com.yahoo.vespa.curator.stats.LockStats Maven / Gradle / Ivy

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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 statsByThread = new ConcurrentHashMap<>();

    /** Modified only by Thread actually holding the lock on the path (key). */
    private final ConcurrentHashMap 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 interestingRecordings =
            new PriorityQueue<>(MAX_RECORDINGS, Comparator.comparing(RecordedLockAttempts::duration));

    private final ConcurrentHashMap 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 getLockMetricsByPath() { return Map.copyOf(metricsByLockPath); }
    public List getThreadLockStats() { return List.copyOf(statsByThread.values()); }
    public List getLockAttemptSamples() { return completedLockAttemptSamples.asList(); }

    public List 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 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);
            }
        }

    }
}