Add a simple heap

Author: JalonWong

Cargo.toml

@@ -24,13 +24,15 @@ name = "embedded-alloc"
 version = "0.6.0"
 
 [features]
-default = ["llff", "tlsf"]
+default = ["llff", "tlsf", "simplest"]
 allocator_api = []
 
 # Use the Two-Level Segregated Fit allocator
 tlsf = ["rlsf", "const-default"]
- # Use the LinkedList first-fit allocator
+# Use the LinkedList first-fit allocator
 llff = ["linked_list_allocator"]
+# Use the simplest allocator
+simplest = []
 
 [dependencies]
 critical-section = "1.0"

examples/global_alloc.rs

@@ -10,6 +10,7 @@ use cortex_m_rt::entry;
 use embedded_alloc::LlffHeap as Heap;
 // Two-Level Segregated Fit Heap allocator (feature = "tlsf")
 // use embedded_alloc::TlsfHeap as Heap;
+// use embedded_alloc::SimplestHeap as Heap;
 
 #[global_allocator]
 static HEAP: Heap = Heap::empty();

src/lib.rs

@@ -3,11 +3,15 @@
 #![cfg_attr(feature = "allocator_api", feature(allocator_api, alloc_layout_extra))]
 #![warn(missing_docs)]
 
+#[cfg(feature = "simplest")]
+mod simplest;
 #[cfg(feature = "llff")]
 mod llff;
 #[cfg(feature = "tlsf")]
 mod tlsf;
 
+#[cfg(feature = "simplest")]
+pub use simplest::Heap as SimplestHeap;
 #[cfg(feature = "llff")]
 pub use llff::Heap as LlffHeap;
 #[cfg(feature = "tlsf")]

src/simplest.rs

@@ -0,0 +1,115 @@
+use core::alloc::{GlobalAlloc, Layout};
+use core::cell::RefCell;
+use core::ptr;
+use critical_section::Mutex;
+
+/// The simplest possible heap.
+///
+/// # Safety
+///
+/// This heap does **NOT** free allocated memory.
+pub struct Heap {
+    heap: Mutex<RefCell<SimplestHeap>>,
+}
+
+impl Heap {
+    /// Create a new UNINITIALIZED heap allocator
+    ///
+    /// You must initialize this heap using the
+    /// [`init`](Self::init) method before using the allocator.
+    pub const fn empty() -> Heap {
+        Heap {
+            heap: Mutex::new(RefCell::new(SimplestHeap::empty())),
+        }
+    }
+
+    /// Initializes the heap
+    ///
+    /// This function must be called BEFORE you run any code that makes use of the
+    /// allocator.
+    ///
+    /// `start_addr` is the address where the heap will be located.
+    ///
+    /// `size` is the size of the heap in bytes.
+    ///
+    /// # Safety
+    ///
+    /// Obey these or Bad Stuff will happen.
+    ///
+    /// - This function must be called exactly ONCE.
+    /// - `size > 0`
+    pub unsafe fn init(&self, start_addr: usize, size: usize) {
+        critical_section::with(|cs| {
+            self.heap
+                .borrow(cs)
+                .borrow_mut()
+                .init(start_addr as *mut u8, size);
+        });
+    }
+
+    /// Returns an estimate of the amount of bytes in use.
+    pub fn used(&self) -> usize {
+        critical_section::with(|cs| self.heap.borrow(cs).borrow().used())
+    }
+
+    /// Returns an estimate of the amount of bytes available.
+    pub fn free(&self) -> usize {
+        critical_section::with(|cs| self.heap.borrow(cs).borrow().free())
+    }
+}
+
+unsafe impl GlobalAlloc for Heap {
+    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+        critical_section::with(|cs| self.heap.borrow(cs).borrow_mut().alloc(layout))
+    }
+
+    unsafe fn dealloc(&self, _ptr: *mut u8, _layout: Layout) {}
+}
+
+struct SimplestHeap {
+    arena: *mut u8,
+    remaining: usize,
+    size: usize,
+}
+
+unsafe impl Send for SimplestHeap {}
+
+impl SimplestHeap {
+    const fn empty() -> Self {
+        Self {
+            arena: ptr::null_mut(),
+            remaining: 0,
+            size: 0,
+        }
+    }
+
+    fn init(&mut self, start_addr: *mut u8, size: usize) -> Self {
+        Self {
+            arena: start_addr,
+            remaining: size,
+            size,
+        }
+    }
+
+    fn free(&self) -> usize {
+        self.remaining
+    }
+
+    fn used(&self) -> usize {
+        self.size - self.remaining
+    }
+
+    fn alloc(&mut self, layout: Layout) -> *mut u8 {
+        if layout.size() > self.remaining {
+            return ptr::null_mut();
+        }
+
+        // `Layout` contract forbids making a `Layout` with align=0, or align not power of 2.
+        // So we can safely use a mask to ensure alignment without worrying about UB.
+        let align_mask_to_round_down = !(layout.align() - 1);
+
+        self.remaining -= layout.size();
+        self.remaining &= align_mask_to_round_down;
+        self.arena.wrapping_add(self.remaining)
+    }
+}