reduce memory overhead

by storing indices (u8) in the queues instead of pointers (*mut u8)

in the binary heap we store the baseline inline along with the index and the task name. Before we
stored a pointer to the message and had to lookup the baseline when comparing two nodes in the heap.

Cargo.toml

@@ -52,7 +52,7 @@ required-features = ["timer-queue"]
 [dependencies]
 cortex-m = "0.4.0"
 cortex-m-rtfm-macros = { path = "macros", version = "0.3.1" }
-heapless = "0.3.5"
+heapless = "0.3.6"
 typenum = "1.10.0"
 
 [target.'cfg(target_arch = "x86_64")'.dev-dependencies]

examples/async.rs

@@ -1,3 +1,11 @@
+// # Pointers (old)
+//
+// ~40~ 32 bytes .bss
+//
+// # Indices (new)
+//
+// 12 bytes .bss
+
 #![deny(unsafe_code)]
 #![deny(warnings)]
 #![feature(proc_macro)]

examples/periodic-payload.rs

@@ -1,16 +1,36 @@
-// 52 bytes .bss
+// # Pointers (old)
+//
+// ~52~ 48 bytes .bss
 //
 // # -Os
+//
 // init
 // a(bl=8000000, now=8000180, input=0)
 // a(bl=16000000, now=16000180, input=1)
 // a(bl=24000000, now=24000180, input=2)
 //
 // # -O3
+//
 // init
 // a(bl=8000000, now=8000168, input=0)
 // a(bl=16000000, now=16000168, input=1)
 // a(bl=24000000, now=24000168, input=2)
+//
+// # Indices (new)
+//
+// 32 bytes .bss
+//
+// ## -O3
+//
+// init
+// a(bl=8000000, now=8000170, input=0)
+// a(bl=16000000, now=16000170, input=1)
+//
+// ## -Os
+//
+// init
+// a(bl=8000000, now=8000179, input=0)
+// a(bl=16000000, now=16000179, input=1)
 
 #![deny(unsafe_code)]
 #![deny(warnings)]

examples/periodic-preemption-payload.rs

@@ -1,6 +1,9 @@
-// 104 bytes .bss
+// # Pointers (old)
+//
+// ~104~ 88 bytes .bss
+//
+// ## -Os
 //
-// # -Os
 // a(bl=16000000, now=16000248, input=0)
 // b(bl=24000000, now=24000251, input=0)
 // a(bl=32000000, now=32000248, input=1)
@@ -11,8 +14,9 @@
 // a(bl=80000000, now=80000248, input=4)
 // b(bl=96000000, now=96000283, input=3)
 // a(bl=96000000, now=96002427, input=5)
-
+//
-// # -O3
+// ## -O3
+//
 // init
 // a(bl=16000000, now=16000231, input=0)
 // b(bl=24000000, now=24000230, input=0)
@@ -24,6 +28,37 @@
 // a(bl=80000000, now=80000231, input=4)
 // b(bl=96000000, now=96000259, input=3)
 // a(bl=96000000, now=96002397, input=5)
+//
+// # Indices (new)
+//
+// 56 bytes .bss
+//
+// ## -O3
+//
+// a(bl=16000000, now=16000215, input=0)
+// b(bl=24000000, now=24000214, input=0)
+// a(bl=32000000, now=32000215, input=1)
+// b(bl=48000000, now=48000236, input=1)
+// a(bl=48000000, now=48002281, input=2)
+// a(bl=64000000, now=64000215, input=3)
+// b(bl=72000000, now=72000214, input=2)
+// a(bl=80000000, now=80000215, input=4)
+// b(bl=96000000, now=96000236, input=3)
+// a(bl=96000000, now=96002281, input=5)
+//
+// ## -Os
+//
+// init
+// a(bl=16000000, now=16000257, input=0)
+// b(bl=24000000, now=24000252, input=0)
+// a(bl=32000000, now=32000257, input=1)
+// b(bl=48000000, now=48000284, input=1)
+// a(bl=48000000, now=48002326, input=2)
+// a(bl=64000000, now=64000257, input=3)
+// b(bl=72000000, now=72000252, input=2)
+// a(bl=80000000, now=80000257, input=4)
+// b(bl=96000000, now=96000284, input=3)
+// a(bl=96000000, now=96002326, input=5)
 
