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Don't box block descriptors #17

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Don't box block descriptors #17

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6396261
Don't heap-allocate block descriptors
TellowKrinkle Oct 2, 2022
3d715d2
Only add BLOCK_HAS_COPY_DISPOSE when needed
TellowKrinkle Oct 2, 2022
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40 changes: 20 additions & 20 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -52,7 +52,6 @@ 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 { }

Expand Down Expand Up @@ -236,7 +235,7 @@ concrete_block_impl!(concrete_block_invoke_args12, a: A, b: B, c: C, d: D, e: E,
#[repr(C)]
pub struct ConcreteBlock<A, R, F> {
base: BlockBase<A, R>,
descriptor: Box<BlockDescriptor<ConcreteBlock<A, R, F>>>,
descriptor: &'static BlockDescriptor,
closure: F,
}

Expand All @@ -256,15 +255,16 @@ impl<A, R, F> ConcreteBlock<A, R, F> {
/// correct arguments.
unsafe fn with_invoke(invoke: unsafe extern fn(*mut Self, ...) -> R,
closure: F) -> Self {
let descriptor = &BlockDescriptorImpl::<ConcreteBlock<A, R, F>>::DESCRIPTOR;
const BLOCK_HAS_COPY_DISPOSE: c_int = 1 << 25;
ConcreteBlock {
base: BlockBase {
isa: &_NSConcreteStackBlock,
// 1 << 25 = BLOCK_HAS_COPY_DISPOSE
flags: 1 << 25,
flags: if descriptor.dispose_helper.is_some() { BLOCK_HAS_COPY_DISPOSE } else { 0 },
_reserved: 0,
invoke: mem::transmute(invoke),
},
descriptor: Box::new(BlockDescriptor::new()),
descriptor: descriptor,
closure: closure,
}
}
Expand Down Expand Up @@ -308,32 +308,32 @@ impl<A, R, F> DerefMut for ConcreteBlock<A, R, F> {
}
}

unsafe extern fn block_context_dispose<B>(block: &mut B) {
unsafe extern fn block_context_dispose<B>(block: *mut c_void) {
// Read the block onto the stack and let it drop
ptr::read(block);
block.cast::<B>().read();
}

unsafe extern fn block_context_copy<B>(_dst: &mut B, _src: &B) {
unsafe extern fn block_context_copy(_dst: *mut c_void, _src: *const c_void) {
// The runtime memmoves the src block into the dst block, nothing to do
}

#[repr(C)]
struct BlockDescriptor<B> {
struct BlockDescriptor {
_reserved: c_ulong,
block_size: c_ulong,
copy_helper: unsafe extern fn(&mut B, &B),
dispose_helper: unsafe extern fn(&mut B),
copy_helper: Option<unsafe extern fn(*mut c_void, *const c_void)>,
dispose_helper: Option<unsafe extern fn(*mut c_void)>,
}

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>,
}
}
struct BlockDescriptorImpl<B>(PhantomData<B>);

impl<B> BlockDescriptorImpl<B> {
const DESCRIPTOR: BlockDescriptor = BlockDescriptor {
_reserved: 0,
block_size: mem::size_of::<B>() as c_ulong,
copy_helper: if std::mem::needs_drop::<B>() { Some(block_context_copy) } else { None },
dispose_helper: if std::mem::needs_drop::<B>() { Some(block_context_dispose::<B>) } else { None },
};
}

#[cfg(test)]
Expand Down