I cannot send non null type between threads in rust. I need to call a method on a NonNull pointer for the Windows rust API.

I have tried Arc<Mutex< NonNull>> and Arc<Mutex<RefCell<Box< NonNull>>> but cannot find a way to get send and sync for NonNull.

I would like the thread to halt and await the mutex, so calling a method or even mutating the NonNull type shouldnt be a threading problem but even with runtime borrow checking I get the error: 'NonNull<c_void> cannot be sent between threads safely' and then a list of:

required because of the requirements on the impl of 'Send'

..etc.

I am about to try passing in the method as dyn but this should be possible right?

CodePudding user response：

You need to provide an unsafe implementation of Send to inform the compiler that you've taken into account the thread-safety of the objects behind the pointer (which you did, since you want to use a mutex for synchronization). For example:

// Wrapper around `NonNull<RawType>` that just implements `Send`
struct WrappedPointer(NonNull<RawType>);
unsafe impl Send for WrappedPointer {}

// Safe wrapper around `WrappedPointer` that gives access to the pointer
// only with the mutex locked.
struct SafeType {
    inner: Mutex<WrappedPointer>,
}

impl SafeType {
    fn some_method(&self) {
        let locked = self.inner.lock();
        // use ptr in `locked` to implement functionality, but don't return it
    }
}