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Java example source code file (ResourceLeakDetector.java)

This example Java source code file (ResourceLeakDetector.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

atomicboolean, default_level, default_sampling_interval, defaultresourceleak, jvm, level, max_records, override, prop_level, resourceleakdetector, stack_trace_element_exclusions, stacktraceelement, string, stringbuilder, threading, threads, util

The ResourceLeakDetector.java Java example source code

/*
 * Copyright 2013 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */

package io.netty.util;

import io.netty.util.internal.MathUtil;
import io.netty.util.internal.PlatformDependent;
import io.netty.util.internal.SystemPropertyUtil;
import io.netty.util.internal.logging.InternalLogger;
import io.netty.util.internal.logging.InternalLoggerFactory;

import java.lang.ref.PhantomReference;
import java.lang.ref.ReferenceQueue;
import java.util.ArrayDeque;
import java.util.Deque;
import java.util.EnumSet;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.atomic.AtomicBoolean;

import static io.netty.util.internal.StringUtil.EMPTY_STRING;
import static io.netty.util.internal.StringUtil.NEWLINE;
import static io.netty.util.internal.StringUtil.simpleClassName;

public class ResourceLeakDetector<T> {

    private static final String PROP_LEVEL_OLD = "io.netty.leakDetectionLevel";
    private static final String PROP_LEVEL = "io.netty.leakDetection.level";
    private static final Level DEFAULT_LEVEL = Level.SIMPLE;

    private static final String PROP_MAX_RECORDS = "io.netty.leakDetection.maxRecords";
    private static final int DEFAULT_MAX_RECORDS = 4;
    private static final int MAX_RECORDS;

    /**
     * Represents the level of resource leak detection.
     */
    public enum Level {
        /**
         * Disables resource leak detection.
         */
        DISABLED,
        /**
         * Enables simplistic sampling resource leak detection which reports there is a leak or not,
         * at the cost of small overhead (default).
         */
        SIMPLE,
        /**
         * Enables advanced sampling resource leak detection which reports where the leaked object was accessed
         * recently at the cost of high overhead.
         */
        ADVANCED,
        /**
         * Enables paranoid resource leak detection which reports where the leaked object was accessed recently,
         * at the cost of the highest possible overhead (for testing purposes only).
         */
        PARANOID
    }

    private static Level level;

    private static final InternalLogger logger = InternalLoggerFactory.getInstance(ResourceLeakDetector.class);

    static {
        final boolean disabled;
        if (SystemPropertyUtil.get("io.netty.noResourceLeakDetection") != null) {
            disabled = SystemPropertyUtil.getBoolean("io.netty.noResourceLeakDetection", false);
            logger.debug("-Dio.netty.noResourceLeakDetection: {}", disabled);
            logger.warn(
                    "-Dio.netty.noResourceLeakDetection is deprecated. Use '-D{}={}' instead.",
                    PROP_LEVEL, DEFAULT_LEVEL.name().toLowerCase());
        } else {
            disabled = false;
        }

        Level defaultLevel = disabled? Level.DISABLED : DEFAULT_LEVEL;

        // First read old property name
        String levelStr = SystemPropertyUtil.get(PROP_LEVEL_OLD, defaultLevel.name()).trim().toUpperCase();

        // If new property name is present, use it
        levelStr = SystemPropertyUtil.get(PROP_LEVEL, levelStr).trim().toUpperCase();
        Level level = DEFAULT_LEVEL;
        for (Level l: EnumSet.allOf(Level.class)) {
            if (levelStr.equals(l.name()) || levelStr.equals(String.valueOf(l.ordinal()))) {
                level = l;
            }
        }

        MAX_RECORDS = SystemPropertyUtil.getInt(PROP_MAX_RECORDS, DEFAULT_MAX_RECORDS);

        ResourceLeakDetector.level = level;
        if (logger.isDebugEnabled()) {
            logger.debug("-D{}: {}", PROP_LEVEL, level.name().toLowerCase());
            logger.debug("-D{}: {}", PROP_MAX_RECORDS, MAX_RECORDS);
        }
    }

    // Should be power of two.
    private static final int DEFAULT_SAMPLING_INTERVAL = 128;

    /**
     * @deprecated Use {@link #setLevel(Level)} instead.
     */
    @Deprecated
    public static void setEnabled(boolean enabled) {
        setLevel(enabled? Level.SIMPLE : Level.DISABLED);
    }

    /**
     * Returns {@code true} if resource leak detection is enabled.
     */
    public static boolean isEnabled() {
        return getLevel().ordinal() > Level.DISABLED.ordinal();
    }

    /**
     * Sets the resource leak detection level.
     */
    public static void setLevel(Level level) {
        if (level == null) {
            throw new NullPointerException("level");
        }
        ResourceLeakDetector.level = level;
    }

    /**
     * Returns the current resource leak detection level.
     */
    public static Level getLevel() {
        return level;
    }

