allocator_api: provide a grow_zeroed implementation

src/lib.rs

@@ -1800,6 +1800,17 @@ unsafe impl<'a> Allocator for &'a Bump {
  .map(|p| NonNull::slice_from_raw_parts(p, new_size))
  .map_err(|_| AllocError)
  }
+
+ unsafe fn grow_zeroed(
+ &self,
+ ptr: NonNull<u8>,
+ old_layout: Layout,
+ new_layout: Layout,
+ ) -> Result<NonNull<[u8]>, AllocError> {
+ let mut ptr = self.grow(ptr, old_layout, new_layout)?;
+ ptr.as_mut()[old_layout.size()..].fill(0);
+ Ok(ptr)
+ }
 }
 
 #[cfg(test)]

tests/allocator_api.rs

@@ -2,9 +2,9 @@
 #![cfg(feature = "allocator_api")]
 use bumpalo::Bump;
 
-use std::sync::atomic::{AtomicUsize, Ordering::Relaxed};
+use std::alloc::{AllocError, Allocator, Layout};
 use std::ptr::NonNull;
-use std::alloc::{Layout, AllocError, Allocator};
+use std::sync::atomic::{AtomicUsize, Ordering::Relaxed};
 
 #[derive(Debug)]
 struct AllocatorDebug {
@@ -27,8 +27,6 @@ impl AllocatorDebug {
  }
 }
 
-
-
 unsafe impl Allocator for AllocatorDebug {
  fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
  self.allocs.fetch_add(1, Relaxed);
@@ -63,7 +61,6 @@ unsafe impl Allocator for AllocatorDebug {
  let ref bump = self.bump;
  bump.grow(ptr, old_layout, new_layout)
  }
-
 }
 
 #[test]
@@ -93,3 +90,22 @@ fn allocator_api_push_a_bunch_of_items() {
  drop(v);
  assert_eq!(b.deallocs.load(Relaxed), 1);
 }
+
+#[test]
+fn allocator_grow_zeroed() {
+ // Create a new bump arena.
+ let ref bump = Bump::new();
+
+ // Make a first allocation
+ let first = Layout::from_size_align(4, 4).expect("create a layout");
+ let mut p = bump.allocate_zeroed(first).expect("allocate a first chunk");
+ let allocated = bump.allocated_bytes();
+ unsafe { p.as_mut().fill(42) };
+ let p = p.cast();
+
+ // Should we grow the last allocation, that just allocate new bytes, not more
+ let second = Layout::from_size_align(5, 8).expect("create a expanded layout");
+ let p = unsafe { bump.grow_zeroed(p, first, second) }.expect("allocate a second chunk");
+ assert!(bump.allocated_bytes() <= allocated * 2);
+ assert_eq!(unsafe { p.as_ref() }, [42, 42, 42, 42, 0])
+}

valgrind.supp

@@ -19,3 +19,17 @@
  fun:syscall
  fun:statx
 }
+{
+ <false positive fixed in valgrind 3.16 and higher part 3>
+ Memcheck:Param
+ statx(buf)
+ fun:statx
+ fun:statx
+}
+{
+ <false positive fixed in valgrind 3.16 and higher part 4>
+ Memcheck:Param
+ statx(file_name)
+ fun:statx
+ fun:statx
+}