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diff --git a/src/arch_goals.md b/src/arch_goals.md new file mode 100644 index 0000000000..92c86d9df8 --- /dev/null +++ b/src/arch_goals.md @@ -0,0 +1,31 @@ +@page arch_goals High level code design practices + +This page describes the high level design practices for Tor's code. +This design is a long-term goal of what we want our code to look like, +rather than a description of how it currently is. + +Overall, we want various parts of tor's code to interact with each +other through a small number of interfaces. + +We want to avoid having "god objects" or "god modules". These are +objects or modules that know far too much about other parts of the +code. God objects/modules are generally recognized to be an +antipattern of software design. + +Historically, there have been modules in tor that have tended toward +becoming god modules. These include modules that help more +specialized code communicate with the outside world: the configuration +and control modules, for example. Others are modules that deal with +global state, initialization, or shutdown. + +If a centralized module needs to invoke code in almost every other +module in the system, it is better if it exports a small, general +interface that other modules call. The centralized module should not +explicitly call out to all the modules that interact with it. + +Instead, modules that interact with the centralized module should call +registration interfaces. These interfaces allow modules to register +handlers for things like configuration parsing and control command +execution. (The config and control modules are examples of this.) +Alternatively, registration can happen through statically initialized +data structures. (The subsystem mechanism is an example of this.) |