 #![deny(unsafe_code)]
 #![deny(warnings)]

examples/periodic-preemption.rs

@@ -1,6 +1,9 @@
-// 96 bytes .bss
+// # Pointers (old)
+//
+// ~96~ 80 bytes .bss
 //
 // # -Os
+//
 // init
 // a(bl=16000000, now=16000249)
 // b(bl=24000000, now=24000248)
@@ -12,8 +15,9 @@
 // a(bl=80000000, now=80000249)
 // b(bl=96000000, now=96000282)
 // a(bl=96000000, now=96001731)
-
+//
 // # -O3
+//
 // init
 // a(bl=16000000, now=16000228)
 // b(bl=24000000, now=24000231)
@@ -25,6 +29,38 @@
 // a(bl=80000000, now=80000228)
 // b(bl=96000000, now=96000257)
 // a(bl=96000000, now=96001705)
+//
+// # Indices (new)
+//
+// 48 bytes .bss
+//
+// ## -O3
+//
+// init
+// a(bl=16000000, now=16000213)
+// b(bl=24000000, now=24000212)
+// a(bl=32000000, now=32000213)
+// b(bl=48000000, now=48000234)
+// a(bl=48000000, now=48001650)
+// a(bl=64000000, now=64000213)
+// b(bl=72000000, now=72000212)
+// a(bl=80000000, now=80000213)
+// b(bl=96000000, now=96000234)
+// a(bl=96000000, now=96001650)
+//
+// ## -Os
+//
+// init
+// a(bl=16000000, now=16000253)
+// b(bl=24000000, now=24000251)
+// a(bl=32000000, now=32000253)
+// b(bl=48000000, now=48000283)
+// a(bl=48000000, now=48001681)
+// a(bl=64000000, now=64000253)
+// b(bl=72000000, now=72000251)
+// a(bl=80000000, now=80000253)
+// b(bl=96000000, now=96000283)
+// a(bl=96000000, now=96001681)
 
 #![deny(unsafe_code)]
 #![deny(warnings)]

examples/periodic.rs

@@ -1,13 +1,33 @@
-// 52 bytes .bss
+// # Pointers (old)
+//
+// ~52~ 40 bytes .bss
+//
+// ## -Os
 //
-// # -Os
 // init
 // a(bl=8000000, now=8000180)
 // a(bl=16000000, now=16000180)
 //
-// # -O3
+// ## -O3
+//
 // a(bl=8000000, now=8000168)
 // a(bl=16000000, now=16000168)
+//
+// # Indices (new)
+//
+// 28 bytes .bss
+//
+// ## -Os
+//
+// init
+// a(bl=8000000, now=8000176)
+// a(bl=16000000, now=16000176)
+//
+// ## -O3
+//
+// init
+// a(bl=8000000, now=8000167)
+// a(bl=16000000, now=16000167)
 
 #![deny(unsafe_code)]
 #![deny(warnings)]

macros/src/trans.rs

@@ -280,18 +280,19 @@ pub fn app(ctxt: &Context, app: &App) -> Tokens {
                 });
             }
             Either::Right(capacity) => {
-                let capacity = Ident::from(format!("U{}", capacity));
+                let ucapacity = Ident::from(format!("U{}", capacity));
+                let capacity = capacity as usize;
 
                 root.push(quote! {
                     #[allow(unsafe_code)]
                     unsafe impl #hidden::#krate::Resource for #name::SQ {
                         const NVIC_PRIO_BITS: u8 = ::#device::NVIC_PRIO_BITS;
                         type Ceiling = #name::Ceiling;
-                        type Data = #hidden::#krate::SlotQueue<#input, #hidden::#krate::#capacity>;
+                        type Data = #hidden::#krate::SlotQueue<#hidden::#krate::#ucapacity>;
 
                         unsafe fn get() -> &'static mut Self::Data {
                             static mut SQ:
-                                #hidden::#krate::SlotQueue<#input, #hidden::#krate::#capacity> =
+                                #hidden::#krate::SlotQueue<#hidden::#krate::#ucapacity> =
                                 #hidden::#krate::SlotQueue::u8();
 
