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// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License..
use crate::sys::lazy_box::{LazyBox, LazyInit};
use crate::sys::locks::futex;
use crate::sys::locks::generic;
use core::ptr;
use core::sync::atomic::{AtomicPtr, Ordering};

pub trait CondvarCheck {
    type Check;
}

/// For boxed mutexes, a `Condvar` will check it's only ever used with the same
/// mutex, based on its (stable) address.
impl<T: LazyInit> CondvarCheck for LazyBox<T> {
    type Check = SameMutexCheck;
}

pub struct SameMutexCheck {
    addr: AtomicPtr<()>,
}

#[allow(dead_code)]
impl SameMutexCheck {
    pub const fn new() -> Self {
        Self {
            addr: AtomicPtr::new(ptr::null_mut()),
        }
    }
    pub fn verify(&self, mutex: &generic::mutex::MovableMutex) {
        let raw: &generic::mutex::Mutex = mutex;
        let addr = raw as *const generic::mutex::Mutex as *const () as *mut _;
        // Relaxed is okay here because we never read through `self.addr`, and only use it to
        // compare addresses.
        match self.addr.compare_exchange(
            ptr::null_mut(),
            addr,
            Ordering::Relaxed,
            Ordering::Relaxed,
        ) {
            Ok(_) => {}               // Stored the address
            Err(n) if n == addr => {} // Lost a race to store the same address
            _ => panic!("attempted to use a condition variable with two mutexes"),
        }
    }
}

/// Unboxed mutexes may move, so `Condvar` can not require its address to stay
/// constant.
impl CondvarCheck for futex::mutex::Mutex {
    type Check = NoCheck;
}

pub struct NoCheck;

#[allow(dead_code)]
impl NoCheck {
    pub const fn new() -> Self {
        Self
    }
    pub fn verify(&self, _: &futex::mutex::MovableMutex) {}
}