Welcome to the Mochi project

The Mochi project is a collaboration between Argonne National Laboratory, Los Alamos National Laboratory, Carnegie Mellon University, and the HDF Group. The objective of this project is to explore a software defined storage approach for composing storage services that provides new levels of functionality, performance, and reliability for science applications at extreme scale.

This website gathers documentation and tutorials for the main libraries used or developed in the context of the Mochi project: Margo, Thallium, Argobots, and Mercury.

The Mochi libraries

Margo is a C library enabling the development of distributed HPC services. It relies on Mercury for RPC/RDMA, and Argobots for threading/tasking, hidding the complexity of these two libraries under a simple programming model.

Thallium is a C++14 library wrapping Margo and enabling the development of the same sort of services using all the power of modern C++. It is the recommended library for C++ developers. Note that Thallium also provides C++ wrappers to Argobots.

Mercury is Mochi’s underlying RPC/RDMA library. While it is not necessary to understand how to use Mercury itself when developing with Margo or Thallium (which we recommend), we provide a set of tutorials for those who would need to use it directly rather than through higher level libraries.

Argobots is used for threading/tasking in Mochi. Understanding its underlying programming model may not be necessary at first, for simple Margo or Thallium services, but may become useful to optimize performance or customize the scheduling and placement of threads and tasks in a Mochi service.


The tutorials for each of these libraries are independent of one another. Feel free to start with the most relevant for you.

Additionally, ABT-IO is a small library that can be used to offload POSIX I/O operations to dedicated execution stream to better integrate with the core Mochi libraries. ABT-IO depends on Argobots only.


In all the tutorials, we use the term “server” to denote a process to which one can send RPC requests, and “client” to denote a process that sends such RPC requests. It is important to note however that a server can also send RPC requests to other servers, and even to itself.

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