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Add wasm32 atomic intrinsics #561

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Sep 6, 2018
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100 changes: 100 additions & 0 deletions coresimd/wasm32/atomic.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,100 @@
//! Intrinsics associated with WebAssembly's upcoming threads proposal.
//!
//! These intrinsics are all unstable because they're not actually stable in
//! WebAssembly itself yet. The signatures may change as [the
//! specification][spec] is updated.
//!
//! [spec]: https://github.com/WebAssembly/threads

#![cfg(target_feature = "atomics")]
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I think this should be in the parent hiding the module, and the re-export of these.

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Ah wait, I see you did the same in the memory module, do we want to export the modules themselves (atomic, memory, simd128, etc.) ?

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Sure yeah, do you mean just the attribute or the functions too?

On a possibly random tangent about function names...

I'm starting to get a little torn on the naming of the functions here. Technically the function name should be wasm32::i32::atomic::wait but that's a lot of ::. Currently wasm32::atomic::i32_wait is sort of weirdly inconsistent. What do you think of wasm32::i32_atomic_wait? Basically translating all . to _ and we have toplevel functions for all the operations? (this'd affect the SIMD proposal slightly)

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I'm starting to get a little torn on the naming of the functions here.

Me too, in the simd module we also had problems with this. Maybe we should just open an issue to discuss this, e.g., show examples of the wasm names, and how could we make them consistent in Rust.

In the mean time I think we can do "whatever". The other PR puts the intrinsics behind a memory:: so I don't mind them here being behind atomic:: and the simd module puts them behind e.g. i32x4:: IIRC and the other vector type names, so at least it remains consistent for now.

About the best way to do this, I am not a super huge fan of i32_atomic_wait, but I don't really like the many :: either :/ What does clang do? __builtin_... ?

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Sure thing, done! - #562


#[cfg(test)]
use stdsimd_test::assert_instr;
#[cfg(test)]
use wasm_bindgen_test::wasm_bindgen_test;

extern "C" {
#[link_name = "llvm.wasm.atomic.wait.i32"]
fn llvm_atomic_wait_i32(ptr: *mut i32, exp: i32, timeout: i64) -> i32;
#[link_name = "llvm.wasm.atomic.wait.i64"]
fn llvm_atomic_wait_i64(ptr: *mut i64, exp: i64, timeout: i64) -> i32;
#[link_name = "llvm.wasm.atomic.notify"]
fn llvm_atomic_notify(ptr: *mut i32, cnt: i32) -> i32;
}

/// Corresponding intrinsic to wasm's [`i32.atomic.wait` instruction][instr]
///
/// This function, when called, will block the current thread if the memory
/// pointed to by `ptr` is equal to `expression` (performing this action
/// atomically).
///
/// The argument `timeout_ns` is a maxinum number of nanoseconds the calling
/// thread will be blocked for, if it blocks. If the timeout is negative then
/// the calling thread will be blocked forever.
///
/// The calling thread can only be woken up with a call to the `wake` intrinsic
/// once it has been blocked. Changing the memory behind `ptr` will not wake the
/// thread once it's blocked.
///
/// # Return value
///
/// * 0 - indicates that the thread blocked and then was woken up
/// * 1 - the loaded value from `ptr` didn't match `expression`, the thread
/// didn't block
/// * 2 - the thread blocked, but the timeout expired.
///
/// [instr]: https://github.com/WebAssembly/threads/blob/master/proposals/threads/Overview.md#wait
#[inline]
#[cfg_attr(test, assert_instr("i32.atomic.wait"))]
pub unsafe fn wait_i32(ptr: *mut i32, expression: i32, timeout_ns: i64) -> i32 {
llvm_atomic_wait_i32(ptr, expression, timeout_ns)
}

/// Corresponding intrinsic to wasm's [`i64.atomic.wait` instruction][instr]
///
/// This function, when called, will block the current thread if the memory
/// pointed to by `ptr` is equal to `expression` (performing this action
/// atomically).
///
/// The argument `timeout_ns` is a maxinum number of nanoseconds the calling
/// thread will be blocked for, if it blocks. If the timeout is negative then
/// the calling thread will be blocked forever.
///
/// The calling thread can only be woken up with a call to the `wake` intrinsic
/// once it has been blocked. Changing the memory behind `ptr` will not wake the
/// thread once it's blocked.
///
/// # Return value
///
/// * 0 - indicates that the thread blocked and then was woken up
/// * 1 - the loaded value from `ptr` didn't match `expression`, the thread
/// didn't block
/// * 2 - the thread blocked, but the timeout expired.
///
/// [instr]: https://github.com/WebAssembly/threads/blob/master/proposals/threads/Overview.md#wait
#[inline]
#[cfg_attr(test, assert_instr("i64.atomic.wait"))]
pub unsafe fn wait_i64(ptr: *mut i64, expression: i64, timeout_ns: i64) -> i32 {
llvm_atomic_wait_i64(ptr, expression, timeout_ns)
}

/// Corresponding intrinsic to wasm's [`atomic.wake` instruction][instr]
///
/// This function will wake up a number of threads blocked on the address
/// indicated by `ptr`. Threads previously blocked with the `wait_i32` and
/// `wait_i64` functions above will be woken up.
///
/// The `waiters` argument indicates how many waiters should be woken up (a
/// maximum). If the value is negative all waiters are woken up, and if the
/// value is zero no waiters are woken up.
///
/// # Return value
///
/// Returns the number of waiters which were actually woken up.
///
/// [instr]: https://github.com/WebAssembly/threads/blob/master/proposals/threads/Overview.md#wake
#[inline]
#[cfg_attr(test, assert_instr("atomic.wake"))]
pub unsafe fn wake(ptr: *mut i32, waiters: i32) -> i32 {
llvm_atomic_notify(ptr, waiters)
}
2 changes: 2 additions & 0 deletions coresimd/wasm32/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -47,3 +47,5 @@ pub unsafe fn current_memory() -> i32 {
pub unsafe fn grow_memory(delta: i32) -> i32 {
llvm_grow_memory(delta)
}

pub mod atomic;