Remove allocations from SliceTransform's callback

master
Martin Ek 6 years ago
parent 559d7a7eab
commit 91a536d03b
  1. 40
      src/slice_transform.rs
  2. 4
      tests/test_slice_transform.rs

@ -13,11 +13,9 @@
// limitations under the License.
use std::ffi::CString;
use std::mem;
use std::ptr;
use std::slice;
use libc::{self, c_char, c_void, size_t};
use libc::{c_char, c_void, size_t};
use ffi;
@ -41,15 +39,15 @@ impl SliceTransform {
transform_fn: TransformFn,
in_domain_fn: Option<InDomainFn>,
) -> SliceTransform {
let cb = Box::new(TransformCallback {
let cb = Box::into_raw(Box::new(TransformCallback {
name: CString::new(name.as_bytes()).unwrap(),
transform_fn,
in_domain_fn,
});
}));
let st = unsafe {
ffi::rocksdb_slicetransform_create(
mem::transmute(cb),
cb as *mut c_void,
Some(slice_transform_destructor_callback),
Some(transform_callback),
// this is ugly, but I can't get the compiler
@ -82,18 +80,17 @@ impl SliceTransform {
}
}
pub type TransformFn = fn(&[u8]) -> Vec<u8>;
pub type TransformFn<'a> = fn(&'a [u8]) -> &'a [u8];
pub type InDomainFn = fn(&[u8]) -> bool;
pub struct TransformCallback {
pub struct TransformCallback<'a> {
pub name: CString,
pub transform_fn: TransformFn,
pub transform_fn: TransformFn<'a>,
pub in_domain_fn: Option<InDomainFn>,
}
pub unsafe extern "C" fn slice_transform_destructor_callback(raw_cb: *mut c_void) {
let transform: Box<TransformCallback> = mem::transmute(raw_cb);
drop(transform);
Box::from_raw(raw_cb as *mut TransformCallback);
}
pub unsafe extern "C" fn slice_transform_name_callback(raw_cb: *mut c_void) -> *const c_char {
@ -109,16 +106,9 @@ pub unsafe extern "C" fn transform_callback(
) -> *mut c_char {
let cb = &mut *(raw_cb as *mut TransformCallback);
let key = slice::from_raw_parts(raw_key as *const u8, key_len as usize);
let mut result = (cb.transform_fn)(key);
result.shrink_to_fit();
// copy the result into a C++ destroyable buffer
let buf = libc::malloc(result.len() as size_t);
assert!(!buf.is_null());
ptr::copy(result.as_ptr() as *mut c_void, &mut *buf, result.len());
*dst_length = result.len() as size_t;
buf as *mut c_char
let prefix = (cb.transform_fn)(key);
*dst_length = prefix.len() as size_t;
prefix.as_ptr() as *mut c_char
}
pub unsafe extern "C" fn in_domain_callback(
@ -128,10 +118,6 @@ pub unsafe extern "C" fn in_domain_callback(
) -> u8 {
let cb = &mut *(raw_cb as *mut TransformCallback);
let key = slice::from_raw_parts(raw_key as *const u8, key_len as usize);
if (cb.in_domain_fn.unwrap())(key) {
1
} else {
0
}
let in_domain = cb.in_domain_fn.unwrap();
in_domain(key) as u8
}

@ -13,8 +13,8 @@ pub fn test_slice_transform() {
let b1: Box<[u8]> = key(b"bbb1");
let b2: Box<[u8]> = key(b"bbb2");
fn first_three(k: &[u8]) -> Vec<u8> {
k.iter().take(3).cloned().collect()
fn first_three<'a>(k: &'a [u8]) -> &'a [u8] {
&k[..3]
}
let prefix_extractor = SliceTransform::create("first_three", first_three, None);

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