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    //! 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(any(target_feature = "atomics", dox))]

    #[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.
    ///
    /// # Availability
    ///
    /// This intrinsic is only available **when the standard library itself is
    /// compiled with the `atomics` target feature**. This version of the standard
    /// library is not obtainable via `rustup`, but rather will require the standard
    /// library to be compiled from source.
    ///
    /// [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.
    ///
    /// # Availability
    ///
    /// This intrinsic is only available **when the standard library itself is
    /// compiled with the `atomics` target feature**. This version of the standard
    /// library is not obtainable via `rustup`, but rather will require the standard
    /// library to be compiled from source.
    ///
    /// [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.
    ///
    /// # Availability
    ///
    /// This intrinsic is only available **when the standard library itself is
    /// compiled with the `atomics` target feature**. This version of the standard
    /// library is not obtainable via `rustup`, but rather will require the standard
    /// library to be compiled from source.
    ///
    /// [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)
    }

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