'already mutably borrowed: BorrowError': src/plugin/host.rs:359

[SamWindell]

I'm sporadically getting some panics firing. I'm seeing this on any OS.

Error: 1 [ERROR] thread 'main' panicked at 'already mutably borrowed: BorrowError': src/plugin/host.rs:359
Error: 1 [ERROR] thread 'main' panicked at 'already borrowed: BorrowMutError': src/plugin/host.rs:309
Error: 1 [ERROR] thread 'main' panicked at 'panic in a destructor during cleanup': core/src/panicking.rs:229

Looking at the first error message, it's related to code for checking if there were main thread callbacks requested:

clap-validator/src/plugin/host.rs

Line 359 in 2f71690

let instances = self.instances.borrow();

A recent change in my plugin is more frequent use of request_callback().

Repro:

1. Download 'Manual Install' files to get the CLAP plugin (either Windows or macOS): https://github.com/Floe-Project/Floe/releases/tag/v0.0.4-alpha
2. Run clap-validator validate on the CLAP plugin. Within around 10 tries you will get the error.