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/*
* Copyright 2011-2015 the original author or authors.
*
* 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 org.glowroot.transaction.model;
import java.io.IOException;
import java.util.List;
import javax.annotation.Nullable;
import org.glowroot.shaded.fasterxml.jackson.core.JsonGenerator;
import org.glowroot.shaded.google.common.base.Ticker;
import org.glowroot.shaded.google.common.collect.ImmutableList;
import org.glowroot.shaded.google.common.collect.Lists;
import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
import org.glowroot.shaded.slf4j.Logger;
import org.glowroot.shaded.slf4j.LoggerFactory;
import org.glowroot.api.Timer;
import org.glowroot.api.TimerName;
import org.glowroot.common.Tickers;
// instances are updated by a single thread, but can be read by other threads
// memory visibility is therefore an issue for the reading threads
//
// memory visibility could be guaranteed by making selfNestingLevel volatile
//
// selfNestingLevel is written after other fields are written and it is read before
// other fields are read, so it could be used to create a memory barrier and make the latest values
// of the other fields visible to the reading thread
//
// but benchmarking shows making selfNestingLevel non-volatile reduces timer capture overhead
// from 88 nanoseconds down to 41 nanoseconds, which is very good since System.nanoTime() takes 17
// nanoseconds and each timer capture has to call it twice
//
// the down side is that the latest updates to timers for transactions that are captured
// in-flight (e.g. partial traces and active traces displayed in the UI) may not be visible
//
// all timing data is in nanoseconds
public class TimerImpl implements Timer {
private static final Logger logger = LoggerFactory.getLogger(TimerImpl.class);
private static final Ticker ticker = Tickers.getTicker();
private final Transaction transaction;
private final @Nullable TimerImpl parent;
private final TimerNameImpl timerName;
// nanosecond rollover (292 years) isn't a concern for total time on a single transaction
private long total;
private long count;
private long startTick;
private int selfNestingLevel;
// nestedTimers is only accessed by the transaction thread so no need for volatile or
// synchronized access during timer capture which is important
//
// lazy initialize to save memory in common case where this is a leaf timer
private @MonotonicNonNull NestedTimerMap nestedTimers;
// separate list for thread safe access by other threads (e.g. partial trace capture and
// active trace viewer)
//
// lazy initialize to save memory in common case where this is a leaf timer
private volatile @MonotonicNonNull List threadSafeNestedTimers;
public static TimerImpl createRootTimer(Transaction transaction, TimerNameImpl timerName) {
return new TimerImpl(transaction, null, timerName);
}
private TimerImpl(Transaction transaction, @Nullable TimerImpl parent,
TimerNameImpl timerName) {
this.timerName = timerName;
this.parent = parent;
this.transaction = transaction;
}
// safe to be called from another thread
public void writeValue(JsonGenerator jg) throws IOException {
jg.writeStartObject();
jg.writeStringField("name", timerName.name());
if (timerName.extended()) {
// only write this rare attribute when needed
jg.writeBooleanField("extended", true);
}
boolean active = selfNestingLevel > 0;
if (active) {
// try to grab a quick, consistent view, but no guarantee on consistency since the
// transaction is active
//
// grab total before curr, to avoid case where total is updated in between
// these two lines and then "total + curr" would overstate the correct value
// (it seems better to understate the correct value if there is an update to the
// timer values in between these two lines)
long theTotal = total;
// capture startTick before ticker.read() so curr is never < 0
long theStartTick = startTick;
long curr = ticker.read() - theStartTick;
if (theTotal == 0) {
jg.writeNumberField("total", curr);
jg.writeNumberField("count", 1);
jg.writeBooleanField("active", true);
} else {
jg.writeNumberField("total", theTotal + curr);
jg.writeNumberField("count", count + 1);
jg.writeBooleanField("active", true);
}
} else {
jg.writeNumberField("total", total);
jg.writeNumberField("count", count);
