Quick Start

This quick start guide goes over the bare minimum you need to do to get up and running with Lumberjack. You can find this example in the repository under Lumberjack’s examples directory.

This example uses the Binary Tree Communicator and queues one unique message and three similar messages per rank. They are combined and then pushed fully through the tree.

The following files need to be included for Lumberjack:

# Lumberjack specific header
#include "axom/lumberjack.hpp"

# MPI and C++
#include <mpi.h>
#include <iostream>

Basic MPI setup and information:

// Initialize MPI and get rank and comm size
MPI_Init(&argc, &argv);

int commRank = -1;
MPI_Comm_rank(MPI_COMM_WORLD, &commRank);
int commSize = -1;
MPI_Comm_size(MPI_COMM_WORLD, &commSize);

Initialize Lumberjack:

// Determine how many ranks we want to individually track per message
int ranksLimit = commSize/2;

// Initialize which lumberjack communicator we want
axom::lumberjack::BinaryTreeCommunicator communicator;
communicator.initialize(MPI_COMM_WORLD, ranksLimit);

// Initialize lumberjack
axom::lumberjack::Lumberjack lj;
lj.initialize(&communicator, ranksLimit);

This queues the individual messages into Lumberjack:

// Queue messages into lumberjack
if (commRank == 0){
    lj.queueMessage("This message will not be combined");
else {
    lj.queueMessage("This message will be combined");
    lj.queueMessage("This message will be combined");
    lj.queueMessage("This message will be combined");

This is how you fully push all Messages through the Communicator, which also combines Messages before and after pushing :

// Push messages fully through lumberjack's communicator

Optionally, you could spread the pushing over the course of your work by doing the following:

int cycleCount = 0;
int cycleLimit = 10;
for (int i = 0; i < someLoopLength; ++i){
    // Do some work
    lj.queueMessage("This message will combine")
    if (cycleCount > cycleLimit) {
        // Incrementally push messages through system
        cycleCount = 0;

Once you are ready to retrieve your messages, do so by the following:

// Determine if this is an output node
if (lj.isOutputNode()){
    // Get Messages from Lumberjack
    std::vector<axom::lumberjack::Message*> messages = lj.getMessages();
    for(int i=0; i<(int)(messages.size()); ++i){
        // Output a single Message at a time to screen
        std::cout << "(" << messages[i]->stringOfRanks() << ") " << messages[i]->count() <<
                     " '" << messages[i]->text() << "'" << std::endl;
    // Clear already outputted Messages from Lumberjack

Finalize Lumberjack, the Lumberjack Communicator and MPI in the following order to guarantee nothing goes wrong:

// Finalize lumberjack
// Finalize the lumberjack communicator
// Finalize MPI