src/liballoc/raw_vec/tests.rs

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