    /** the linked list of active resources */
    private final DefaultResourceLeak head = new DefaultResourceLeak(null);
    private final DefaultResourceLeak tail = new DefaultResourceLeak(null);

    private final ReferenceQueue<Object> refQueue = new ReferenceQueue();
    private final ConcurrentMap<String, Boolean> reportedLeaks = PlatformDependent.newConcurrentHashMap();

    private final String resourceType;
    private final int samplingInterval;
    private final int mask;
    private final long maxActive;
    private long active;
    private final AtomicBoolean loggedTooManyActive = new AtomicBoolean();

    private long leakCheckCnt;

    public ResourceLeakDetector(Class<?> resourceType) {
        this(simpleClassName(resourceType));
    }

    public ResourceLeakDetector(String resourceType) {
        this(resourceType, DEFAULT_SAMPLING_INTERVAL, Long.MAX_VALUE);
    }

    public ResourceLeakDetector(Class<?> resourceType, int samplingInterval, long maxActive) {
        this(simpleClassName(resourceType), samplingInterval, maxActive);
    }

    public ResourceLeakDetector(String resourceType, int samplingInterval, long maxActive) {
        if (resourceType == null) {
            throw new NullPointerException("resourceType");
        }
        if (samplingInterval <= 0) {
            throw new IllegalArgumentException("samplingInterval: " + samplingInterval + " (expected: 1+)");
        }
        if (maxActive <= 0) {
            throw new IllegalArgumentException("maxActive: " + maxActive + " (expected: 1+)");
        }

        this.resourceType = resourceType;
        this.samplingInterval = MathUtil.findNextPositivePowerOfTwo(samplingInterval);
        // samplingInterval is a power of two so we calculate a mask that we can use to
        // check if we need to do any leak detection or not.
        mask = this.samplingInterval - 1;
        this.maxActive = maxActive;

        head.next = tail;
        tail.prev = head;
    }

    /**
     * Creates a new {@link ResourceLeak} which is expected to be closed via {@link ResourceLeak#close()} when the
     * related resource is deallocated.
     *
     * @return the {@link ResourceLeak} or {@code null}
     */
    public ResourceLeak open(T obj) {
        Level level = ResourceLeakDetector.level;
        if (level == Level.DISABLED) {
            return null;
        }

        if (level.ordinal() < Level.PARANOID.ordinal()) {
            if ((leakCheckCnt ++ & mask) == 0) {
                reportLeak(level);
                return new DefaultResourceLeak(obj);
            } else {
                return null;
            }
        } else {
            reportLeak(level);
            return new DefaultResourceLeak(obj);
        }
    }

    private void reportLeak(Level level) {
        if (!logger.isErrorEnabled()) {
            for (;;) {
                @SuppressWarnings("unchecked")
                DefaultResourceLeak ref = (DefaultResourceLeak) refQueue.poll();
                if (ref == null) {
                    break;
                }
                ref.close();
            }
            return;
        }

        // Report too many instances.
        int samplingInterval = level == Level.PARANOID? 1 : this.samplingInterval;
        if (active * samplingInterval > maxActive && loggedTooManyActive.compareAndSet(false, true)) {
            reportInstancesLeak(resourceType);
        }

        // Detect and report previous leaks.
        for (;;) {
            @SuppressWarnings("unchecked")
            DefaultResourceLeak ref = (DefaultResourceLeak) refQueue.poll();
            if (ref == null) {
                break;
            }

            ref.clear();

            if (!ref.close()) {
                continue;
            }

            String records = ref.toString();
            if (reportedLeaks.putIfAbsent(records, Boolean.TRUE) == null) {
                if (records.isEmpty()) {
                    reportUntracedLeak(resourceType);
                } else {
                    reportTracedLeak(resourceType, records);
                }
            }
        }
    }

    /**
     * This method is called when a traced leak is detected. It can be overridden for tracking how many times leaks
     * have been detected.
     */
    protected void reportTracedLeak(String resourceType, String records) {
        logger.error(
                "LEAK: {}.release() was not called before it's garbage-collected. " +
                "See http://netty.io/wiki/reference-counted-objects.html for more information.{}",
                resourceType, records);
    }

    /**
     * This method is called when an untraced leak is detected. It can be overridden for tracking how many times leaks
     * have been detected.
     */
    protected void reportUntracedLeak(String resourceType) {
        logger.error("LEAK: {}.release() was not called before it's garbage-collected. " +
                "Enable advanced leak reporting to find out where the leak occurred. " +
                "To enable advanced leak reporting, " +
                "specify the JVM option '-D{}={}' or call {}.setLevel() " +
                "See http://netty.io/wiki/reference-counted-objects.html for more information.",
                resourceType, PROP_LEVEL, Level.ADVANCED.name().toLowerCase(), simpleClassName(this));
    }

