JBoss EAP 5.1.2 is hung with many AJP threads waiting on HTTPS connection to remote service

Issue

Users were getting “Service Unavailable” Error in JBoss EAP 5.1.2

AJP threads are waiting on a backend connection. The thread dumps are below:

"ajp-10.229.71.144-8109-299" daemon prio=10 tid=0x00002b643c3cd800 nid=0x1ea6 runnable [0x00002b646a7fa000]
   java.lang.Thread.State: RUNNABLE
    at java.net.SocketInputStream.socketRead0(Native Method)
    at java.net.SocketInputStream.read(SocketInputStream.java:129)
    at com.sun.net.ssl.internal.ssl.InputRecord.readFully(InputRecord.java:293)
    at com.sun.net.ssl.internal.ssl.InputRecord.read(InputRecord.java:331)
    at com.sun.net.ssl.internal.ssl.SSLSocketImpl.readRecord(SSLSocketImpl.java:798)
    - locked <0x00000007065849f0> (a java.lang.Object)
    at com.sun.net.ssl.internal.ssl.SSLSocketImpl.performInitialHandshake(SSLSocketImpl.java:1138)
    - locked <0x00000007065849b0> (a java.lang.Object)
    at com.sun.net.ssl.internal.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1165)
    at com.sun.net.ssl.internal.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1149)
    at sun.net.www.protocol.https.HttpsClient.afterConnect(HttpsClient.java:434)
    at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(AbstractDelegateHttpsURLConnection.java:166)
    at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1177)
    - locked <0x0000000706583f88> (a sun.net.www.protocol.https.DelegateHttpsURLConnection)
    at sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java:234)
    - locked <0x0000000706583f10> (a sun.net.www.protocol.https.HttpsURLConnectionImpl)
    at org.apache.taglibs.standard.tag.common.core.ImportSupport.acquireReader(ImportSupport.java:348)
    at org.apache.taglibs.standard.tag.common.core.ImportSupport.acquireString(ImportSupport.java:259)
    at org.apache.taglibs.standard.tag.common.core.ImportSupport.doEndTag(ImportSupport.java:179)
    at org.apache.jsp.activation.handsetIdentifier_jsp._jspx_meth_c_005fimport_005f0(handsetIdentifier_jsp.java:1113)
    at org.apache.jsp.activation.handsetIdentifier_jsp._jspx_meth_c_005fcatch_005f0(handsetIdentifier_jsp.java:1078)
    at org.apache.jsp.activation.handsetIdentifier_jsp._jspx_meth_c_005fif_005f0(handsetIdentifier_jsp.java:1045)
    at org.apache.jsp.activation.handsetIdentifier_jsp._jspx_meth_c_005fotherwise_005f0(handsetIdentifier_jsp.java:1012)
    at org.apache.jsp.activation.handsetIdentifier_jsp._jspx_meth_c_005fchoose_005f0(handsetIdentifier_jsp.java:956)
    at org.apache.jsp.activation.handsetIdentifier_jsp._jspService(handsetIdentifier_jsp.java:226)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:369)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:322)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:249)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:638)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:444)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:382)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:310)
    at org.apache.struts.action.RequestProcessor.doForward(RequestProcessor.java:1069)
    at org.apache.struts.action.RequestProcessor.processForwardConfig(RequestProcessor.java:455)
    at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:279)
    at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482)
    at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:507)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:235)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:183)
    at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:95)
    at org.jboss.web.tomcat.security.SecurityContextEstablishmentValve.process(SecurityContextEstablishmentValve.java:126)
    at org.jboss.web.tomcat.security.SecurityContextEstablishmentValve.invoke(SecurityContextEstablishmentValve.java:70)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
    at org.jboss.web.tomcat.service.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:158)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:330)
    at org.apache.coyote.ajp.AjpProcessor.process(AjpProcessor.java:436)
    at org.apache.coyote.ajp.AjpProtocol$AjpConnectionHandler.process(AjpProtocol.java:384)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:451)
    at java.lang.Thread.run(Thread.java:662)