In a Java application, is it a good idea to use a shutdown hook to auto-update the app?

Question

The idea is to check for updates while the application is running. The update consists of one main jar and a couple of third party jars. If updates are available:

Download them
Put them in a temp directory
Add a shutdown hook that replaces all the actual jars with the jars from the temp directory

Is this a good idea?

if you prior ask the user for confirmation, **YES** is a good idea... ;) — Jordi Castilla, Oct 07 '15 at 09:02

score 1 · Accepted Answer · answered Oct 07 '15 at 09:35

1

No. From the Javadoc:

Shutdown hooks should also finish their work quickly. When a program invokes exit the expectation is that the virtual machine will promptly shut down and exit. When the virtual machine is terminated due to user logoff or system shutdown the underlying operating system may only allow a fixed amount of time in which to shut down and exit. It is therefore inadvisable to attempt any user interaction or to perform a long-running computation in a shutdown hook.

Ergo you should not engage in long-running or blocking activities in a shutdown hook.

answered Oct 07 '15 at 09:35

user207421

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Is copying a couple of (small) files from a temporary directory to another considered a long-running activity? Note that this does not include the download time as the updates were already downloaded before the shutdown and put in this temp directory. – Chadi Oct 07 '15 at 10:04
In addition, we had issues with the update of the main JAR on Windows and Java 8 (file being in use). We finally opted for a safer, already done solution: [getdown](https://github.com/threerings/getdown/). – Chadi Jan 04 '16 at 15:09

score 0 · Answer 2 · edited Jun 20 '20 at 09:12

0

If you want a well reliable system around shutDown hook then its not a good idea due to following guidelines :-
a) Shutdown Hooks may not be executed on certain scenarios.
b) Once started, the shutdown hooks can be forcibly stopped before completion.
c) If defined more than one shutdown hooks, their execution order is not guaranteed.
d) Can't register/unregister Shutdown Hooks with in Shutdown Hooks.

In a Java application, is it a good idea to use a shutdown hook to auto-update the app?

2 Answers2