启动服务-有向无环图

Question

The framework I'm working with consists of stateful services that have dependencies on other services, forming a directed acyclic graph http://en.wikipedia.org/wiki/Directed_acyclic_graph

I want to start the services as efficiently as possible. This means starting services in parallel, where possible. For example, in the graph on the wikipedia link. I would start 3, 5, and 7 at the same time, since they don't have any dependencies. I've seen topological sorts, but that alone doesn't tell you what can be started in parallel. I'm looking for a library/api to group services, something like:

a
b, c, d,
e.
f, g,
h

Where this tells me to start "a" first, then "b", "c", and "d" in parallel, then "e", and so on.

I've found a few libraries that model Vertices, but nothing does the grouping I'm looking for. So far I've found some implementations for directed graph, however, I need a permissive license (eg non gpl). I've found ComputeNodeOrder http://www.docjar.com/docs/api/org/eclipse/osgi/internal/resolver/ComputeNodeOrder.Digraph.html (from equinox org.eclipse.osgi_3.6.2.R36x_v20110210), Jgrapht (lgpl) http://www.jgrapht.org/javadoc/ , Jung http://jung.sourceforge.net/index.html , Plexus http://plexus.codehaus.org/plexus-utils/apidocs/org/codehaus/plexus/util/dag/DAG.html but not sure if any/all of these will do what I need.

Answer 1

It sounds like a tree iterated using a breadth first search to me. Each level has the services that can be started in parallel; later dependencies are further down in the tree.