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According to the Java API \[[API 2006|AA. Bibliography#API 06]\] Class {{Runtime}}, method {{addShutdownHook}}:

A shutdown hook is simply an initialized but unstarted thread. When the virtual machine begins its shutdown sequence it will start all registered shutdown hooks in some unspecified order and let them run concurrently. When all the hooks have finished it will then run all uninvoked finalizers if finalization-on-exit has been enabled. Finally, the virtual machine will halt. Once the shutdown sequence has begun it can be stopped only by invoking the halt method, which forcibly terminates the virtual machine. Once the shutdown sequence has begun it is impossible to register a new shutdown hook or de-register a previously-registered hook.

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• Hook threads should be light-weight and simple
• They should be thread safe
• They should hold locks when accessing data and release them when done

• Wiki Markup
  They should not rely on system services as the services themselves may be shutting down (for example, the logger may shutdown from another hook). Instead of one service it may be better to run a series of shutdown tasks from one thread by using a single shutdown hook. \[[Goetz 2006|AA. Bibliography#Goetz 06]\].

This compliant solution shows the standard method to install a hook.

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It is still possible for the JVM to abort because of external issues, such as an external SIGKILL signal (UNIX) or the TerminateProcess call (Microsoft Windows), or memory corruption caused by native methods. In such cases, it is not guaranteed that the hooks will execute as expected.

Exceptions

*EXC09-EX1:* It is permissible for a command line utility to call {{System.exit()}} or terminate prematurely,; for example, when the required number of arguments are not input. \[[Bloch 2008|AA. Bibliography#Bloch 08]\] and \[[ESA 2005|AA. Bibliography#ESA 05]\].

Risk Assessment

Allowing inadvertent calls to System.exit() may lead to denial of service.

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