Immutable reference to ArrayRef is not Sync #1569
Description
I am writing a code for feature tracking in rust and I would like to parallelize my code over the features. For this I need to have the images shared across the threads, however I cannot do so when the type of the images are &ArrayRef2, however it works if the type of the images are &ArrayBase<S, Ix2> with the required trait bounds .
Below is a minimal reproducible example:
use ndarray::{ArrayBase, ArrayRef2, Data, Ix2, ScalarOperand, Zip, arr2};
use num_traits::{Float, FromPrimitive};
// Fails to compile
pub fn track_level<A>(
image_host: &ArrayRef2<A>,
image_target: &ArrayRef2<A>,
keypoints_host: &ArrayRef2<A>,
keypoints_target: &mut ArrayRef2<A>
)
where
A: Float + Send + Sync + ScalarOperand + FromPrimitive
{
Zip::from(keypoints_host.rows()).and(keypoints_target.rows_mut()).par_for_each(
|kp_host, mut kp_target|
{
let t = arr2(&[[image_host.mean().unwrap()], [image_target.mean().unwrap()]]);
kp_target.assign(&(&kp_host + &t));
}
);
}
// Compiles succesfully
pub fn track_level_array_base<A, SH, ST>(
image_host: &ArrayBase<SH, Ix2>,
image_target: &ArrayBase<ST, Ix2>,
keypoints_host: &ArrayRef2<A>,
keypoints_target: &mut ArrayRef2<A>
)
where
A: Float + Send + Sync + ScalarOperand + FromPrimitive,
SH: Data<Elem = A> + Send + Sync,
ST: Data<Elem = A> + Send + Sync
{
Zip::from(keypoints_host.rows()).and(keypoints_target.rows_mut()).par_for_each(
|kp_host, mut kp_target|
{
let t = arr2(&[[image_host.mean().unwrap()], [image_target.mean().unwrap()]]);
kp_target.assign(&(&kp_host + &t));
}
);
}The compiler error I get is the following:
error[E0277]: `NonNull<A>` cannot be shared between threads safely
--> src/patch_tracker/test.rs:16:9
|
15 | Zip::from(keypoints_host.rows()).and(keypoints_target.rows_mut()).par_for_each(
| ------------ required by a bound introduced by this call
16 | |kp_host, mut kp_target|
| ^-----------------------
| |
| _________within this `{closure@src/patch_tracker/test.rs:16:9: 16:33}`
| |
17 | | {
18 | | let t = arr2(&[[image_host.mean().unwrap()], [image_target.mean().unwrap()]]);
19 | | kp_target.assign(&(&kp_host + &t));
20 | | }
| |_________^ `NonNull<A>` cannot be shared between threads safely
|
= help: within `{closure@src/patch_tracker/test.rs:16:9: 16:33}`, the trait `Sync` is not implemented for `NonNull<A>`
Is this an expected behavior ?