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/*!
A Rust interface for Objective-C blocks.
For more information on the specifics of the block implementation, see
# Invoking blocks
The `Block` struct is used for invoking blocks from Objective-C. For example,
consider this Objective-C function:
``` objc
int32_t sum(int32_t (^block)(int32_t, int32_t)) {
return block(5, 8);
}
```
We could write it in Rust as the following:
```
# use block::Block;
unsafe fn sum(block: &Block<(i32, i32), i32>) -> i32 {
block.call((5, 8))
}
```
Note the extra parentheses in the `call` method, since the arguments must be
passed as a tuple.
# Creating blocks
Creating a block to pass to Objective-C can be done with the `ConcreteBlock`
struct. For example, to create a block that adds two `i32`s, we could write:
```
# use block::ConcreteBlock;
let block = ConcreteBlock::new(|a: i32, b: i32| a + b);
let block = block.copy();
assert!(unsafe { block.call((5, 8)) } == 13);
```
It is important to copy your block to the heap (with the `copy` method) before
passing it to Objective-C; this is because our `ConcreteBlock` is only meant
to be copied once, and we can enforce this in Rust, but if Objective-C code
were to copy it twice we could have a double free.
*/
#[cfg(test)]
mod test_utils;
use std::marker::PhantomData;
use std::mem;
use std::ops::{Deref, DerefMut};
use std::os::raw::{c_int, c_ulong, c_void};
use std::ptr;
enum Class { }
#[cfg_attr(any(target_os = "macos", target_os = "ios"),
link(name = "System", kind = "dylib"))]
#[cfg_attr(not(any(target_os = "macos", target_os = "ios")),
link(name = "BlocksRuntime", kind = "dylib"))]
extern {
static _NSConcreteStackBlock: Class;
fn _Block_copy(block: *const c_void) -> *mut c_void;
fn _Block_release(block: *const c_void);
}
/// Types that may be used as the arguments to an Objective-C block.
pub trait BlockArguments: Sized {
/// Calls the given `Block` with self as the arguments.
///
/// Unsafe because `block` must point to a valid `Block` and this invokes
/// foreign code whose safety the compiler cannot verify.
unsafe fn call_block<R>(self, block: *mut Block<Self, R>) -> R;
}
macro_rules! block_args_impl {
($($a:ident : $t:ident),*) => (
impl<$($t),*> BlockArguments for ($($t,)*) {
unsafe fn call_block<R>(self, block: *mut Block<Self, R>) -> R {
let invoke: unsafe extern fn(*mut Block<Self, R> $(, $t)*) -> R = {
let base = block as *mut BlockBase<Self, R>;
mem::transmute((*base).invoke)
};
let ($($a,)*) = self;
invoke(block $(, $a)*)
}
}
);
}
block_args_impl!();
block_args_impl!(a: A);
block_args_impl!(a: A, b: B);
block_args_impl!(a: A, b: B, c: C);
block_args_impl!(a: A, b: B, c: C, d: D);
block_args_impl!(a: A, b: B, c: C, d: D, e: E);
block_args_impl!(a: A, b: B, c: C, d: D, e: E, f: F);
block_args_impl!(a: A, b: B, c: C, d: D, e: E, f: F, g: G);
block_args_impl!(a: A, b: B, c: C, d: D, e: E, f: F, g: G, h: H);
block_args_impl!(a: A, b: B, c: C, d: D, e: E, f: F, g: G, h: H, i: I);
block_args_impl!(a: A, b: B, c: C, d: D, e: E, f: F, g: G, h: H, i: I, j: J);
block_args_impl!(a: A, b: B, c: C, d: D, e: E, f: F, g: G, h: H, i: I, j: J, k: K);
block_args_impl!(a: A, b: B, c: C, d: D, e: E, f: F, g: G, h: H, i: I, j: J, k: K, l: L);
#[repr(C)]
struct BlockBase<A, R> {
isa: *const Class,
flags: c_int,
_reserved: c_int,
invoke: unsafe extern fn(*mut Block<A, R>, ...) -> R,
}
/// An Objective-C block that takes arguments of `A` when called and
/// returns a value of `R`.
#[repr(C)]
pub struct Block<A, R> {
_base: PhantomData<BlockBase<A, R>>,
}
impl<A: BlockArguments, R> Block<A, R> where A: BlockArguments {
/// Call self with the given arguments.
