How layer prioritization works

Products

• Workspace Virtualization (formerly SVS)

Issue/Introduction

 

Resolution

How layer prioritization works

The Workspace Virtualization Agent assigns an HKCR priority to each layer. If a system request applies to more than one activated layer, the system uses the layer with the highest HKCR priority. If two activated layers have the same HKCR priority, you cannot predict which layer the system request accesses. To resolve this problem, you can set a layer's HKCR priority.

Prioritization works as follows:

• If two virtualized applications are registered to open a file type, it determines which layer opens that file type.

  For example, you have activated layers for two different Web browser applications. Both applications are registered to open HTML files. You can assign a higher priority to one of the layers so that it is used to open the HTML files.

• If two virtualized applications use different versions of the same DLL file, it determines which layer's DLL file appears in the Windows directory.

For each system request, the Workspace Virtualization Agent does the following in order:

• Builds a list of activated layers.

• Assigns each layer a priority value.

• Orders a list of activated layers based on these priorities.

HKCR (HKEY_CLASSES_ROOT) requests are based on file type. For example, the system would make an HKEY_CLASSES_ROOT request if a user clicked on a text file. If the request involves a process, the Workspace Virtualization Agent also takes into consideration the owner layer of a process. The owner layer of a process is the layer that houses the executable file that starts the process. The owner layer of a child process is the same as the owner layer of its parent process. The owner is the same even if the executable file that starts the child process is in a different layer.

The following table lists the default priority values assigned by Workspace Virtualization (the lowest numerical value representing the highest priority):

Table: Layer priority values

Type of Request	Description	Default Priority
Normal owner	Priority of the layer's registry entries from the perspective of an application running from that layer.	55.5 highest
Normal	Priority of the layer's registry entries from the perspective of an application running outside the layer.	65.5
Base owner	Priority of the base's registry entries from the perspective of an application running from the base.	75.5
Base	Priority of the base's registry entries from the perspective of an application running from a layer.	85.5 lowest

For example, you have an activated layer for Firefox with Internet Explorer installed on the base layer. When you open an HTML file, the Workspace Virtualization Agent does the following in order:

• Builds a list of all activated layers and the base.

• Assigns the following priorities:

  • 65.5 to the Firefox layer

  • 85.5 to the Internet Explorer

• Launches Firefox because it has the highest priority.