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Native Image Service 

The native image service is a Windows service that generates and maintains native images. The native image service allows the developer to defer the installation and update of native images to periods when the computer is idle.

Normally, the native image service is initiated by the installation program (installer) for an application or update. For priority 3 actions, the service executes during idle time on the computer. The service saves its state and is capable of continuing through multiple reboots if necessary. Multiple image compilations can be queued.

The service also interacts with the manual Ngen.exe command. Manual commands take precedence over background activity.

Launching Deferred Operations

Before beginning an installation or upgrade, pausing the service is recommended. This ensures that the service does not execute while the installer is copying files or putting assemblies in the global assembly cache. The following Ngen.exe command line pauses the service:

ngen queue pause

When all deferred operations have been queued, the following command allows the service to resume:

ngen queue continue

To defer native image generation when installing a new application or when updating a shared component, use the /queue option with the install or update actions. The following Ngen.exe command lines install a native image for a shared component and perform an update of all roots that may have been affected:

ngen install MyComponent /queue
ngen update /queue

The update action regenerates all native images that have been invalidated, not just those that use MyComponent.

If your application consists of many roots, you can control the priority of the deferred actions. The following commands queue the installation of three roots. Assembly1 is installed first, without waiting for idle time. Assembly2 is also installed without waiting for idle time, but after all priority 1 actions have completed. Assembly3 is installed when the service detects that the computer is idle.

ngen install Assembly1 /queue:1
ngen install Assembly2 /queue:2
ngen install Assembly3 /queue:3

You can force queued actions to occur synchronously by using the executeQueuedItems action. If you supply the optional priority, this action affects only the queued actions that have equal or lower priority. The default priority is 3, so the following Ngen.exe command processes all queued actions immediately, and does not return until they are finished:

ngen executeQueuedItems

Synchronous commands are executed by Ngen.exe and do not use the native image service. You can execute actions using Ngen.exe while the native image service is running.

Service Shutdown

After being initiated by the execution of an Ngen.exe command that includes the /queue option, the service runs in the background until all actions have been completed. The service saves its state so that it can continue through multiple reboots if necessary. When the service detects that there are no more actions queued, it resets its status so that it will not restart the next time the computer is booted, and then it shuts itself down.

Service Interaction with Clients

In the .NET Framework version 2.0, the only interaction with the native image service is through the command-line tool Ngen.exe. Use the command-line tool in installation scripts to queue actions for the native image service and to interact with the service.

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