While we’re at it, can someone explain Go contexts for me? I suspect they are a way to keep thread safe data that would otherwise be global or, in the C world, static, but I’m not quite sure. The go documentation just describes how to use them, not why they should be used.
Suppose that you spawn a Goroutine for handling an HTTP request from client A. While the request is being processed (e.g. calling DB, external services, etc.), client A drops the TCP connection. With contexts we can notify the handler to cancel any ongoing/pending task. Otherwise, the handler will be still running the remaining tasks, hence wasting resources.
Note that if we pass a context to a function, it entirely depends on the function as to when or whether it will cancel its tasks. It's a cooperative multitasking after all.
In Rust, it's easy to cancel a future: Just drop it. It's not that the Rust's approach is perfect. Rust has the opposite problem: Since a future can be dropped anytime (in any await point), dropping a future in the middle of an execution might lead to an inconsistent state, if the future isn't properly implemented.