A building block for concurrent programming in Perl6 inspired by Go's context package
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A building block for concurrent programming based on Go's context

Go's context (https://golang.org/pkg/context/) solves two important problems for concurrent programming. First, it provides a mechanism for sharing a safe cancellation mechanism. Second, it provides a safe abstraction for sharing values between concurrent execution contexts.

Consider a program which spawns workers concurrently but then wants to terminate them. The Context package provides a standard building block for providing this.

Now assume the same program encodes values into some protocol mechanism such as HTTP headers or query parameters for spawned workers to access. The problem with this is it results in brittleness; if a developer wishes to move some value from a query parameter to a header, they must chase down every piece of code that works thusly and edit it. The better approach is to eliminate protocol details as early in the process of spawning workers entirely, and to use a protocol-agnostic mechanism like a Context instance to communicate these values safely to spawned workers.

It is often good practice to not make assumptions about the concurrent environment library code will be used in, but the Context package only makes sense as a building block for concurrent development, so it is enabled for safe use in concurrent environments by default. Context is not recommended as a way of passing persistent references like DB connection handles etc, instead it is recommended that Context only be used for request-scope values.

Like the Go equivalent, this library doesn't reduce keystrokes. Indeed, it increases keystrokes as it implies adopting a new pattern for concurrent development.