At $work, we have a lot of java processes that are ran via cron and other wrappers that do some pretty critical tasks. The apps have been written so that the whole thing is wrapped in a try/catch that will call system.exit(1) should something not go right. Our wrapper scripts watch for a non-zero exit code, and alert Nagios if something went wrong. This works great except for when a VM encounters an outOfMemory exception (OOM). The Java VM attempts to continue on, but if the main thread hits this exception, the entire VM will exit. However, the application code that exits with a status of 1 never gets called, so the application ends up dying with a status of 0. Well, Sun (Oracle now I guess) gave us a new option in Java 6 that was backported to 1.4.2_12 and up that allows us to tell Java to run a shell command when it encounters an OOM exception. By adding the option
-XX:OnOutOfMemoryError="kill -9 %p"
to our Java command line, the VM will execute a shell that calls the kill command, with an argument of the PID of the VM. The -9 option to kill will cause the VM to exit with a non-zero status, so that our wrappers will pick up the error and alert the right people. Note: this feature was never backported to Java5 - sorry!