High CPU due to threads looping in OutputBuffer.realWriteChars

Issue

• We're seeing JBoss consumes high CPU and the thread dumps and CPU data indicates that the high consuming threads are always in some point of the OutputBuffer.realWriteChars method and its underlying char to byte conversions and buffer flushes, for example:

  "ajp-127.0.0.1-8009-1" daemon prio=10 tid=0x00002aabd4fb2000 nid=0x7a6 runnable [0x00002b24a1517000]
     java.lang.Thread.State: RUNNABLE
          at sun.nio.cs.ISO_8859_1$Encoder.encodeArrayLoop(ISO_8859_1.java:148)
          at sun.nio.cs.ISO_8859_1$Encoder.encodeLoop(ISO_8859_1.java:187)
          at java.nio.charset.CharsetEncoder.encode(CharsetEncoder.java:544)
          at org.apache.tomcat.util.buf.C2BConverter.convert(C2BConverter.java:91)
          at org.apache.catalina.connector.OutputBuffer.realWriteChars(OutputBuffer.java:465)
          at org.apache.tomcat.util.buf.CharChunk.flushBuffer(CharChunk.java:440)
          at org.apache.tomcat.util.buf.CharChunk.append(CharChunk.java:295)
          at org.apache.catalina.connector.OutputBuffer.write(OutputBuffer.java:499)
          at org.apache.catalina.connector.CoyoteWriter.write(CoyoteWriter.java:143)
          at org.apache.jasper.runtime.JspWriterImpl.flushBuffer(JspWriterImpl.java:119)
          at org.apache.jasper.runtime.JspWriterImpl.write(JspWriterImpl.java:326)