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use std::mem;
use std::vec::Vec;
extern "C" {
fn realloc(ptr: *mut u8, bytes: usize) -> *mut u8;
fn malloc(bytes: usize) -> *mut u8;
}
pub trait FallibleVec<T> {
fn try_push(&mut self, value: T) -> Result<(), ()>;
fn try_reserve(&mut self, new_cap: usize) -> Result<(), ()>;
}
impl<T> FallibleVec<T> for Vec<T> {
#[inline]
fn try_push(&mut self, val: T) -> Result<(), ()> {
if self.capacity() == self.len() {
let old_cap: usize = self.capacity();
let new_cap: usize
= if old_cap == 0 { 4 } else { old_cap.checked_mul(2).ok_or(()) ? };
try_extend_vec(self, new_cap)?;
debug_assert!(self.capacity() > self.len());
}
self.push(val);
Ok(())
}
#[inline]
fn try_reserve(&mut self, cap: usize) -> Result<(), ()> {
let new_cap = cap + self.capacity();
try_extend_vec(self, new_cap)?;
debug_assert!(self.capacity() == new_cap);
Ok(())
}
}
#[inline(never)]
#[cold]
fn try_extend_vec<T>(vec: &mut Vec<T>, new_cap: usize) -> Result<(), ()> {
let old_ptr = vec.as_mut_ptr();
let old_len = vec.len();
let old_cap: usize = vec.capacity();
if old_cap >= new_cap {
return Ok(());
}
let new_size_bytes
= new_cap.checked_mul(mem::size_of::<T>()).ok_or(()) ? ;
let new_ptr = unsafe {
if old_cap == 0 {
malloc(new_size_bytes)
} else {
realloc(old_ptr as *mut u8, new_size_bytes)
}
};
if new_ptr.is_null() {
return Err(());
}
let new_vec = unsafe {
Vec::from_raw_parts(new_ptr as *mut T, old_len, new_cap)
};
mem::forget(mem::replace(vec, new_vec));
Ok(())
}
#[test]
fn oom_test() {
let mut vec: Vec<char> = Vec::new();
match vec.try_reserve(std::usize::MAX) {
Ok(_) => panic!("it should be OOM"),
_ => (),
}
}