Freddie Internals

The model is a pure function of state and event, and that purity is bought by pushing every impure thing to the edges: threads, operating system handles, and the memory both of those own. This section is about those edges. It is for changing a freddie_* crate or adding one, not for writing bindings.

The rules here were mostly learned by getting them wrong. Where a claim has a number attached, that number came from measuring a running mercury, and the page says how so you can repeat it.

The short version

• Three long-lived threads, each with one job, joined only by channels. Nothing shares mutable state, so nothing takes a lock.
• A thread that calls into Cocoa needs an autorelease pool unless it is inside a run loop or about to exit. Mercury's worker thread is neither.
• A Drop impl can only release what you were handed. Some operating system calls allocate on your behalf and hand you nothing.
• A balanced reference count is not a reclaimed resource. The only way to know a resource came back is to measure the process.

In this section

• Threads is which threads exist, what each may do, and how work moves between them.
• Autorelease Pools is who drains them, which threads get one for free, and what happens on the one that does not.
• Owning Operating System Resources is the ownership newtype, and the two cases it cannot express.
• Measuring Memory is how to tell a leak from a resting size, with the commands.