Answer: 1. Open MPI is a large project containing many different sub-systems and a relatively large code base. Let's first cover some fundamental terminology in order to make the rest of the discussion easier. Open MPI has three sections of code: * OMPI: The MPI API and supporting logic * ORTE: The Open Run-Time Environment (support for different back-end run-time systems) * OPAL: The Open Portable Access Layer (utility and "glue" code used by OMPI and ORTE) There are strict abstraction barriers in the code between these sections. That is, they are compiled into three separate libraries: libmpi, liborte, and libopal with a strict dependency order: OMPI depends on ORTE and OPAL, and ORTE depends on OPAL. More specifically, OMPI executables are linked with: shell$ mpicc myapp.c -o myapp # This actually turns into: shell$ cc myapp.c -o myapp -lmpi -lopen-rte -lopen-pal ... More system-level libraries may listed after -lopal, but you get the idea. Strictly speaking, these are not "layers" in the classic software engineering sense (even though it is convenient to refer to them as such). They are listed above in dependency order, but that does not mean that, for example, the OMPI code must go through the ORTE and OPAL code in order to reach the operating system or a network interface. As such, this code organization more reflects abstractions and software engineering, not a strict hierarchy of functions that must be traversed in order to reach lower layer. For example, OMPI can call OPAL functions directly -- it does not have to go through ORTE. Indeed, OPAL has a different set of purposes than ORTE, so it wouldn't even make sense to channel all OPAL access through ORTE. OMPI can also directly call the operating system as necessary. For example, many top-level MPI API functions are quite performance sensitive; it would not make sense to force them to traverse an abritrarily deep call stack just to move some bytes across a network. Here's a list of terms that are frequently used in discussions about the Open MPI code base: * MCA: The Modular Component Architecture (MCA) is the foundation upon which the entire Open MPI project is built. It provides all the component architecture services that the rest of the system use. Although it is the fundamental heart of the system, it's implementation is actually quite small and lightweight -- it is nothing like CORBA, COM, JINI, or many other well-known component architectures. It was designed for HPC -- meaning that it is small, fast, and resonably efficient -- and therefore offers few services other finding, loading, and unloading components. * Framework: An MCA framework is a construct that is created for a single, targeted purpose. It provides a public interface that is used by external code, but it also its own internal services. A list of Open MPI frameworks is available here. An MCA framework uses the MCA's services to find and load components at run time -- implementations of the framework's interface. An easy example framework to discuss is the MPI framework named "btl", or the Byte Transfer Layer. It is used to sends and receive data on different kinds of networks. Hence, Open MPI has btl components for shared memory, TCP, Infiniband, Myrinetc, etc. * Component: An MCA component is an implementation of a framework's interface. Another common word for component is "plugin." It is a standalone collection of code that can be bundled into a plugin that can be inserted into the Open MPI code base, either at run-time and/or compile-time. * Module: An MCA module is an instance of a component (in the C++ sense of the word "instance"; an MCA component is analogous to a C++ class). For example, if a node running an Open MPI application has multiple ethernet NICs, the Open MPI application will contain one TCP btl component, but two TCP btl modules. This difference between components and modules is important becaue modules have private state; components do not. Frameworks, components, and modules can be dynamic or static. That is, they can be available as plugins or they may be compiled statically into libraries (e.g., libmpi).

Answer: 2. Yes. In early 2006, Cisco hosted an Open MPI workshop where the Open MPI Team provided several days of intensive dive-into-the-code tutorials. The slides from these tutorials are available here. Additionally, an OpenRTE (ORTE) workshop was held for similar purposes in late 2006. The slides from the ORTE workshop are available here.