mutex example initialization procedure appears to be incorrectly synchronized

[soooch]

shared_memory/examples/mutex.rs

Lines 65 to 89 in fda4134

	let mutex = if shmem.is_owner() {
	is_init.store(0, Ordering::Relaxed);
	// Initialize the mutex
	let (lock, _bytes_used) = unsafe {
	Mutex::new(
	raw_ptr, // Base address of Mutex
	raw_ptr.add(Mutex::size_of(Some(raw_ptr))), // Address of data protected by mutex
	)
	.unwrap()
	};
	is_init.store(1, Ordering::Relaxed);
	lock
	} else {
	// wait until mutex is initialized
	while is_init.load(Ordering::Relaxed) != 1 {}
	// Load existing mutex
	let (lock, _bytes_used) = unsafe {
	Mutex::from_existing(
	raw_ptr, // Base address of Mutex
	raw_ptr.add(Mutex::size_of(Some(raw_ptr))), // Address of data protected by mutex
	)
	.unwrap()
	};
	lock
	};

    let mutex = if shmem.is_owner() {
        // is_init.store(0, Ordering::Relaxed); // not actually needed
        // Initialize the mutex
        let (lock, _bytes_used) = unsafe {
            Mutex::new(
                raw_ptr,                                    // Base address of Mutex
                raw_ptr.add(Mutex::size_of(Some(raw_ptr))), // Address of data protected by mutex
            )
            .unwrap()
        };
        // is_init.store(1, Ordering::Relaxed); // relaxed wouldn't restrict reordering of mutex init unless i'm missing something
        is_init.store(1, Ordering::Release);
        lock
    } else {
        // wait until mutex is initialized
        // while is_init.load(Ordering::Relaxed) != 1 {} // need acquire for release store to is_init to synchronize-with load
        // could also do a relaxed loop with a acquire fence, but that adds an extra instruction in the common case
        while is_init.load(Ordering::Acquire) != 1 {
            std::hint::spin_loop();
        }
        // Load existing mutex
        let (lock, _bytes_used) = unsafe {
            Mutex::from_existing(
                raw_ptr,                                    // Base address of Mutex
                raw_ptr.add(Mutex::size_of(Some(raw_ptr))), // Address of data  protected by mutex
            )
            .unwrap()
        };
        lock
    };