    /**
     * This method is called when instance leaks are detected. It can be overridden for tracking how many times leaks
     * have been detected.
     */
    protected void reportInstancesLeak(String resourceType) {
        logger.error("LEAK: You are creating too many " + resourceType + " instances.  " +
                resourceType + " is a shared resource that must be reused across the JVM," +
                "so that only a few instances are created.");
    }

    private final class DefaultResourceLeak extends PhantomReference<Object> implements ResourceLeak {
        private final String creationRecord;
        private final Deque<String> lastRecords = new ArrayDeque();
        private final AtomicBoolean freed;
        private DefaultResourceLeak prev;
        private DefaultResourceLeak next;
        private int removedRecords;

        DefaultResourceLeak(Object referent) {
            super(referent, referent != null? refQueue : null);

            if (referent != null) {
                Level level = getLevel();
                if (level.ordinal() >= Level.ADVANCED.ordinal()) {
                    creationRecord = newRecord(null, 3);
                } else {
                    creationRecord = null;
                }

                // TODO: Use CAS to update the list.
                synchronized (head) {
                    prev = head;
                    next = head.next;
                    head.next.prev = this;
                    head.next = this;
                    active ++;
                }
                freed = new AtomicBoolean();
            } else {
                creationRecord = null;
                freed = new AtomicBoolean(true);
            }
        }

        @Override
        public void record() {
            record0(null, 3);
        }

        @Override
        public void record(Object hint) {
            record0(hint, 3);
        }

        private void record0(Object hint, int recordsToSkip) {
            if (creationRecord != null) {
                String value = newRecord(hint, recordsToSkip);

                synchronized (lastRecords) {
                    int size = lastRecords.size();
                    if (size == 0 || !lastRecords.getLast().equals(value)) {
                        lastRecords.add(value);
                    }
                    if (size > MAX_RECORDS) {
                        lastRecords.removeFirst();
                        ++removedRecords;
                    }
                }
            }
        }

        @Override
        public boolean close() {
            if (freed.compareAndSet(false, true)) {
                synchronized (head) {
                    active --;
                    prev.next = next;
                    next.prev = prev;
                    prev = null;
                    next = null;
                }
                return true;
            }
            return false;
        }

        @Override
        public String toString() {
            if (creationRecord == null) {
                return EMPTY_STRING;
            }

            final Object[] array;
            final int removedRecords;
            synchronized (lastRecords) {
                array = lastRecords.toArray();
                removedRecords = this.removedRecords;
            }

            StringBuilder buf = new StringBuilder(16384).append(NEWLINE);
            if (removedRecords > 0) {
                buf.append("WARNING: ")
                .append(removedRecords)
                .append(" leak records were discarded because the leak record count is limited to ")
                .append(MAX_RECORDS)
                .append(". Use system property ")
                .append(PROP_MAX_RECORDS)
                .append(" to increase the limit.")
                .append(NEWLINE);
            }
            buf.append("Recent access records: ")
            .append(array.length)
            .append(NEWLINE);

            if (array.length > 0) {
                for (int i = array.length - 1; i >= 0; i --) {
                    buf.append('#')
                       .append(i + 1)
                       .append(':')
                       .append(NEWLINE)
                       .append(array[i]);
                }
            }

            buf.append("Created at:")
               .append(NEWLINE)
               .append(creationRecord);

            buf.setLength(buf.length() - NEWLINE.length());
            return buf.toString();
        }
    }

    private static final String[] STACK_TRACE_ELEMENT_EXCLUSIONS = {
            "io.netty.util.ReferenceCountUtil.touch(",
            "io.netty.buffer.AdvancedLeakAwareByteBuf.touch(",
            "io.netty.buffer.AbstractByteBufAllocator.toLeakAwareBuffer(",
            "io.netty.buffer.AdvancedLeakAwareByteBuf.recordLeakNonRefCountingOperation("
    };

    static String newRecord(Object hint, int recordsToSkip) {
        StringBuilder buf = new StringBuilder(4096);

        // Append the hint first if available.
        if (hint != null) {
            buf.append("\tHint: ");
            // Prefer a hint string to a simple string form.
            if (hint instanceof ResourceLeakHint) {
                buf.append(((ResourceLeakHint) hint).toHintString());
            } else {
                buf.append(hint);
            }
            buf.append(NEWLINE);
        }

        // Append the stack trace.
        StackTraceElement[] array = new Throwable().getStackTrace();
        for (StackTraceElement e: array) {
            if (recordsToSkip > 0) {
                recordsToSkip --;
            } else {
                String estr = e.toString();

                // Strip the noisy stack trace elements.
                boolean excluded = false;
                for (String exclusion: STACK_TRACE_ELEMENT_EXCLUSIONS) {
                    if (estr.startsWith(exclusion)) {
                        excluded = true;
                        break;
                    }
                }

                if (!excluded) {
                    buf.append('\t');
                    buf.append(estr);
                    buf.append(NEWLINE);
                }
            }
        }

        return buf.toString();
    }
}




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