System and method for profile-based, on-the-fly optimization of library code

A system and method for profiling the execution of a software library used by an application, creating an optimized library based on the profiling, and updating to the optimized library without halting the application. The application is running using an unoptimized version of a replaceable library. The replaceable library is profiled while being used by the application and produces a set of profile data. The profile data, generated by actual execution of the replaceable library on the end-user application, is used to create an optimized version of the library. The application can then update from the unoptimized version of the library to the optimized version of the library. The invention also allows for a system with several applications, each using a different version of an optimized library simultaneously, each optimized version of the library custom optimized for the application using it.