Struct rstubs::interrupts::guard::Guard

pub struct Guard {
    guarded: Ticket<Guarded>,
    active: [AtomicBool; 4],
    epilogues: UnsafeCell<[ArrayDeque<Epilogue, LEN>; 4]>,
}

Synchronizes the kernel with interrupts using the Prologue/Epilogue Model

The Guard is used to synchronize between “normal” core activities (currently just the text output, later system calls) and interrupt handling routines. For this purpose, Guard has to contain one or more “queues”, in which Epilogue objects can be added. This is necessary if the critical section is occupied at the time when an interrupt occurs, and the Epilogue::run method cannot be executed immediately. The queued epilogues are processed when leaving the critical section.

The Guard protects and synchronizes various global kernel objects. These objects are only accessible when the guard is locked, by the control flow holding the lock. This prevents concurrent access and race conditions.

Hints

The epilogue queue is a central data structure, whose consistency must be ensured. The implementation provided by the ArrayDeque is not safe against concurrency, i.e. there must never be accesses by two cores at the same time. You need to disable interrupts during operations on the queue.

For SMP, you need a separate epilogue queue for each core, in which each processor serializes its epilogues. However, epilogues on different cores could then be executed in parallel, since the critical section is managed separately on a per-core basis. This must be prevented by using a global Ticket lock to avoid concurrent execution of epilogues – there must never be more than one epilogue active on the whole system at the same time!

Please note: This giant lock (synchronizing all cores) should not be confused with the (core-specific) flag variable that marks only the entry to the epilogue level on the corresponding core!

Interrupts should be disabled for as short as possible. Due to this reason, the prologue/epilogue model allows epilogues to be interrupted by prologues. This means that interrupts should be enabled again before the epilogue is executed (this includes notifying the APIC about the “End-Of-Interrupt”)

Fields

guarded: Ticket<Guarded>

active: [AtomicBool; 4]

Indicates whether the epilogue layer is active on the corresponding core

epilogues: UnsafeCell<[ArrayDeque<Epilogue, LEN>; 4]>

CPU-local queues for epilogues

Implementations

impl Guard

pub const fn new() -> Self

fn epilogues(&self) -> &mut ArrayDeque<Epilogue, LEN>

pub unsafe fn read(&self) -> &Guarded

Temporary read-only access.

Safety: beware race conditions!

pub fn enter(&self) -> GuardedGuard<'_>

Enter the epilogue layer or wait synchronously if it is already occupied.

A guard object is returned that unlocks the epilogue layer when it falls out of scope.

pub fn relay(&self, _epilogue: Epilogue)

Register the given epilogue, which is either executed directly if possible or it is enqueued for later execution.

pub fn leave(&self)

Leave the epilogue layer.

pub fn active(&self) -> bool

Returns wether the layer 1/2 is active

Trait Implementations

impl Sync for Guard