this.cacheTimeDelta <= -300000 || 300000 <= this.cacheTimeDelta) {
logger.warn(
LocalizedMessage.create(LocalizedStrings.DistributionManager_Time_Skew_Warning, coord));
}
String cacheTime = DateFormatter.formatDate(new Date(theTime + offset));
if (Math.abs(this.cacheTimeDelta) > 1000) {
Object src = coord;
if (src == null) {
src = "local clock adjustment";
}
logger.info(LocalizedMessage.create(LocalizedStrings.DistributionManager_Cache_Time,
new Object[] {src, cacheTime, this.cacheTimeDelta}));
}
} else if (!isJoin && offset < this.cacheTimeDelta) {
// We need to suspend the cacheTimeMillis for (cacheTimeDelta - offset) ms.
if ((this.cacheTimeDelta
- offset) >= MAX_TIME_OFFSET_DIFF /* Max offset difference allowed */) {
logger.warn(LocalizedMessage.create(
LocalizedStrings.DistributionManager_Cache_Time_Offset_Skew_Warning,
(this.cacheTimeDelta - offset)));
}
cancelAndScheduleNewCacheTimerTask(offset);
}
}
/**
* This method is called by a timer task which takes control of cache time and increments the
* cache time at each call of this method.
*
* The timer task must be called each millisecond. We need to revisit the method implementation if
* that condition is changed.
*
* @param stw True if Stop the world for this cache for a while.
*/
private void suspendCacheTimeMillis(boolean stw) {
// Increment stop time at each call of this method.
if (stw) {
long oldSt;
long newSt;
do {
oldSt = this.suspendedTime.get();
if (oldSt == 0) {
newSt = System.currentTimeMillis();
} else {
newSt = oldSt + 1;
}
} while (!this.suspendedTime.compareAndSet(oldSt, newSt));
} else {
this.suspendedTime.set(0);
}
}
/**
* Cancel the previous slow down task (If it exists) and schedule a new one.
*
* @param offset
*/
private void cancelAndScheduleNewCacheTimerTask(long offset) {
GemFireCacheImpl cache = GemFireCacheImpl.getInstance();
if (cache != null && !cache.isClosed()) {
if (this.cacheTimeTask != null) {
this.cacheTimeTask.cancel();
}
cacheTimeTask = new CacheTimeTask(offset);
SystemTimer timer = cache.getCCPTimer();
timer.scheduleAtFixedRate(cacheTimeTask, 1/* Start after 1ms */ , 2 /* Run task every 2ms */);
if (logger.isDebugEnabled()) {
logger.debug(
"Started a timer task to suspend cache time for new lower offset of {}ms and current offset is: {}",
offset, cacheTimeDelta);
}
}
}
public long getStopTime() {
return this.suspendedTime.get();
}
/**
* This timer task makes the cache dependent on this DM, to wait (OR in other words stop it's
* cacheTimeMillis() to return constant value until System.currentTimeMillis() + newOffset
* reaches/crosses over that constant time) for difference between old time offset and new one if
* new one is < old one. Because then we need to slow down the cache time aggressively.
*
*
*/
private class CacheTimeTask extends SystemTimerTask {
private long lowerCacheTimeOffset = 0L;
public CacheTimeTask(long cacheTimeOffset) {
super();
this.lowerCacheTimeOffset = cacheTimeOffset;
}
@Override
public void run2() {
boolean isCancelled = false;
suspendCacheTimeMillis(true);
long currTime = System.currentTimeMillis();
long cacheTime = cacheTimeMillis();
if (testHook != null) {
testHook.suspendAtBreakPoint(1);
testHook.addInformation("CacheTime", cacheTime);
testHook.addInformation("AwaitedTime", currTime + lowerCacheTimeOffset);
}
if (logger.isDebugEnabled()) {
logger.debug("CacheTime: {}ms and currTime with offset: {}", cacheTime,
(currTime + this.lowerCacheTimeOffset) + "ms");
}
// Resume cache time as system time once cache time has slowed down enough.
long systemTime = currTime + this.lowerCacheTimeOffset;
if (cacheTime <= systemTime) {
setCacheTimeOffset(null, this.lowerCacheTimeOffset, true);
suspendCacheTimeMillis(false);
this.cancel();
isCancelled = true;
if (testHook != null) {
testHook.suspendAtBreakPoint(2);
testHook.addInformation("FinalCacheTime", cacheTimeMillis());
}
}
if (testHook != null && isCancelled) {
testHook.suspendAtBreakPoint(3);
testHook.addInformation("TimerTaskCancelled", true);
}
}
@Override
public boolean cancel() {
GemFireCacheImpl cache = GemFireCacheImpl.getInstance();
if (cache != null && !cache.isClosed()) {
suspendCacheTimeMillis(false);
}
return super.cancel();
}
}
public static interface DSClockTestHook {
public void suspendAtBreakPoint(int breakPoint);
public void addInformation(Object key, Object value);
public Object getInformation(Object key);
}
public DSClockTestHook getTestHook() {
return this.testHook;
}
public void setTestHook(DSClockTestHook th) {
this.testHook = th;
}
}