Logstash silently stops processing events and does not respond to SIGTERM

Thanks for the reply...The symptom has manifested after barely one hour...I'd love to troubleshoot this while in this state....

ps -ef |grep logstash |grep java

logstash 1110 1 99 09:08 ? 13:27:08 java -XX:+UseParNewGC -XX:+UseConcMarkSweepGC -Djava.awt.headless=true -XX:CMSInitiatingOccupancyFraction=75 -XX:+UseCMSInitiatingOccupancyOnly -Djava.io.tmpdir=/var/lib/logstash -Xmx2g -Xss2048k -Djffi.boot.library.path=/opt/logstash/vendor/jruby/lib/jni -XX:+UseParNewGC -XX:+UseConcMarkSweepGC -Djava.awt.headless=true -XX:CMSInitiatingOccupancyFraction=75 -XX:+UseCMSInitiatingOccupancyOnly -Djava.io.tmpdir=/var/lib/logstash -Xbootclasspath/a:/opt/logstash/vendor/jruby/lib/jruby.jar -classpath : -Djruby.home=/opt/logstash/vendor/jruby -Djruby.lib=/opt/logstash/vendor/jruby/lib -Djruby.script=jruby -Djruby.shell=/bin/sh org.jruby.Main --1.9 /opt/logstash/lib/bootstrap/environment.rb logstash/runner.rb agent -f /etc/logstash/conf.d -l /var/log/logstash/logstash.log -w 6

type logstash_open_logs

logstash_open_logs is a function
logstash_open_logs ()
{
lsof -p $(ps ax |grep java |grep logstash |awk '{print $1}') | LC_ALL="C" LC_ALL="C" grep --color=auto --color=auto "syslog-ng" | awk '{print $NF}'
}

logstash_open_logs |wc -l

385

top -b -n1 |head

top - 12:25:48 up 62 days, 29 min, 10 users, load average: 0.01, 0.07, 0.33
Tasks: 232 total, 1 running, 231 sleeping, 0 stopped, 0 zombie
%Cpu(s): 5.0 us, 0.8 sy, 25.7 ni, 68.3 id, 0.1 wa, 0.0 hi, 0.1 si, 0.0 st
KiB Mem : 8011104 total, 146784 free, 5940436 used, 1923884 buff/cache
KiB Swap: 1679356 total, 1346700 free, 332656 used. 1642880 avail Mem

ps -efT |grep logstash |grep java |wc -l

176