com.couchbase.client.core.deps.org.LatencyUtils.SimplePauseDetector Maven / Gradle / Ivy
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/**
* Written by Gil Tene of Azul Systems, and released to the public domain,
* as explained at http://creativecommons.org/publicdomain/zero/1.0/
*/
package com.couchbase.client.core.deps.org.LatencyUtils;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;
/**
* A Simple PauseDetector that detects pauses using a consensus observation across a configurable number of
* detection thread. Detection threads can be set to periodically wakeup or continually spin.
*
* All times and time units are in nanoseconds
*/
public class SimplePauseDetector extends PauseDetector {
// All times and time units are in nanoseconds
private final static long DEFAULT_SleepInterval = 1000000L; // 1 msec
private final static long DEFAULT_PauseNotificationThreshold = 1000000L; // 1 msec
private final static int DEFAULT_NumberOfDetectorThreads = 3;
private final static boolean DEFAULT_Verbose = false;
private final long sleepInterval;
private final long pauseNotificationThreshold;
final AtomicLong consensusLatestTime = new AtomicLong();
private volatile long stallThreadMask = 0;
private volatile long stopThreadMask = 0;
private final SimplePauseDetectorThread detectors[];
private boolean verbose;
/**
* Creates a SimplePauseDetector
* @param sleepInterval sleep interval used by detector threads
* @param pauseNotificationThreshold minimum threshold for reporting detected pauses
* @param numberOfDetectorThreads number of consensus detector threads to use
*/
public SimplePauseDetector(long sleepInterval, long pauseNotificationThreshold,
int numberOfDetectorThreads) {
this(sleepInterval, pauseNotificationThreshold, numberOfDetectorThreads, false);
}
/**
* Creates a SimplePauseDetector
* @param sleepInterval sleep interval used by detector threads
* @param pauseNotificationThreshold minimum threshold for reporting detected pauses
* @param numberOfDetectorThreads number of consensus detector threads to use
* @param verbose provide verbose output when pauses are detected
*/
public SimplePauseDetector(long sleepInterval, long pauseNotificationThreshold,
int numberOfDetectorThreads, boolean verbose) {
this.sleepInterval = sleepInterval;
this.pauseNotificationThreshold = pauseNotificationThreshold;
this.verbose = verbose;
detectors = new SimplePauseDetectorThread[numberOfDetectorThreads];
for (int i = 0 ; i < numberOfDetectorThreads; i++) {
detectors[i] = new SimplePauseDetectorThread(i);
detectors[i].start();
}
}
/**
* Creates a SimplePauseDetector with a default sleep interval (1 msec), a default pause notification threshold
* (1 msec), and using the default number of consensus detection threads (3).
*/
public SimplePauseDetector() {
this(DEFAULT_SleepInterval, DEFAULT_PauseNotificationThreshold,
DEFAULT_NumberOfDetectorThreads, DEFAULT_Verbose);
}
public void setVerbose(boolean verbose) {
this.verbose = verbose;
}
/**
* Shut down the pause detector operation and terminate it's threads.
*/
@Override
public void shutdown() {
stopThreadMask = 0xffffffffffffffffL;
for (SimplePauseDetectorThread detector : detectors) {
detector.interrupt();
}
super.shutdown();
}
private class SimplePauseDetectorThread extends Thread {
volatile long observedLasUpdateTime;
final int threadNumber;
final long threadMask;
SimplePauseDetectorThread(final int threadNumber) {
if ((threadNumber < 0) || (threadNumber > 63)) {
throw new IllegalArgumentException("threadNumber must be between 0 and 63.");
}
this.threadNumber = threadNumber;
this.threadMask = 1 << threadNumber;
this.setDaemon(true);
this.setName("SimplePauseDetectorThread_" + threadNumber);
}
public void run() {
long shortestObservedTimeAroundLoop = Long.MAX_VALUE;
observedLasUpdateTime = consensusLatestTime.get();
long now = TimeServices.nanoTime();
long prevNow = now;
consensusLatestTime.compareAndSet(observedLasUpdateTime, now);
while ((stopThreadMask & threadMask) == 0) {
if (sleepInterval != 0) {
TimeServices.sleepNanos(sleepInterval);
}
// This is ***TEST FUNCTIONALITY***: Spin as long as we are externally asked to stall:
while ((stallThreadMask & threadMask) != 0);
observedLasUpdateTime = consensusLatestTime.get();
// Volatile store above makes sure new "now" is measured after observedLasUpdateTime sample
now = TimeServices.nanoTime();
// Track shortest time around loop:
shortestObservedTimeAroundLoop = Math.min(now - prevNow, shortestObservedTimeAroundLoop);
// Update consensus time as long as it is is the past:
while (now > observedLasUpdateTime) {
if (consensusLatestTime.compareAndSet(observedLasUpdateTime, now)) {
// Successfully and atomically moved consensus time forward. Act on the known delta:
final long deltaTimeNs = now - observedLasUpdateTime;
// Calculate hiccup time (accounting for known time around loop):
long hiccupTime = Math.max(deltaTimeNs - shortestObservedTimeAroundLoop, 0);
if (hiccupTime > pauseNotificationThreshold) {
if (verbose) {
System.out.println("SimplePauseDetector thread " + threadNumber +
": sending pause notification message: pause of " + hiccupTime +
" nsec detected at nanoTime: " + now);
}
notifyListeners(hiccupTime, now);
}
} else {
// Failed to atomically move consensus time forward. Try again with current value:
observedLasUpdateTime = consensusLatestTime.get();
}
}
prevNow = now;
}
if (verbose) {
System.out.println("SimplePauseDetector thread " + threadNumber + " terminating...");
}
}
}
/**
* A test method that allows the caller to artificially stall a requested set of the detector threads for
* a given amount of time. Used to verify pause detection when consensus occurs, as well as lack of detection
* when it does not.
* @param threadNumberMask a mask designating which threads should be stalled.
* @param stallLength stall length, in nanosecond units
* @throws InterruptedException if internal sleep implementation throws it
*/
public void stallDetectorThreads(long threadNumberMask, long stallLength) throws InterruptedException {
long savedMask = stallThreadMask;
stallThreadMask = threadNumberMask;
long startTime = TimeServices.nanoTime();
long endTime = startTime + stallLength;
for (long remainingTime = stallLength;
remainingTime > 0;
remainingTime = endTime - TimeServices.nanoTime()) {
long timeDelta = Math.min(remainingTime, (pauseNotificationThreshold / 2));
TimeServices.moveTimeForward(timeDelta);
TimeUnit.NANOSECONDS.sleep(50000); // give things a chance to propagate.
}
stallThreadMask = savedMask;
}
/**
* A test method that allows the caller to artificially move the consensus observed time forward
* without causing a pause to be detected as a result of the time skip. Useful for test programs
* that wish to use artificial time services.
* @param newConsensusTime time to skip to
*/
public void skipConsensusTimeTo(long newConsensusTime) {
consensusLatestTime.set(newConsensusTime);
}
}