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Fix thread safety issues within BasicStatusManager #851

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Fix thread safety issues within BasicStatusManager #851

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27 changes: 17 additions & 10 deletions logback-core/src/main/java/ch/qos/logback/core/BasicStatusManager.java
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Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
/**
* Logback: the reliable, generic, fast and flexible logging framework.
* Copyright (C) 1999-2015, QOS.ch. All rights reserved.
* Copyright (C) 1999-2024, QOS.ch. All rights reserved.
*
* This program and the accompanying materials are dual-licensed under
* either the terms of the Eclipse Public License v1.0 as published by
Expand All @@ -15,6 +15,8 @@

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.LongAdder;

import ch.qos.logback.core.helpers.CyclicBuffer;
import ch.qos.logback.core.spi.LogbackLock;
Expand All @@ -28,14 +30,14 @@ public class BasicStatusManager implements StatusManager {
public static final int MAX_HEADER_COUNT = 150;
public static final int TAIL_SIZE = 150;

int count = 0;
final LongAdder count = new LongAdder();

// protected access was requested in http://jira.qos.ch/browse/LBCORE-36
final protected List<Status> statusList = new ArrayList<Status>();
final protected CyclicBuffer<Status> tailBuffer = new CyclicBuffer<Status>(TAIL_SIZE);
final protected LogbackLock statusListLock = new LogbackLock();

int level = Status.INFO;
final AtomicInteger level = new AtomicInteger(Status.INFO);

// protected access was requested in http://jira.qos.ch/browse/LBCORE-36
final protected List<StatusListener> statusListenerList = new ArrayList<StatusListener>();
Expand All @@ -57,10 +59,15 @@ public void add(Status newStatus) {
// LBCORE-72: fire event before the count check
fireStatusAddEvent(newStatus);

count++;
if (newStatus.getLevel() > level) {
level = newStatus.getLevel();
}
count.increment();
int newLevel = newStatus.getLevel();
int currentLevel;
do {
currentLevel = level.get();
if (newLevel <= currentLevel) {
break;
}
} while (!level.compareAndSet(currentLevel, newLevel));
Comment on lines +62 to +70
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How about

synchronized (statusListLock) {
      count++;
       if (newStatus.getLevel() > level) {
           level = newStatus.getLevel();
       }
       if (statusList.size() < MAX_HEADER_COUNT) {
          statusList.add(newStatus);
      } else {
          tailBuffer.add(newStatus);
      }
  }

The code might be more simple.

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Yes, we certainly could take advantage of the existing lock that's going to be taken out.

However, for correctness, the reads would also need to use the same lock:

    public int getLevel() {
        synchronized (statusListLock) {
            return level;
        }
    }

    public int getCount() {
        synchronized (statusListLock) {
            return count;
        }
    }

Otherwise the fields would need to be made volatile:

    volatile int count = 0;
    volatile int level = Status.INFO;

It also occurred to me that perhaps the level should be reset when the count is reset:

    public void clear() {
        synchronized (statusListLock) {
            count = 0;
            level = Level.INFO;
            statusList.clear();
            tailBuffer.clear();
        }
    }


synchronized (statusListLock) {
Comment on lines +62 to 72
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Here's an alternate approach to CAS

Suggested change
count.increment();
int newLevel = newStatus.getLevel();
int currentLevel;
do {
currentLevel = level.get();
if (newLevel <= currentLevel) {
break;
}
} while (!level.compareAndSet(currentLevel, newLevel));
synchronized (statusListLock) {
synchronized (statusListLock) {
count.increment();
int newLevel = newStatus.getLevel();
if (newLevel > level.get()) {
level.set(newLevel);
}

if (statusList.size() < MAX_HEADER_COUNT) {
Expand Down Expand Up @@ -90,18 +97,18 @@ private void fireStatusAddEvent(Status status) {

public void clear() {
synchronized (statusListLock) {
count = 0;
count.reset();
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Should level be reset as well?

Suggested change
count.reset();
count.reset();
level.set(Status.INFO);

statusList.clear();
tailBuffer.clear();
}
}

public int getLevel() {
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@mches mches Oct 26, 2024 •
edited
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Should StatusManager#getLevel() be uncommented?

package ch.qos.logback.core.status;
…
public interface StatusManager {
…
    /**
     * Return the highest level of all the statii.
     * 
     * @return
     */
    // int getLevel();
…
}

Should @Override be added to all implemented methods? (Available since Java 6)

See also #845

return level;
return level.get();
}

public int getCount() {
return count;
return count.intValue();
}

/**
Expand Down