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[RFC] Blocking calls handling #36

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[RFC] Blocking calls handling #36

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27 changes: 27 additions & 0 deletions doc/blocking.md
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# Blocking calls handling

## Use case

1. The process wants to start a blocking operation (`sleep`, disk operation...).
Via an interrupt, it calls the corresponding function from the driver.
2. The driver launches the operation and keeps the pid of the process.
3. The driver calls `scheduler_wait_blocking`, with a callback to cancel the
operation as parameter (see below). The process is stopped and marked as
`WAITING`.
4. When the operation completes (usually via a hardware interrupt), the driver
calls `scheduler_wake_blocking` with the pid and a return value as parameter.
The process is marked as `READY`. Its saved value for `A` is set to the
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not sure A is the correct register, as it gets reset by rfi

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It's the return value from scheduler_wait_blocking, not from the interrupt

return value.
5. The execution of the process can restart from the line after the call to
`scheduler_wait_blocking`. The result code is the return value of
`scheduler_wait_blocking`.

## Scheduler

The scheduler only launches processes in the `READY` state. If none are
available, it runs `HLT`.

## Process end

If a process is killed while `WAITING`, the scheduler calls the callback with
the pid as parameter.