                             &mut SQ
@@ -306,6 +307,10 @@ pub fn app(ctxt: &Context, app: &App) -> Tokens {
                         .unwrap_or(0)
                 ));
                 mod_.push(quote! {
+                    #[allow(unsafe_code)]
+                    pub static mut BUFFER: [#krate::Node<#input>; #capacity] =
+                        unsafe { #krate::uninitialized() };
+
                     pub struct SQ { _0: () }
 
                     #[allow(unsafe_code)]
@@ -372,13 +377,15 @@ pub fn app(ctxt: &Context, app: &App) -> Tokens {
                         {
                             unsafe {
                                 let slot = ::#name::SQ::new().claim_mut(t, |sq, _| sq.dequeue());
-                                if let Some(slot) = slot {
+                                if let Some(index) = slot {
-                                    let tp = slot
+                                    let task = ::#__priority::Task::#name;
-                                        .write(self.baseline, payload)
+                                    core::ptr::write(
-                                        .tag(::#__priority::Task::#name);
+                                        ::#name::BUFFER.get_unchecked_mut(index as usize),
+                                        #krate::Node { baseline: self.baseline, payload }
+                                    );
 
                                     ::#__priority::Q::new().claim_mut(t, |q, _| {
-                                        q.split().0.enqueue_unchecked(tp);
+                                        q.split().0.enqueue_unchecked((task, index));
                                     });
 
                                     #krate::set_pending(#device::Interrupt::#interrupt);
@@ -417,17 +424,19 @@ pub fn app(ctxt: &Context, app: &App) -> Tokens {
                             #krate::Maximum<P, #krate::#qc>: #krate::Unsigned,
                         {
                             unsafe {
-                                if let Some(slot) =
+                                if let Some(index) =
                                     ::#name::SQ::new().claim_mut(t, |sq, _| sq.dequeue()) {
-                                    let tp = slot
+                                    let task = ::#__priority::Task::#name;
-                                        .write(payload)
+                                    core::ptr::write(
-                                        .tag(::#__priority::Task::#name);
+                                        ::#name::BUFFER.get_unchecked_mut(index as usize),
+                                        #krate::Node { payload }
+                                    );
 
                                     ::#__priority::Q::new().claim_mut(t, |q, _| {
-                                        q.split().0.enqueue_unchecked(tp);
+                                        q.split().0.enqueue_unchecked((task, index));
                                     });
 
-                                        #krate::set_pending(#device::Interrupt::#interrupt);
+                                    #krate::set_pending(#device::Interrupt::#interrupt);
 
                                     Ok(())
                                 } else {
@@ -487,14 +496,21 @@ pub fn app(ctxt: &Context, app: &App) -> Tokens {
                         #krate::Maximum<P, #krate::#tqc>: #krate::Unsigned,
                     {
                         unsafe {
-                            if let Some(slot) =
+                            if let Some(index) =
                                 ::#name::SQ::new().claim_mut(t, |sq, _| sq.dequeue()) {
                                 let bl = self.baseline + after;
-                                let tp = slot
+                                let task = ::__tq::Task::#name;
-                                    .write(bl, payload)
+                                    core::ptr::write(
-                                    .tag(::__tq::Task::#name);
+                                        ::#name::BUFFER.get_unchecked_mut(index as usize),
+                                        #krate::Node { baseline: bl, payload },
+                                    );
+                                let m = #krate::Message {
+                                    baseline: bl,
+                                    index,
+                                    task,
+                                };
 
-                                ::__tq::TQ::new().claim_mut(t, |tq, _| tq.enqueue(bl, tp));
+                                ::__tq::TQ::new().claim_mut(t, |tq, _| tq.enqueue(m));
 
