PostSharp.Samples.CustomCaching

Caching your method's return value makes the method execution faster, trading memory for time by storing the return value in a cache. If you call the method again then you can return a value stored in the cache, instead of doing time consuming calculation all over again.

Typical candidates for caching are methods talking to snail-paced counterparts like databases or web services.

You can add the Cache aspect to any method with a return value.

When you call a method decorated by the Cache for the first time then the method calculates a return value and the Cache aspect stores the return value in a cache. The execution flow looks like this:

1. OnEntry method calculates a cache key and stores the cache key in MethodExecutionTag.
2. Cache aspect passes the execution to the decorated method which calculates the return value.
3. OnSuccess method reads the cache key from MethodExecutionTag and stores the return value in the cache.

When you call the method for the second time then the Cache aspect returns the cached return value. The execution flow looks like this:

1. OnEntry method reads the return value from the cache, stores the value ReturnValue and sets FlowBehavior to FlowBehavior.Return.
2. FlowBehavior.Return terminates decorated method execution without doing the time consuming calculation.
3. The decorated method returns the cached value.

MethodExecutionTag provides a communication channel between different events (OnEntry, OnSuccess in this example). You can store any state information MethodExecutionTag. Both OnEntry and OnSuccess methods requires the cache key. The Cache uses MethodExecutionTag to pass cache key from OnEntry method to OnSuccess method and to avoid calculating the cache key twice.

Limitations

This example is purely educational. It has the following limitations:

• Simplistic algorithm to compute the cache key.
• No cache eviction.
• Not optimized for run-time performance.
• MemoryCache only.
• No dependency management.