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// Copyright Vespa.ai. 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.List;
import java.util.Map;
import java.util.Optional;
import java.util.PriorityQueue;
import java.util.concurrent.ConcurrentHashMap;
import java.util.logging.Logger;
/**
* This class manages statistics related to lock attempts on {@link com.yahoo.vespa.curator.Lock}.
*
* @author hakon
*/
public class LockStats {
private static final Logger logger = Logger.getLogger(LockStats.class.getName());
// No 'volatile' is needed because field is only ever changed for testing which is single-threaded.
private static LockStats stats = new LockStats();
private final ConcurrentHashMap<Thread, ThreadLockStats> statsByThread = new ConcurrentHashMap<>();
/** Modified only by Thread actually holding the lock on the path (key). */
private final ConcurrentHashMap<String, Thread> lockPathsHeld = new ConcurrentHashMap<>();
private final LockAttemptSamples completedLockAttemptSamples = new LockAttemptSamples(3);
// Keep recordings in a priority queue, with the smallest element having the smallest duration.
// Recordings can be large, so keep the number of recordings low.
private static final int MAX_RECORDINGS = 3;
private final Object interestingRecordingsMonitor = new Object();
private final PriorityQueue<RecordedLockAttempts> interestingRecordings =
new PriorityQueue<>(MAX_RECORDINGS, Comparator.comparing(RecordedLockAttempts::duration));
private final ConcurrentHashMap<String, LockMetrics> metricsByLockPath = new ConcurrentHashMap<>();
/** Returns global stats. */
public static LockStats getGlobal() { return stats; }
/** Returns stats tied to the current thread. */
public static ThreadLockStats getForCurrentThread() { return stats.getForThread(Thread.currentThread()); }
public static void clearForTesting() {
stats = new LockStats();
}
private LockStats() {}
public Map<String, LockMetrics> getLockMetricsByPath() { return Map.copyOf(metricsByLockPath); }
public List<ThreadLockStats> getThreadLockStats() { return List.copyOf(statsByThread.values()); }
public List<LockAttempt> getLockAttemptSamples() { return completedLockAttemptSamples.asList(); }
public List<RecordedLockAttempts> getHistoricRecordings() {
synchronized (interestingRecordingsMonitor) {
return List.copyOf(interestingRecordings);
}
}
/** Non-private for testing. */
ThreadLockStats getForThread(Thread thread) {
return statsByThread.computeIfAbsent(thread, ThreadLockStats::new);
}
/** Must be invoked only after the first and non-reentry acquisition of the lock. */
void notifyOfThreadHoldingLock(Thread currentThread, String lockPath) {
Thread oldThread = lockPathsHeld.put(lockPath, currentThread);
if (oldThread != null) {
getLockMetrics(lockPath).incrementAcquireWithoutReleaseCount();
logger.warning("Thread " + currentThread.getName() + " reports it has the lock on " +
lockPath + ", but thread " + oldThread.getName() +
" has not reported it released the lock");
}
}
/** Must be invoked only before the last and non-reentry release of the lock. */
void notifyOfThreadReleasingLock(Thread currentThread, String lockPath) {
Thread oldThread = lockPathsHeld.remove(lockPath);
if (oldThread == null) {
getLockMetrics(lockPath).incrementNakedReleaseCount();
logger.warning("Thread " + currentThread.getName() + " is releasing the lock " + lockPath +
", but nobody owns that lock");
} else if (oldThread != currentThread) {
getLockMetrics(lockPath).incrementForeignReleaseCount();
logger.warning("Thread " + currentThread.getName() +
" is releasing the lock " + lockPath + ", but it was owned by thread " +
oldThread.getName());
}
}
/**
* Returns the ThreadLockStats holding the lock on the path, but the info may be outdated already
* on return, either no-one holds the lock or another thread may hold the lock.
*/
Optional<ThreadLockStats> getThreadLockStatsHolding(String lockPath) {
return Optional.ofNullable(lockPathsHeld.get(lockPath)).map(statsByThread::get);
}
LockMetrics getLockMetrics(String lockPath) {
return metricsByLockPath.computeIfAbsent(lockPath, __ -> new LockMetrics());
}
void maybeSample(LockAttempt lockAttempt) {
completedLockAttemptSamples.maybeSample(lockAttempt);
}
void reportNewStoppedRecording(RecordedLockAttempts recording) {
synchronized (interestingRecordings) {
if (interestingRecordings.size() < MAX_RECORDINGS) {
interestingRecordings.add(recording);
} else if (recording.duration().compareTo(interestingRecordings.peek().duration()) > 0) {
// peek() retrieves the smallest element according to the PriorityQueue's
// comparator.
interestingRecordings.poll();
interestingRecordings.add(recording);
}
}
}
}
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