I am modifiying a crate (rust-argon2
) to some custom needs. That crate uses multithreading with scoped threads using crossbeam
. I want to have a mutable state between threads, that may depend on each other.
The following snippet showcases the situation: fill_memory_blocks_mt
gets some mutable state reference state
, that will be mutated in fill_segment
across multiple threads using crossbeam_utils::thread::scope
. They are synced via common::SYNC_POINTS
.
fn fill_memory_blocks_mt(context: &Context, memory: &mut Memory, state: &mut Argon2Result) {
for p in 0..context.config.time_cost {
for s in 0..common::SYNC_POINTS {
let _ = scope(|scoped| {
for (l, mem) in (0..context.config.lanes).zip(memory.as_lanes_mut()) {
let position = Position {
pass: p,
lane: l,
slice: s,
index: 0,
};
scoped.spawn(move |_| {
fill_segment(context, &position, mem, state);
});
}
});
}
}
}
The compiler outputs following message:
error[E0382]: use of moved value: `state`
--> src/core.rs:223:34
|
223 | scoped.spawn(move |_| {
| ^^^^^^^^ value moved into closure here, in previous iteration of loop
224 | fill_segment(context, &position, mem, state);
| ----- use occurs due to use in closure
|
= note: move occurs because `state` has type `&mut Argon2Result`, which does not implement the `Copy` trait
help: consider creating a fresh reborrow of `state` here
|
223 | scoped.spawn(&mut *move |_| {
| ++++++
error[E0382]: use of moved value: `state`
--> src/core.rs:215:27
|
212 | fn fill_memory_blocks_mt(context: &Context, memory: &mut Memory, state: &mut Argon2Result) {
| ----- move occurs because `state` has type `&mut Argon2Result`, which does not implement the `Copy` trait
...
215 | let _ = scope(|scoped| {
| ^^^^^^^^ value moved into closure here, in previous iteration of loop
...
224 | fill_segment(context, &position, mem, state);
| ----- use occurs due to use in closure
|
help: consider creating a fresh reborrow of `state` here
|
215 | let _ = scope(&mut *|scoped| {
| ++++++
For more information about this error, try `rustc --explain E0382`.
error: could not compile `rust-argon2-wasm` due to 2 previous errors
Of course I don't want to copy state
but use one instance for all threads. They don't overwrite fields between each other, but may depend on each other.