                                 Ok(())
                             } else {
@@ -531,7 +547,7 @@ pub fn app(ctxt: &Context, app: &App) -> Tokens {
                 quote! {
                     __tq::Task::#name => {
                         #__priority::Q::new().claim_mut(t, |q, _| {
-                            q.split().0.enqueue_unchecked(tp.retag(#__priority::Task::#name))
+                            q.split().0.enqueue_unchecked((#__priority::Task::#name, index))
                         });
                         #hidden::#krate::set_pending(#device::Interrupt::#interrupt);
                     }
@@ -585,8 +601,8 @@ pub fn app(ctxt: &Context, app: &App) -> Tokens {
                 #hidden::#krate::dispatch(
                     &mut #hidden::#krate::Threshold::<__tq::Priority>::new(),
                     &mut __tq::TQ::new(),
-                    |t, tp| {
+                    |t, task, index| {
-                        match tp.tag() {
+                        match task {
                             #(#arms,)*
                         }
                     })
@@ -644,20 +660,18 @@ pub fn app(ctxt: &Context, app: &App) -> Tokens {
                 if cfg!(feature = "timer-queue") {
                     quote! {
                     #__priority::Task::#name => {
-                        let (bl, payload, slot) = payload.coerce().read();
+                        let node = core::ptr::read(::#name::BUFFER.get_unchecked(index as usize));
-                        // priority
+                        #name::SQ::get().split().0.enqueue_unchecked(index);
-                        #name::SQ::get().split().0.enqueue_unchecked(slot);
+                        #name::HANDLER(#name::Context::new(node.baseline, node.payload));
-                        #name::HANDLER(#name::Context::new(bl, payload));
                     }
 
                     }
                 } else {
                     quote! {
                     #__priority::Task::#name => {
-                        let (payload, slot) = payload.coerce().read();
+                        let node = core::ptr::read(::#name::BUFFER.get_unchecked(index as usize));
-                        // priority
+                        #name::SQ::get().split().0.enqueue_unchecked(index);
-                        #name::SQ::get().split().0.enqueue_unchecked(slot);
+                        #name::HANDLER(#name::Context::new(node.payload));
-                        #name::HANDLER(#name::Context::new(payload));
                     }
                     }
                 }
@@ -675,8 +689,8 @@ pub fn app(ctxt: &Context, app: &App) -> Tokens {
                 use #hidden::#krate::Resource;
 
                 // NOTE(get) the dispatcher is the only consumer of this queue
-                while let Some(payload) = #__priority::Q::get().split().1.dequeue() {
+                while let Some((task, index)) = #__priority::Q::get().split().1.dequeue() {
-                    match payload.tag() {
+                    match task {
                         #(#arms,)*
                     }
                 }
@@ -691,16 +705,9 @@ pub fn app(ctxt: &Context, app: &App) -> Tokens {
         let input = &task.input;
 
         if let Either::Right(capacity) = task.interrupt_or_capacity {
-            let capacity = capacity as usize;
-
             pre_init.push(quote! {
-                {
+                for i in 0..#capacity {
-                    static mut N: [#hidden::#krate::Node<#input>; #capacity] =
+                    #name::SQ::get().enqueue_unchecked(i);
-                        unsafe { #hidden::#krate::uninitialized() };
-
-                    for node in N.iter_mut() {
-                        #name::SQ::get().enqueue_unchecked(node.into());
-                    }
                 }
             })
         }

src/lib.rs

@@ -37,13 +37,12 @@ pub use typenum::{Max, Maximum, Unsigned};
 
 pub use instant::Instant;
 pub use node::Node;
-use node::{Slot, TaggedPayload};
 pub use resource::{Resource, Threshold};
 #[cfg(feature = "timer-queue")]
-pub use tq::{dispatch, TimerQueue};
+pub use tq::{dispatch, Message, TimerQueue};
 
-pub type PayloadQueue<T, N> = RingBuffer<TaggedPayload<T>, N, u8>;
+pub type PayloadQueue<T, N> = RingBuffer<(T, u8), N, u8>;
-pub type SlotQueue<T, N> = RingBuffer<Slot<T>, N, u8>;
+pub type SlotQueue<N> = RingBuffer<u8, N, u8>;
 pub type Ceiling<R> = <R as Resource>::Ceiling;
 
 pub struct Core {

src/node.rs

@@ -4,171 +4,11 @@ use core::{mem, ptr};
 use instant::Instant;
 
