# I always wonder a little bit why dependency-tracking systems that don’t
strictly require ordering…

It’s one thing if we’re talking about a package manager that builds
dependencies from source as they are needed, and therefore must run a…

* * *

I always wonder a little bit why dependency-tracking systems that don’t
strictly require ordering don’t perform pooling.

It’s one thing if we’re talking about a package manager that builds
dependencies from source as they are needed, and therefore must run a
particular set of commands in order to make other resources available to a
future build. But, if all injected dependencies are available to all their
children in the dependency tree, we’re essentially talking about flattening a
walk through a graph into a list, right? In other words, if what Guice is
doing is creating a list of strings corresponding to classpath elements, and
that classpath is made available to every VM we spawn, then circular
dependencies are a non-issue because we can check for cycles by searching the
already-stored list of dependencies for each new one we find.

(It’s a different matter if we need to make it possible for different versions
of a jar with the same canonical name to be used by different classes. I think
that could be managed with some reflection-based name mangling.)

This is not a complaint about your solution, of course. This is more of a
complaint directed at the authors of these systems, who don’t seem to have
realized that they are not operating under the same memory restrictions as
Dijkstra & are already storing the information necessary to identify & break
cycles in what functionally isn’t really a dependency tree.

(Python imports have a similar kind of solution: a module enters a dictionary
of loaded modules before its own imports are handled, and module loading is
idempotent, so a circular import is a non-issue.)

By [John Ohno](https://medium.com/@enkiv2) on [April 13,
2018](https://medium.com/p/85e75fbf7cce).

[Canonical link](https://medium.com/@enkiv2/i-always-wonder-a-little-bit-why-
dependency-tracking-systems-that-dont-strictly-require-ordering-85e75fbf7cce)

Exported from [Medium](https://medium.com) on September 18, 2020.