///
/// Unsafe because this invokes foreign code that the caller must verify
/// doesn't violate any of Rust's safety rules. For example, if this block
/// is shared with multiple references, the caller must ensure that calling
/// it will not cause a data race.
pub unsafe fn call(&self, args: A) -> R {
args.call_block(self as *const _ as *mut _)
}
}
/// A reference-counted Objective-C block.
pub struct RcBlock<A, R> {
ptr: *mut Block<A, R>,
}
impl<A, R> RcBlock<A, R> {
/// Construct an `RcBlock` for the given block without copying it.
/// The caller must ensure the block has a +1 reference count.
///
/// Unsafe because `ptr` must point to a valid `Block` and must have a +1
/// reference count or it will be overreleased when the `RcBlock` is
/// dropped.
pub unsafe fn new(ptr: *mut Block<A, R>) -> Self {
RcBlock { ptr: ptr }
}
/// Constructs an `RcBlock` by copying the given block.
///
/// Unsafe because `ptr` must point to a valid `Block`.
pub unsafe fn copy(ptr: *mut Block<A, R>) -> Self {
let ptr = _Block_copy(ptr as *const c_void) as *mut Block<A, R>;
RcBlock { ptr: ptr }
}
}
impl<A, R> Clone for RcBlock<A, R> {
fn clone(&self) -> RcBlock<A, R> {
unsafe {
RcBlock::copy(self.ptr)
}
}
}
impl<A, R> Deref for RcBlock<A, R> {
type Target = Block<A, R>;
fn deref(&self) -> &Block<A, R> {
unsafe { &*self.ptr }
}
}
impl<A, R> Drop for RcBlock<A, R> {
fn drop(&mut self) {
unsafe {
_Block_release(self.ptr as *const c_void);
}
}
}
/// Types that may be converted into a `ConcreteBlock`.
pub trait IntoConcreteBlock<A>: Sized where A: BlockArguments {
/// The return type of the resulting `ConcreteBlock`.
type Ret;
/// Consumes self to create a `ConcreteBlock`.
fn into_concrete_block(self) -> ConcreteBlock<A, Self::Ret, Self>;
}
macro_rules! concrete_block_impl {
($f:ident) => (
concrete_block_impl!($f,);
);
($f:ident, $($a:ident : $t:ident),*) => (
impl<$($t,)* R, X> IntoConcreteBlock<($($t,)*)> for X
where X: Fn($($t,)*) -> R {
type Ret = R;
fn into_concrete_block(self) -> ConcreteBlock<($($t,)*), R, X> {
unsafe extern fn $f<$($t,)* R, X>(
block_ptr: *mut ConcreteBlock<($($t,)*), R, X>
$(, $a: $t)*) -> R
where X: Fn($($t,)*) -> R {
let block = &*block_ptr;
(block.closure)($($a),*)
}
let f: unsafe extern fn(*mut ConcreteBlock<($($t,)*), R, X> $(, $a: $t)*) -> R = $f;
unsafe {
ConcreteBlock::with_invoke(mem::transmute(f), self)
}
}
}
);
}
concrete_block_impl!(concrete_block_invoke_args0);
concrete_block_impl!(concrete_block_invoke_args1, a: A);
concrete_block_impl!(concrete_block_invoke_args2, a: A, b: B);
concrete_block_impl!(concrete_block_invoke_args3, a: A, b: B, c: C);
concrete_block_impl!(concrete_block_invoke_args4, a: A, b: B, c: C, d: D);
concrete_block_impl!(concrete_block_invoke_args5, a: A, b: B, c: C, d: D, e: E);
concrete_block_impl!(concrete_block_invoke_args6, a: A, b: B, c: C, d: D, e: E, f: F);
concrete_block_impl!(concrete_block_invoke_args7, a: A, b: B, c: C, d: D, e: E, f: F, g: G);
concrete_block_impl!(concrete_block_invoke_args8, a: A, b: B, c: C, d: D, e: E, f: F, g: G, h: H);
concrete_block_impl!(concrete_block_invoke_args9, a: A, b: B, c: C, d: D, e: E, f: F, g: G, h: H, i: I);
concrete_block_impl!(concrete_block_invoke_args10, a: A, b: B, c: C, d: D, e: E, f: F, g: G, h: H, i: I, j: J);
concrete_block_impl!(concrete_block_invoke_args11, a: A, b: B, c: C, d: D, e: E, f: F, g: G, h: H, i: I, j: J, k: K);
concrete_block_impl!(concrete_block_invoke_args12, a: A, b: B, c: C, d: D, e: E, f: F, g: G, h: H, i: I, j: J, k: K, l: L);
/// An Objective-C block whose size is known at compile time and may be
/// constructed on the stack.
