I recently uninstalled Oracle Developer Tools for Visual Studio to try and pinpoint the source of another issue I was having. However, the uninstall failed with the following log (apparently, there was still a Visual Studio process running):

10/18/2018 2:52:09 PM - Microsoft VSIX Installer
10/18/2018 2:52:09 PM - -------------------------------------------
10/18/2018 2:52:09 PM - vsixinstaller.exe version:
10/18/2018 2:52:09 PM - 15.8.3252
10/18/2018 2:52:09 PM - -------------------------------------------
10/18/2018 2:52:09 PM - Command line parameters:

...

10/18/2018 2:52:23 PM - Pre-check verification: The following process is running and needs to be closed. Select Continue to save its current state, close it, and restart it when the installation is done:
 * vsls-agent
10/18/2018 2:52:23 PM - Pre-check verification failed with warning(s) :  VSProcessesRunning.
10/18/2018 2:52:23 PM - System.OperationCanceledException: Pre-check verification failed with warning(s) :  VSProcessesRunning.
   at Microsoft.VisualStudio.Setup.PrecheckManager.RunPrechecks(PrecheckParameters precheckParameters, VariableCollection properties)
   at Microsoft.VisualStudio.Setup.Engine.RunPrecheck(String destination, Product product, ExecuteAction action, IWindowsRestartManager rmService, ITelemetryOperation installOperation, InstallOperation install)
   at Microsoft.VisualStudio.Setup.Engine.Install(Product product, String destination, CancellationToken token)
   at Microsoft.VisualStudio.ExtensionManager.ExtensionEngineImpl.PerformSetupEngineUnInstall(IInstalledExtension extension, InstallFlags installFlags, Boolean downgrade)
   at Microsoft.VisualStudio.ExtensionManager.ExtensionEngineImpl.UninstallInternal(IInstalledExtension extension, Boolean forceDelete, Version targetedVSVersion, InstallFlags installFlags, Boolean downgrade)
   at Microsoft.VisualStudio.ExtensionManager.ExtensionEngineImpl.Uninstall(IInstalledExtension extension, InstallFlags installFlags, Version targetedVSVersion)
   at VSIXInstaller.App.UninstallExtensionFromSKU(String vsixID, SupportedVSSKU sku)
   at VSIXInstaller.App.UninstallSilently(String vsixId, IEnumerable`1 validSKUs)
   at VSIXInstaller.App.OnStartup(StartupEventArgs e)

The uninstaller did not fail gracefully and left my computer in a bad state. When I attempted to re-run the installer for Oracle Developer Tools for Visual Studio, I received the following error dialog:

Oracle Developer Tools for Visual Studio 2017 is already installed. Please uninstall and try again.

After more research, I was finally able to come up with a solution. Basically, the installer was looking to see if the Oracle.VsDevTools.15.0.vsix ins already installed. If so, it will present that error.

I had to uninstall the vsix from Visual Studio to continue. Using a great post by Rick Strahl, I was able to run the command to uninstall the vsix (you need to open the Visual Studio 2017 Command Prompt) :

vsixinstaller /a /u:"Oracle.VsDevTools.15.0"

Then, simply run the installer for Oracle Developer Tools for Visual Studio 2017 and it should run all the way through this time.