We have a minimal 'updater' exe that checks a remote URL for updates, downloads them and replaces files on disk prior to launching the real application. However if we want to replace the updater EXE then AFAIK we have two options:
Shadow Copying Assemblies whereby .Net will create a shadow copy of the EXE (and any referenced assemblies) and load those assemblies, such that the non-shadow assemblies can be replaced and will be used when the application is next launched.
Identify which files are replaced and rename/move them on disk. Windows seems to allow the renaming/moving of locked files, so we can move the files and copy in the new assemblies. Again, on next launching the application we will be launching the new assemblies. This approach is mentioned here
Is this second method a recommended method? Are there any pitfalls to this approach?
What about ClickOnce deployment?
Im using the second method without any problems. Just make sure the downloaded assembly was correctly downloaded. ;)
Run Update.exe and let it do this:
- download the new update.exe as update.ex_
- rename the update.exe to update.bak (you can rename it, but not overwrite it)
- rename the update.ex_ to update.exe
- restart update.exe
Im doing this with no problems at all so its tested and are running in live environment in about 400 customers as we speak.
Another option: when the main application wants to update itself, it spawns a new updater process and then closes itself. The spawned process in the meantime waits for the main application to close (the process to disappear) and then updates all of the necessary files (including the .exe). After that it simply restarts the main application and exits the updater process.
In a project i worked on, there where 2 executables. Let's call them A and B.
The only reason A existed was to start B.
So, when B (the 'real' application) downloaded an update, it was able to replace A if neccesary.
If the application was restarted (via A), A checked if B downloaded some files and replaced them before it started B.
The way we do it with our in-house app:
The application shortcut points to the updater.
- Downtime notifications/deadline messages are displayed.
- the updater performs an update check.
- Updates are downloaded and installed.
- Application is launched.
- Application performs update of the updater (checks for Updater.fp7.gz in the /update folder)
Edit: Oops - missed step 5.
I mostly agree with Stefan's Answer except for that it may not work if you want to properly deal with UAC on Windows Vista or Windows 7 and your app is properly installed under the Program Files folder or requires other dependencies to be installed that need elevated permissions.
In this case you are either doing an msi based install/patch or installing a Windows Service that runs with the necessary security to overwrite files in the Program Files folder.
The other option if your app is interactive is to do as Igor Brejc suggests and spawn a new process that does the updating which gives your app a chance to prompt to elevate permissions during the update. Using the patch or Windows Service option as mentioned above though would give a better user experience regardless of the scenario (interactive/non-interactive).