}
if (threadSafeNestedTimers != null) {
ImmutableList copyOfNestedTimers;
synchronized (threadSafeNestedTimers) {
copyOfNestedTimers = ImmutableList.copyOf(threadSafeNestedTimers);
}
jg.writeArrayFieldStart("nestedTimers");
for (TimerImpl nestedTimer : copyOfNestedTimers) {
nestedTimer.writeValue(jg);
}
jg.writeEndArray();
}
jg.writeEndObject();
}
@Override
public void stop() {
if (--selfNestingLevel == 0) {
endInternal(ticker.read());
}
}
public void end(long endTick) {
if (--selfNestingLevel == 0) {
endInternal(endTick);
}
}
public TimerNameImpl getTimerName() {
return timerName;
}
public String getName() {
return timerName.name();
}
public boolean isExtended() {
return timerName.extended();
}
// only called after transaction completion
public long getTotal() {
return total;
}
// only called after transaction completion
public long getCount() {
return count;
}
// only called after transaction completion
public List getNestedTimers() {
if (threadSafeNestedTimers == null) {
return ImmutableList.of();
} else {
return threadSafeNestedTimers;
}
}
// only called by transaction thread
public TimerImpl startNestedTimer(TimerName timerName) {
// timer names are guaranteed one instance per name so pointer equality can be used
if (this.timerName == timerName) {
selfNestingLevel++;
return this;
}
long nestedTimerStartTick = ticker.read();
return startNestedTimerInternal(timerName, nestedTimerStartTick);
}
// only called by transaction thread
public TimerImpl startNestedTimer(TimerName timerName, long startTick) {
// timer names are guaranteed one instance per name so pointer equality can be used
if (this.timerName == timerName) {
selfNestingLevel++;
return this;
}
return startNestedTimerInternal(timerName, startTick);
}
public TimerImpl extend() {
TimerImpl currentTimer = transaction.getCurrentTimer();
if (currentTimer == null) {
logger.warn("extend() transaction currentTimer is null");
return this;
}
if (currentTimer == parent) {
// restarting a previously stopped execution, so need to decrement count
count--;
start(ticker.read());
return this;
}
if (currentTimer == this) {
selfNestingLevel++;
return this;
}
// otherwise can't just restart timer, so need to start an "extended" timer under the
// current timer
TimerNameImpl extendedTimer = timerName.extendedTimer();
if (extendedTimer == null) {
logger.warn("extend() should only be accessible to non-extended timers");
return this;
}
return currentTimer.startNestedTimer(extendedTimer);
}
// copy of no-arg extend() that by-passes ticker read when it is already available
public TimerImpl extend(long startTick) {
TimerImpl currentTimer = transaction.getCurrentTimer();
if (currentTimer == null) {
logger.warn("extend() transaction currentTimer is null");
return this;
}
if (currentTimer == parent) {
// restarting a previously stopped execution, so need to decrement count
count--;
start(startTick);
return this;
}
if (currentTimer == this) {
selfNestingLevel++;
return this;
}
// otherwise can't just restart timer, so need to start an "extended" timer under the
// current timer
TimerNameImpl extendedTimer = timerName.extendedTimer();
if (extendedTimer == null) {
logger.warn("extend() should only be accessible to non-extended timers");
return this;
}
return currentTimer.startNestedTimer(extendedTimer);
}
void start(long startTick) {
this.startTick = startTick;
selfNestingLevel++;
transaction.setCurrentTimer(this);
}
Transaction getTransaction() {
return transaction;
}
private void endInternal(long endTick) {
total += endTick - startTick;
count++;
transaction.setCurrentTimer(parent);
}
private TimerImpl startNestedTimerInternal(TimerName timerName, long nestedTimerStartTick) {
if (nestedTimers == null) {
nestedTimers = new NestedTimerMap();
}
TimerNameImpl timerNameImpl = (TimerNameImpl) timerName;
TimerImpl nestedTimer = nestedTimers.get(timerNameImpl);
if (nestedTimer != null) {
nestedTimer.start(nestedTimerStartTick);
return nestedTimer;
}
nestedTimer = new TimerImpl(transaction, this, timerNameImpl);
nestedTimer.start(nestedTimerStartTick);
nestedTimers.put(timerNameImpl, nestedTimer);
if (threadSafeNestedTimers == null) {
threadSafeNestedTimers = Lists.newArrayList();
}
synchronized (threadSafeNestedTimers) {
threadSafeNestedTimers.add(nestedTimer);
}
return nestedTimer;
}
}
