From a9aad11dd72a1c3c7e99ef40cf29cf8d1936b324 Mon Sep 17 00:00:00 2001
From: Corwin Kuiper <corwin@kuiper.dev>
Date: Thu, 24 Jun 2021 00:58:25 +0100
Subject: [PATCH] make interrupt system interrupt safe(r)

FnMut is not something that can be used in a interrupt safe manner.
Instead use Fn with a Mutex that disables interrupts with a lock.
---
 agb/src/interrupt.rs | 90 ++++++++++++++++++++++++++++++++++++++------
 1 file changed, 79 insertions(+), 11 deletions(-)

diff --git a/agb/src/interrupt.rs b/agb/src/interrupt.rs
index c8ffa02a..9f73970e 100644
--- a/agb/src/interrupt.rs
+++ b/agb/src/interrupt.rs
@@ -1,6 +1,7 @@
 use core::{
-    cell::Cell,
+    cell::{Cell, UnsafeCell},
     marker::{PhantomData, PhantomPinned},
+    ops::{Deref, DerefMut},
     pin::Pin,
 };
 
@@ -132,7 +133,7 @@ pub struct InterruptClosureBounded<'a> {
 }
 
 struct InterruptClosure {
-    closure: *mut (dyn FnMut()),
+    closure: *const (dyn Fn()),
     next: Cell<*const InterruptClosure>,
     root: *const InterruptRoot,
 }
@@ -142,7 +143,7 @@ impl InterruptRoot {
         let mut c = self.next.get();
         while !c.is_null() {
             let closure_ptr = unsafe { &*c }.closure;
-            let closure_ref = unsafe { &mut *closure_ptr };
+            let closure_ref = unsafe { &*closure_ptr };
             closure_ref();
             c = unsafe { &*c }.next.get();
         }
@@ -188,12 +189,12 @@ fn interrupt_to_root(interrupt: Interrupt) -> &'static InterruptRoot {
 }
 
 fn get_interrupt_handle_root<'a>(
-    f: &'a mut dyn FnMut(),
+    f: &'a dyn Fn(),
     root: &InterruptRoot,
 ) -> InterruptClosureBounded<'a> {
     InterruptClosureBounded {
         c: InterruptClosure {
-            closure: unsafe { core::mem::transmute(f as *mut _) },
+            closure: unsafe { core::mem::transmute(f as *const _) },
             next: Cell::new(core::ptr::null()),
             root: root as *const _,
         },
@@ -202,7 +203,10 @@ fn get_interrupt_handle_root<'a>(
     }
 }
 
-pub fn get_interrupt_handle(f: &mut dyn FnMut(), interrupt: Interrupt) -> InterruptClosureBounded {
+pub fn get_interrupt_handle(
+    f: &(dyn Fn() + Send + Sync),
+    interrupt: Interrupt,
+) -> InterruptClosureBounded {
     let root = interrupt_to_root(interrupt);
 
     get_interrupt_handle_root(f, root)
@@ -229,11 +233,11 @@ pub fn add_interrupt<'a>(interrupt: Pin<&'a InterruptClosureBounded<'a>>) {
 #[test_case]
 fn test_vblank_interrupt_handler(gba: &mut crate::Gba) {
     {
-        let mut counter = 0;
-        let mut counter_2 = 0;
+        let counter = Mutex::new(0);
+        let counter_2 = Mutex::new(0);
 
-        let mut vblank_interrupt = || counter += 1;
-        let mut vblank_interrupt_2 = || counter_2 += 1;
+        let mut vblank_interrupt = || *counter.lock() += 1;
+        let mut vblank_interrupt_2 = || *counter_2.lock() += 1;
 
         let interrupt_closure = get_interrupt_handle(&mut vblank_interrupt, Interrupt::VBlank);
         let interrupt_closure = unsafe { Pin::new_unchecked(&interrupt_closure) };
@@ -245,7 +249,7 @@ fn test_vblank_interrupt_handler(gba: &mut crate::Gba) {
 
         let vblank = gba.display.vblank.get();
 
-        while counter < 100 || counter_2 < 100 {
+        while *counter.lock() < 100 || *counter_2.lock() < 100 {
             vblank.wait_for_VBlank();
         }
     }
@@ -256,3 +260,67 @@ fn test_vblank_interrupt_handler(gba: &mut crate::Gba) {
         "expected the interrupt table for vblank to be empty"
     );
 }
+
+#[derive(Clone, Copy)]
+enum MutexState {
+    Locked,
+    Unlocked(bool),
+}
+
+pub struct Mutex<T> {
+    internal: UnsafeCell<T>,
+    state: UnsafeCell<MutexState>,
+}
+
+unsafe impl<T> Send for Mutex<T> {}
+unsafe impl<T> Sync for Mutex<T> {}
+
+impl<T> Mutex<T> {
+    pub fn lock(&self) -> MutexRef<T> {
+        let state = INTERRUPTS_ENABLED.get();
+        INTERRUPTS_ENABLED.set(0);
+        unsafe { *self.state.get() = MutexState::Unlocked(state != 0) };
+        MutexRef {
+            internal: &self.internal,
+            state: &self.state,
+        }
+    }
+    pub fn new(val: T) -> Self {
+        Mutex {
+            internal: UnsafeCell::new(val),
+            state: UnsafeCell::new(MutexState::Locked),
+        }
+    }
+}
+
+pub struct MutexRef<'a, T> {
+    internal: &'a UnsafeCell<T>,
+    state: &'a UnsafeCell<MutexState>,
+}
+
+impl<'a, T> Drop for MutexRef<'a, T> {
+    fn drop(&mut self) {
+        unsafe {
+            let state = &mut *self.state.get();
+            let prev_state = *state;
+            *state = MutexState::Locked;
+            match prev_state {
+                MutexState::Unlocked(b) => INTERRUPTS_ENABLED.set(b as u16),
+                MutexState::Locked => {}
+            }
+        }
+    }
+}
+
+impl<'a, T> Deref for MutexRef<'a, T> {
+    type Target = T;
+    fn deref(&self) -> &Self::Target {
+        unsafe { &*self.internal.get() }
+    }
+}
+
+impl<'a, T> DerefMut for MutexRef<'a, T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        unsafe { &mut *self.internal.get() }
+    }
+}