Running algorithms in compiled C/C++ code within a Java/PHP/Python framework?
For Java, you can search JNI (Java Native Interface), there're a lot of guides telling how to use it.
Occasionally, I have come across programming techniques that involve creating application frameworks or websites in Java, PHP or Python, but when complex algorithms are needed, writing those out in C or C++ and running them as API-like function calls within your Java/PHP/Python code.
I have been googling and searching around the net for this, and unless I don't know the name of the practice, I can't seem to find anything on it.
To put simply, how can I:

Create functions or classes in C or C++
Compile them into a DLL/binary/some form
Run the functions from - 

Java
PHP
Python

I suspect JSON/XML like output and input must be created between the Java/PHP/Python and the C/C++ function so the data can be easily bridged, but that is okay.

I'm just not sure how to approach this technique, but it seems like a very smart way to take advantage of the great features of Java, PHP, and Python while at the same time utilizing the very fast programming languages for large, complex tasks.
The other thought going through my head is if I am creating functions using only literals in Java/PHP/Python, will it go nearly as fast as C anyway?
The specific tasks I'm looking to work with C/C++ on is massive loops, pinging a database, and analyzing maps. No work has started yet, its all theory now.