 #[doc(hidden)]
-#[repr(C)]
 pub struct Node<T>
 where
     T: 'static,
 {
     #[cfg(feature = "timer-queue")]
-    baseline: Instant,
+    pub baseline: Instant,
-    payload: T,
+    pub payload: T,
-}
-
-#[cfg(feature = "timer-queue")]
-impl<T> Eq for Node<T> {}
-
-#[cfg(feature = "timer-queue")]
-impl<T> PartialEq for Node<T> {
-    fn eq(&self, other: &Node<T>) -> bool {
-        self.baseline == other.baseline
-    }
-}
-
-#[cfg(feature = "timer-queue")]
-impl<T> Ord for Node<T> {
-    fn cmp(&self, other: &Node<T>) -> Ordering {
-        self.baseline.cmp(&other.baseline)
-    }
-}
-
-#[cfg(feature = "timer-queue")]
-impl<T> PartialOrd for Node<T> {
-    fn partial_cmp(&self, other: &Node<T>) -> Option<Ordering> {
-        Some(self.cmp(other))
-    }
-}
-
-#[doc(hidden)]
-pub struct Slot<T>
-where
-    T: 'static,
-{
-    node: &'static mut Node<T>,
-}
-
-impl<T> Slot<T> {
-    #[cfg(feature = "timer-queue")]
-    pub fn write(self, bl: Instant, data: T) -> Payload<T> {
-        self.node.baseline = bl;
-        unsafe { ptr::write(&mut self.node.payload, data) }
-        Payload { node: self.node }
-    }
-
-    #[cfg(not(feature = "timer-queue"))]
-    pub fn write(self, data: T) -> Payload<T> {
-        unsafe { ptr::write(&mut self.node.payload, data) }
-        Payload { node: self.node }
-    }
-}
-
-impl<T> Into<Slot<T>> for &'static mut Node<T> {
-    fn into(self) -> Slot<T> {
-        Slot { node: self }
-    }
-}
-
-#[doc(hidden)]
-pub struct Payload<T>
-where
-    T: 'static,
-{
-    node: &'static mut Node<T>,
-}
-
-impl<T> Payload<T> {
-    #[cfg(feature = "timer-queue")]
-    pub fn read(self) -> (Instant, T, Slot<T>) {
-        let data = unsafe { ptr::read(&self.node.payload) };
-        (self.node.baseline, data, Slot { node: self.node })
-    }
-
-    #[cfg(not(feature = "timer-queue"))]
-    pub fn read(self) -> (T, Slot<T>) {
-        let data = unsafe { ptr::read(&self.node.payload) };
-        (data, Slot { node: self.node })
-    }
-
-    pub fn tag<A>(self, tag: A) -> TaggedPayload<A>
-    where
-        A: Copy,
-    {
-        TaggedPayload {
-            tag,
-            payload: unsafe { mem::transmute(self) },
-        }
-    }
-}
-
-#[doc(hidden)]
-pub struct TaggedPayload<A>
-where
-    A: Copy,
-{
-    tag: A,
-    payload: Payload<!>,
-}
-
-impl<A> TaggedPayload<A>
-where
-    A: Copy,
-{
-    pub unsafe fn coerce<T>(self) -> Payload<T> {
-        mem::transmute(self.payload)
-    }
-
-    #[cfg(feature = "timer-queue")]
-    pub fn baseline(&self) -> Instant {
-        self.payload.node.baseline
-    }
-
-    pub fn tag(&self) -> A {
-        self.tag
-    }
-
-    pub fn retag<B>(self, tag: B) -> TaggedPayload<B>
-    where
-        B: Copy,
-    {
-        TaggedPayload {
-            tag,
-            payload: self.payload,
-        }
-    }
-}
-
-#[cfg(feature = "timer-queue")]
-impl<T> Eq for TaggedPayload<T>
-where
-    T: Copy,
-{
-}
-
-#[cfg(feature = "timer-queue")]
-impl<T> Ord for TaggedPayload<T>
-where
-    T: Copy,
-{
-    fn cmp(&self, rhs: &Self) -> Ordering {
-        self.payload.node.cmp(&rhs.payload.node)
-    }
-}
-
-#[cfg(feature = "timer-queue")]
-impl<T> PartialEq for TaggedPayload<T>
-where
-    T: Copy,
-{
-    fn eq(&self, rhs: &Self) -> bool {
-        self.payload.node.eq(&rhs.payload.node)
-    }
-}
-
-#[cfg(feature = "timer-queue")]
-impl<T> PartialOrd for TaggedPayload<T>
-where
-    T: Copy,
-{
-    fn partial_cmp(&self, rhs: &Self) -> Option<Ordering> {
-        Some(self.cmp(rhs))
-    }
 }

src/tq.rs

@@ -1,4 +1,4 @@
-use core::cmp;
+use core::cmp::{self, Ordering};
 
 use cortex_m::peripheral::{SCB, SYST};
 use heapless::binary_heap::{BinaryHeap, Min};
@@ -6,14 +6,39 @@ use heapless::ArrayLength;
 use typenum::{Max, Maximum, Unsigned};
 
 use instant::Instant;
-use node::{Slot, TaggedPayload};
 use resource::{Resource, Threshold};
 
