我有一个外部库(例如libcisland.so),其接口如下:
size_t lib_handle_size();
typedef void* handle;
int lib_init(handle h);
int lib_store(handle h, int value);
int lib_restore(handle h, int *pvalue);
该库的用户应该执行以下操作:
// allocate some buffer in client address space
handle h = malloc(lib_handle_size());
// pass this buffer to library for initialization
if (lib_init(h)) { /* handle errors */ }
// library initializes this handle by some opaque fashion
// then user uses it
lib_store(h,42);
int r;
lib_restore(h,&r);
// after all work is done, user frees this handle
free(h);
我不知道如何正确地将此接口包装到Rust。这就是我最终的结果:
pub struct Island {
h : Handle,
v : Vec<u8>,
}
impl Island {
pub fn new() -> Island {
let len = unsafe { lib_handle_size() };
let mut v: Vec<u8> = Vec::with_capacity(len);
let h: Handle = v.as_mut_ptr();
Island { v:v, h:h, }
}
pub fn store(&mut self, v: i32) {
unsafe { lib_store(self.h, v); }
}
pub fn restore(&mut self) -> i32 {
let mut v = 0;
unsafe { lib_restore(self.h, &mut v); }
v
}
}
impl Drop for Island {
fn drop(&mut self) {
drop(&mut self.v);
}
}
/// unsafe part
use libc::size_t;
pub type Handle = *mut u8;
#[link(name="cisland")]
extern {
pub fn lib_handle_size() -> size_t;
pub fn lib_init(h: Handle) -> i32;
pub fn lib_store(h: Handle, value: i32) -> i32;
pub fn lib_restore(h: Handle, pvalue: &mut i32) -> i32;
}
为此目的可以使用Vec(u8)
吗?此Drop
特性是否正确实施?
为此目的可以使用
Vec(u8)
吗?
一个向量并不意味着要那样使用,即使您的代码可以工作,这也不是一个好方法。
要正确执行此操作,您需要一个实验功能(此功能相当稳定),需要使用System
结构和System
特征。不幸的是,您的库没有为其句柄提供任何对齐要求,因此我们必须使用Alloc
。
Alloc
,1
是不正确的(顺便说一下,隐藏指针不好)。应该是pub type Handle = *mut u8;
。
typedef void* handle;
我稍微改变一下pub type Handle = *mut libc::c_void;
和#![feature(allocator_api)]
use std::alloc::{Alloc, Layout, System};
use std::ptr::NonNull;
pub struct Island {
handle: NonNull<u8>,
layout: Layout,
}
impl Island {
pub fn new() -> Island {
let size = unsafe { lib_handle_size() };
let layout = Layout::from_size_align(size, 1).unwrap();
let handle = unsafe { System.alloc(layout).unwrap() };
Self { handle, layout }
}
pub fn store(&mut self, v: i32) -> Result<(), ()> {
unsafe {
lib_store(self.handle.as_ptr() as Handle, v);
}
Ok(())
}
pub fn restore(&mut self, v: &mut i32) -> Result<(), ()> {
unsafe {
lib_restore(self.handle.as_ptr() as Handle, v);
}
Ok(())
}
}
impl Drop for Island {
fn drop(&mut self) {
unsafe { System.dealloc(self.handle, self.layout) }
}
}
/// unsafe part
use libc::size_t;
pub type Handle = *mut libc::c_void;
#[link(name = "cisland")]
extern "C" {
pub fn lib_handle_size() -> size_t;
pub fn lib_init(h: Handle) -> i32;
pub fn lib_store(h: Handle, value: i32) -> i32;
pub fn lib_restore(h: Handle, pvalue: &mut i32) -> i32;
}
函数以返回结果。我敢打赌,您的C函数也是如此。