DO NOT REPLY [Bug 23019] New: - NullPointerException in RollingFileAppender when called by AsyncAppender

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http://nagoya.apache.org/bugzilla/show_bug.cgi?id=23019

NullPointerException in RollingFileAppender when called by AsyncAppender

           Summary: NullPointerException in RollingFileAppender when called
                    by AsyncAppender
           Product: Log4j
           Version: 1.2
          Platform: Other
        OS/Version: Other
            Status: NEW
          Severity: Normal
          Priority: Other
         Component: Appender
        AssignedTo: [EMAIL PROTECTED]
        ReportedBy: [EMAIL PROTECTED]


Log4j Version: 1.2.2

The subAppend(...) method in org.apache.log4j.WriterAppender throws in very 
rare cases a NullPointerException when used with an AsyncAppender. This occured 
during a loadtest with heavy load, only after many hours of opperation and with 
number of parallel requests more than 100 (120 simulated users with LoadRunner).

There seems to be a running condition, where the string array returned by 
loggingEvent.getThrowableStrRep() is not properly filled up when used 
immediately after above call. The string array was created (check for non-null 
successfull), but the elements of that array was (in rare conditions) null at 
one moment and non-null some ms later. Trace output and modified code see below.

The appender attached to the AsyncAppender is an own implementation deriving 
from RollingFileAppender. 

To find out the location where the NullPointerException is thrown, the 
WriterAppender class has been complemented with additional trace statements:

  protected
  void subAppend(LoggingEvent event) {
    try {
    this.qw.write(this.layout.format(event));
    } catch (NullPointerException e) {
      System.out.println("WriterAppender.subAppend: this.qw.write
(this.layout.format(event))");
      throw e;
    }

    int len = -1;
    int i = -1;
    String[] s = null;
    String line = null;
    try {
      if(layout.ignoresThrowable()) {
        s = event.getThrowableStrRep();
        if (s != null) {
          len = s.length;
          for(i = 0; i < len; i++) {
            line = s[i];
            this.qw.write(line);
            this.qw.write(Layout.LINE_SEP);
          }
        }
      }
    } catch (NullPointerException e) {
      System.out.println("WriterAppender.subAppend: len="+len+", i="+i);
      System.out.println("  line="+line);
      if ((s != null) && (i>=0))
        System.out.println("  s[i]="+s[i]);
      ThrowableInformation ti = event.getThrowableInformation();
      if (ti != null)
        System.out.println("  event.throwableInfo.wasCloned="+ti.wasCloned());
      throw e;
    }

    try {
      if(this.immediateFlush) {
        this.qw.flush();
      }
    } catch (NullPointerException e) {
      System.out.println("WriterAppender.subAppend: flush");
      throw e;
    }
  }


This resulted in following trace output:

WriterAppender.subAppend: len=40, i=0
  line=null
  s[i]=com.frontwerks.jdf.net.BrokerException: Cannot get a socket connection, 
cannot invoke the request
  event.throwableInfo.wasCloned=false
---> TRACE-ERROR: could not append event: 
[EMAIL PROTECTED]
java.lang.NullPointerException
        at java.io.Writer.write(Unknown Source)
        at org.apache.log4j.helpers.CountingQuietWriter.write
(CountingQuietWriter.java:36)
        at org.apache.log4j.WriterAppender.subAppend(WriterAppender.java:316)
        at org.apache.log4j.RollingFileAppender.subAppend
(RollingFileAppender.java:225)
        at org.apache.log4j.WriterAppender.append(WriterAppender.java:151)
        at org.apache.log4j.AppenderSkeleton.doAppend(AppenderSkeleton.java:222)
        .....
        at org.apache.log4j.helpers.AppenderAttachableImpl.appendLoopOnAppenders
(AppenderAttachableImpl.java:58)
        at org.apache.log4j.Dispatcher.run(AsyncAppender.java:326)

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