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Update post to use x86_64 v0.13.2

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Philipp Oppermann
2021-02-02 11:01:53 +01:00
parent 18930ccad7
commit c5eeea29e2
14 changed files with 94 additions and 94 deletions
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6
blog/content/edition-2/posts/12-async-await/index.md
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@@ -1744,8 +1744,8 @@ impl Executor {
Since we call `sleep_if_idle` directly after `run_ready_tasks`, which loops until the `task_queue` becomes empty, checking the queue again might seem unnecessary. However, a hardware interrupt might occur directly after `run_ready_tasks` returns, so there might be a new task in the queue at the time the `sleep_if_idle` function is called. Only if the queue is still empty, we put the CPU to sleep by executing the `hlt` instruction through the [`instructions::hlt`] wrapper function provided by the [`x86_64`] crate.
[`instructions::hlt`]: https://docs.rs/x86_64/0.12.1/x86_64/instructions/fn.hlt.html
[`x86_64`]: https://docs.rs/x86_64/0.12.1/x86_64/index.html
[`instructions::hlt`]: https://docs.rs/x86_64/0.13.2/x86_64/instructions/fn.hlt.html
[`x86_64`]: https://docs.rs/x86_64/0.13.2/x86_64/index.html
Unfortunately, there is still a subtle race condition in this implementation. Since interrupts are asynchronous and can happen at any time, it is possible that an interrupt happens right between the `is_empty` check and the call to `hlt`:
@@ -1760,7 +1760,7 @@ In case this interrupt pushes to the `task_queue`, we put the CPU to sleep even
The answer is to disable interrupts on the CPU before the check and atomically enable them again together with the `hlt` instruction. This way, all interrupts that happen in between are delayed after the `hlt` instruction so that no wake-ups are missed. To implement this approach, we can use the [`enable_interrupts_and_hlt`] function provided by the [`x86_64`] crate. This function is only available since version 0.9.6, so you might need to update your `x86_64` dependency to use it.
[`enable_interrupts_and_hlt`]: https://docs.rs/x86_64/0.12.1/x86_64/instructions/interrupts/fn.enable_interrupts_and_hlt.html
[`enable_interrupts_and_hlt`]: https://docs.rs/x86_64/0.13.2/x86_64/instructions/interrupts/fn.enable_interrupts_and_hlt.html
The updated implementation of our `sleep_if_idle` function looks like this: