cpp-lru-decorator

Header only LRU decorator for C++03 and C++1x based on boost::bimaps (algorithm heavily based on Tim Day's work: http://timday.bitbucket.org/lru.html).

It let you can simply change function signature to add LRU cache to a function or method.

Features

• Simple to use and revert.
• Automatically remember combination of arguments to return cached result.
• Header only.
• Support multithreading via simply define LRU_DEFAULT_LOCK_LEVEL.
• User defined types (class, struct) are also supported, not limited to primitive types.

Usage

• For normal function, use LRU_DECL# and LRU_CACHED# macro where # is parameter number. For example, int f(char v1, float v2) changes to LRU_DECL2(int, f, char, float) and LRU_CACHED2(int, f, char, float).
• For method, only LRU_CACHED# macro required.
• #define LRU_DEFAULT_LOCK_LEVEL if required; 0 means no lock used, 1 means object level lock used, 2 is class level lock. Default value is 1 for safety. If you run a single-threaded program, you can use 0 to improve performance.
• For every function, capacity is default to 4096, you can define LRU_DEFAULT_CAPACITY to change it.

Example:

#include "LRU.hpp"

//int Fib(int n) // This is oringnal function signature, you simply change it to:
LRU_DECL1(int, Fib, int, n)
LRU_CACHED1(int, Fib, int, n)
{
 if(n == 0)
  return 0;
 
 if(n == 1)
  return 1;
 
 return Fib(n - 1) + Fib(n - 2);
}

On my machine (Intel i5 2400 3.10GHz), orignal Fib(50) run 93.18 seconds, LRU cached version run 0.002 seconds.

Example2: (method)

#include "LRU.hpp"

struct A
{
 // int Method1(int p) // Only LRU_CACHED required.
 LRU_CACHED1(int, Method1, int, p)
 {
  // ... implemetation.
 }
};

Limitations

• Maximum 10 parameters supported.
• Return type void is not supported. (LRU expects cache the result, if no result, no cache required.)
• Function without parameter is not supported. (Without the parameter, a function supposes to return the same result every time, you can do a simple cache by yourself.)
• Parameters must support default/copy constructor and hashable (almost all standard and user defined types are fulfilled).
• Tested with Boost 1.43, Microsoft Visual Studio 2010 and GCC 4.4. Higher version of Boost, Visual Studio and GCC should work also.