+pub struct Message<T> {
+    pub baseline: Instant,
+    pub index: u8,
+    pub task: T,
+}
+
+impl<T> Eq for Message<T> {}
+
+impl<T> Ord for Message<T> {
+    fn cmp(&self, other: &Message<T>) -> Ordering {
+        self.baseline.cmp(&other.baseline)
+    }
+}
+
+impl<T> PartialEq for Message<T> {
+    fn eq(&self, other: &Message<T>) -> bool {
+        self.baseline == other.baseline
+    }
+}
+
+impl<T> PartialOrd for Message<T> {
+    fn partial_cmp(&self, other: &Message<T>) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
 enum State<T>
 where
     T: Copy,
 {
-    Payload(TaggedPayload<T>),
+    Payload { task: T, index: u8 },
     Baseline(Instant),
     Done,
 }
@@ -21,16 +46,16 @@ where
 #[doc(hidden)]
 pub struct TimerQueue<T, N>
 where
-    N: ArrayLength<TaggedPayload<T>>,
+    N: ArrayLength<Message<T>>,
     T: Copy,
 {
     pub syst: SYST,
-    pub queue: BinaryHeap<TaggedPayload<T>, N, Min>,
+    pub queue: BinaryHeap<Message<T>, N, Min>,
 }
 
 impl<T, N> TimerQueue<T, N>
 where
-    N: ArrayLength<TaggedPayload<T>>,
+    N: ArrayLength<Message<T>>,
     T: Copy,
 {
     pub const fn new(syst: SYST) -> Self {
@@ -41,10 +66,10 @@ where
     }
 
     #[inline]
-    pub unsafe fn enqueue(&mut self, bl: Instant, tp: TaggedPayload<T>) {
+    pub unsafe fn enqueue(&mut self, m: Message<T>) {
         if self.queue
             .peek()
-            .map(|head| bl < head.baseline())
+            .map(|head| m.baseline < head.baseline)
             .unwrap_or(true)
         {
             self.syst.enable_interrupt();
@@ -52,25 +77,29 @@ where
             unsafe { (*SCB::ptr()).icsr.write(1 << 26) }
         }
 
-        self.queue.push_unchecked(tp);
+        self.queue.push_unchecked(m);
     }
 }
 
 pub fn dispatch<T, TQ, N, F, P>(t: &mut Threshold<P>, tq: &mut TQ, mut f: F)
 where
-    F: FnMut(&mut Threshold<P>, TaggedPayload<T>),
+    F: FnMut(&mut Threshold<P>, T, u8),
     Maximum<P, TQ::Ceiling>: Unsigned,
-    N: 'static + ArrayLength<TaggedPayload<T>>,
+    N: 'static + ArrayLength<Message<T>>,
     P: Unsigned + Max<TQ::Ceiling>,
     T: 'static + Copy + Send,
     TQ: Resource<Data = TimerQueue<T, N>>,
 {
     loop {
         let state = tq.claim_mut(t, |tq, _| {
-            if let Some(bl) = tq.queue.peek().map(|p| p.baseline()) {
+            if let Some(bl) = tq.queue.peek().map(|p| p.baseline) {
                 if Instant::now() >= bl {
                     // message ready
-                    State::Payload(unsafe { tq.queue.pop_unchecked() })
+                    let m = unsafe { tq.queue.pop_unchecked() };
+                    State::Payload {
+                        task: m.task,
+                        index: m.index,
+                    }
                 } else {
                     // set a new timeout
                     State::Baseline(bl)
@@ -83,7 +112,7 @@ where
         });
 
         match state {
-            State::Payload(p) => f(t, p),
+            State::Payload { task, index } => f(t, task, index),
             State::Baseline(bl) => {
                 const MAX: u32 = 0x00ffffff;