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small fix to the tutorial-ffi destructor example 

The previous example was erroneously attempting to destroy
uninitialized memory, which was often zeroed (masking the bug).
This commit is contained in:
Daniel Micay 2013-05-04 21:53:43 -04:00
parent d74ac9ea03
commit 8f2d71ac00
1 changed files with 4 additions and 7 deletions
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11
doc/tutorial-ffi.md
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@ -150,11 +150,7 @@ wrapping `malloc` and `free`:
~~~~ ~~~~
use core::libc::{c_void, size_t, malloc, free}; use core::libc::{c_void, size_t, malloc, free};
use core::unstable::intrinsics;
#[abi = "rust-intrinsic"]
extern "rust-intrinsic" mod rusti {
fn init<T>() -> T;
}
// a wrapper around the handle returned by the foreign code // a wrapper around the handle returned by the foreign code
pub struct Unique<T> { pub struct Unique<T> {
@ -166,7 +162,8 @@ pub impl<'self, T: Owned> Unique<T> {
unsafe { unsafe {
let ptr = malloc(core::sys::size_of::<T>() as size_t) as *mut T; let ptr = malloc(core::sys::size_of::<T>() as size_t) as *mut T;
assert!(!ptr::is_null(ptr)); assert!(!ptr::is_null(ptr));
*ptr = value; // `*ptr` is uninitialized, and `*ptr = value` would attempt to destroy it
intrinsics::move_val_init(&mut *ptr, value);
Unique{ptr: ptr} Unique{ptr: ptr}
} }
} }
@ -186,7 +183,7 @@ pub impl<'self, T: Owned> Unique<T> {
impl<T: Owned> Drop for Unique<T> { impl<T: Owned> Drop for Unique<T> {
fn finalize(&self) { fn finalize(&self) {
unsafe { unsafe {
let mut x = rusti::init(); // dummy value to swap in let mut x = intrinsics::init(); // dummy value to swap in
x <-> *self.ptr; // moving the object out is needed to call the destructor x <-> *self.ptr; // moving the object out is needed to call the destructor
free(self.ptr as *c_void) free(self.ptr as *c_void)
} }