Lightweight Communication Wrapper (LCW)

A flexible communication wrapper layer.

Authors

• @JiakunYan ([email protected])

Overview

The Lightweight Communication Wrapper (LCW) is designed to be a common denominator of multiple communication libraries. It is originated as a minimum communication interface to efficiently support Asynchronous Many-Task Systems (AMTs) while with the expectation to also be applicable to a broad array of applications. It can also be viewed as a testbed to evaluate different communication libraries in the contexts of multithreaded, irregular, fine-grained communications. The major features of its API includes

• Communication backend selection during runtime.
• The communication device abstraction.
• One-sided dynamic put primitives.
• Two-sided send/recv primitives.
• Queue-based completion notification mechanisms.
• Explicit progress functions.

The actual API and (some) documentation are located in lcw.hpp.

Currently, it has the following communication backend implementation

• MPI
• LCI

Currently, it supports the following clients

• HPX (The HPX/LCW backend sits in a special fork branch. It has not been merged to the HPX master branch.)

Installation

LCW depends on LCT (The Lightweight Communication Tools), which is co-located with LCI (Check LCI's LCI_WITH_LCT_ONLY cmake variable). LCT does not have any special dependents and should be easy to install.

After that,

cmake .
make
make install

Important CMake variables

• CMAKE_INSTALL_PREFIX=/path/to/install: Where to install LCW
  • This is the same across all the cmake projects.
• LCW_DEBUG=ON/OFF: Enable/disable the debug mode (more assertions and logs). The default value is OFF.
• LCW_TRY_ENABLE_BACKEND_LCI: whether to try to find LCI and, if found, enable the LCI backend. The default value is ON.
• LCW_TRY_ENABLE_BACKEND_MPI: whether to try to find MPI and, if found, enable the MPI backend. The default value is ON.

Run LCI applications

We use the same mechanisms as MPI to launch LCW processes, so you can use the same way you run MPI applications to run LCW applications. Typically, it would be mpirun or srun. For example,

mpirun -n 2 ./hello_world

or

srun -n 2 ./hello_world

Write an LCI program

See examples for some example code.

See lcw.hpp for public APIs.