vertexclique commented on a change in pull request #7061:
URL: https://github.com/apache/arrow/pull/7061#discussion_r419000857
##########
File path: rust/arrow/src/memory.rs
##########
@@ -20,34 +20,56 @@
use std::alloc::Layout;
use std::mem::align_of;
+use std::ptr::NonNull;
pub const ALIGNMENT: usize = 64;
+///
+/// As you can see this is global and lives as long as the program lives.
+/// Be careful to not write anything to this pointer in any scenario.
+/// If you use allocation methods shown here you won't have any problems.
+const BYPASS_PTR: NonNull<u8> = unsafe { NonNull::new_unchecked(0xDEADBEEF as
*mut u8) };
+
pub fn allocate_aligned(size: usize) -> *mut u8 {
unsafe {
- let layout = Layout::from_size_align_unchecked(size, ALIGNMENT);
- std::alloc::alloc_zeroed(layout)
+ if size == 0 {
+ // In a perfect world, there is no need to request zero size
allocation.
+ // Currently, passing zero sized layout to alloc is UB.
+ // This will dodge allocator api for any type.
+ BYPASS_PTR.as_mut()
+ } else {
+ let layout = Layout::from_size_align_unchecked(size, ALIGNMENT);
+ std::alloc::alloc_zeroed(layout)
+ }
}
}
-pub unsafe fn free_aligned(p: *mut u8, size: usize) {
- std::alloc::dealloc(p, Layout::from_size_align_unchecked(size, ALIGNMENT));
+pub unsafe fn free_aligned(ptr: *mut u8, size: usize) {
+ if size != 0x00 && ptr != BYPASS_PTR.as_mut() {
+ std::alloc::dealloc(ptr, Layout::from_size_align_unchecked(size,
ALIGNMENT));
+ }
}
pub unsafe fn reallocate(ptr: *mut u8, old_size: usize, new_size: usize) ->
*mut u8 {
- let new_ptr = std::alloc::realloc(
- ptr,
- Layout::from_size_align_unchecked(old_size, ALIGNMENT),
- new_size,
- );
- if !new_ptr.is_null() && new_size > old_size {
- new_ptr.add(old_size).write_bytes(0, new_size - old_size);
+ if old_size == 0x00 && ptr == BYPASS_PTR.as_mut() {
Review comment:
Addressed.
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