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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.vespa.curator.stats;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.PriorityQueue;
/**
* Collection containing "interesting" {@code LockAttempt}s.
*
* @author hakon
*/
// @ThreadSafe
public class LockAttemptSamples {
private final int maxSamples;
/** Ensure atomic operations on this collection. */
private final Object monitor = new Object();
/** Keep at most one sample for each lock path. */
private final Map<String, LockAttempt> byLockPath;
/**
* Priority queue containing all samples. The head of this queue (peek()/poll())
* returns the LockAttempt with the smallest duration.
*/
private final PriorityQueue<LockAttempt> priorityQueue =
new PriorityQueue<>(Comparator.comparing(LockAttempt::getStableTotalDuration));
LockAttemptSamples(int maxSamples) {
this.maxSamples = maxSamples;
this.byLockPath = new HashMap<>(maxSamples);
}
int size() { return byLockPath.size(); }
boolean maybeSample(LockAttempt lockAttempt) {
final boolean added;
synchronized (monitor) {
if (shouldAdd(lockAttempt)) {
byLockPath.put(lockAttempt.getLockPath(), lockAttempt);
priorityQueue.add(lockAttempt);
added = true;
} else {
added = false;
}
}
if (added) {
// Unnecessary to invoke under synchronized, although it means that some samples
// may be without stack trace (just retry if that happens).
lockAttempt.fillStackTrace();
}
return added;
}
private boolean shouldAdd(LockAttempt lockAttempt) {
LockAttempt existingLockAttempt = byLockPath.get(lockAttempt.getLockPath());
if (existingLockAttempt != null) {
if (hasLongerDurationThan(lockAttempt, existingLockAttempt)) {
byLockPath.remove(existingLockAttempt.getLockPath());
priorityQueue.remove(existingLockAttempt);
return true;
}
return false;
}
if (size() < maxSamples) {
return true;
}
// peek() and poll() retrieves the smallest element.
existingLockAttempt = priorityQueue.peek(); // cannot be null
if (hasLongerDurationThan(lockAttempt, existingLockAttempt)) {
priorityQueue.poll();
byLockPath.remove(existingLockAttempt.getLockPath());
return true;
}
return false;
}
List<LockAttempt> asList() {
synchronized (monitor) {
return List.copyOf(byLockPath.values());
}
}
private static boolean hasLongerDurationThan(LockAttempt lockAttempt, LockAttempt otherLockAttempt) {
// Use stable total duration to avoid messing up priority queue.
return lockAttempt.getStableTotalDuration().compareTo(otherLockAttempt.getStableTotalDuration()) > 0;
}
}
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