Cocol Probabilistic Finality

Based on DAGs, it manages chains, sidechains and orphans. Given a threshold of confirmations it returns the next finalized block.


  1. Add the dependency to your shard.yml:
       github: cocol-project/probfin
  1. Run shards install


require "probfin"
# (a0)---aa---ba---ca---da---ea---fa
#              \    \
#               bb   cb---cc

# add blocks (aa, a0 should be block hashes)
ProbFin.push(block: "aa", parent: "a0")
ProbFin.push(block: "ba", parent: "aa")
ProbFin.push(block: "bb", parent: "ba")

ProbFin.finalize from: "aa",
    chain_length_threshold: 5, # 5 confirmations (fa being the 5th) 
    tip_diff_threshold: 0 # how many more confirmations should it have compared to sidechains
# => ba

How ProbFin works

Alt Text

The data structure above resembles a Directed Acyclic Graph (DAG) and fortunately DAGs allow for an easy way to find the longest chain. This is an important part of achieving probabilistic finality.

A DAG is made up of nodes (also called vertices) and edges. An edge represents a link between 2 vertices (e.g. 3000.1->3001.1). We can and should traverse a DAG to find out more about its structure, like how far away is vertex 3005.1 from vertex 3000.1

Additionally a DAG has some unique properties. Find out more about it here

2. How to find the longest chain

If we look again at the example above, it becomes apparent that 3005.1 is the tip of the longest chain. But how can we find it out programmatically?

We are going to use Depth First Search to traverse the graph and mark every vertex with its distance from the starting vertex. We start at 3000.1 and give it a distance of 0. Now we traverse through all vertices and give each a distance of parent distance + 1. So 3001.1 has a parent distance of 0 and +1 gives a distance of 1.

Alt Text


  1. Fork it (
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create a new Pull Request


  • cserb - creator and maintainer
github statistic
  • 3
  • 1
  • 1
  • 0
  • over 1 year ago
  • September 17, 2019

Mozilla Public License 2.0

Synced at

Mon, 02 Aug 2021 09:32:54 GMT