We often have scenarios where we need nimble restarts for our web applications. (The reason for the restarts can be quite creative - from stale file handles to it being a strategy to deal with leaky libraries). Let's take Tomcat as our container. In most cases, we rely on our catalina.sh stop force to bring our application to a halt and then we proceed to start. Internally, catalina.sh stop force, does a kill -9 on the $CATALINA_PID. However, the kill itself is not synchronous, even the kill -9 will halt if there is a kernel thread that is doing some operation. A snippet as suggested from the references which can work is something like
kill with the 0 signal seems to be a special signal which can be used to check if the process is up. It returns 0 (a good return code) if it is able to signal to the other process and returns 1 if it can't (either due to invalid PID or due to insufficient permissions). I have seen the while loop when using the regular stop in catalina.sh, however, when forced, it only does the kill -9 and sometimes it takes a non-trivial amount of time (say 10 secs) to completely halt. Was wondering if it would make sense for tomcat to include it in its stop force section also? Have logged a bugzilla ticket for it as an enhancement to Tomcat.
References:
kill-9 $CATALINA_PID; while kill -0 $CATALINA_PID 2>/dev/null; do sleep 1; donekill with the 0 signal seems to be a special signal which can be used to check if the process is up. It returns 0 (a good return code) if it is able to signal to the other process and returns 1 if it can't (either due to invalid PID or due to insufficient permissions). I have seen the while loop when using the regular stop in catalina.sh, however, when forced, it only does the kill -9 and sometimes it takes a non-trivial amount of time (say 10 secs) to completely halt. Was wondering if it would make sense for tomcat to include it in its stop force section also? Have logged a bugzilla ticket for it as an enhancement to Tomcat.
References:
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