azriel91
commented
4 years ago Hiya, sorry for the late reply, but in the snippet, I suspect dispatcher2 contains a system that is accessing State mutably:
let mut state = world.fetch_mut::<State>(); // Get hold of a `Write<'_, State>`
state.do_something_else_mutably();
dispatcher2.dispatch(&world); // Trying to get another `Write'_, State>` causes the panic.If you do this instead, it should work:
{
let mut state = world.fetch_mut::<State>(); // Get hold of a `Write<'_, State>`
state.do_something_else_mutably();
// drop the `Write<'_, State>`
}
dispatcher2.dispatch(&world); // Now you can get a `Write'_, State>` without panickingA potential improvement is to allow multiple Write's to be held, but only panic if both are dereferenced together. I haven't gotten familiar with the code to implement that yet.
Imberflur
Description
I'm getting a runtime panic with:
Tried to fetch data, but it was already borrowedMeta
Rust version: 1.39.0 Specs version / commit: 0.15.1 Operating system: Arch Linux
Reproduction
Steps to reproduce the behavior: Issue seems to only happen if I call dispatch on two different Dispatchers under specific conditions when in between I modify a resource inside a separate code block.
I suspect this forces the mut reference to that resource to be dropped but somehow the second dispatcher run panics with this error.
Execution quasi-example:
Expected behavior
Both dispatchers should've executed fine.
Backtrace