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icacheprovider-getcachekey-method.md

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ICacheProvider::GetCacheKey Method
Describes the ICacheProvider::GetCacheKey method and provides the method's syntax, return value, remarks, notes for implementers, an example, and requirements.
10/07/2016
557ae36c-12e4-cbda-4178-67c3620067c6

ICacheProvider::GetCacheKey Method

Returns the cache key for the cache provider.

Syntax

virtual IHttpCacheKey* GetCacheKey(  
   VOID  
) const = 0;

Parameters

This method takes no parameters.

Return Value

A pointer to an IHttpCacheKey for the cache provider.

Remarks

CGlobalModule derived classes that register for GL_CACHE_OPERATION events receive an ICacheProvider pointer as a parameter on the CGlobalModule::OnGlobalCacheOperationvirtual method. You can retrieve an IHttpCacheKey pointer by calling the GetCacheKey method on the ICacheProvider pointer.

Notes for Implementers

ICacheProvider implementers are responsible for memory management with this data; therefore, ICacheProvider implementers that use dynamic memory allocation must release or call delete on the IHttpCacheKey pointer when it is no longer needed.

The following table is a sample of one-to-one interface mappings that must be returned from the GetCacheKey and GetCacheRecord methods from the same implementer of the ICacheProvider interface.

GetCacheKey interface GetCacheRecord interface
IFileKey IHttpFileInfo
IHttpTokenKey IHttpTokenEntry
IHttpCacheKey IHttpCacheSpecificData

Notes for Callers

ICacheProvider implementers are responsible for memory management with this data; therefore, ICacheProvider clients must not release or call delete on the returned IHttpCacheKey pointer when this data is no longer needed.

In some cases, an IHttpCacheSpecificData pointer returned from GetCacheRecord may be downcast to a more specific interface to access extended behavior. Call the GetCacheKey method to retrieve the IHttpCacheKey pointer, and then call the IHttpCacheKey::GetCacheName method to retrieve the name of the cache. The following table is a sample of values returned from GetCacheName and the corresponding interface to which the current IHttpCacheSpecificData pointer may then be safely downcast, assuming an otherwise correct downcast procedure takes place. See IIS Caching Constants for constant values.

GetCacheName value Interface
FILE IHttpFileInfo
TOKEN IHttpTokenEntry

Caution

Before performing any downcast operation, always verify that the cast is correct to guarantee correct program behavior.

Note

Consider using the dynamic_cast operator whenever possible when you perform a downcast operation.

Example

The following code example demonstrates how to create a global module that listens for GL_CACHE_OPERATION and GL_CACHE_CLEANUP events and then writes the ICacheProvider information to the Event Viewer.

Caution

[!INCLUDEiisver] generates a large number of events in the Event Viewer. To avoid a log overflow error in a production environment, you should generally avoid writing cache information to the event log. For demonstration purposes, this code example writes an entry to the Event Viewer in debug mode only.

[!code-cppICacheProvider#2]

For more information on how to create and deploy a native DLL module, see Walkthrough: Creating a Request-Level HTTP Module By Using Native Code.

The above code writes new events to the application log of the Event Viewer, where the Data box contains XML similar to the following (depending on the IHttpCacheKey type).

<cacheProvider>  
    <uriKey />  
</cacheProvider>  

<cacheProvider>  
    <tokenKey />  
</cacheProvider>  

<cacheProvider>  
   <fileKey />  
</cacheProvider>

You can optionally compile the code by using the __stdcall (/Gz) calling convention instead of explicitly declaring the calling convention for each function.

Requirements

Type Description
Client - IIS 7.0 on [!INCLUDEwinvista]
- IIS 7.5 on Windows 7
- IIS 8.0 on Windows 8
- IIS 10.0 on Windows 10
Server - IIS 7.0 on [!INCLUDEwinsrv2008]
- IIS 7.5 on Windows Server 2008 R2
- IIS 8.0 on Windows Server 2012
- IIS 8.5 on Windows Server 2012 R2
- IIS 10.0 on Windows Server 2016
Product - IIS 7.0, IIS 7.5, IIS 8.0, IIS 8.5, IIS 10.0
- [!INCLUDEiisexp75], [!INCLUDEiisexp80], [!INCLUDEiisexp100]
Header Httpserv.h

See Also

ICacheProvider Interface