#[repr(C)]
pub struct ConcreteBlock<A, R, F> {
base: BlockBase<A, R>,
descriptor: Box<BlockDescriptor<ConcreteBlock<A, R, F>>>,
closure: F,
}
impl<A, R, F> ConcreteBlock<A, R, F>
where A: BlockArguments, F: IntoConcreteBlock<A, Ret=R> {
/// Constructs a `ConcreteBlock` with the given closure.
/// When the block is called, it will return the value that results from
/// calling the closure.
pub fn new(closure: F) -> Self {
closure.into_concrete_block()
}
}
impl<A, R, F> ConcreteBlock<A, R, F> {
/// Constructs a `ConcreteBlock` with the given invoke function and closure.
/// Unsafe because the caller must ensure the invoke function takes the
/// correct arguments.
unsafe fn with_invoke(invoke: unsafe extern fn(*mut Self, ...) -> R,
closure: F) -> Self {
ConcreteBlock {
base: BlockBase {
isa: &_NSConcreteStackBlock,
// 1 << 25 = BLOCK_HAS_COPY_DISPOSE
flags: 1 << 25,
_reserved: 0,
invoke: mem::transmute(invoke),
},
descriptor: Box::new(BlockDescriptor::new()),
closure: closure,
}
}
}
impl<A, R, F> ConcreteBlock<A, R, F> where F: 'static {
/// Copy self onto the heap as an `RcBlock`.
pub fn copy(self) -> RcBlock<A, R> {
unsafe {
let mut block = self;
let copied = RcBlock::copy(&mut *block);
// At this point, our copy helper has been run so the block will
// be moved to the heap and we can forget the original block
// because the heap block will drop in our dispose helper.
mem::forget(block);
copied
}
}
}
impl<A, R, F> Clone for ConcreteBlock<A, R, F> where F: Clone {
fn clone(&self) -> Self {
unsafe {
ConcreteBlock::with_invoke(mem::transmute(self.base.invoke),
self.closure.clone())
}
}
}
impl<A, R, F> Deref for ConcreteBlock<A, R, F> {
type Target = Block<A, R>;
fn deref(&self) -> &Block<A, R> {
unsafe { &*(&self.base as *const _ as *const Block<A, R>) }
}
}
impl<A, R, F> DerefMut for ConcreteBlock<A, R, F> {
fn deref_mut(&mut self) -> &mut Block<A, R> {
unsafe { &mut *(&mut self.base as *mut _ as *mut Block<A, R>) }
}
}
unsafe extern fn block_context_dispose<B>(block: &mut B) {
// Read the block onto the stack and let it drop
ptr::read(block);
}
unsafe extern fn block_context_copy<B>(_dst: &mut B, _src: &B) {
// The runtime memmoves the src block into the dst block, nothing to do
}
#[repr(C)]
struct BlockDescriptor<B> {
_reserved: c_ulong,
block_size: c_ulong,
copy_helper: unsafe extern fn(&mut B, &B),
dispose_helper: unsafe extern fn(&mut B),
}
impl<B> BlockDescriptor<B> {
fn new() -> BlockDescriptor<B> {
BlockDescriptor {
_reserved: 0,
block_size: mem::size_of::<B>() as c_ulong,
copy_helper: block_context_copy::<B>,
dispose_helper: block_context_dispose::<B>,
}
}
}
#[cfg(test)]
mod tests {
use test_utils::*;
use super::{ConcreteBlock, RcBlock};
#[test]
fn test_call_block() {
let block = get_int_block_with(13);
unsafe {
assert!(block.call(()) == 13);
}
}
#[test]
fn test_call_block_args() {
let block = get_add_block_with(13);
unsafe {
assert!(block.call((2,)) == 15);
}
}
#[test]
fn test_create_block() {
let block = ConcreteBlock::new(|| 13);
let result = invoke_int_block(&block);
assert!(result == 13);
}
#[test]
fn test_create_block_args() {
let block = ConcreteBlock::new(|a: i32| a + 5);
let result = invoke_add_block(&block, 6);
assert!(result == 11);
}
#[test]
fn test_concrete_block_copy() {
let s = "Hello!".to_string();
let expected_len = s.len() as i32;
let block = ConcreteBlock::new(move || s.len() as i32);
assert!(invoke_int_block(&block) == expected_len);
let copied = block.copy();
assert!(invoke_int_block(&copied) == expected_len);
}
#[test]
fn test_concrete_block_stack_copy() {
fn make_block() -> RcBlock<(), i32> {
let x = 7;
let block = ConcreteBlock::new(move || x);
block.copy()
}
let block = make_block();
assert!(invoke_int_block(&block) == 7);
}
}