make childrenList initialize early

Signed-off-by: Wenjun Ruan <wenjun@apache.org>

logback-classic/src/main/java/ch/qos/logback/classic/Logger.java

@@ -67,15 +67,15 @@ public final class Logger
     /**
      * The children of this logger. A logger may have zero or more children.
      */
-    transient private List<Logger> childrenList;
+    private final transient List<Logger> childrenList = new CopyOnWriteArrayList<>();
 
     /**
      * It is assumed that once the 'aai' variable is set to a non-null value, it
      * will never be reset to null. it is further assumed that only place where the
      * 'aai variable is set is within the addAppender method. This method is
      * synchronized on 'this' (Logger) protecting against simultaneous
      * re-configuration of this logger (a very unlikely scenario).
-     *
+     * 
      * <p>
      * It is further assumed that the AppenderAttachableImpl is responsible for its
      * internal synchronization and thread safety. Thus, we can get away with *not*
@@ -130,9 +130,6 @@ private boolean isRootLogger() {
     }
 
     Logger getChildByName(final String childName) {
-        if (childrenList == null) {
-            return null;
-        }
         for (final Logger child : childrenList) {
             if (childName.equals(child.getName())) {
                 return child;
@@ -159,11 +156,9 @@ public synchronized void setLevel(Level newLevel) {
             effectiveLevelInt = newLevel.levelInt;
         }
 
-        if (childrenList != null) {
-            for (Logger childLogger : childrenList) {
-                // tell child to handle parent levelInt change
-                childLogger.handleParentLevelChange(effectiveLevelInt);
-            }
+        for (Logger childLogger : childrenList) {
+            // tell child to handle parent levelInt change
+            childLogger.handleParentLevelChange(effectiveLevelInt);
         }
         // inform listeners
         loggerContext.fireOnLevelChange(this, newLevel);
@@ -182,10 +177,8 @@ private synchronized void handleParentLevelChange(int newParentLevelInt) {
             effectiveLevelInt = newParentLevelInt;
 
             // propagate the parent levelInt change to this logger's children
-            if (childrenList != null) {
-                for (Logger childLogger : childrenList) {
-                    childLogger.handleParentLevelChange(newParentLevelInt);
-                }
+            for (Logger childLogger : childrenList) {
+                childLogger.handleParentLevelChange(newParentLevelInt);
             }
         }
     }
@@ -241,7 +234,7 @@ public Appender<ILoggingEvent> getAppender(String name) {
 
     /**
      * Invoke all the appenders of this logger.
-     *
+     * 
      * @param event The event to log
      */
     public void callAppenders(ILoggingEvent event) {
@@ -280,11 +273,11 @@ public boolean detachAppender(Appender<ILoggingEvent> appender) {
      * Create a child of this logger by suffix, that is, the part of the name
      * extending this logger. For example, if this logger is named "x.y" and the
      * lastPart is "z", then the created child logger will be named "x.y.z".
-     *
+     * 
      * <p>
      * IMPORTANT: Calls to this method must be within a synchronized block on this
      * logger.
-     *
+     * 
      * @param lastPart the suffix (i.e. last part) of the child logger name. This
      *                 parameter may not include dots, i.e. the logger separator
      *                 character.
@@ -297,9 +290,6 @@ Logger createChildByLastNamePart(final String lastPart) {
                     "Child name [" + lastPart + " passed as parameter, may not include [" + CoreConstants.DOT + "]");
         }
 
-        if (childrenList == null) {
-            childrenList = new CopyOnWriteArrayList<Logger>();
-        }
         Logger childLogger;
         if (this.isRootLogger()) {
             childLogger = new Logger(lastPart, this, this.loggerContext);
@@ -324,9 +314,6 @@ void recursiveReset() {
         detachAndStopAllAppenders();
         localLevelReset();
         additive = true;
-        if (childrenList == null) {
-            return;
-        }
         for (Logger childLogger : childrenList) {
             childLogger.recursiveReset();
         }
@@ -339,9 +326,6 @@ synchronized Logger createChildByName(final String childName) {
                     + " passed as parameter, may not include '.' after index" + (this.name.length() + 1));
         }
 
-        if (childrenList == null) {
-            childrenList = new CopyOnWriteArrayList<>();
-        }
         final Logger childLogger = new Logger(childName, this, this.loggerContext);
         childrenList.add(childLogger);
         childLogger.effectiveLevelInt = this.effectiveLevelInt;
@@ -729,11 +713,11 @@ public String toString() {
     /**
      * Method that calls the attached TurboFilter objects based on the logger and
      * the level.
-     *
+     * 
      * It is used by isYYYEnabled() methods.
-     *
+     * 
      * It returns the typical FilterReply values: ACCEPT, NEUTRAL or DENY.
-     *
+     * 
      * @param level
      * @return the reply given by the TurboFilters
      */
@@ -743,7 +727,7 @@ private FilterReply callTurboFilters(Marker marker, Level level) {
 
     /**
      * Return the context for this logger.
-     *
+     * 
      * @return the context
      */
     public LoggerContext getLoggerContext() {
@@ -752,7 +736,7 @@ public LoggerContext getLoggerContext() {
 
     /**
      * Creates a {@link LoggingEventBuilder} of type {@link DefaultLoggingEventBuilder}.
-     *
+     * 
      * @since 1.3
      */
     @Override
@@ -806,7 +790,7 @@ public void log(org.slf4j.event.LoggingEvent slf4jEvent) {
      * After serialization, the logger instance does not know its LoggerContext. The
      * best we can do here, is to return a logger with the same name returned by
      * org.slf4j.LoggerFactory.
-     *
+     * 
      * @return Logger instance with the same name
      * @throws ObjectStreamException
      */