/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF 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 org.apache.logging.log4j.core.impl;

import java.util.List;

import org.apache.logging.log4j.Level;
import org.apache.logging.log4j.Marker;
import org.apache.logging.log4j.ThreadContext;
import org.apache.logging.log4j.core.ContextDataInjector;
import org.apache.logging.log4j.core.LogEvent;
import org.apache.logging.log4j.core.async.ThreadNameCachingStrategy;
import org.apache.logging.log4j.core.config.Property;
import org.apache.logging.log4j.core.util.Clock;
import org.apache.logging.log4j.core.util.ClockFactory;
import org.apache.logging.log4j.message.Message;
import org.apache.logging.log4j.message.TimestampMessage;
import org.apache.logging.log4j.util.StringMap;

/**
 * Garbage-free LogEventFactory that reuses a single mutable log event.
 * @since 2.6
 */
public class ReusableLogEventFactory implements LogEventFactory {
    private static final ThreadNameCachingStrategy THREAD_NAME_CACHING_STRATEGY = ThreadNameCachingStrategy.create();
    private static final Clock CLOCK = ClockFactory.getClock();

    private static ThreadLocal<MutableLogEvent> mutableLogEventThreadLocal = new ThreadLocal<>();
    private final ContextDataInjector injector = ContextDataInjectorFactory.createInjector();

    /**
     * Creates a log event.
     *
     * @param loggerName The name of the Logger.
     * @param marker An optional Marker.
     * @param fqcn The fully qualified class name of the caller.
     * @param level The event Level.
     * @param message The Message.
     * @param properties Properties to be added to the log event.
     * @param t An optional Throwable.
     * @return The LogEvent.
     */
    @Override
    public LogEvent createEvent(final String loggerName, final Marker marker,
                                final String fqcn, final Level level, final Message message,
                                final List<Property> properties, final Throwable t) {
        MutableLogEvent result = mutableLogEventThreadLocal.get();
        if (result == null || result.reserved) {
            final boolean initThreadLocal = result == null;
            result = new MutableLogEvent();

            // usually no need to re-initialize thread-specific fields since the event is stored in a ThreadLocal
            result.setThreadId(Thread.currentThread().getId());
            result.setThreadName(Thread.currentThread().getName()); // Thread.getName() allocates Objects on each call
            result.setThreadPriority(Thread.currentThread().getPriority());
            if (initThreadLocal) {
                mutableLogEventThreadLocal.set(result);
            }
        }
        result.reserved = true;
        result.clear(); // ensure any previously cached values (thrownProxy, source, etc.) are cleared

        result.setLoggerName(loggerName);
        result.setMarker(marker);
        result.setLoggerFqcn(fqcn);
        result.setLevel(level == null ? Level.OFF : level);
        result.setMessage(message);
        result.setThrown(t);
        result.setContextData(injector.injectContextData(properties, (StringMap) result.getContextData()));
        result.setContextStack(ThreadContext.getDepth() == 0 ? ThreadContext.EMPTY_STACK : ThreadContext.cloneStack());// mutable copy
        result.setTimeMillis(message instanceof TimestampMessage
                ? ((TimestampMessage) message).getTimestamp()
                : CLOCK.currentTimeMillis());
        result.setNanoTime(Log4jLogEvent.getNanoClock().nanoTime());

        if (THREAD_NAME_CACHING_STRATEGY == ThreadNameCachingStrategy.UNCACHED) {
            result.setThreadName(Thread.currentThread().getName()); // Thread.getName() allocates Objects on each call
            result.setThreadPriority(Thread.currentThread().getPriority());
        }
        return result;
    }

    /**
     * Switches the {@code reserved} flag off if the specified event is a MutableLogEvent, otherwise does nothing.
     * This flag is used internally to verify that a reusable log event is no longer in use and can be reused.
     * @param logEvent the log event to make available again
     * @since 2.7
     */
    public static void release(final LogEvent logEvent) { // LOG4J2-1583
        if (logEvent instanceof MutableLogEvent) {
            ((MutableLogEvent) logEvent).reserved = false;
        }
    }
}

@@ -839,16 +839,52 @@
 .impl;%0A%0A
+import java.lang.ref.WeakReference;%0A
 import j
@@ -898,16 +898,16 @@
 l.List;%0A
-
 %0Aimport 
@@ -1889,16 +1889,30 @@
 adLocal%3C
+WeakReference%3C
 MutableL
@@ -1919,16 +1919,17 @@
 ogEvent%3E
+%3E
  mutable
@@ -2757,16 +2757,30 @@
         
+WeakReference%3C
 MutableL
@@ -2786,19 +2786,23 @@
 LogEvent
+%3E
  re
+fRe
 sult = m
@@ -2830,24 +2830,101 @@
 ocal.get();%0A
+        MutableLogEvent result = refResult == null ? null : refResult.get();%0A
         if (
@@ -3469,24 +3469,81 @@
 eadLocal) %7B%0A
+                refResult = new WeakReference%3C%3E(result);%0A
             
@@ -3579,16 +3579,19 @@
 l.set(re
+fRe
 sult);%0A 

Use WeakReferences in org.apache.logging.log4j.core.impl.ReusableLogEventFactory