45 lines
3.0 KiB
Markdown
45 lines
3.0 KiB
Markdown
# Hints
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## General
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- Read about links and tasks in the official [Getting Started guide][getting-started-links].
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- Take a look at the [documentation of the `Task` module][task].
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- Read ["Demystifying processes in Elixir" on blog.appsignal.com][appsignal-processes].
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- Read ["Understanding Exit Signals in Erlang/Elixir" on crypt.codemancers.com][codemancers-exit-signals].
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## 1. Start a reliability check for a single input
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- You don't need a task for this step, a regular linked process is enough.
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- There is a [built-in function][spawn-link] that runs a given anonymous function in a new process and links it to the current process.
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## 2. Interpret the results of a reliability check
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- To receive a single message, call [`receive`][receive] once. It will read the first message that matches any of the given patterns, leaving other messages in the process inbox.
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- Either a guard or [the pin operator][pin-operator] can be used to ensure that only messages from a process whose PID matches the PID given to `await_reliability_check_result/2` as an argument will be received.
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- [`receive`][receive] accepts an `after` clause to handle timeouts.
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## 3. Run a concurrent reliability check for many inputs
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- The current process must start trapping exits before any new linked processes are spawned.
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- Trapping exits in a process is achieved by setting a flag on that process.
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- There is a [built-in function][process-flag] that sets a flag on a process and returns the old value of that flag.
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- The flag for trapping exits is called `:trap_exit` and accepts a boolean value.
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- Make use of `Enum` functions to first start a process for each input, and then await messages from each process. Use the functions implemented in the two previous steps. Note that the map returned by `start_reliability_check/2` matches the map that `await_reliability_check_result/2` expects as the first argument.
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## 4. Run a concurrent correctness check for many inputs
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- Use an asynchronous task for this step.
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- There is a [built-in function][task-async] that starts an asynchronous task.
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- There is a [built-in function][task-await] that waits for an asynchronous task to finish executing and returns its result. It accepts a timeout as a second argument.
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- Make use of `Enum` functions to first start a task for each input, and then wait for each task.
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[spawn-link]: https://hexdocs.pm/elixir/Kernel.html#spawn_link/1
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[pin-operator]: https://hexdocs.pm/elixir/Kernel.SpecialForms.html#%5E/1
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[receive]: https://hexdocs.pm/elixir/Kernel.SpecialForms.html#receive/1
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[process-flag]: https://hexdocs.pm/elixir/Process.html#flag/2
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[task-async]: https://hexdocs.pm/elixir/Task.html#async/1
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[task-await]: https://hexdocs.pm/elixir/Task.html#await/2
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[task]: https://hexdocs.pm/elixir/Task.html
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[appsignal-processes]: https://blog.appsignal.com/2017/05/18/elixir-alchemy-demystifying-processes-in-elixir.html
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[getting-started-links]: https://hexdocs.pm/elixir/processes.html#links
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[codemancers-exit-signals]: https://crypt.codemancers.com/posts/2016-01-24-understanding-exit-signals-in-erlang-slash-elixir/ |