library/alloc/src/raw_vec/tests.rs

   1 use super::*;
   2 use std::cell::Cell;
   3
   4 #[test]
   5 fn allocator_param() {
   6     use crate::alloc::AllocError;
   7
   8     // Writing a test of integration between third-party
   9     // allocators and `RawVec` is a little tricky because the `RawVec`
  10     // API does not expose fallible allocation methods, so we
  11     // cannot check what happens when allocator is exhausted
  12     // (beyond detecting a panic).
  13     //
  14     // Instead, this just checks that the `RawVec` methods do at
  15     // least go through the Allocator API when it reserves
  16     // storage.
  17
  18     // A dumb allocator that consumes a fixed amount of fuel
  19     // before allocation attempts start failing.
  20     struct BoundedAlloc {
  21         fuel: Cell<usize>,
  22     }
  23     unsafe impl Allocator for BoundedAlloc {
  24         fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
  25             let size = layout.size();
  26             if size > self.fuel.get() {
  27                 return Err(AllocError);
  28             }
  29             match Global.allocate(layout) {
  30                 ok @ Ok(_) => {
  31                     self.fuel.set(self.fuel.get() - size);
  32                     ok
  33                 }
  34                 err @ Err(_) => err,
  35             }
  36         }
  37         unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout) {
  38             unsafe { Global.deallocate(ptr, layout) }
  39         }
  40     }
  41
  42     let a = BoundedAlloc { fuel: Cell::new(500) };
  43     let mut v: RawVec<u8, _> = RawVec::with_capacity_in(50, a);
  44     assert_eq!(v.alloc.fuel.get(), 450);
  45     v.reserve(50, 150); // (causes a realloc, thus using 50 + 150 = 200 units of fuel)
  46     assert_eq!(v.alloc.fuel.get(), 250);
  47 }
  48
  49 #[test]
  50 fn reserve_does_not_overallocate() {
  51     {
  52         let mut v: RawVec<u32> = RawVec::new();
  53         // First, `reserve` allocates like `reserve_exact`.
  54         v.reserve(0, 9);
  55         assert_eq!(9, v.capacity());
  56     }
  57
  58     {
  59         let mut v: RawVec<u32> = RawVec::new();
  60         v.reserve(0, 7);
  61         assert_eq!(7, v.capacity());
  62         // 97 is more than double of 7, so `reserve` should work
  63         // like `reserve_exact`.
  64         v.reserve(7, 90);
  65         assert_eq!(97, v.capacity());
  66     }
  67
  68     {
  69         let mut v: RawVec<u32> = RawVec::new();
  70         v.reserve(0, 12);
  71         assert_eq!(12, v.capacity());
  72         v.reserve(12, 3);
  73         // 3 is less than half of 12, so `reserve` must grow
  74         // exponentially. At the time of writing this test grow
  75         // factor is 2, so new capacity is 24, however, grow factor
  76         // of 1.5 is OK too. Hence `>= 18` in assert.
  77         assert!(v.capacity() >= 12 + 12 / 2);
  78     }
  79 }