IHttpCacheSpecificData::DecrementTTL Method

Article
05/20/2022

Decrements the Time-to-Live (TTL) setting of the cached data.

Syntax

virtual VOID DecrementTTL(  
   OUT BOOL* pfTTLExpired  
) = 0;

Parameters

pfTTLExpired
[OUT] true to indicate that the TTL count has reached 0; otherwise, false.

Thread Safety

Classes that implement the IHttpCacheSpecificData interface are thread safe for the DecrementTTL and ResetTTL methods.

Remarks

The pfTTLExpired parameter must not be NULL; otherwise, the DecrementTTL method will cause an access violation in some implementations.

The TTL setting specifies when cached data is no longer valid and, therefore, when that data should be reloaded. Most IHttpCacheSpecificData implementations set an initial internal count to a positive value and then allow that count to be reduced through successive calls to the DecrementTTL method. If the TTL value becomes 0, the data should be reloaded.

The behavior of DecrementTTL is implementation specific. You should use the following information as a guideline, but it may not be correct in all scenarios:

Classes that implement the IHttpCacheSpecificData or IHttpTokenEntry interfaces initialize the internal count to 2 at construction and decrement that count by 1 on each call to DecrementTTL.
Classes that implement the IHttpFileInfo interface are varied. Some classes implement the scheme defined above, while others perform empty operations on both the ResetTTL and DecrementTTL methods.

Notes for Implementers

The DecrementTTL and ResetTTL method implementations must be thread safe for an IHttpCacheSpecificData pointer.

Notes for Callers

Most callers may disregard the DecrementTTL method, because this method is meant to be used internally.

Example

The following code example demonstrates a class called MySpecificData that implements the IHttpCacheSpecificData methods.

class MySpecificData : public IHttpCacheSpecificData  
{  
public:  
    MySpecificData()  
    {  
        m_ttl = 2;  
    }  
  
    virtual ~MySpecificData()  
    {  
        m_ttl = 0;  
    }  
  
    virtual VOID ResetTTL(VOID)  
    {  
        m_ttl = 2;  
    }  
  
    virtual VOID DecrementTTL(BOOL* pfTTLExpired)  
    {  
        *pfTTLExpired = (InterlockedDecrement(&m_ttl) == 0);  
    }  
  
private:  
    LONG m_ttl;  
};

Requirements

Type	Description
Client	- IIS 7.0 on Windows Vista - IIS 7.5 on Windows 7 - IIS 8.0 on Windows 8 - IIS 10.0 on Windows 10
Server	- IIS 7.0 on Windows Server 2008 - 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 - IIS Express 7.5, IIS Express 8.0, IIS Express 10.0
Header	Httpserv.h

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